From PLI’s Course Handbook Developments in Pharmaceutical and Biotech Patent Law#17180

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PATENTABILITY OF ACTIVE PHARMACEUTICAL INGREDIENTS

David K. BarrKaye Scholer LLP

Adapted from Chapter 7 of the PLI Treatise,Pharmaceutical and Biotech Patent Law (PLI 2007).

Patentability of Active Pharmaceutical Ingredients1

David K. BarrKaye Scholer LLP

The foundation for most pharmaceutical products is the active pharmaceutical ingredient (API). Since pharmaceutical research is often first directed to the discovery and identification of lead compounds for development and testing, patent applications claiming chemical compounds are usually the first applications to be filed for a drug product. Patents covering the active molecule for a drug product are generally among the most valuable and most difficult to design around.

This paper focuses on the principles governing the patentability of chemical compounds and compositions of matter in terms of satisfying the novelty and non-obviousness requirements of 35 U.S.C. §§ 102 and 103. Over time, courts created standards for determining the patentability of these chemical entities based on more general principles.2 The standards that have evolved apply to small molecules as well as nucleic acids, genes, and proteins.3

I. Novelty of a Claim to a Chemical Compound Over the Prior Art: The Requirement That an Anticipating Reference Be Enabling

A claim to a specific chemical compound is rendered non-novel (i.e., “anticipated”) by a prior art description of that compound as long as the prior art enables one skilled in the art to make the compound.4 Therefore, the mere depiction or naming in a prior art reference of a claimed compound will not anticipate unless it can also be shown that, based on the teachings of the prior art, one skilled in the art would have been able to make the compound without undue experimentation.5 Accordingly, a prior art reference describing a claimed compound will

1 Adapted from Chapter 7 of Pharmaceutical and Biotech Patent Law (PLI 2007).2 In re Mayne, 104 F.3d 1339, 1342 (Fed. Cir. 1997) (“Standards for the patenting of chemical

entities have evolved.”).3 See Amgen, Inc. v. Chugai Pharm. Co., 927 F.2d 1200, 1206 (Fed. Cir. 1991) (“A gene is a

chemical compound, albeit a complex one, and it is well established in our law that conception of a chemical compound requires that the inventor be able to define it so as to distinguish it from other materials, and to describe how to obtain it.”); Burroughs Wellcome Co. v. Barr Labs., Inc., 40 F.3d 1223, 1229 (Fed. Cir. 1994) (“DNA encoding a human protein [is] a chemical compound.”); see also Univ. of Rochester v. G.D. Searle & Co., Inc., 358 F.3d 916, 925 (Fed. Cir. 2004) ([w]ith respect to written description requirement of 35 U.S.C. § 112, the distinction between genetic and non-genetic materials is “irrelevant; the statute applies to all types of inventions.”).

4 In re Donohue, 766 F.2d 531, 533 (Fed. Cir. 1985) (“It is well settled that prior art under 35 U.S.C. § 102(b) must sufficiently describe the claimed invention to have placed the public in possession of it. Such possession is effected if one of ordinary skill in the art could have combined the publication’s description of the invention with his own knowledge to make the claimed invention.”) (citations omitted).

5 Forest Labs., Inc. v. Ivax Pharm., Inc., 2007 WL 2482122 (Fed. Cir. Sept. 5, 2007) (no anticipation because paper did “not enable the preparation of the (+)-enantiomer of citalopram.”); In re Wiggins, 488 F.2d 538, 542-43 (C.C.PA. 1973) (prior art reference naming of compounds “whose syntheses were unsuccessfully attempted” did not anticipate later claim to compounds).

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anticipate if it also describes a method of making the claimed compound, or if a method of making the claimed compound is otherwise available to one of ordinary skill in the art.6

The enablement requirement for anticipation can be satisfied by the description of a process in a different prior art reference from the prior art reference that describes the compound at issue.7 The requirement that an anticipatory reference be enabling is necessary to show that the prior art placed the public “in possession” of the claimed subject matter. Recourse to an additional prior art reference to demonstrate that the public was “in possession” of the invention does not shift the basis for unpatentability from anticipation to obviousness.8 The additional prior art reference used to show enablement can be dated after the primary reference describing the chemical structure.9 In other words, one can demonstrate anticipation of a claimed chemical compound with a prior art description of the compound and a subsequently dated prior art reference describing a method of making the compound as long as all of the information necessary to enable making the compound was in the prior art.

A. Obviousness of a Claim to a Chemical Entity and the Impact of the Supreme Court’s Decision in KSR

Claims to novel chemical entities can still be challenged as obvious in view of the combined teachings of the prior art pursuant to section 103 of Title 35. An obviousness challenge to a claimed compound is typically based on similarities between its chemical structure and the structures of prior art compounds.10 The Federal Circuit has developed a body of case law holding that obviousness of a chemical compound is to be predicated on a showing that one skilled in the art would have been “motivated” to have made the changes to a prior art compound

6 Donohue, 766 F.2d at 533. Under Donohue, “[i]t is not, however, necessary that an invention disclosed in a publication shall have actually been made in order to satisfy the enablement requirement” The Donohue court distinguished Wiggins, in which no anticipation was found because in that case the prior art reference reported a failure to make the claimed compound: “Such failures by those skilled in the art (having possession of the information disclosed by the publication) are strong evidence that the disclosure of the publication was nonenabling. By contrast, the fact that the author of a publication did not attempt to make his disclosed invention does not indicate one way or the other whether the publication would have been enabling.” Id. See also In re Coker, 463 F.2d 1344, 1347-48 (C.C.P.A. 1972) (no anticipation when prior art reference naming the claimed compound described an unsuccessful attempt to make it, notwithstanding that the applicant used that same method to make the compound; the prior art “direct[ed] the public away from the only” way to make the compound by reporting that the method “has not been successful.”).

7 In re Sasse; 629 F.2d 675, 681 (C.C.P.A. 1980) (enablement of prior art compound described in one reference established in another reference describing method for making a required precursor compound).

8 In re Samour; 571 F.2d 559, 563 (C.C.P.A. 1978) (“Additional references cited in a rejection under 35 U.S.C. § 102(b) are not relied on for a suggestion or incentive to combine teachings to meet claim limitations (as in a rejection under 35 U.S.C. § 103), but, rather, to show that the claimed subject matter, every material element of which is disclosed in the primary reference, was in possession of the public.”).

9 Id. (“The critical issue under 35 U.S.C. § 102(b) is whether the claimed subject matter was in possession of the public more than one year prior to applicant’s filing date, not whether the evidence showing such possession came before or after the date of the primary reference.”).

10 Eli Lilly & Co. v. Zenith Goldline Pharms., Inc., 2001 WL 1397304, at *4 (S.D. Ind. Oct. 29, 2001) (“Chemical compounds present special issues of obviousness because of the limited number of elements, recurring groups or substituents in complex molecules, the structural similarities within classes of related compounds, and the ability of chemists to undertake systematic experiments modifying known compounds.”).

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necessary to arrive at the claimed compound.11 Under Federal Circuit authority the motivation can be an expectation that the claimed compound will have useful properties similar to the prior art compound.12 Numerous cases, however, observe that even small changes in chemical structure frequently result in unpredictable changes in biological activity.13 Ultimately, the degree of predictability in any case depends on the skill and the teachings in the relevant prior art.

Accordingly, cases deciding the obviousness of a chemical entity have generally involved a comparison between the structure and the activity of the claimed compound (or composition of matter) with the structures and activities of prior art compounds and evidence of motivation to modify the prior art to achieve the claimed compound. Over time, the Federal Circuit had articulated a test for obviousness that required a finding of a “teaching, suggestion, or motivation” to combine prior art teaching or to otherwise modify the prior art to achieve the claimed invention.14 When this test is met, the Federal Circuit stated that the claimed invention is “prima facie” obvious, requiring the patent owner or applicant to come forward with rebuttal evidence of non-obviousness.15

However, in KSR International Co. v. Teleflex Inc.,16 the Supreme Court rejected what it called the Federal Circuit’s “rigid approach” in its test for obviousness, which required a finding of a “teaching, suggestion, or motivation” (“TSM test”) in the prior art to combine the teachings

11 E.g., Yamanouchi Pharm. Co. v. Danbury Pharmacal Inc., 231 F.3d 1339, 1343 (Fed. Cir. 2000) (“For a chemical compound, a prima facie case of obviousness requires ‘structural similarity between claimed and prior art subject matter . . . where the prior art gives reason or motivation to make the claimed compositions.’”) (quoting In re Dillon, 919 F.2d 688, 692 (Fed. Cir. 1990)).

12 See Dillon, 919 F.2d at 693 (holding that a prima facie case of obviousness can be made out if the prior art “provided the motivation to make the claimed compositions in the expectation that they would have similar properties”).

13 Fujikawa v. Wattanasin, 93 F.3d 1559, 1564 (Fed. Cir. 1996) (“It may be difficult to predict, however, whether a novel compound will exhibit pharmacological activity, even when the behavior of analogous compounds is known to those skilled in the art. Consequently, testing is often required to establish practical utility.”); In re Soni, 54 F.3d 746, 750 (Fed. Cir. 1995) (“The principle applies most often to the less predictable fields, such as chemistry, where minor changes in a product or process may yield substantially different results.”); In re Brana, 51 F.3d 1560, 1567 (Fed. Cir. 1995) (“minor changes in chemical compounds can radically alter their effects on the human body”); Ortho Pharm. Corp. v. Smith, 959 F.2d 936, 943 (Fed. Cir 1992) (“In the 1950s and early 1960s, when these compounds were being developed, one could not predict the effect of small structural changes on the biological activity of steroid hormones. Given the structure and properties of the components claimed in ‘081 and ‘909, there would have been no suggestion in the art (and, hence, it would not have been obvious) to modify those structures in order to achieve the compounds of ‘322 claims 5, 19, 40, and 43 having properties similar to those of ‘081 and ‘909”) (citation omitted); Eli Lilly, 2001 WL 1397304, at *5 (“The unpredictable nature of chemical reactions is especially pronounced, of course, when dealing with medicinal chemistry, where the biological effects of chemical reactions may be exceedingly difficult to predict from the chemical structure of a compound.”).

14 See Teleflex, Inc. v. KSR Int’l, 119 F. App’x 282, 285 (Fed. Cir. 2005), rev’d, KSR Int’l Co. v. Teleflex Inc., 127 S. Ct. 1727 (2007) (citing Tec Air, Inc. v. Denso Mfg. Mich. Inc., 192 F.3d 1353, 1359-60 (Fed. Cir. 1999), and Pro-Mold & Tool Co. v. Great Lakes Plastics, Inc., 75 F.3d 1568, 1573 (Fed. Cir. 1996)).

15 Teleflex, 119 F. App’x at 285, citing WMS Gaming, Inc. v. Intl. Game Tech., 184 F.3d 1339, 1359 (Fed. Cir. 1999). The establishment of prima facie obviousness for chemical compounds and the rebuttal of a prima facie case are discussed in infra sections 7:2.2[A] & [B].

16 KSR Int’l Co. v. Teleflex Inc., 127 S. Ct. 1727 (2007).

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of the prior art to achieve the claimed invention.17 KSR involved a patent claim directed to a mechanical invention, which was an automobile pedal assembly that combined an electronic sensor with an adjustable automobile pedal. The Federal Circuit had reversed a district court’s grant of summary judgment that the claimed invention was obvious, concluding that the district court had improperly applied the TSM test. On certiorari, the Supreme Court reversed the Federal Circuit.

While the Supreme Court acknowledged that “it can be important to identify a reason that would have prompted a person of ordinary skill in the relevant field to combine the elements in the way the claimed new invention does,”18 it held that a “rigid and mandatory” application of the “TSM” test “is incompatible with our precedents.”19 The Supreme Court admonished that “[g]ranting patent protection to advances that would occur in the ordinary course without real innovation retards progress and may, in the case of patents combining previously known elements, deprive prior inventions of their value or utility.”20 Thus, the Supreme Court stated that “[i]f a person of ordinary skill can implement a predictable variation, § 103 likely bars its patentability.”21

The Supreme Court criticized the Federal Circuit for “look[ing] only to the problem the patentee was trying to solve,” because “any need or problem known in the field of endeavor at the time of invention and addressed by the patent can provide a reason for combining the elements in the manner claimed.”22 Moreover, the Supreme Court held that the Federal Circuit erred in concluding that “a patent claim cannot be proved obvious merely by showing that the combination was ‘obvious to try.’”23 On the contrary, the Supreme Court held:

When there is a design need or market pressure to solve a problem and there are a finite number of identified, predictable solutions, a person of ordinary skill has good reason to pursue the known options within his or her technical grasp. If this leads to the anticipated success, it is likely the product not of innovation but of

17 Id. at 1739-41.18 Id. at 1741. Similarly, the Supreme Court stated that “[o]ften, it will be necessary for a court to

look at interrelated teachings of multiple patents; the effects of demands known in the design community or present in the marketplace; and the background knowledge possessed by a person having ordinary skill in the art, all in order to determine whether there was an apparent reason to combine the known elements in the fashion claimed by the patent at issue.” Id.

19 Id. Among its prior cases, the Court discussed its seminal decision on obviousness in Graham v. John Deere, 383 U.S. 1 (1966). The Supreme Court concluded that “[t]here is no necessary inconsistency between the idea underlying the TSM test and the Graham analysis. But when a court transforms the general principle into a rigid rule that limits the obviousness inquiry, as the Court of Appeals did here, it errs.” KSR, 127 S. Ct. at 1741.

20 KSR, 127 S. Ct. at 1741.21 Id. at 1740. In reviewing its precedent, the Supreme Court in KSR restated its “earlier

instructions,” which pre-dated the enactment of 35 U.S.C. § 103 and its Graham decision, “concerning the need for caution in granting a patent based on the combination of elements found in the prior art.” Id. at 1739. Thus, the Supreme Court admonished that “[t]he combination of familiar elements according to known methods is likely to be obvious when it does no more than yield predictable results.” Id. It remains to be seen how this principle will be applied post-KSR in the chemical and biotech fields in which the effects of changes to chemical compounds are generally considered to be unpredictable.

22 Id. at 1742.23 Id.

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ordinary skill and common sense. In that instance the fact that a combination was obvious to try might show that it was obvious under § 103.24

The Court in KSR concluded by stating that “as progress beginning from higher levels of achievement is expected in the normal course, the results of ordinary innovation are not the subject of exclusive rights under patent laws.”25

While the invention at issue in KSR was a mechanical apparatus, the Supreme Court’s decision is generally applicable to the obviousness determination for all inventions, including chemical compounds. The first occasion for the Federal Circuit to consider the impact of KSR on an obviousness determination for a chemical compound was in Takeda Chemical Industries, Ltd. v. Alphapharm Pty., Ltd.26

Takeda involved a claim to the antidiabetic drug compound pioglitazone27 which, critical to the case, includes the following structure (a 5-ethyl substituted pyridyl ring):

In challenging Takeda’s patent claiming pioglitazone, Alphapharm, a generic drug manufacturer, argued that pioglitazone was obvious in view of the closest prior art compound, known as “compound b,” which included the following structure (a 6-methyl substituted pyridyl ring):

The Federal Circuit affirmed the district court’s determination that the claimed pioglitazone compound was not obvious over the asserted prior art. In particular, the Federal Circuit agreed that the structure of the asserted prior art compound did not render the claimed pioglitazone compound prima facie obvious. In reaching this conclusion, the Federal Circuit, while cognizant of KSR, reviewed and reconfirmed its case law regarding a determination of prima facie obviousness based on a similarity in structure between a claimed compound and a prior art compound:

Our case law concerning prima facie obviousness of structurally similar compounds is well-established. We have held that “structural similarity between claimed and prior art subject matter, proved by combining references or

24 Id.25 Id. at 1746.26 Takeda Chem. Indus., Ltd. v. Alphapharm Pty, Ltd., 492 F.3d 1350 (Fed. Cir. 2007).27 The chemical name for pioglitazone is 5-{4-[2-5-ethyl-2-pyridyl)ethoxyl] benzyl}-2,4-

thiazolidinedione. Id. at 1353.

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otherwise, where the prior art gives reason or motivation to make the claimed compositions, creates a prima facie case of obviousness.” Dillon, 919 F.2d at 692. In addition to structural similarity between the compounds, a prima facie case of obviousness also requires a showing of “adequate support in the prior art” for the change in structure. In re Grabiak, 769 F.2d 729, 731-32 (Fed. Cir. 1985).28

Thus, the Federal Circuit in Takeda reconfirmed its pre-KSR view that a prima facie case of obviousness based on a structural relationship between a claimed compound and the prior art is premised on “‘the requisite motivation or suggestion to modify known compounds to obtain the new compounds.’”29 Moreover, the Federal Circuit quoted its own precedent in stating that “in order to find a prima facie case of unpatentability in such circumstance, a showing that the ‘prior art would have suggested making the specific molecular modifications necessary to achieve the claimed invention’ was also required.”30

In discussing KSR, the Federal Circuit in Takeda maintained that the Supreme Court had not eliminated the “TSM” test because, using the Supreme Court’s words, “[a]s long as the test is not applied as a ‘rigid and mandatory’ formula, that test can provide ‘helpful insight’ to an obviousness inquiry.”31 Accordingly, the Federal Circuit stated that “in cases involving new chemical compounds, it remains necessary to identify some reason that would have led a chemist to modify a known compound in a particular manner to establish prima facie obviousness of a new claimed compound.”32 Thus, the panel in Takeda was apparently of the view that the body of Federal Circuit law on the obviousness determination for chemical compounds based on an asserted structural similarity to prior art compounds remains largely intact following KSR.

On the merits in Takeda, the Federal Circuit concluded that the asserted prior art “compound b” did not render the claimed pioglitazone compound prima facie obvious because “Alphapharm’s obviousness argument rested entirely on the court making a preliminary finding that the prior art would have led to the selection of compound b as the lead compound” and the prior art “taught away” from the selection of compound b, which was described as having adverse, toxic properties.33 Contrary to the facts of KSR, the Federal Circuit stated that in Takeda, “(r)ather than identify predictable solutions for antidiabetic treatment, the prior art disclosed a broad selection of compounds any one of which could have been selected as lead compound for further investigation. Significantly, the closest prior art compound (compound b, the 6-methyl) exhibited negative properties that would have directed one of ordinary skill in the art away from that compound.”34 Moreover, even if one skilled in the art would have selected compound b as a lead compound in developing an antidiabetic drug, the court concluded that the changes necessary to achieve the claimed pioglitazone compound were “unpredictable” and that there was no “reasonable expectation” that making those changes would reduce or eliminate the toxic properties of compound b.35

28 Id. at 1356.29 Id., quoting In re Deuel, 51 F.3d 1552, 1558 (Fed. Cir. 1995).30 Id., quoting In re Deuel, 51 F.3d 1552, 1558 (Fed. Cir. 1995).31 Takeda, 492 F.3d at 1357.32 Id.33 Id. at 1358-60.34 Id. at 1359.35 Id. at 1360.

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Subsequently, in Ortho-McNeil Pharmaceutical, Inc. v. Mylan Labs, Inc.,36 the Federal Circuit held the anticonvulsive compound topiramate non-obvious after taking KSR into consideration. Topiramate (marketed by Ortho-McNeil under the trademark TOPOMAX®) is an epilepsy drug that was discovered during a search for a reaction intermediate in the synthesis efforts directed to finding antidiabetic drugs. The Federal Circuit rejected Mylan’s argument that under KSR, it would have been obvious to have arrived at topiramate in the search for a diabetes drug:

“[T]he ordinarily skilled artisan would have to have some reason to select (among several unpredictable alternatives) the exact route that produces topiramate as an intermediate. Even beyond that, the ordinary artisan in this field would have had to (at the time of invention without any clue of potential utility of topiramate) stop at that intermediate and test it for properties far afield from the purpose for the development in the first place (epilepsy rather than diabetes). In sum, this is clearly not the easily traversed, small and finite number of alternatives that KSR suggested might support an inference of obviousness.”37

Moreover, the Federal Circuit rejected the obviousness challenge because it was based on “hindsight” which “simply retraced the path of the inventor.”38

Thus, the Federal Circuit’s holdings in Takeda and Ortho-McNeil are consistent with the body of pre-KSR Federal Circuit decisional law on the structural obviousness of chemical compounds.39

1. Prima Facie Obviousness

a. An Evidentiary Mechanism

“Prima facie” obviousness is an evidentiary mechanism, usually applied in Patent Office proceedings after the examiner presents a threshold showing of obviousness that shifts the burden to the applicant to present evidence of non-obviousness.40 While a finding of prima facie obviousness most often finds application in Patent Office proceedings, it is also used in patent infringement litigation when a court deems that a patent challenger has made a threshold showing of obviousness.41 In infringement litigation, prima facie obviousness is viewed in the context of the statutory presumption of validity, which “‘remains intact and [the burden of proof

36 520 F.3d 1358 (Fed. Cir. 2008).37 520 F.3d at 1364.38 520 F.3d at 1364. The Federal Circuit also made clear its position that KSR did not reject the TSM

test as long as the test is “flexibly applied.” Id. at 1365.39 Several days after KSR was decided, the PTO published a memorandum stating that “(t)he Office

is studying the opinion and will issue guidance to the patent examining corps in view of the KSR decision in the near future.” Memorandum from Deputy Commissioner for Patent Operations [May 3, 2007]. However, the PTO’s initial interpretation of KSR is that “in formulating a rejection under 35 U.S.C. § 103 based upon a combination of prior art elements, it remains necessary to identify the reason why a person of ordinary skill in the art would have combined the prior art elements in the manner claimed.” It therefore remains to be seen how the PTO will react to KSR in its patentability determinations.

40 In re Piasecki, 745 F.2d 1468, 1471-72 (Fed. Cir. 1984) (“The concept of prima facie obviousness in ex parte patent examination is but a procedural mechanism to allocate in an orderly way the burdens of going forward and of persuasion as between the examiner and the applicant”).

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remains] on the challenger throughout the litigation, and the clear and convincing standard does not change.’”42 Accordingly, the Federal Circuit has stated that “once a challenger has presented a prima facie case of invalidity, the patentee has the burden of going forward with rebuttal evidence. . . . . But, all that means is that even though a patentee never must submit evidence to support a conclusion by a judge or jury that a patent remains valid, once a challenger introduces evidence that might lead to a conclusion of invalidity—what we call a prima facie case—the patentee ‘would be well advised to introduce evidence sufficient to rebut that of the challenger.’”43

The failure to rebut a proper prima facie case of obviousness results in the unpatentability (in the PTO) or invalidity (in infringement litigation) of the claim at issue.44 Once an applicant presents sufficient rebuttal evidence, “the prime facie case dissolves, and the decision is made on the entirety of the evidence.”45 The failure to consider rebuttal evidence has been held to be reversible error.46

b. Demonstrating Prima Facie Obviousness

In the case of chemical compounds, prima facie obviousness is generally based on a finding of structural similarity between the claimed compound and the prior art with a reason or suggestion in the art to make the claimed compound.47 The reason or suggestion can arise from the existence “of a reference to a similar composition” that has some useful property, “the presumption being that similar compositions have similar properties.”48

41 See Kao Corp. v. Unilever U.S., Inc., 441 F.3d 963, 970-71 (Fed. Cir. 2006), reh’g denied, 2006 U.S. App. LEXIS 14543 (Fed. Cir. May 31, 2006); Ecolochem, Inc. v. S. Cal. Edison Co., 227 F.3d 1361, 1375-76 (Fed. Cir. 2000); Yamanouchi Pharm. Co. v. Danbury Pharmacal, Inc., 231 F.3d 1339, 1345 (Fed. Cir. 2000); Pfizer Inc. v. Apotex, Inc., 480 F.3d 1348, 1359-60 (Fed. Cir. 2007).

42 Pfizer, 480 F.3d at 1359-60 (citation omitted). See infra section 5:1.1 for a discussion of the statutory presumption of patent validity under 35 U.S.C. § 282.

43 Pfizer, 480 F.3d at 1360 (emphasis in original, citations omitted).44 See In re Dillon, 919 F.2d 688, 693 (Fed. Cir. 1990) (claim to compound held unpatentable

because Patent Office established prima facie case of obviousness unrebutted by applicant). “Patentability” is used to refer to the determination of whether the PTO should grant a patent. “Patent validity” is used to refer to a determination made in an infringement litigation when the validity of a granted patent is at issue.

45 In re Kumar, 418 F.3d 1361, 1366 (Fed. Cir. 2005); see also In re Oetiker, 977 F.2d 1443, 1445-46 (Fed. Cir, 1992); M.P.E.P. § 2142.

46 In re Sullivan, 2007 WL 2433841, at *6 (Fed. Cir. 2007) (“By failing to consider the submitted (rebuttal) evidence, the Board thus committed error.”)) Kumar, 418 F.3d at 1369 (“[t]he entirety of the evidence must be reviewed in order to determine whether the claimed invention” would be invalid over prior art); see also Oetiker, 977 F.2d at 1445.

47 See, e.g., Yamanouchi, 231 F.3d at 1343 (“For a chemical compound, a prima facie case of obviousness requires ‘structural similarity between claimed and prior art subject matter . . . where the prior art gives reason or motivation to make the claimed compositions.’”(emphasis added)) (quoting Dillon, 919 F.2d at 692).

48 In re Soni, 54 F.3d 746, 750 (Fed. Cir. 1995); see also Dillon, 919 F.2d at 692 (“[s]tructural similarity between claimed and prior art subject matter, proved by combining references or otherwise, where the prior art gives reason or motivation to make the claimed compositions, creates a prima facie case of obviousness, and that the burden (and opportunity) then falls on an applicant to rebut that prima facie case.”). As discussed below, “[s]uch rebuttal or argument can consist of a comparison of test data showing that the claimed compositions possess unexpectedly improved properties or properties that the prior art does not have.” Id. at 692-93.

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(1) Properties of Claimed and Prior Art Compounds

The properties of a claimed compound are important in determining non-obviousness over the prior art.49 “There is no question that all evidence of the properties of the claimed compositions and the prior art must be considered in determining the ultimate question of patentability. . . .”50

(a) New Property Alone Does Not Defeat A Prima Facie Case

The mere fact, however, that “a claimed composition possesses a property not disclosed for the prior art subject matter, does not by itself defeat a prima facie case.”51 Thus, “it is not necessary in order to establish a prima facie case of obviousness that both a structural similarity between a claimed and prior art compound (or a key component of a composition) be shown and that there be a suggestion in or expectation from the prior art that the claimed compound or composition will have the same or a similar utility as one newly discovered by the applicant.”52

Accordingly, a prima facie case of obviousness can be made out if the prior art “provided the motivation to make the claimed compositions in the expectation that they would have similar properties.”53 This is not to say that the new properties of the claimed compound are irrelevant. They may be used to rebut prima facie obviousness.54

(b) Prior Art Compound Must Suggest Some Useful Property

An obviousness rejection based on similarity in chemical structure and function is generally predicated on “the motivation of one skilled in the art to make a claimed compound, in the expectation that compounds similar in structure will have similar properties.”55 Therefore, the existence of a prior art compound with no known utility having structural similarity to a claimed compound alone will not support a prima facie case of obviousness.56

49 In re Papesch, 315 F.2d 381, 391 (C.C.P.A. 1963) (“a compound and all of its properties are inseparable”).

50 Dillon, 919 F.2d at 693.51 Id. (“[I]t is not correct that similarity of structure and a suggestion of the activity of an applicant’s

compounds in the prior art are necessary before a prima facie case is established.”). Id. at 698.52 Id. at 693. In reaching this conclusion, the Federal Circuit expressly overruled its prior decision in

In re Wright, 848 F.2d 1216 (Fed. Cir. 1988).53 Dillon, 919 F.2d at 693; see also In re Sullivan, 2007 WL 2433841, at *6 (Fed. Cir. Aug. 29,

2007).54 See infra 7:2.2[B].55 In re Payne, 606 F.2d 303, 313 (C.C.P.A. 1979).56 In re Stemniski, 444 F.2d 581, 586 (C.C.P.A. 1971) (no obviousness based on similarity in

structure alone where no use was described for prior art compounds; “[h]ow can there be obviousness of structure, or particularly of the subject matter as a whole, when no apparent purpose or result is to be achieved, no reason or motivation to be satisfied, upon modifying the reference compounds’ structure?”).

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(c) In re Dillon

In In re Dillon,57 the Federal Circuit, in an en banc opinion, attempted to clarify the law regarding prima facie obviousness. Dillon related to a claimed composition comprising a hydrocarbon fuel containing tetra-orthoester compounds in an amount sufficient to reduce particulate emissions. The prior art relied on by the patent examiner consisted, among other things, of a primary reference showing the use of tri-orthoesters to dewater hydrocarbon fuels and a secondary reference that showed the use of both tri-orthoesters and tetra-orthoesters as water scavengers in hydraulic (that is, non-hydrocarbon) fluids. The court concluded that the secondary reference showed an equivalency between tri-orthoesters and tetra-orthoesters. Moreover, the claims were directed to a composition, and were not limited to any particular use. Accordingly, the combination of prior art references rendered the claimed composition prima facie obvious: “The art provided the motivation to make the claimed compositions in the expectation that they would have similar properties.”58 Thus, the combination of prior art references rendered the claimed composition prima facie obvious because there was motivation in the art to make the claimed composition, although the motivation in the prior art (to use the tetra-orthoesters in hydrocarbon fuels as water scavengers) was not the motivation of the patent applicant (to use the tetraorthoesters to reduce particulate emissions in hydrocarbon fuels).59

In summary, as held in Dillon, “a prima facie case has been established . . . [when] [t]he art provided the motivation to make the claimed compositions in the expectation that they would have similar properties.”60

(2) Prima Facie Obviousness Based on Similarity in Structure: “Structural Obviousness”

Obviousness attacks on claims to chemical compounds that are novel, but structurally similar to prior art compounds, are usually predicated on the assumption that activity can be predicted from knowledge of prior art chemical structures, creating an expectation that structurally similar compounds will have similar activities.61 Thus, the Federal Circuit has stated that “‘[s]tructural similarity, alone, may be sufficient to give rise to an expectation that compounds similar in structure will have similar properties’”62 and that “[w]hen chemical compounds have ‘very close’ structural similarities and similar utilities, without more a prima facie case may be made.”63

Patents directed to chemical compounds have generated many attempts to establish generalized rules governing when a claimed chemical structure is prima facie obvious in view of prior art chemical structures. Indeed, the Federal Circuit has observed that “[t]he question of ‘structural similarity’ in chemical patent cases has generated a body of patent law unto itself,” 64

57 In re Dillon, 919 F.2d 688 (Fed. Cir. 1990).58 Id. at 693, 107. 59 The applicant in Dillon did not attempt to rebut the prima facie case of obviousness. Id.60 Id.61 Payne, 606 F.2d at 313 (“An obviousness rejection based on similarity in chemical structure and

function entails the motivation of one skilled in the art to make a claimed compound, in the expectation that compounds similar in structure will have similar properties.”).

62 In re Merck & Co., 800 F.24 1091, 1096 (Fed. Cir. 1986) (quoting Payne, 606 F.2d at 313).63 In re Grabiak, 769 F.2d 729, 731 (Fed. Cir. 1985).64 In re Jones, 958 F.2d 347, 349 (Fed. Cir 1992).

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and has noted the historical efforts of the courts to create categories of chemical structures that would be amenable to generalizations based on structure.65 Ultimately, however, the Federal Circuit has concluded generalized rules and categories of structural obviousness are to be avoided. As the court stated in Grabiak:

Analysis of those circumstances in which a prima facie case has or has not been made in view of the degree of structural similarity or dissimilarity, or the presence or absence of similar utility between the prior art compound and that of the applicant, has inspired generations of applicants, courts, and scholars. Upon review of this history, we have concluded that generalization should be avoided insofar as specific chemical structures are alleged to be prima facie obvious one from the other.66

Accordingly, prima facie obviousness based on structural similarities between a claimed compound and prior art compounds is in general determined on a case by case basis by analyzing and comparing the structure and asserted activities of the claimed compound with the evidence presented on the prior art compounds.

The Federal Circuit’s decision in In re Merck & Co.67 is an example of a finding of prima facie obviousness of a claimed compound in view of a structurally related prior art compound.68

Merck related to a claim to a method of treating depression with the compound amitriptyline. While amitriptyline had been described in the art as having central nervous system activity, it was not known to be an antidepressant. The court relied on the prior art teaching that a compound with a closely-related structure, imipramine, was an antidepressant and that the prior art suggested testing amitriptyline for antidepressant properties.69 In reaching a conclusion of prima facie obviousness, the court stated:

65 The Federal Circuit in Grabiak, 769 F.2d at 731, noted prior cases finding prima facie obviousness with respect to “adjacent homologues and structural isomers” (citing In re Wilder, 563 F.2d 457 (C.C.P.A. 1977)), “stereoisomers” (citing In re May, 574 F.2d 1082 (C.C.P.A. 1978)), and “acid and ethyl ester” (citing In re Hoch, 428 F.2d 1341 (C.C.P.A. 1970)). In its subsequent case of Jones, 958 F.2d at 350, the Federal Circuit repeated this list and added “tri-orthoesters and tetra-orthoesters” (citing Dillon, 919 F.2d 688. Other earlier cases attempted to create a rule of prima facie structural obviousness when a claimed compound was an “adjacent homologue” of a prior art compound. See In re Hass, 141 F.2d 122 (C.C.P.A. 1944), and In re Henze, 181 F.2d 196 (C.C.P.A. 1950), which together formed the so-called “Hass-Henze Doctrine” of structural obviousness for adjacent homologues. It should be noted that Henze was overruled by In re Stemniski, 444 F.2d 581, 586-87 (C.C.P.A. 1971), to the extent Henze held that a claimed compound could be rendered prima facie obvious by a structurally-related prior art compound where “the prior art reference neither discloses nor suggests a utility for [the] described compounds.” As the Federal Circuit commented in Dillon, 919 F.2d at 697, in such a case, “a presumption [of obviousness] is not created when the reference compound is so lacking in any utility that there is no motivation to make close relatives.” However, the Dillon court nevertheless stated that “[t]he cases of Hass and Henze established the rule that, unless an applicant showed that the prior art compound lacked the property or advantage asserted for the claimed compound, the presumption of unpatentability was not overcome.” 919 F.2d at 696.

66 Grabiak, 769 F.2d at 731.67 In re Merck & Co., 800 F.2d 1091 (Fed. Cir. 1986).68 Id. at 1096.69 Id. at 1095.

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In view of these teachings, which show a close structural similarity and a similar use (psychotropic drugs) between amitriptyline and imipramine, one of ordinary skill in the medicinal chemical arts, possessed of the knowledge of the investigative techniques used in the field of drug design and pharmacological predictability, would have expected amitriptyline to resemble imipramine in the alleviation of depression in humans.70

Where the prior art does not show a reason or motivation to make the necessary changes in prior art compounds to achieve the claimed compound, a prima facie case of obviousness will generally fail.71 In Yamanouchi Pharmaceutical Co. v. Danbury Pharmacal, Inc.,72 the Federal Circuit rejected an argument that it would have been obvious to have made the claimed compound by combining different structural aspects of prior art compounds. The court found an absence of reason or motivation in the prior art to take the complex series of steps needed to achieve the claimed compound.73 The Federal Circuit followed its Yamanouchi decision in rejecting a similar structural obviousness challenge presented in Eli Lilly and Co. v. Zenith Goldline Pharmaceuticals, Inc.74 involving claims to the anti-schizophrenia drug, olanzapine. The Federal Circuit concluded that the prior art taught a preference for a halogen (fluorine or chlorine) substituent at the position in which olanzapine had a hydrogen atom. Thus, “[t]he prior art references at the time of this invention taught away from using a non-halogenated compound at a substituent in the benzene ring, exactly where olanzapine has a hydrogen atom.”75 The court concluded that the claimed compound was not prima facie obvious.76

(3) Reason to Combine77

In the absence of a sufficient structural similarity between a prior art and a claimed compound to give a reason to the skilled artisan to make the claimed compound, one may attempt to demonstrate prima facie obviousness by combining multiple references describing

70 Id. at 1097. The court rejected applicant’s argument that it showed unexpected results sufficient to rebut the prima facie case of obviousness. The court concluded that “the alleged difference in properties [between the two compounds] is a matter of degree rather than kind.” Id. at 1099. Thus, “[i]n the absence of evidence to show that the properties of the compounds differed in such an appreciable degree that the difference was really unexpected, we do not think that the Board erred in its determination that appellant’s evidence was insufficient to rebut the prima facie case.” Id.

71 Yamanouchi Pharm. Co. v. Danbury Pharmacal, Inc., 231 F.3d 1339, 1345 (Fed. Cir. 2000).72 Id.73 Id. at 1344-45; see also In re Grabiak, 769 F.2d 729 (Fed. Cir. 1985) (prior art did not suggest

substituting sulfur for oxygen in prior art compound; therefore, claimed compound was not prima facie obvious and it was irrelevant that claimed compound was not more effective than prior art compound). Section 7:2.2[A][4], infra, provides examples, including Merck and Yamanouchi, of cases addressing the issue of structural obviousness.

74 Eli Lilly and Co. v. Zenith Goldline Pharms., Inc., 471 F.3d 1369, 1377-80 (Fed. Cir. 2006).75 Id. at 1378.76 Id. at 1380. The court, in the alternative, concluded that even if the claimed compound was prima

facie obvious, such a finding was rebutted by “extensive secondary considerations.” For a discussion on rebutting a prima facie case of obviousness, see infra § 7:2.2[B].

77 As discussed previously, the Supreme Court’s expected decision in KSR Int’l Co. v. Teleflex, Inc., 127 S. Ct. 1727 (2007), rejected what it called the Federal Circuit’s “rigid” application of the “TSM” test for obviousness, which requires a teaching, suggestion, or motivation to combine the teachings of the prior art to make the changes needed to achieve the claimed invention. The effect of KSR on Federal Circuit law on chemical obviousness remains to be seen.

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different portions of the compound if there is sufficient reason or motivation to combine the references.78 Several cases illustrate finding prima facie obviousness based on a suggestion in the art to combine references.79 The mere fact that different prior art compounds, if combined, yield the claimed compound does not make a prima facie case of obviousness.80 In Takeda Chemical Industries, Ltd. v. Alphapharm Pty., Ltd., the Federal Circuit stated that even after KSR, “it remains necessary to identify some reason that would have led a chemist to modify a known compound in a particular manner to establish prima facie obviousness of a new claimed compound.”81 If the prior art fails to suggest the precise changes required to obtain the claimed compound, the prior art should not provide a motivation to combine.82 The fact that any changes to the steps required to modify the prior art into the claimed compound yield compounds with inferior activity can show the modification was not obvious.83

c. Non-Obviousness Where Prior Art Teaches Away From Claimed Compound

An assertion that a chemical compound is obvious can be negated by a showing that the prior art “taught away” from the claimed compound. For example, in Takeda Chemical Industries, Ltd. v. Alphapharm Pty. Ltd.,84 the generic challenger argued that the claimed pharmaceutical compound was obvious in view of a structurally-related prior art compound. The Federal Circuit rejected the challenge and concluded that the claimed compound was not prima facie obvious because, among other things, the prior art “taught away” from the use of structurally-related prior art compound because of its adverse side effects.85 Similarly, a finding that the prior art taught away from non-halogenated compounds was held in Eli Lilly and Company v. Zenith Goldline Pharmaceuticals, Inc.86 to support the non-obviousness of the compound olanzapine, which had 78 See Yamanouchi, 231 F.3d at 1343 (“At the heart of this validity dispute is whether one of skill in

this art would have found motivation to combine pieces from one compound in a prior art patent with a piece of another compound in the second prior art patent through a series of manipulations.”); Eli Lilly & Co. v. Teva Pharms. USA, Inc., 2004 WL 1724632, at *35 (S.D. Ind. July 29, 2004) (“Teva must point to ‘the specific sources of the motivation to combine prior art references’ in order to prevail on this theory.”) (quoting Ecolochem, Inc. v. S. Cal. Edison Co., 227 F.3d 1361, 1374 (Fed. Cir. 2000)).

79 In re Zenitz, 333 F.2d 924, 925 (C.C.P.A. 1964) (noting board affirmance of obviousness based on reference that “discloses compounds identical to those claimed except for a chloro (Cl) substituent in place of the trifluoromethyl (CF3) substituent in the claimed compounds” and references that establish “the substitution of Cl and CF3 potentiating groups in phenothiazines analogous to those now claimed.”); In re Herr, 304 F.2d 906, 909 (C.C.P.A. 1962) (claimed testosterone derivative obvious over prior art disclosing same compound without “a methyl group in the 17 position” and “two compounds used as standards in the art hav[ing] exactly the same structural difference”).

80 See Yamanouchi, 231 F.3d at 1345 (“Danbury also does not show the motivation to combine the polar tail of example 44 with the substituted heterocycle of tiotidine, then to substitute the carbamoyl with a sulfamoyl.”).

81 492 F.3d 1350, 1357 (Fed. Cir. 2007).82 Yamanouchi, 231 F.3d at 1345 (“[T]he prior art offers no suggestion to pursue the particular order

of manipulating parts of the compounds. Danbury’s proposed obvious course of invention requires a very specific series of steps.”).

83 Id. (“Any deviation in the order of combination would have taught away from famotidine. If, for instance, the sulfamoyl group were substituted for the carbamoyl group on example 44 without attaching the substituted heterocycle from tiotidine, the evidence showed that the resulting compounds would have 1/100th the activity of cimetidine [the prior art standard drug].”).

84 Takeda Chem. Indus., Ltd. v. Alphapharm Pty. Ltd., 492 F.3d 1350 (Fed. Cir. 2007).85 Id. at 1358-59.86 Eli Lilly and Co. v. Zenith Goldline Pharms., Inc., 471 F.3d 1369, 1377-80 (Fed. Cir. 2006).

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a hydrogen atom at the relevant position instead of a halogen (fluorine or chlorine) as taught by the prior art. Also, in In re Baird,87 the Federal Circuit concluded that a claimed bisphenol A chemical compound that was encompassed by a broad prior art genus of more than 100 million different diphenol compounds was not obvious where the prior art taught away “from the selection of bisphenol A by focusing on more complex diphenols.”88

Accordingly, evidence that the prior art would have led a person of ordinary skill in the art away from, rather than toward, a claimed compound can support patentability.

d. Examples

(1) Finding Structural Obviousness

In re Merck & Co.89

Claim: Method of treating depression in humans by the oral administration of amitriptyline.

Prior Art: (a) The compound imipramine

and its use as an antidepressant in humans.

87 In re Baird, 16 F.3d 380 (Fed. Cir. 1994).88 Id. at 382.89 In re Merck & Co., 800 F.2d 1091 (Fed. Cir. 1986).

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(b) The theory of “biosterism” where the substitution of one atom or group of atoms for another atom or group of atoms having similar size, shape and electron density provides molecules having the same type of biological activity and a teaching that the interchange of the nitrogen atom in the central ring of chlorpromazine

for an unsaturated carbon atom as in the compound chlorprothiazine

does not change the strong tranquillizing activity of the compound.

(c) A suggestion that amitriptyline, based on its structural relationship to imipramine, should be tested for alleviation of depression.

Holding: The claim was prima facie obvious because the prior art teachings “show a close structural similarity and a similar use (psychotropic drugs) between amitriptyline and imipramine, one of ordinary skill in the medicinal chemical arts . . . would have expected amitriptyline to resemble imipramine in the alleviation of depression in humans.”90

In re Dillon91

Claim: A composition comprising a hydrocarbon fuel and a sufficient amount of a tetra-orthoester to reduce particulate emissions from the combustion of the hydrocarbon fuel.

Prior Art: (a) The use of tri-orthoesters to dewater hydrocarbon fuels.

(b) The use of tri-orthoesters and tetra-orthoesters to dewater hydraulic (non-hydrocarbon) fuels.

Holding: Claimed composition was prima facie obvious because prior art would have motivated one skilled in the art to have made the claimed composition using tetra-

90 Id. at 1097.91 In re Dillon, 919 F.2d 688 (Fed. Cir. 1990).

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orthoesters, albeit for a different purpose (dewatering) than the purpose recited in the claim (reduction of particulate emissions). The claim recited a composition, and was not limited to any particular use.

In re Mayne92

Claim: A fusion protein comprising a polypeptide sequence linking an enterokinase cleavage site to either human growth hormone (HGH) or bovine growth hormone (BGH).

Met-Phe-Pro-Leu-(Asp)4-Lys (HGH or BGH)

The enzyme enterokinase recognizes the cleavage site to produce mature HGH or BGH; “Met necessarily results from translation of RNA into proteins.”

Prior Art: (a) The prior art taught fusion proteins having the sequence X-(Asp)4-Lys-Y, where X is an enterokinase cleavage site and Y is the desired protein.

(b) The sequences for HGH and BGH and a motivation to link an enterokinase cleavage site to create a fusion protein.

(c) Enterokinase cleavage sites, including Phe-Pro-Ile.

Holding: Claimed polypeptide sequence was prima facie obvious; the amino acids Leu and Ile are isomers with the same number of hydrogen and carbon atoms and both are non-polar, hydrophobic amino acids. “The structure of Leu and Ile alone suggest their functional equivalency.” Therefore the prior art disclosure of Phe-Pro-Ile rendered Phe-Pro-Leu obvious.

(2) Finding No Structural Obviousness

In re Grabiak93

Claim: A compound that protects crops against herbicides (also known as a “safener”) having the structure:

having a sulfur atom in the ester moiety.

92 In re Mayne, 104 F.3d 1339 (Fed. Cir. 1997).93 In re Grabiak, 769 F.2d 729 (Fed. Cir. 1985).

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Prior Art: (a) A primary reference (Howe) showing safener compounds having the general structure:

Having an oxygen in the ester moiety, and describing the following specific compound:

(b) A secondary reference (Bollinger) showing safener compounds having the structure

that the examiner argues showed the interchangeability of sulfur and oxygen in safener compounds.

Holding: No prima facie based on structural similarities. The teaching of substitutability of sulfur for oxygen in the ring of the structure of the secondary reference does not suggest substituting sulfur for oxygen in the ester moiety of the primary reference. There is no teaching of the predictability of making the change required to achieve the claimed compound.

Yamamouchi Pharmaceutical Co. v. Danbury Pharmacal, Inc.94

Claim: The compound famotidine, useful for treating heartburn and ulcers, having a structure:

94 Yamamouchi Pharm. Co. v. Danbury Pharmacal, Inc., 231 F.3d 1339 (Fed. Cir. 2000).

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Prior Art: Defendant argued it would have been prima facie obvious to have made famotidine by combining the polar tail from:

with the substituted heterocycle from:

and then to substitute a sulfamoyl group (SO2NH2) for the carbonyl group (CON H2) of the intermediate to achieve famotidine.

Defendant argued that it would have been obvious to select Example 44 and tiotidine as “leads for making famotidine” because “[t]hese compounds, respectively, are three and eleven times more active than cimetidine—the benchmark compound at the time of the invention.”95

95 Id. at 1343-44.

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Holding: Famotidine is not structurally obvious; defendant’s argument was a hindsight reconstruction of the claimed compound; no suggestion to select the lead compounds or to manipulate them in the precise way to arrive at famotidine.

2. Rebutting a Prima Facie Case of Obviousness

A prima facie case of obviousness shifts the burden to the applicant to come forward with evidence or argument in rebutta1.96 It is well-settled that “a compound and all of its properties are inseparable” and that the properties of a compound are to be considered in determining obviousness.97 “A prima facie case of obviousness based on structural similarity is rebuttable by proof that the claimed compounds possess unexpectedly advantageous or superior properties.”98

Unexpected results are used:

to show that the claimed invention exhibits some superior property or advantage that a person of ordinary skill in the relevant art would have found surprising or unexpected. The basic principle behind this rule is straightforward—that which would have been surprising to a person of ordinary skill in a particular art would not have been obvious. The principle applies most often to the less predictable fields, such as chemistry, where minor changes in a product or process may yield substantially different results.99

a. Unexpected Results Require a Showing of Actual Differences

Evidence of unexpected properties cannot be based merely on evidence that the prior art did not describe the property possessed by the new compound. It requires proof that actual differences exist in the properties of the prior art and claimed compounds.100 Moreover, a

96 Mayne, 104 F.3d at 1343; In re Soni, 54 F.3d 746, 749 (Fed. Cir. 1995); In re Rijckaert, 9 F.3d 1531, 1532 (Fed. Cir. 1993).

97 In re Papesch, 315 F.2d 381, 391 (C.C.P.A. 1963) (close structural similarity between a claimed compound and a prior art compound, such as between homologs, does not prove obviousness in the face of proof that a claimed compound has “an advantageous pharmacological property shown not to be possessed by the prior art compound”); id. at 383, 387.

98 In re Payne, 606 F.2d 303, 315-16 (C.C.P.A. 1979); see also In re Merck & Co., 800 F.2d 1091, 1098 (Fed. Cir. 1986) (“A prima facie case of obviousness can be rebutted by evidence of unexpected results.”); In re Mehta, 347 F.2d 859, 864 (C.C.P.A. 1965) (“The similarity of properties of a reference compound as compared with a claimed compound gives rise to an even stronger inference of obviousness than that of structural similarity alone, and conversely, where the properties are different, they imply non-obviousness, when they are unexpected.”). In addition, a prima facie case of obviousness can be rebutted by the so-called “secondary indicia” of non-obviousness. See supra section 5:3.7.

99 Soni, 54 F.3d at 750.100 In re Albrecht, 514 F.2d 1389, 1396 (C.C.P.A. 1975) (“That a claimed novel compound possesses

a certain advantageous activity which is not in fact possessed by a prior art compound is itself evidence of the nonobviousness of the subject matter as a whole.”); In re Hoch, 428 F.2d 1341, 1344 (C.C.P.A. 1970) (“[A]ctual differences in properties are required to overcome a prima facie case of obviousness because the prima facie case, at least to a major extent, is based on the expectation that compounds that are very similar in structure will have similar properties. Therefore, to overcome the prima facie case, it must be shown that the expectation on which it is based was in fact unsound—as by showing that there are substantial, actual differences in properties.”); In re Mod, 408 F.2d 1055, 1056 (C.C.P.A. 1969) (“In view of this showing by appellants that actually the prior art compounds do possess antimicrobial activity, we are not persuaded that

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property or feature inherently in the prior art, although unknown to the prior art, “is not a basis for rebutting a prima facie finding of obviousness.”101

b. Compared to Closest Prior Art

Comparative tests to show unexpected results of a claimed compound must be with the closest prior art compounds.102 “Direct comparison,” however, “with the closest prior art is not required in all cases.”103 Whether direct or indirect, unexpected properties must be assessed against the entire teaching of the closest prior art reference, not simply an unrepresentative example.104

c. Differences Must Match Scope of Claim

A showing of unexpected results “must be commensurate in scope with the claims to which it pertains.”105 Thus, a broader claim requires proof that the showing of unexpected results is applicable across the breadth of the claim, and not just to a limited number of species.106

the particular compounds claimed possess an unobvious property and are, therefore, patentable.”). It should be noted that other references may bear on the issue of whether results of a comparison with the closest prior art are in fact “unexpected.” See In re Merchant, 575 F.2d 865, 869 (C.C.P.A. 1978) (“Though particular results appear unexpected in a comparison with the closest single prior art reference, the teaching of another reference may establish that those results would have been expected by those skilled in the art.”).

101 In re Baxter Travenol Labs., 952 F.2d 388, 392 (Fed. Cir. 1991) (“Since the prior art bags plasticized with DEHP were inherently suppressing hemolysis, albeit unknown at the time of the Becker document, this hemolysis-suppressing function is not a basis for rebutting a prima facie finding of obviousness.”).

102 Payne, 606 F.2d at 316; Baxter, 952 F.2d at 392 (“[W]hen unexpected results are used as evidence of nonobviousness, the results must be shown to be unexpected compared with the closest prior art.”); In re De Blauwe, 736 F.2d 699, 705 (Fed. Cir. 1984) (“[A]n applicant relying on comparative tests to rebut a prima facie case of obviousness must compare his claimed invention to the closest prior art.”); Merchant, 575 F.2d at 869 (“An applicant relying upon a comparative showing to rebut a prima facie case must compare his claimed invention with the closest prior art.”).

103 Merchant, 575 F.2d at 869 n.8 (citing In re Blondel, 499 F.2d 1311, 1317 (C.C.PA 1974)); see also In re Fouche, 439 F.2d 1237, 1241 (C.C.P.A. 1971) (comparison with unsaturated compound permissible even though closest prior art was a saturated compound because literature “indicate[s] that the unsaturated derivatives are more active than the saturated ones, and [applicant’s] evidence showed that the claimed compound was more active than the best of the unsaturated derivatives”).

104 See Payne, 606 F.2d at 316-18 (“Payne may not, however, rely on his mere assertion that the Addor I compound is ‘representative and superior in pesticidal properties to the compounds described in Addor II, Addor III, Ghosh and Nikles.’ None of the latter, allegedly inferior compounds was tested.”); In re Chapman, 357 F.2d 418, 423-24 (C.C.P.A. 1966) (rejecting evidence of difference from prior art because, inter alia, applicant only compared one example involving polyethylene of 60,000 molecular weight in prior art that was not representative of other examples at a molecular weight of 500,000 to 3,000,000).

105 In re Dill, 604 F.2d 1356, 1361 (C.C.P.A. 1979).106 See Soni, 54 F.3d at 751 (noting that where evidence of unexpected superiority is limited to a

single species within a claimed range, an issue is raised as to whether proof is commensurate with the scope of the claims).

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Narrower claims require fewer examples of unexpected properties.107 Several cases illustrate failure to comply with this requirement.108

d. Magnitude of Difference in Properties

For results to be “unexpected,” the differences between the claimed compound and the prior art should be a matter of kind rather than merely a matter of degree.109 Thus, a “[m]ere improvement in properties does not always suffice to show unexpected results.”110 However, “substantially improved properties are ipso facto unexpected.”111 In Soni, the court found substantially improved properties when a species of a high molecular weight polymer within the scope of the claim was stated in the specification to have “at least a fifty-fold increase in tensile strength” and a “five-fold increase in peel strength as well as improved resistivity and recovery behavior properties” compared to a lower molecular weight polymer outside the scope of the claim.112

e. Multiple Properties

A claimed compound usually possesses a number of properties that can be compared with the prior art. This raises the question as to whether a showing of unexpected results with regard to fewer than all the properties of a claimed invention can be used to rebut a finding of prima facie obviousness. In other words, is a claimed invention non-obvious when it is unexpectedly superior to the closest prior art in one property, but is essentially the same with respect to all other properties?

This issue was addressed by the Federal Circuit in In re Chupp,113 which involved a claimed herbicidal compound that was found prima facie obvious over a prior art homolog, also known to be a herbicide, which differed from the claimed compound by a single methylene (-CH2-) group. In an effort to overcome the Patent Office’s prima facie obviousness rejection, the applicant submitted experimental evidence that the claimed compound possessed at least five times the herbicidal activity and specificity of the prior art compound in two crops, corn and soybeans. The Patent Office was not persuaded by this evidence because it was limited to two crops and, as it turned out, the claimed compound was “at best run-of-the-mill” when used on other crops.

107 In re Greenfield, 571 F.2d 1185, 1188 (C.C.P.A. 1978) (“If appellants had established that several of the species within claims 7 and 9,” which claim a small number of species, “were subject to decomposition . . . they would have a basis for arguing that the burden has been shifted back to the PTO.”).

108 Dill, 604 F.2d at 1361 (rebuttal evidence insufficient because it is limited to inserts that had been “tumbled two hours in a milling jar” while the claims do not require this); Greenfield, 571 F.2d at 1189 (“Establishing that one (or a small number of) species” in a claim covering thousands of compounds “gives unexpected results is inadequate proof. . . .”).

109 In re Merck & Co., 800 F.2d 1091, 1099 (Fed. Cir. 1986) (finding prima facie obviousness was not overcome where “the alleged difference in properties between amitriptyline [the claimed compound] and imipramine [the prior art compound] is a matter of degree rather than kind.”); In re Lohr, 317 F.2d 388, 392 [C.C.P.A. 1963) (“substantially greater effectiveness is needed”).

110 Soni, 54 F.3d at 751.111 Id.112 Id. at 747-48. In Soni, the court also stated that “when an applicant demonstrates substantially

improved results, as Soni did [to the Patent Office] here, and states that the results were unexpected, this should suffice to establish unexpected results in the absence of evidence to the contrary.” Id. at 751.

113 In re Chupp, 816 F.2d 643, 644 (Fed. Cir. 1987).

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The Federal Circuit reversed, concluding that the unexpected superiority with respect to two crops was sufficient to render the compound non-obvious over the prior art: “To be patentable, a compound need not excel over prior art compounds in all common properties. Evidence that a compound is unexpectedly superior in one of a spectrum of common properties . . . can be enough to rebut a prima facie obviousness.”114

Similarly instructive is the decision of In re May,115 which involved, among other issues, the patentability of novel analgesic compounds that were structurally obvious over prior art analgesic compounds such that “it would have been prima facie obvious to use the compounds recited in these claims as analgesics.”116 In appealing the PTO’s rejection of claims to the use of such compounds and to pharmaceutical compositions of such compounds, applicants relied on evidence that their analgesic compounds were unexpectedly nonaddictive. The court concluded that the prima facie showing of obviousness was overcome because “it was totally unexpected that [the claimed compounds] would have exhibited . . . nonaddictive analgesia.”117 Thus, the unexpected property of nonaddictiveness overcame the expectation from the prior art that the claimed compounds would be analgesic.118

However, it should be noted that whether a showing of unexpected superiority for less than all properties can overcome a prima facie case of obviousness may depend on whether the showing of unexpected superiority is with respect to a significant property of the claimed invention. For example, if one skilled in the art would have been motivated to make the claimed invention to achieve an expected result in its most significant property, obviousness may not be negated by a showing that the claimed invention possesses other properties of lesser significance that were unexpectedly superior.119

114 Id. at 646 (citation omitted). In reaching its conclusion, the Chupp court distinguished In re Payne, 606 F.2d 303, 316 (C.C.P.A. 1979), which held that “[a] finding of obviousness is not precluded, however, when only some, but not all, of the properties of a claimed compound are predictable from the prior art.” In particular, the Chupp court stated that the showing of unexpected results failed in Payne because “[t]he Payne court held that the evidence submitted in that case was insufficient to rebut a prima facie case of obviousness, because the claimed compound was compared with too few prior art compounds.” 816 F.2d at 646.

115 In re May, 574 F.2d 1082 (C.C.P.A. 1978).116 Id. at 1090.117 Id. at 1092 (emphasis added).118 As the court stated, “[w]e are of the opinion that a novel chemical compound can be nonobvious

to one having ordinary skill in the art notwithstanding that it may possess a known property in common with a known structurally similar compound.” Id. at 1093. See also In re Murch, 464 F.2d 1051, 1055-56 (C.C.P.A. 1972) (claimed thermoplastic composition found nonobvious where it exhibited an unexpectedly improved property when compared to the prior art (weld line toughness) notwithstanding that the claimed composition would have been expected from the prior art to possess an improvement in another property (blend toughness)).

119 Illustrative of this point is the non-pharmaceutical case, In re Nolan, 553 F.2d 1261, 1267 (C.C.P.A. 1977). Nolan involved a gaseous discharge display/memory device that used a mixture of neon and argon gases in a specified range, which the PTO concluded was obvious from a combination of prior art references. On appeal, the court found that one skilled in the art would have been motivated to use the recited gas mixture in the claimed invention to lower the operating voltage to increase the memory margin, which was a property “of particular significance since it appears to be the most significant improvement for a memory device.” This “expected” improvement in a property of “particular significance” supported the conclusion of obviousness, notwithstanding that other properties of the claimed device (higher luminous efficiency and lower peak discharge current) that were of a lesser significance were unexpectedly superior when compared to the prior art. See also In re Crounse, 363 F.2d 881, 884 (C.C.P.A. 1966) (a prima facie

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f. Evidence of Unexpected Properties Not limited to Specification

(1) Evidence Need Not Be in Specification

Proof of unexpected results or superiority is often presented in the form of comparative tests with the prior art. Such evidence can be presented at any time, including:

disclosing it in the patent specification,120

introducing it in a post-filing declaration submitted to the Patent Office,121

developing it during a patent infringement litigation.122

Accordingly, “[t]here is no requirement that an invention’s properties and advantages were fully known before the patent application was filed, or that the patent application contains all of the work done in studying the invention, in order for that work to be introduced into evidence in response to litigation attack.”123

(2) The Unexpected Property Need Not Be in the Specification

Evidence of unexpected properties may be used to rebut obviousness even if the patent does not disclose that the claimed compound possesses the unexpected property, and even if the inventor was unaware of this property.”124 Nevertheless, there is some authority for questioning the evidentiary weight of unexpected properties that do not “‘inherently flow’ from what was

showing that a claimed dye compound was structurally obvious in view of the prior art was not overcome by a showing that the color of the claimed dye compound was unpredictable where it shared a number of significant properties with prior art dye compounds of similar structure).

120 In re Soni, 54 F.3d 746, 749 (Fed. Cir. 1995).121 Evidence of unexpected properties may be submitted in the form of a declaration under 37 C.F.R.

§ 1.132. See Richardson-Vicks Inc. v. Upjohn Co., 122 F.3d 1476, 1482-83 (Fed. Cir. 1997) (holding that it is appropriate to consider evidence of unexpected results not set forth in the patent specification that was subsequently developed). The Federal Circuit has expressly rejected “the position that a patent applicant’s evidence and/or arguments traversing a section 103 rejection must be contained within the specification.” In re Chu, 66 F.3d 292, 299 (Fed. Cir 1995).

122 Knoll Pharm. Co. v. Teva Pharms. USA, Inc., 367 F.3d 1381, 1385 (Fed. Cir. 2004) (“Evidence developed after the patent grant is not excluded from consideration, for understanding of the full range of an invention is not always achieved at the time of filing the patent application. It is not improper to obtain additional support consistent with the patented invention, to respond to litigation attacks on validity”); Richardson-Vicks, 122 F.3d at 1483 (rebuking trial court for “discounting the evidence of unexpected results” because it was not in the specification and because it was unknown at the date of invention).

123 Knoll, 367 F.3d at 1385 (It is not “improper to conduct additional experiments and provide later-obtained data in support of patent validity.”).

124 Id. (“no requirement that an invention’s properties were fully known before the patent application was filed”); Chu, 66 F.3d at 299 (“arguments traversing a § 103 rejection” need not be in specification); In re Davies, 475 F.2d 667, 671 (C.C.P.A. 1973) (“there is no specific statutory requirement that compels an applicant to disclose all properties of chemical compounds or compositions in his application”).

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disclosed in the specification.”125 Many cases have found that the cited unexpected property did “inherently flow” from the disclosure in the specification.126

g. Illustrative Cases

(a) Prima facie Obviousness Rebutted

In re Chupp127

Claim: The compound N-(ethoxymethyl)-2’-trifluorormethy1-6’-methyl-2-chloroacetanilide, stated to have herbicidal activity.

Prior Art: The compound N-(ethoxyethyl)-2’-trifluorormethyl-6’-methyl-2-chloroacetanilide, also identified as having herbicidal activity.

RebuttalEvidence: In declarations submitted during prosecution, applicant showed that the claimed

compound was five times superior in terms of crop safety and weed killing as the prior art compound when used on corn and soybeans. However, the claimed compound did not possess such superiority with respect to other crops.

Holding: Prima facie obviousness rebutted: “Evidence that a compound is unexpectedly superior in one of a spectrum of common properties . . . can be enough to rebut a prima facie case of obviousness.”128

In re Soni129

Claim: A melt-processed composition comprising, among other things, an organic polymer having a molecular weight greater than 150,000 and a particulate

125 Davies, 475 F.2d at 670-71 (declining to credit affidavits describing unexpectedly “improved gloss, transparency and processibility” because the disclosure only revealed “improved mechanical properties” for use in bearing loads; “we do not consider this to be a statement of utility sufficiently clear to insure that others would be led to observe the improved properties which appellants now urge in support of their claims.”); In re Herr, 304 F.2d 906, 908 (C.C.P.A. 1962) (failure to disclose property in specification puts applicant in unfavorable position to assert an affidavit to rely upon to show unexpected properties where the “‘specification discloses no utility for the claimed compounds other than as intermediates for the production of other compounds having oral anabolic and androgenic activity.’”).

126 See, e.g., In re Khelghatian, 364 F.2d 870, 876 (C.C.PA. 1966) (greater efficiency relied upon in affidavit entitled to weight because it “inherently flows” from disclosure); In re Zenitz, 333 F.2d 924, 928 (C.C.P.A. 1964) (applicant “disclosed a tranquilizer [that] is a better one for it minimizes the side effects of hypotensive activity [t]herefore . . . the latter property must be considered in determining [patentability].”); In re Lorenz, 333 F.2d 908, 912 (C.C.P.A. 1964) (“there is no requirement that superiority over the prior art be disclosed . . . it is enough if the basic property or utility is disclosed”); Ex parte Böttcher, 2002 WL 99677 (Bd. Pat. App. & Interferences 2002) (unexpected antidopaminergic inherently flows from disclosing compound’s use as an anti-anxiety, anti-depression treatment); Ex parte Mueller, 2001 WL 87827 (Bd. Pat. App. & Interferences 2001) (unpublished) (stability inherently flows from disclosing compound’s use as a pharmaceutical).

127 In re Chupp, 816 F.2d 643 (Fed. Cir. 1987).128 Id. at 646.129 In re Soni, 54 F.3d 746 (Fed. Cir. 1995).

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conductive filler. The composition was stated to have “significantly improved physical and electrical properties.”

Prior Art: Disclosure of the same composition, but no disclosure of using a polymer having a molecular weight greater than 150,000.

RebuttalEvidence: The specification contained data comparing a composition within the claim

wherein the organic polymer had a molecular weight of 203,000 and another composition wherein the organic polymer had a molecular weight of 148,000. The data showed that the claimed composition had at least a fifty-fold increase in tensile strength, five-fold increase in peel strength, as well as improved resistivity and recovery behavior properties.

Holding: Prima facie obviousness rebutted: “When an applicant demonstrates substantially improved results . . . and states that the results were unexpected this should suffice to establish unexpected results in the absence of evidence to the contrary.”130

(2) Prima Facie Obviousness Not Rebutted

In re Mayne131

Claim: A fusion protein comprising a polypeptide sequence linking an enterokinase cleavage site to either HGH or BGH.

Met-Phe-Pro-Leu-(Asp)4-Lys (HGH or BGH)

The enzyme enterokinase recognizes the cleavage site to produce mature HGH or BGH; “Met necessarily results from translation of RNA into proteins.”

Prior Art: (a) The prior art taught fusion proteins having the sequence X-(Asp)4-Lys-Y, where X is an enterokinase cleavage site and Y is the desired protein.

(b) The sequences for HGH and BGH and a motivation to link an enterokinase cleavage site to create a fusion protein.

(c) Enterokinase cleavage sites, including Phe-Pro-Ile.

RebuttalEvidence: In response to a finding of prima facie obviousness, applicants argued two

unexpected results: (1) it was unexpected that the claimed engineered proteins would induce a low immune response when administered by injection to rats; and (2) it was unexpected that the claimed proteins would be biologically active even before cleavage of the initial peptide chain.

130 Id. at 751.131 In re Mayne, 104 F.3d 1339 (Fed. Cir. 1997).

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Holding: Prima facie obviousness not rebutted: (1) as to the low immune response of the claimed proteins, applicants failed to show comparative data that shows low immunogenicity of the claimed compound compared to similar fused proteins; and (2) with respect to the biological activity of the fused proteins prior to cleavage, applicants failed to show any evidence that HGH or BGH would be expected to be biologically inactive when fused to an enterokinase cleavage site.132 In sum, applicants failed to make a proper showing that the properties of the claimed protein would have been unexpected from the state of the art.

In re Merck & Co.133

Claim: Method of treating depression in humans by the oral administration of amitriptyline.

Prior Art: (a) The compound imipramine

and its use as an antidepressant in humans.

(b) The theory of “biosterism,” where the substitution of one atom or group of atoms for another atom or group of atoms having similar size, shape, and electron density provides molecules having the same type of biological activity, and a teaching that the interchange of the nitrogen atom in the central ring of chlorpromazine

for an unsaturated carbon atom as in the compound chlorprothiazine

132 Id. at 1344.133 In re Merck & Co., 800 F.2d 1091 (Fed. Cir. 1986).

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does not change the strong tranquillizing activity of the compound.

(c) A suggestion that amitriptyline, based on its structural relationship to imipramine, should be tested for alleviation of depression.

Holding: Prima facie obviousness not rebutted: The differences in activity between the claimed properties of amitriptyline and the prior art compound imipramine are insufficient to rebut the prima facie case of obviousness. In particular, the differences between the sedative properties of the two compounds was only “slight” and both compounds had ant cholinergic effects that only differed in degree. The two compounds expectedly have the same type of biological activity. In the absence of evidence to show that the properties of the compounds differed in such an appreciable degree that the difference was really unexpected,” the finding of prima facie obviousness was not rebutted.134

B. Genus and Species Inventions

The discovery and development of chemical compounds often leads to patents that describe the invention both in terms of specific chemical compounds and in terms of a broader group or genus of compounds. For example, the inventor of a specific compound having a particular utility may conclude that the invention is broader than the single compound because other structurally related compounds should have the same or similar activities. The inventor may then synthesize a number of these related compounds and conclude that he has invented a genus of compounds. Such a genus is typically represented by a structure depicting variables that can be substituted with various chemical substituents to arrive at particular compounds within the genus.

The following structure represents a genus of compounds:

wherein R is selected from substituted and unsubstituted alkylene radicals having from about two to about twelve carbon atoms, alkylidene radicals having from one to twelve carbon atoms and cycloalkylidene radicals having from three to twelve carbon atoms; R’ and R” are selected from substituted and unsubstituted alkylene radicals having from two to twelve carbon atoms, alkylene 134 Id. at 1099.

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arylene radicals having from eight to twelve carbon atoms and arylene radicals; X and X’ are selected from hydrogen or an alkyl radical having from one to four carbon atoms; and each n is a number of from zero to four.

Such genus structures may include an extraordinary number of compounds, taking into consideration each of the possible substitutions that can be made.135 In most cases, only a small fraction of these possible compounds are specifically described or exemplified in the patent specification.

The patentability of claims to both species inventions and genus inventions in view of the disclosures of the prior art have been the subject of many litigated cases. The Court of Appeals for the Federal Circuit has set forth the following general rule:

On the one hand, this court has explained, ‘case law firmly establishes that a later genus claim limitation is anticipated by, and therefore not patentably distinct from, an earlier species claim.’ On the other hand, earlier disclosure of a genus does not necessarily prevent patenting a species member of the genus.136

The various issues relating to the patentability of both species and genus chemical compound inventions over the prior art are discussed below.

1. Anticipation of a Chemical Genus by a Prior Art Species

a. Prior Species Anticipates Genus

As a general rule, a claimed genus is anticipated by the description in the prior art of a single species within that genus.137 With respect to a claim to a genus of chemical compounds, the prior art description of one or more compounds within the genus anticipates the genus claim. For example, in the case of In re Gosteli, the patent applicant attempted to claim a genus of antibiotic compounds having the following general formula:138

135 Indeed, the above genus, described in U.S. Patent 4,634,649, was found by the Federal Circuit in In re Baird, 16 F.3d 380, 382 (Fed. Cir. 1994), to encompass more than 100 million compounds.

136 Eli Lilly & Co. v. Bd. of Regents of the Univ. of Wash., 334 F.3d 1264, 1270 (Fed. Cir. 2003) (citation omitted).

137 Titanium Metals Corp. of Am. v. Banner, 778 F.2d 775, 782 (Fed. Cir. 1985) (“It is also an elementary principle of patent law that when, as by a recitation of ranges or otherwise, a claim covers several compositions, the claim is ‘anticipated’ if one of them is in the prior art.”); Brown v. 3M, 265 F.3d 1349, 1351 (Fed. Cir. 2001) (“When a claim covers several structures or compositions, either generically or as alternatives, the claim is deemed anticipated if any of the structures or compositions within the scope of the claim is known in the prior art.”); In re Gosteli, 872 F.2d 1008, 1010 (Fed. Cir. 1989) (“generic claims are anticipated by prior art disclosing individual chemical species”).

138 Gosteli, 872 F.2d at 1013. The variables in the genus formula are as follows: Z’ represents oxygen, sulphur or a methylidene group optionally mono- or di-substituted by lower aklyl, cycloalkyl, cycloalkyl-lower alkyl, phenyl, phenyl-lower aklyl or esterified carboxy, R1 represents hydrogen; lower aklyl; lower aklyl monosubstituted by hydroxy, lower alkoxy, lower alkanoyloxy, halogen, mercapto, lower aklylthio, carboxyl, carbamoyl, cyano, nitro, amino, amino mono- or di-substituted by lower alkyl, lower alkyleneamino or amino acylated by acetyl, phenoxyacetyl, tert.butoxy-carbonyl, benzyloxy-carbonyl or p-nitrobenzeyl-oxycarbonyl; carboxyl; protected carboxyl; aminocarbonyl; aminocarbonyl mono- or di-substituted by lower alkyl; cycloalkyl; cyclo-alkyl-lower alkyl; phenyl; naphthyl; phenyl-lower alkyl; phenyl, naphthyl or phenyl-lower alkyl mono-substituted by lower alkyl, lower alkoxy, halogen, nitro,

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The Federal Circuit held this genus claim anticipated by the prior art disclosure of two species within the scope of the claim.139 This illustrates that a risk of pursuing broad generic claim coverage is the possibility of the claim being rendered invalid if it includes within its scope a prior art compound as a species.

b. Conception of Species Before Prior Art Can Defeat Anticipation of Broader Genus

If the asserted prior art qualifies under section 102(b) of Title 35, the inventor or patentee has no recourse to overcome the prior art reference.140 However, if the asserted prior art describing the species became public less than one year before the filing of the patent application at issue, the disclosure can be overcome, and entitlement to the genus claim can be established, if the inventor can show prior invention of the same species described in the prior art reference or of different species within the claimed genus coupled with evidence that the inventor considered the invention to be generic in nature.141 The need to establish a prior date of invention to antedate a

amino or di-lower alkylamino; pyridyl; thienyl; furyl; pyridyl-lower alkyl; thienyl-lower alkyl; furyl-lower alkyl; lower alkylthio; lower alkenylthio; cycloalkylthio; cycloalky-lower alkyl-thio; phenylthio or phenyl-lower alkylthio monosubstituted by hydroxy, lower alkoxy, lower alkanoyloxy, halogen, mercapto, lower alkylthio, carboxyl, carbamoyl, cyan, nitro, amino, amino mono- or di-substituted by lower alkyl, lower alkanoylamino or lower alkyleneamino; and R2A together with the carbonyl grouping -C (=O)- to which it is attached represents a protected carboxyl group, in racemic or optically active form.

139 Id. at 1010. The two prior art species compounds that anticipated the genus were: 2[(4R,S)-4-Acetylthio-2-oxo-1-azetidinyl]-2-hydroxyacetic acid p-nitrobenzyl ester; 2-[(4R,S)-4-Acetylthio-2-oxo-1-azetidinyl] -2-chloroacetic acid p-nitrobenzyl ester. Id. at 1009.

140 Prior art under § 102(b) is “statutory” prior art because it became public more than one year before the filing of the patent application at issue.

141 Under In re Stempel, 241 F.2d 755 (C.C.P.A. 1957), the prior art disclosure of the species was overcome by a showing that the inventor had in fact made the same species prior to the date of the reference. The court held that “all the applicant can be required to show is priority with respect to so much of the claimed invention as the reference happens to show.” Id. at 759. In subsequent cases, the holding of Stempel was extended to permit a patent applicant to antedate a prior art reference disclosing a genus by citing to prior work disclosing a species within that genus. See In re DaFano, 392 F.2d 280, 283, 284 (C.C.P.A. 1968) (holding that “reduction to practice of the copper naphthentate species, coupled with evidence that the inventor considered his invention to be a generic one, is adequate to remove a reference disclosing the genus”); In re Walsh, 424 F.2d 1105, 1108 (C.C.P.A. 1970) (prior reduction of species was adequate to antedate reference disclosing a different species within the same genus). It should be noted, however, that where one seeks to antedate a genus reference by citing to a species, “[i]t is necessary that the species which were reduced to practice provide an adequate basis for inferring that the invention has generic applicability.” Id. at 1108.

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reference may arise either in the PTO or in patent infringement litigation. In practice before the PTO, proof of prior invention is generally submitted in the form of inventor declarations.142 In litigation, such proof would be provided by evidence in the form of documents or oral testimony.

2. Validity of a Claimed Species over a Prior Art Genus

More complex issues arise when determining the patentability of a claim to a particular chemical compound in view of a prior art description of a genus.

a. Anticipation of Chemical Species by a Prior Art Genus

(1) General Rule

In general, a prior art disclosure of a genus does not anticipate a species falling within the genus.143 This is because, with certain exceptions, the description of a genus does not usually describe to one skilled in the art each of the individual members of the genus, a requirement for anticipation.144

(2) Exception for Small Prior Art Genus: In re Petering

Under special circumstances, “the disclosure of a small genus may anticipate the species of that genus even if the species are not themselves recited.”145 The classic example of such an anticipation is illustrated in In re Petering.146 In Petering, a prior art patent disclosed a class of compounds, which, taking into consideration the “specific preferences in connection with [the] generic formula,” had only twenty members. Given this disclosure, the court found that “one skilled in this art would, on reading [the prior art patent], at once envisage each member of this

142 37 C.F.R. § 1.131.143 Eli Lilly & Co. v. Bd. of Regents of the Univ. of Wash, 334 F.3d 1264, 1270 (Fed. Cir. 2003); see

also Metabolite Labs., Inc. v. Lab. Corp. of Am. Holdings, 370 F.3d 1354, 1367 (Fed. Cir. 2004) (“A prior art reference that discloses a genus still does not inherently disclose all species within that broad category.”); Corning Glass Works v. Sumitomo Elec. U.S.A., Inc., 868 F.2d 1251, 1262 (Fed. Cir. 1989) (rejecting argument that “a claim to a genus would inherently disclose all species”); In re Benno, 768 F.2d 1340, 1346 (Fed. Cir 1985) (“The scope of a patent’s claims determines what infringes the patent; it is no measure of what it discloses. A patent discloses only that which it describes, whether specifically or in general terms, so as to convey intelligence to one capable of understanding.”); In re Luvisi, 342 F.2d 102, 107 n.2 (C.C.P.A. 1965).

144 See, e.g., Corning Glass Works v. Sumitomo Elec. U.S.A., Inc., 868 F.2d 1251, 1262 (Fed. Cir. 1989) (rejecting argument that “a claim to a genus would inherently disclose all species”).

145 Bristol-Myers Squibb Co. v. Ben Venue Labs., Inc., 246 F.3d 1368, 1380 (Fed. Cir. 2001); In re Schaumann, 572 F.2d 312, 316-17 (C.C.P.A. 1978) (“When we consider also that claim 1 of [the prior art] patent, read in conjunction with the signification given the expression ‘alkyl radical’ in the specification, embraces a very limited number of compounds closely related to one another in structure, we are led inevitably to the conclusion that the reference provides a description of those compounds just as surely as if they were identified in the reference by name.”); Schering Corp. v. Precision-Cosmet Co., 614 F. Supp. 1368, 1373 (D. Del. 1985) (“The general rule is that a prior genus does not anticipate a later species. If, however, it is possible to derive a class of compounds of lesser scope than the genus disclosed in a prior art reference on the basis of preferences ascertainable from the remainder of the reference, anticipation may be found.”) (citations omitted).

146 In re Petering, 301 F.2d 676 (C.C.PA. 1962).

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limited class.”147 Thus, the court held that the prior art patent “has described to those with ordinary skill in this art each of the various permutations here involved as fully as if he had drawn each structural formula or had written each name.”148 In effect, based on the particularity of the disclosure, the prior art described each specific individual compound. “For these reasons, we hold that each compound within the limited class in [the prior art patent] has been described in a printed publication within the meaning of 35 U.S.C. § 102(b), and that it is of no moment that each compound is not specifically named or shown in that publication.”149 Therefore, the prior art genus was held to anticipate a claim to a specifically claimed compound falling within the prior art genus.150

Recent Federal Circuit cases have rejected attempts to apply Petering in cases in which the asserted prior art reference did not establish preferences which would lead to the claimed compound. For example, in Eli Lilly and Company v. Zenith Goldline Pharmaceuticals Inc.,151

the court concluded that claims to the anti-schizophrenia drug olazapine (sold under the trademark Zyprexa®) were not anticipated by a prior art reference which, among other things, expressed a preference for compounds having either fluorine or chlorine at a position whereas olazapine had a hydrogen atom at the corresponding position.152 Accordingly, unlike in Petering, “(n)o possible combination of those preferred substituents would lead to the components that make up olanzapine, because each would contain a fluorine or a chlorine.”153 The Federal Circuit concluded that Petering did not apply because to make olanzapine based on the asserted prior art reference, “one would have to depart from the teaching of the [prior art] article.”154 In Sanofi-Synthelabo v. Apotex, Inc.,155 the Federal Circuit also rejected a Petering anticipation challenge to a claim to the platelet aggregation inhibiting drug clopidogrel bisulfate (sold under the trademark Plavix®) because the asserted prior art patent “does not point to bisulfates as preferred salts for clopidogrel.”156

b. Obviousness of a Chemical Species over a Prior Art Genus

(1) General Rule

Absent the special Petering-type circumstances described above, the patentability of a specific compound or sub-genus of compounds over a broader prior art genus is based on obviousness. As the Federal Circuit has stated, the “earlier disclosure of a genus does not

147 Id. at 681.148 Id. at 682.149 Id. 150 See also Schaumann, 572 F.2d at 316-17 (following In re Petering, finding anticipation: Where

prior art “embraces a very limited number of compounds closely related to one another in structure, we are led inevitably to the conclusion that the reference provides a description of those compounds just as surely as if they were identified in the reference by name.”).

151 Eli Lilly and Co. v. Zenith Goldline Pharms. Inc., 471 F.3d 1369, 1376-77 (Fed. Cir. 2006).152 Id. 153 Id. 154 Id. 155 Sanofi-Synthelabo v. Apotex, Inc., 470 F.3d 1368, 1377-78 (Fed. Cir. 2007).156 Id.

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necessarily prevent patenting a species member of the genus.”157 The test is whether the prior art genus renders obvious the claimed species or sub-genus.

(2) Prima Facie Case Based on Prior Art Genus Can Be Rebutted

In some cases, a prior art description of a genus will render the claimed compound or sub-genus prima facie obvious in view of the description of the genus. As discussed above, in such circumstances, the burden shifts to the applicant or patentee to come forward with evidence that the claimed compound has unexpected properties compared with other members of the genus or other evidence of secondary consideration.158 Thus, a claim to a specific compound or a sub-genus of compounds may be patentable over the prior art disclosure of a genus within which the claimed subject matter falls.

Some species inventions are called “selection inventions” because they are based on the identification or “selection” of a narrower aspect of a prior art genus. As the Federal Circuit has stated, “improvement and selection inventions are ubiquitous in patent law.”159 Thus, “[i]nventions based on the identification or selection of a specific material or compound with particularly desirable properties within a previously disclosed genus of such materials or compounds do not violate any of the substantive requirements of patentability.”160 As discussed above, a conclusion that the selected species is prima facie obvious over a prior art genus of which the species is a member can be overcome by a showing that the selected species possesses unexpected properties over the genus.

(3) Size of Prior Art Genus and Nature of Examples May Negate Prima Facie Case

In cases where the claimed compound is not prima facie obvious over the prior art genus, the compound should in general be found patentable over the prior art.

When the prior art genus is so large that it does not suggest the claimed species, it has been held that a case of prima facie obviousness is not made out even though the species is a member of the described prior art genus.161 Two cases illustrate this point: In re Jones and In re Baird.

157 Eli Lilly & Co. v. Bd. of Regents of the Univ. of Wash., 334 F.3d 1264, 1270 (Fed. Cir. 2003); see also Atofina v. Great Lakes Chem. Corp., 441 F.3d 991, 999 (Fed. Cir. 2006); Iron Grip Barbell Co. v. USA. Sports, Inc., 392 F.3d 1317, 1321 (Fed. Cir. 2004) (“[S]imply because an invention falls within a range disclosed by the prior art does not necessarily make it per se obvious. The genus and species may be patentable.”).

158 See, e.g., Merck & Co. v. Biocraft Labs., Inc., 874 F.2d 804, 806-09 (Fed. Cir. 1989) (claimed species held obvious where patentee failed to rebut prima facie case based on description of genus).

159 CFMT, Inc. v. Yieldup Int’l Corp., 349 F.3d 1333, 1340 (Fed. Cir. 2003). 160 Eli Lilly & Co. v. Zenith Goldline Pharm., Inc., 364 F. Supp. 2d 820, 897 (S.D. Ind. 2005), aff’d,

471 F.3d 1369 (Fed. Cir. 2006). 161 It should be noted that in a concurring opinion in Takeda Chem. Indus., Ltd. v. Alapharm Pty.,

Ltd., 492 F.3d 1350, 1364 (Fed. Cir. 2007), Judge Dyk of the Federal Circuit stated his view that “a species should be patentable over a genus claimed in the prior art only if unexpected results have been established.” Judge Dyk’s concurring opinion does not cite In re Jones or In re Baird.

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(a) In re Jones

In In re Jones,162 the claim at issue was to a specific salt of a known herbicide, dicamba. The PTO had found the claimed salt prima facie obvious over a prior art reference that, although it did not disclose the specifically claimed salt, disclosed salts of dicamba, including “a genus which admittedly encompasses the claimed salt.”163 The Federal Circuit reversed, holding that the claimed salt was not sufficiently similar in structure to any of the specifically disclosed salts of the prior art reference to create a prima facie case of obviousness and that “[t]he lack of close similarity of structure is not negated by the fact that the claimed salt is a member of [the prior art reference’s] broadly disclosed genus of substituted ammonium salts of dicamba.”164 The Federal Circuit rejected the proposition that “regardless of how broad, a disclosure of a chemical genus renders obvious any species that happens to fall within it.”165 Indeed, in Jones, the prior art genus disclosed a “potentially infinite genus of ‘substituted ammonium salts’ of dicamba,” without describing or suggesting the specifically claimed salt.

Therefore, without more, the fact that a claimed compound falls within the scope of a large prior art genus may not render the claimed compound prima facie obvious. And, as discussed above, absent a finding of prima facie obviousness, the burden does not shift to the patent applicant to come forward with evidence of non-obviousness.

(b) In re Baird

In re Baird166 involved a claim to toner composition comprising a bisphenol A. The PTO rejected the claimed composition over a prior art reference that disclosed a broad genus of compounds that included the claimed bisphenol A compound. The Federal Circuit reversed. The prior art genus encompassed more than “100 million different diphenols.”167 “While the [prior art] formula unquestionably encompasses bisphenol A when specific variables are chosen, there is nothing in the disclosure of [the prior art reference] suggesting that one should select such variables.”168 Indeed, the Federal Circuit found that the prior art reference actually “appears to teach away” from the claimed compound because the prior art reference focused on structurally different and more complex sub-classes of compounds within the genus.169 The Federal Circuit summed up by stating that “[a] disclosure of millions of compounds does not render obvious a claim to three compounds, particularly when that disclosure indicates a preference leading away from the claimed compounds.”170

162 In re Jones, 958 F.2d 347 (Fed. Cir. 1992).163 Id. at 349. 164 Id. at 350.165 Id. 166 In re Baird, 16 F.3d 380 (Fed. Cir. 1994).167 Id. at 382. 168 Id. 169 Id. 170 Id. at 383.

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3. Written Description Support for Genus and Species Composition Claims

a. Species or Sub-Genus Claims

A patent that discloses a genus and claims without specifically describing a particular species within that genus, may not satisfy the written description requirement without some disclosure directing one towards that species.171

b. Genus Claims

The disclosure of a limited number of species that are not sufficiently representative of a genus may not satisfy the written description requirement for a claim to the genus. Accordingly, in some cases courts have found the species disclosure to be insufficient to support the genus claim.172 Other cases, on different facts, reached the opposite conclusion.173

171 In re Ruschig, 379 F.2d 990, 994 (C.C.PA. 1967) (“Specific claims to single compounds require reasonably specific supporting disclosure and while . . . naming is not essential, something more than the disclosure of a class of 1,000 or 100, or even 48, compounds is required.”); see also Fujikawa v. Wattanasin, 93 F.3d 1559, 1570-71 (Fed. Cir. 1996) (in the absence of disclosure that provides “blazemarks” leading to the claimed “tree” in the forest, “simply describing a large genus of compounds is not sufficient to satisfy the written description requirement as to particular species or subgenuses”); Fields v. Conover, 443 F.2d 1386, 1391-92 (C.C.P.A. 1971) (broad genus and examples did not support sub-genus); but see In re Edwards, 568 F.2d 1349 (C.C.P.A. 1978); In re Driscoll, 562 F.2d 1245, 1250 (C.C.PA. 1977) (“Any seeming similarity between Ruschig and the present case is illusory, however, because the structural formula there relied on could have described, at best, only a subgenus including the specific compound claimed, and not the compound itself. In this respect, Ruschig is readily distinguishable from the present case where the exact subgenus claimed is clearly discernible in the generalized formula of the thiadiazole urea set forth in the earlier filed application.”).

172 Regents of Univ. of Cal. v Eli Lilly & Co., 119 F.3d 1559, 1569 (Fed. Cir. 1997) (a genus of compounds or DNA sequences was not described where a representative number of the compounds or DNA sequences were not recited); In re Wilder, 736 F.2d 1516 (Fed. Cir. 1984) (“synchronous scanning equipment” species did not support claim to “genus of indicating mechanisms that visually identify positions on a recording medium when” scanned); see also In re Gostelli, 872 F.2d 1008, 1012 (Fed. Cir. 1989); In re Smith, 458 F.2d 1389, 1395-96 (C.C.P.A. 1972) (rejecting argument that “disclosure of a genus and a species of a subgenus is a sufficient description of the subgenus”; “claimed subgenus of coating compounds with at least 8 carbon atoms was not adequately described in the earlier application which disclosed compounds with at least 12 carbons.”); In re Sus, 306 F.2d 494 (C.C.P.A. 1962); In re Cavallito, 306 F.2d 505 (C.C.P.A. 1962); In re Shokal, 242 F.2d 771, 775-76 (C.C.P.A. 1957) (“neither the broad language relied on by appellants nor the specific examples given by them are sufficient to identify or point out the particular genus recited”).

173 In re Wallach, 378 F.3d 1330, 1333 (Fed. Cir. 2004) (“the complete amino acid sequence of a protein may put one in possession of the genus of the DNA sequences encoding it”); Enzo Biochem, Inc. v. Gen-Probe Inc., 323 F.3d 956, 967 (Fed. Cir. 2002) (“If those sequences are representative of the scope of the genus claims, i.e., if they indicate that the patentee has invented species sufficient to constitute the genera, they may be representative of the scope of those claims.”); In re Herschler, 591 F.2d 693, 700 (C.C.P.A. 1979) (using DMSO to enhance penetration across the skin of any steroid supported by example of using DMSO with one specified steroid); In re Surrey, 370 F.2d 349, 353 (C.C.P.A. 1966) (“specific examples . . . along with” statement in “specification that those aromatic radicals can be substituted with the same substituents exemplified for the phenyl radical” adequately supports chemical genus claim); In re Cavillito, 282 F.2d 357, 361 (C.C.P.A. 1960); In re Grimme, 274 F.2d 949, 952 (C.C.PA. 1960).

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Furthermore, one cannot claim a genus that is only supported by choosing an unmentioned characteristic of particular examples.174

C. Stereoisomers, Enantiomers, and Diastereomers

1. Introduction

Stereochemistry is the study of how molecules are arranged in three-dimensional space.175

Stereoisomers are molecules that are made up of the same atoms, connected by the same sequence of bonds, but have different three-dimensional structures.176 Stereoisomers have one or more “chiral centers,” which are “carbon atoms with four non-identical substituent atoms or groups of atoms.”177

Fig. 7-1Chiral Center—Carbon Atom (C)

Attached to Four Different Groups of Atoms (a, b, c, and d)

Stereoisomers can be classified as either “enantiomers” or “diastereomers.” Stereoisomers that are non-superimposable mirror images of each other are called enantiomers.178

174 Purdue Pharma L.P. v. Faulding Inc., 230 F.3d 1320, 1327 (Fed. Cir. 2000) (“[P]ick[ing] a characteristic possessed by two of their [disclosed] formulations, a characteristic that is not discussed even in passing in the disclosure, and then make it the basis of claims that cover not just those two formulations, but any formulation that has that characteristic . . . is exactly the type of overreaching the written description requirement was designed to guard against.”).

175 Pfizer Inc. v. Ranbaxy Labs. Ltd., 457 F.3d 1284, 1286 (Fed. Cir. 2006), reh’g denied, 2006 U.S. App. LEXIS 28925 (Fed. Cir. Oct. 23, 2006); Sanofi-Synthelabo v. Apotex, Inc., 470 F.3d 1368, 1372 (Fed. Cir. 2006).

176 ANDREW STREITWIESER, INTRODUCTION TO ORGANIC CHEMISTRY 124 (Paul F. Corey ed., 4th ed. 1992).

177 Pfizer, 457 F.3d at 1286.178 Id.; Aventis Pharma Deutschland GmbH v. Lupin Ltd., 2006 U.S. Dist. LEXIS 48246, at *11

(E.D. Va. July 17, 2006).

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Fig. 7-2Enantiomers

Enantiomers are often compared to a right and a left hand.179 Stereoisomers that are non-superimposable and not mirror images of each other are known as “diastereomers.”180

Fig. 7-3Diastereomers

Enantiomers are inherently “optically active.”181 Each member of a given pair of enantiomers will always rotate a plane of polarized light in “equal and opposite directions.”182

One enantiomer rotates polarized light in a clockwise direction and is called the dextrorotatory (+) enantiomer and the other enantiomer rotates polarized light in a counterclockwise direction and is called the levorotatory (-) enantiomer.183 An equal mixture of the two enantiomers is called a “racemic mixture” or a “racemate.”184 A racemic mixture is optically inactive because the light rotating properties of the two enantiomers cancel each other out.185 The process for

179 Aventis Pharma, 2006 U.S. Dist. LEXIS 48246, at *11; Ortho-McNeil Pharm., Inc. v. Mylan Labs., Inc., 348 F. Supp. 2d 713, 720 (N.D. W. Va. 2004), aff’d without opinion, 161 F. App’x 944 (Fed. Cir. 2005).

180 Aventis Pharma, 2006 U.S. Dist. LEXIS 48246, at *11 (“Diastereomers are stereoisomers that are not enantiomers.”).

181 Ortho-McNeil, 348 F. Supp. 2d at 720.182 Id. See also Pfizer, 457 F.3d at 1286.183 Pfizer, 457 F.3d at 1286; Ortho-McNeil, 348 F. Supp. 2d at 720.184 Pfizer, 457 F.3d at 1286.185 Id., Ortho-McNeil, 348 F. Supp. 2d at 721.

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separating a racemic mixture into its constituent enantiomers is called “resolution.”186 It may also be possible to perform an “enantioselective” reaction, which will produce either one enantiomer or a mixture that is enriched in a target enantiomer, as opposed to the racemic mixture that most reactions produce.187

Stereoisomers may also be designated “R” or “S” depending on whether the peripheral groups around the chiral center are arranged in a clockwise (R) or counterclockwise (S) orientation.188 The substituent groups attached to separate carbon atoms may be further characterized as having cis or trans configuration. When substituent groups lie on the same side of a plane of a molecule, the stereoisomer is called cis.189 When substituent groups lie on opposite sides of a plane of a molecule, the stereoisomer is called trans.190

Fig. 7-4Trans and Cis Configuration

Of significance to drug discovery is that although enantiomers generally have the same physical and chemical properties, they may have different biological and physiological properties.”191 For example, the proton pump inhibitor Prilosec®, used to control stomach acid, contains as its active ingredient omeprazole, which is a racemic mixture of two enantiomers. The discovery that the S enantiomer is responsible for the activity of omeprazole led to a new product called Nexium® which contains only the S enantiomer.192 Another well-known example is thalidomide—“one enantiomer is effective against morning sickness while the other causes birth defects.”193 Yet another example is the platelet aggregation inhibiting drug Plavix®, which was based on the discovery that the dextrorotatory enantiomer of an enantiomer pair was active and non-toxic while the levorotatory enantiomer was inactive and toxic.194

186 See, e.g., Pfizer, 457 F.3d 1284; see also STREITWIESER, INTRODUCTION TO ORGANIC CHEMISTRY, supra note 226, at 737.

187 See discussion in In re Doyle, 293 F.3d 1355, 1356 (Fed. Cir. 2002).188 Pfizer, 457 F.3d at 1286-87 & n.2, see also STREITWIESER, INTRODUCTION TO ORGANIC

CHEMISTRY, supra note 226, at 133.189 Pfizer, 457 F.3d at 1287; Aventis Pharma Deutschland GmbH v. Lupin Ltd., 2006 U.S. Dist.

LEXIS 48246, at *13 (E.D. Va. July 17, 2006).190 Pfizer, 457 F.3d at 1287; Aventis Pharma, 2006 U.S. Dist. LEXIS 48246, at *13.191 ROBERT THORNTON MORRISON & ROBERT NEILSON BOYD, ORGANIC CHEMISTRY 134-35 (5th ed.

1987) (hereinafter “MORRISON & BOYD”).192 Information relating to the development of Nexium can be found at www.nexium.com.193 Pfizer, 457 F.3d at 1286 n.l. Information relating to thalidomide can be found at

http://cerhr.niehs.nih.gov/common/thalidomide.html.194 Sanofi-Synthelabo v. Apotex Inc., 2006 WL 2516486, at *12 (S.D.N.Y. Aug. 31, 2006), aff’d, 470

F.3d 1368 (Fed. Cir. 2006).

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Diastereomers may have different physical and chemical properties195 and may also have different biological properties.196

2. Patentability of Stereoisomers

a. Anticipation

In general, a claim to a separated enantiomer has not been held to be anticipated by a prior art disclosure of its racemate. Thus, it has been held that “the novelty of an optical isomer is not negated by the prior art disclosure of its racemate.”197 It has also been held that the disclosure of the dextro enantiomer of a compound in a prior art reference does not anticipate a claim to the laevo enantiomer.198 In another case, a claim to a “substantially pure” enantiomer was found not anticipated by the prior art disclosure of the racernate and a disclosure of the individual enantiomers with a prediction of their activity.199

These holdings are apparently premised on a finding that a separated or isolated enantiomer is novel in view of a prior art disclosure of the racemic mixture. This is consistent with the law that a prior art genus does not necessarily anticipate a claimed species.200 Accordingly, the

195 MORRISON & BOYD, supra note 241, at 143.196 See, e.g., Leslie H. Kondejewski et al., Dissociation of Antimicrobial and Hemolytic Activities in

Cyclic Peptide Diastereomers by Systematic Alterations in Amphipathicity, in 274 J. BIOLOGICAL CHEMISTRY 13181 (1999).

197 In re May, 574 F.2d 1082, 1090 (C.C.P.A. 1978). See also In re Williams, 171 F.2d 319, 320 (C.C.P.A. 1948) (“[T]he holding by the tribunals of the Patent Office that the appealed claim, drawn to a laevo rotary compound substantially free from the dextro rotary form of the compound is fully anticipated by a mixture of the laevo and dextro rotary forms of the compound, must be reversed”); Pfizer Inc. v. Ranbaxy Labs. Ltd, 405 F. Supp. 2d 495, 519 (D. Del. 2005), aff’d in part, rev’d in part, 457 F.3d 1284 (Fed. Cir. 2006), reh’g denied, No. 06-1179, 2006 U.S. App. LEXIS 28925 (Fed. Cir. Oct. 23, 2006) (“[C]ourts considering issues related to racemates and their individual isomers have concluded that a prior art disclosure of a racemate does not anticipate the individual isomers of the racemate or render the individual isomers of the racemate obvious.”); Ortho-McNeil Pharm., Inc. v. Mylan Labs., Inc., 267 F. Supp. 2d 533, 545 (N.D. W. Va. 2003), modified, 348 F. Supp. 2d 713 (N.D. W. Va. 2004), aff’d, 161 F. App’x 944 (Fed. Cir. 2005) (claim to a separated laevo enantiomer was not anticipated when the prior art disclosed only the racemic mixture).

198 In re May, 574 F.2d at 1087-90.199 Forest Labs., Inc. v. Ivax Pharms., Inc., 438 F. Supp. 2d 479 (D. Del. 2006), aff’d, 501 F.3d 1263

(Fed. Cir. 2007). The district court found a claim to “substantially pure” (+)-citalopram, which corresponded to the (S)-enantiomer of citalopram, was not anticipated by a prior art reference that disclosed citalopram as a “racemic drug” and incorrectly predicted that the activity of the individual (R)-enantiomer would be “far more potent” as a serotonin uptake inhibitor than the claimed (S)-enantiomer. The court stated that the prior art reference only disclosed the chemical structure of the (R)-enantiomer and did not “disclose anything with regard to the purity of the [claimed] (S)-enantiomer . . . the Court cannot presume that the disclosure of (R)-citalopram, individually and not in any mixture, necessarily discloses substantially pure (S)- or (+)-citalopram.” In addition, the court found that even if the prior art reference described (+)-citalopram, the prior art did not enable one skilled in the art to resolve the racemate to obtain the claimed (+)-citalopram enantiomer. 438 F. Supp. at 486-88. In affirming the district court’s finding of no anticipation, the Federal Circuit agreed that the prior art reference did not enable obtaining the claimed (+)-citalopram enantiomer. In addition, the Federal Circuit noted that the reference incorrectly predicted that the (–) enantiomer would be more potent. 501 F.3d at 1268.

200 Pfizer, 405 F. Supp. 2d at 519 (citing Eli Lilly & Co. v. Bd. of Regents of Univ. of Wash., 334 F.3d 1264, 1270 (Fed. Cir. 2003)). It should be noted that a patent challenger may argue that the genus of stereoisomers disclosed in the prior art is sufficiently small so as to anticipate under the doctrine of In re

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construction of a claim directed to an enantiomer may be very important to validity determinations. For example, a claim to levofloxacin, the levo enantiomer of the antibiotic ofloxacin, was construed to cover “an optically active and substantially pure quantity of levofloxacin” that was not anticipated by the prior art disclosure of the ofloxacin racemate.201 In addition, courts have based conclusions of no anticipation on a finding that the prior art did not enable resolving a racemate into its component enantiomers.202

b. Obviousness

The question of whether a claim to a separated stereoisomer is non-obvious over the prior art disclosure of a mixture of stereoisomers that includes the claimed isolated stereoisomer has also been addressed.

The Federal Circuit has, in dicta, included stereoisomers as among the types of chemical compounds that give rise to prima facie obviousness based on structural similarity.203 However, in practice, courts have not applied a per se rule of prima facie obviousness to a claim reciting an isolated stereoisomer when the prior art discloses a mixture of stereoisomers, and have performed the test for obviousness set forth in Graham v. John Deere Co.204

Petering, 301 F.2d 676 (C.C.P.A. 1962). See supra chapter 5. Such an argument based on In re Petering was rejected in Sanofi-Synthelabo, 470 F.3d at 1377, which held that a prior art patent did not disclose preferences that would limit a generic formula of a racemic compound to the claimed enantiomer in a specific salt form. The Federal Circuit did not decide whether one skilled in the art would interpret the prior art patent as disclosing both the racemate and the dextro and levo enantiomers of the compound at issue. Id. at 1375-76. Instead, the Federal Circuit based its decision of no anticipation on the failure of the prior art patent to describe the compound in the bisulfate salt form. Id. at 1376 n.6. Subsequently, after a bench trial on the merits, the district court concluded that there was no anticipation because the prior art patent did not describe the claimed dextro enantiomer and because it was not described in the claimed bisulfate salt form. In addition, the district court concluded that the prior art patent did not enable making the dextro enantiomer in the bisulfate salt form, which also precluded a finding of anticipation. Sanofi-Synthelabo v. Apotex, Inc., 492 F. Supp. 2d 353, 383-86 (S.D.N.Y. 2007).

201 Ortho-McNeil, 348 F. Supp. 2d at 730. While the court acknowledged that the term “compound” could refer to only a single molecule, it concluded that by specifying the levo enantiomer, one skilled in the art would interpret the claim as requiring a measurable optical activity, which required a certain minimum number of molecules to rotate light. In addition, the court concluded that one skilled in the art would understand that 100% purity of the levo enantiomer could not be achieved, supporting an interpretation of “substantial” purity. Moreover, the claim to levofloxacin was held not to be inherently anticipated by the prior art administration of ofloxacin because of a failure to prove that the claimed levofloxacin compound exists as a monomer in vivo. Id. at 761-64.

202 E.g., Forest Labs., Inc. v. Ivax Pharm., Inc., 501 F.3d 1263, 1269 (Fed. Cir. Sept. 5, 2007) (“[W]e see no error in the finding that the Smith reference does not enable one of ordinary skill to make (+)-citalopram, and hence that the Smith reference does not anticipate claims to (+)-citalopram.”); Sanofi-Synthelabo, 492 F. Supp. 24 at 386-87 (finding lack of enablement in part because “sanofi—whose chemists were highly sophisticated and well-trained in the relevant art—spent a considerable amount of time trying to obtain the enantiomers of PCR 4099 [the racemate]”). The requirement that an anticipating reference must be enabling is discussed above.

203 In re Jones, 958 F.2d 347, 349-50 (Fed. Cir. 1992) (citing In re May, 574 F.2d 1082). Prima facie obviousness of chemical compounds based on structural similarities is discussed above.

204 Graham v. John Deere Co., 383 U.S. 1, 17 (1966). See Ortho-McNeil, 348 F. Supp. 2d at 749 n.19 (“Mylan asserts that enantiomers are prima facie obvious vis-à-vis the racemic compound . . . . Although Jones and May support Mylan’s contention, they are inconsistent with the Federal Circuit’s directive to make Graham findings in every case to establish a prima facie case of obviousness.” (citing In re. Mayne, 104 F.3d 1339, 1341 (Fed. Cir. 1997)).

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In the Federal Circuit’s first decision addressing KSR in the context of the validity of a claimed stereoisomer, the court, in Aventis Pharma Deutschland Gmbh v. Lupin, Ltd.,205 reversed a district court judgment of non-obviousness and held obvious a patent claiming the pharmaceutical compound ramipril “substantially free of other isomers.” Ramipril is the active ingredient in the blood pressure medication Altace®, an ACE inhibitor. The structure of ramipril contains five “stereocenters,” or carbon atoms that may take either of two orientations, “R” or “S.” All five stereocenters in ramipril are in the “S” orientation so that ramipril is known as the “SSSSS” or “5(S)” stereoisomer. While ramipril is one of thirty-two possible stereoisomers, the prior art included a composition that included only the 5(S) form of ramipril and the SSSSR stereoisomer. The court also considered that the prior art ACE inhibitors captopril and enalapril, like ramipril, have stereocenters that are all in the “S” configuration and that the SSS configuration of enalapril is 700 times as potent as the SSR form. The court concluded that “if it is known that some desirable property of a mixture derives in whole or in part from a particular one of its components, or if the prior art would provide a person with reason to believe that this is so, the purified compound is prima facie obvious over the mixture even without an explicit teaching that the ingredient should be concentrated or purified.”206 Moreover, the court concluded that the prior art taught that the stereoisomers of ramipril can be separated by conventional methods.207 Accordingly, the Federal Circuit concluded that claims to ramipril, “substantially free of other isomers,” were prima facie obvious, a finding that was not rebutted by a showing of unexpected results.208 The Federal Circuit cited KSR in concluding that obviousness did not require an “explicit teaching to purify the 5(S) isomer” and “[i]f it is known how to perform such an isolation, doing so ‘is likely the product not of innovation but ordinary skill and common sense.’”209

In Ortho-McNeil Pharmaceutical, Inc. v. Mylan Laboratories, Inc.,210 the district court rejected the argument that levofloxacin was obvious over the prior art disclosure of the racemate ofloxacin. The court stated that the party asserting obviousness had the burden of proving “by clear and convincing evidence that the prior art motivated a person of ordinary skill in the art to produce levofloxacin with a reasonable expectation of success.”211 The court’s conclusion of non-obviousness was based in part on its finding that levofloxacin was unexpectedly superior to the prior art racemate ofloxacin in its combination of greater antibacterial activity and lower toxicity.212 The court found this evidence sufficient to negate a finding of a “reasonable expectation of success” necessary to support a conclusion that the enantiomer was prima facie obvious over the racemate.213 Alternatively, the court concluded that the findings of unexpected

205 Aventis Pharma Deutschland Gmbh v. Lupin, Ltd., 499 F.3d 1293 (Fed. Cir. 2007).206 Id. at 1301.207 Id. at 1302.208 In particular, the court rejected a showing of superiority of the 5(S) isomer over the RRSSS isomer

because it was not a showing over the prior art mixture that contained the 5(S) and the SSSSR stereoisomer. Id.

209 Id. at 1302, quoting KSR, 127 S. Ct. 1727, 1742 (2007).210 Ortho-McNeil, 348 F. Supp. 2d 713 (N.D. W. Va. 2004), aff’d without opinion, 161 F. App’x 944

(Fed. Cir. 2005).211 348 F. Supp. at 752.212 Id. at 755-56.213 Id, at 754-55.

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results and secondary considerations of non-obviousness, including commercial success, rebutted any prima facie case of obviousness.214

The Court of Customs and Patent Appeals came to a different conclusion in the 1960 case of In re Adamson.215 In Adamson, the court found that a claim to an enantiomer was obvious over the prior art disclosure of the racemate combined with an organic chemistry text that described the principles of stereoisomerism and taught that racemates can be separated into enantiomers that may have different physiological properties.216 The court found that non-obviousness was not established by evidence that the claimed enantiomer had substantially greater activity with only a small increase in activity when compared with either the racemate or the other enantiomer.217 The Adamson court distinguished its prior decision in In re Williams218 which held that a claimed enantiomer was patentable over the racemate. The Adamson court stated that the motivation to separate enantiomers, which was presented in the organic chemistry text, was not of record in Williams.219

The Federal Circuit distinguished Adamson in Sanofi-Synthelabo v. Apotex, Inc.220 in affirming the grant of a preliminary injunction to the manufacturers and marketers of the drug Plavix®, which contains the dextro enantiomer of a racemic compound as a bisulfate salt called clopidogrel bisulfate. The Federal Circuit concluded that the generic drug manufacturing defendant had not raised a substantial question that the selection of the active dextro enantiomer in the claimed bisulfate salt form would have been obvious from the prior art disclosure of the “racemate free base” and “the dextrorotatory and levorotatory enantiomers, as well as pharmaceutically acceptable salts, including the bisulfate.”221 Moreover, the Federal Circuit found no error in the district court’s conclusion that it was unexpected that the dextro enantiomer would have “high pharmacological activity and low toxicity—two properties that are not necessarily generally associated with one enantiomer.”222

214 Id. at 760-61.215 In re Adamson, 275 F.2d 952 (C.C.P.A. 1960).216 Id. at 954.217 Id. In Ortho-McNeil, 348 F. Supp. at 754, the Adamson decision was distinguished because,

“when compared to the typical antibiotic, levofloxacin represents the unusual case in which each of the desired properties is superior to (if not considerably superior to) those of its predecessor.” Thus, the Ortho-McNeil court found it significant that the claimed enantiomer was both more active and less toxic than the racemate whereas in Adamson, while the claimed enantiomer was more active, it was also more toxic. Adamson, 275 F.2d at 953.

218 In re Williams, 171 F.2d 319 (C.C.P.A. 1948).219 Adamson, 275 F.2d at 842. Subsequent to Adamson, the court in Brenner v. Ladd, 247 F. Supp.

51, 56 (D.D.C. 1965), cited Adamson in holding that “in the absence of unexpected or unobvious beneficial properties, an optically active isomer is unpatentable over either the isomer of opposite rotation or .  . . the racemic compound itself.” See also In re Anthony, 414 F.2d 1383, 1386 [C.C.PA. 1969]. However, in reviewing this case law, the Patent Office Board of Appeals in Ex parte Bonfils, 64 U.S.P.Q.2d (BNA) 1456, 1462 (Bd. Pat. App. & Interferences 2002), stated “[n]othing in these cases supports the .  . . position that the disclosure of one enantiomer is sufficient by itself to establish a prima facie case of obviousness. . . .” The Board in Bonfils stated that a prima facie case of obviousness requires a showing that “one of ordinary skill in the art would have had a reasonable expectation that the claimed compounds would have similar biological properties as the reference compounds. . . .” Id. at 1463.

220 Sanofi-Synthelabo v. Apotex, Inc., 470 F.3d 1368 (Fed. Cir. 2006).221 Id. at 1375-76.222 Id. at 1378-79.

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The Federal Circuit concluded that “nothing directed a chemist to the particular enantiomer and salt, clopidogrel bisulfate.”223 In distinguishing Adamson, the court found that “[r]esolution of a racemic free base does not lead to a particular unnamed salt” and also credited the district court’s finding that “resolving the racemate was not mere routine experimentation and that it was unexpected that the desirable activity of clopidogrel would be found only in the d-enantiomer.”224

Subsequently, after a trial on the merits, the district court in Sanofi-Synthelabo concluded that the claimed clopidogrel bisulfate compound was non-obvious. While the district court assumed for the purposes of its analysis that the prior art rendered the claimed clopidogrel bisulfate compound prima facie obvious, it held that evidence of the unexpected superiority of the dextro enantiomer supported non-obviousness: “the prior art did not enable a person of ordinary skill in the art to predict with a reasonable expectation of success whether one enantiomer of PCR 4099 [the racemate] would have better pharmaceutical properties than the racemate itself, whether one enantiomer would have all of the activity and none of the toxicity of the racemate as a whole, or whether a single enantiomer would have both all of the activity and all of the toxicity.”225

Similarly, in Forest Laboratories, Inc. v. Ivax Pharmaceuticals, Inc.,226 the district court found that defendants had not demonstrated by clear and convincing evidence that a claim to a “substantially pure” specific enantiomer ((S)-citalopram, or (+)-citalopram) was rendered obvious by prior art disclosing the racemic mixture and its use as an antidepressant. The enantiomer (S)-citalopram, or (+)-citalopram, in the oxalate salt form, is the active ingredient in the antidepressant drug product, Lexapro®, a selective serotonin reuptake inhibitor or (SSRI).227

The court credited the testimony of plaintiff’s expert that “a person of ordinary skill in the art of medicinal chemistry seeking to discover a new SSRI would have been motivated to design a new compound, rather than engage in the time consuming and unpredictable effort of resolving citalopram into its enantiomer.”228 The court discussed the difficulties in resolving racemic compounds into their enantiomers and the difficulty in predicting the activities of the individual enantiomers.229 The court concluded that “[g]iven the significant difficulties identified by [plaintiffs’ expert] in resolving citalopram and the unpredictable nature of the separation techniques and separation results of racemates in general, as well as the minimal gains that were typically predicted by the resolution of racemates into their constituent enantiomers,” one skilled in the art would not have been motivated to resolve citalopram at the time of the invention. 230

The court further found that “a person skilled in the art seeking such a resolution would not have a reasonable expectation of success without undue experimentation.”231 In affirming the district court’s conclusion of non-obviousness, the Federal Circuit agreed with the district court’s

223 Id. at 1379.224 Id. at 1380.225 Sanofi-Synthelabo v. Apotex, Inc., 492 F. Supp. 2d 353, 390 (S.D.N.Y. 2007).226 Forest Labs., Inc. v. Ivax Pharms., Inc., 438 F. Supp. 2d 479 (D. Del. 2006), aff’d, 501 F.3d 1263

(Fed. Cir. 2007).227 438 F. Supp. 2d at 484.228 Id. at 492.229 Id. at 493.230 Id.231 Id.

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analysis, focusing on the difficulty in separating the enantiomers, including “the failure of the inventors and others to resolve citalopram without undue experimentation.”232

In Pfizer Inc. v. Ranbaxy Laboratories, Ltd.,233 the court rejected a challenge that a claim to a specific calcium salt of a specific stereoisomer was obvious over a prior art disclosure of the racemate and a disclosure of calcium among at least fifty salts, without a stated preference.234

The court found a lack of motivation to resolve the racemate of the specific compound, atorvastatin lactone, into individual enantiomers or to use the claimed calcium salt form.235

3. Claim Construction and Infringement

A claim to a compound that exists as stereoisomers can raise the issue as to whether the claim should be construed to cover a particular stereoisomer or enantiomer, or is limited to the racemic mixture. This claim construction issue was raised in Pfizer Inc. v. Ranbaxy Laboratories, Ltd.,236 involving a generic drug company’s challenge to patents protecting the cholesterol-reducing drug Lipitor®.

The active ingredient of Lipitor® is atorvastatin calcium, which is the R-trans enantiomer of a compound that exists in four enantiomeric forms. Pfizer’s ’893 patent in suit claimed a genus compounds that existed as four stereoisomers: R-trans, S-trans, R-cis, and S-cis, but the cis isomers were disclaimed in the specification. The Federal Circuit rejected Ranbaxy’s argument that the claim should be construed as covering only a racemic mixture of the R and S trans enantiomers and as not covering the specific R-trans enantiomer: “[T]he district court correctly found that no intrinsic evidence limits claim 1 of the ’893 patent to trans-racemates, as opposed to an R-trans enantiomer, an S-trans enantiomer or any (equal or unequal) mixtures thereof.”237

Furthermore, the Federal Circuit rejected each of Ranbaxy’s specific grounds for arguing that the claim did not cover the specific R-trans enantiomer. First, the court rejected the argument that the depiction in the ’893 patent of the R-trans enantiomer was meant to represent the racemate:

[E]ven accepting Ranbaxy’s contention that a racemate is commonly represented by depicting one of its constituent enantiomers, it does not follow that the depiction of an R-enantiomer always represents only a racemate. Here, only an R-trans enantiomer is depicted in the ’893 patent, yet the specification expressly indicates that there are four possible isomers of the compounds of structural formula I and limits the invention to the trans-form. If one skilled in the art would have

232 501 F.3d at 1269.233 Pfizer Inc. v. Ranbaxy Labs., Ltd., 405 F. Supp. 2d 495 (D. Del. 2005), aff’d in part, rev’d in part,

457 F.3d 1284 (Fed. Cir. 2006), reh’g denied, 2006 U.S. App. LEXIS 28925 (Fed. Cir. Oct. 23, 2006).234 405 F. Supp. at 517.235 Id. at 517-18. The court found that “the prior art indicates that the motivation at the time was to

develop racemates and make structural changes to the compounds to increase their activity, not to resolve those racemates into individual isomers.” Id. at 517.

236 Pfizer, 457 F.3d 1284.237 Id. at 1289.

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understood the drawing of structural formula I to limit the scope of claim 1 to trans-racemates, then an express disclaimer of the cis-form would not have been necessary.238

Second, the court rejected the argument that the claim should be restricted to racemates because the reactions shown in the examples of the specification produced racemates. To so restrict the claims, the court held, “would improperly import limitations from the specification into the claims.”239 Finally, the Court held that statements made during prosecution of foreign counterpart applications and during prosecution of a later U.S. application could not be used to interpret the claims of the ’893 patent.240

D. Pharmaceutical Salts of Active Ingredients

1. What Is a Salt?

Chemically, a salt is the result of a neutralization reaction that occurs when an acid and a base react.241 According to the Bronstead-Lowery theory, an acid is a substance that can donate (or lose) a proton, and a base is a substance that can accept (or remove) a proton. A neutralization reaction occurs when an acid and base react, and the resulting compound is called a salt.

The general form for a neutralization reaction is as follows:

(acid) + (base) = (salt) + (water)242

When in solution, the base of the salt is a positively charged ion called a “cation,” and the acid of the salt is a negatively charged ion called an “anion.” The active compound in a pharmaceutical salt could be either an acid or a base.

2. Development of Pharmaceutical Salts

The discovery of a compound with desired therapeutic properties is, of course, a major development for a drug discovery program. The therapeutic properties, however, are not the only properties that must be considered in actually formulating an active compound into a drug that can be manufactured and delivered to a patient. Physicochemical properties, such as aqueous solubility, stability, and processing properties must be considered in formulating the active compound into a commercially viable dosage form, such as a tablet, capsule, or injectable solution.

238 Id. at 1290.239 Id.240 Id.241 See, generally, Stephen M. Berge, Lyle D. Bighley, & Donald C. Monkhouse, Pharmaceutical

Salt, 66 J. PHARMACEUTICAL SCI. 1 (1977) (hereinafter “Berge”).242 The reverse of a neutralization reaction, hydrolysis, may occur when a salt is placed in an aqueous

medium. When hydrolyzed, a salt reacts with water in this general form:(salt) + (water) = (acid) + (base)

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Occasionally, the active compound itself will have physicochemical properties, such as solubility and stability, which are sufficient without modification to allow the active compound to be formulated into a commercial dosage form together with inactive ingredients. Often, however, the active compound itself will not have ideal, or even adequate, physical and chemical properties to enable it to be used in a pharmaceutical formulation. For example, the active compound might be too insoluble to allow sufficient absorption by the body, or it may be too unstable to avoid excessive breakdown during commercial distribution.

One way in which pharmaceutical scientists attempt to improve the physiochemical properties of active compounds for formulation into drug products is to convert the active compound into a salt.243 If the active compound is a base, a salt is formed by reacting the base with an acid. If the active compound is an acid, the salt is formed by reacting it with a base. The acid or base that is reacted with the active compound to form the salt can generally be referred to as the “counter-ion.”

The physiochemical properties that a new salt will have are largely unpredictable.244 Berge identifies many counter-ions that had been used to make a salt of active compounds, but cautions that “[u]nfortunately, there is no reliable way of predicting the influence of a particular salt species on the behavior of the parent compound.”245 As a consequence, the selection of a salt for an active compound is usually an empirical exercise.246

3. Patentability of New Salts

Patent issues arise specifically concerning pharmaceutical salts when an active compound, known in the prior art in one salt form or referred to generally in the prior art as useful in the form of pharmaceutically acceptable salts, is formed into a specific new salt by creating a new acid-base combination.

a. Determinations of Obviousness/Non-Obviousness of New Salt Forms of Compounds

The determination of whether a new salt form of a known compound is obvious is likely to involve a fact-intensive inquiry into whether the prior art described the compound in other salt forms, whether the prior art provided any reason or motivation to select the claimed salt form from among the other possible salt forms, and whether there was a reasonable expectation of success for the claimed salt form. The cases discussed below provide insight into the obviousness inquiry for salt forms.

In Pfizer, Inc. v. Apotex, Inc.,247 the Federal Circuit reversed a district court judgment and held a patent claiming the anti-hypertensive compound amlodipine in the besylate (or benzene sulphonate) salt form obvious over the prior art. Pfizer first attempted to develop an amlodipine drug product as a maleate salt, which was the only amlodipine salt disclosed in the prior art, but 243 See, generally, Berge, supra note 242.244 Id.245 Id. at 1, col. 2.246 Id.247 Pfizer Inc. v. Apotex, Inc., 480 F.3d 1348 (Fed. Cir. 2007), reh’g denied, 488 F.3d 1377 (Fed. Cir.

2002).

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determined that the maleate salt of amlodipine in tablet form presented problems with stability and stickiness.248 These problems were solved by using the besylate salt form of amlodipine, which Pfizer then patented.249 The prior art asserted at trial included a patent (the “’909 patent”), which disclosed “that the pharmaceutically acceptable acid addition salts of amlodipine ‘are those formed from acids that form non-toxic acid addition salts containing pharmaceutically acceptable anions, such as hydrochloride, hydrobromide, sulphate, phosphate or acid phosphate, acetate, maleate, fumarate, lactate, tartrate, citrate and gluconate salts,’ and that the preferred salt is maleate.”250 The prior art ’909 patent did not disclose the besylate salt of amlodipine,251 and only disclosed examples of the maleate salt of amlodipine.252 However, other prior art references disclosed the use of the besylate salt with other compounds, and one 1977 reference (“Berge”) included besylate as one of “53” acids that had been previously used to make salts approved by the FDA, although its frequency of use was 0.25%.253

The Federal Circuit concluded that a person skilled in the art would have been motivated to combine the prior art ’909 patent and the Berge reference to make the besylate salt of arnlodipine. In particular, the court pointed to the structural aspects of the maleate salt (acyclic structure with a double bond between carbon atoms) that were responsible for the stability problems and that would have led one skilled in the art to select a salt for arnlodipine, such as the besylate having a different structure (cyclic and lacking the double bond). The court concluded that prior art references described the use of the besylate salt form with other compounds resulting in improved properties, including stability, and that these references would “provide ample motivation to narrow the genus of 53 pharmaceutically-acceptable anions disclosed by Berge to a few, including benzene sulphonate [besylate].”254 In doing so, the court rejected the plaintiffs’ expert testimony that one could not draw a conclusion about the properties of a new salt based on the use of the same acid with a different drug. It drew its own conclusion of reasonable expectation of success based on its reading of a reference that mentioned benzene sulphonic acid as a possible salt forming acid for use with other drug compounds. The court stated that its conclusion on motivation was not undermined by the fact that the besylate salt form was only used in 0.25% of FDA-approved drugs because after the most common salt form, hydrochloride, most anions were used in less than 1% of all drug products.255

The Federal Circuit also concluded that “the skilled artisan would have had [a] reasonable expectation of success that an acid addition salt of besylate would form and would work for its intended purpose.”256 This conclusion was not undermined by the Federal Circuit’s acceptance of the district court’s finding that “it was generally unpredictable as to whether a particular salt would form and what its exact properties would be” because “obviousness cannot be avoided simply by a showing of some degree of unpredictability in the art so long as there is a reasonable probability of success.”257 Thus, the court rejected “a rule of law equating unpredictability to

248 480 F.3d at 1353-54.249 Id. at 1354-56.250 Id. at 1353.251 Id. at 1361.252 Id.253 Id. at 1355.254 Id. at 1363.255 Id.256 Id. at 1364.257 Id.

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patentability.”258 The Federal Circuit also rejected the argument that it was at most “obvious to try” the besylate salt form, concluding that, “on the particularized facts of this case,”259 based on the teachings of the prior art, one skilled in the art had a reasonable expectation of success “and merely had to verify that expectation.”260

Finally, the Federal Circuit rejected the district court’s finding that unexpected properties supported nonobviousness, concluding that “Pfizer engaged in routine, verification testing to optimize selection of one of several known and clearly suggested pharmaceutically-acceptable salts to ease its commercial manufacturing and marketing of the tablet form of the therapeutic amlodipine.”261 The court found the superior properties of stability and ease of processing, and the overall combination of good properties, were not adequate to overcome prima facie obviousness because the improvements did not improve the therapeutic value of the drug compared to the maleate salt that it concluded was also useable.

The selection of a particular salt form for an active pharmaceutical ingredient may be patentable over prior art that teaches the use of that active compound in the form of an unspecified pharmaceutically acceptable salt. In two cases, a new salt of an active compound was found to be non-obvious based on the unpredictability of the properties of a new salt to find that there was no reasonable expectation of success from placing the active compound into the particular salt form.

In Sanofi-Synthelabo v. Apotex, Inc.,262 the patent claimed the bisulfate salt of the d-enantiomer of a compound sold in the form of clopidogrel bisulfate under the trade name Plavix.®263 A prior art patent had disclosed the racemate of the compound and included a disclosure that pharmaceutically acceptable salts could be made of compounds within a genus that included the particular racemate. The prior art patent also gave examples of compounds within the genus, including the particular racemate as a hydrochloride salt and additional compounds outside of the genus as other salts, including bisulfate but without showing a preference for bisulfates.264 The district court granted a preliminary injunction, ruling that Apotex failed to make a substantial showing that the patent was likely invalid. The district court based its conclusion in part on the “unpredictability of salt formation,” relying on the defendants’ expert testimony that the “salt formation was an unpredictable exercise that would require a chemist ‘to engage in experimentation to determine which salt would in fact be suitable.’” 265 On these findings of fact, the Federal Circuit affirmed the district court’s holding that Apotex had not raised a substantial issue of invalidity of the patent because of obviousness.

Subsequently, after a full trial on the merits, the district court in Sanofi-Synthelabo v. Apotex, Inc.,266 rejected Apotex’s challenge that the claimed clopidogrel bisulfate compound was invalid. As to anticipation, the district court found that the prior art patent, which disclosed the racemate

258 Id.259 Id. at 1367 (emphasis in original).260 Id.261 Id. at 1371.262 Sanofi-Synthelabo v. Apotex, Inc., 470 F.3d 1368 (Fed. Cir. 2006).263 Id. at 1372.264 Id. at 1377-78.265 Id. at 1379.266 Sanofi-Synthelabo v. Apotex, Inc., 492 F. Supp. 2d 353 (S.D.N.Y. 2007).

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of which clopidogrel is the d-enantiomer, did not expressly or inherently describe the d-enantiomer or the d-enantiomer in the bisulfate salt form.267 As to obviousness, the district court separately addressed the selection of the d-enantiomer of the racemate and the selection of the bisulfate salt form. While the district court assumed that the d-enantiomer would have been prima facie obvious, it concluded that there was no reasonable expectation of success that the d-enantiomer would have had all of the pharmaceutical activity and none of the toxicity of the racemate.268 In addition, the district court found that the selection of the bisulfate salt form was non-obvious because it was unexpected that the bisulfate would be the only salt form of clopidogrel obtained by Sanofi that demonstrated a highly favorable combination of properties.269

In reaching its decision that the bisulfate salt form of clopidogrel was non-obvious, the district court considered and distinguished the Federal Circuit’s decision in Pfizer, Inc. v. Apotex, Inc.270 First, the district court pointed to the conclusion in Pfizer that there was an identifiable structural feature that would have led one skilled in the art to select the claimed besylate salt to solve the problems experienced with the prior art maleate salt, whereas there were no structural features that would have led to the selection of any particular salt form for clopidogrel.271

Second, the district court pointed out that in Pfizer, prior art references “specifically suggested to a person of ordinary skill in the art that the use of the besylate salt would offer improved stability in the particular compound at issue,”272 whereas there was “no prior art teaching that that the bisulfate salt was particularly likely to be a successful salt form of clopidogrel.”273

In Pfizer Inc. v. Ranbaxy Labs., Ltd.,274 the prior art patent had identified the drug compound and its use in the form of pharmaceutically acceptable salts, and had identified fifty counter-ions, including calcium, that could be used to make salts of the compound. The district court found that the claim of the patent in suit to the calcium salt of the therapeutic compound was at most obvious to try, but was not obvious, because the properties of new salts are unpredictable.275 On

267 Id. at 383-386. The district court also found no anticipation because it concluded that the prior art did not enable making clopidogrel bisulfate without undue experimentation. Id. at 386-387. In particular, the district court concluded that the prior art did not disclose to a person skilled in the art how to separate the enantiomers of the racemate; that the prior art also did not provide any specific guidance leading to the bisulfate salt; and that making the determination to use the bisulfate salt would have taken undue experimentation. Id.

268 Id. at 390.269 Id. at 391. These favorable properties included “a high melting point, long-term stability, non-

hygroscopicity, and good stability.” Id. at 375. The district court also noted that a “prior art reference—the Berge publication—did not even list the bisulfate salt in its list of FDA-approved commercially marketed salts; the bisulfate appears only on the list of non-FDA approved salts, making it all the more surprising that the bisulfate salt of clopidogrel, in fact, proved to be a highly suitable pharmaceutical formulation.” Id.

270 Pfizer, Inc. v. Apotex, Inc., 480 F.3d 1348 (Fed. Cir. 2007), reh’g denied, 488 F.3d 1377 (Fed. Cir. 2007).

271 Sanofi-Synthelabo, 492 F. Supp. 2d at 391.272 Id.273 Id. at 391-92.274 Pfizer Inc. v Ranbaxy Labs., Ltd., 405 F. Supp. 2d 495, 517 (D. Del. 2005), rev’d on other

grounds, 457 F.3d 1284 (Fed. Cir. 2006).275 Patent claims are not obvious if the prior art suggests that their subject matter is merely “obvious

to try.” In re O’Farrell, 853 F.2d 894, 903 (Fed. Cir. 1988); see also In re Geiger, 815 F.2d 686, 688 (Fed. Cir. 1987). Claims are merely “obvious to try” where there is a teaching to “try each of numerous possible choices until [reaching] a successful result,” but no teaching “as to which of many possible choices is likely to be successful.” O’Farrell, 853 F.2d at 903.

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appeal, the Federal Circuit held that the claim was invalid because it was improperly dependent, but did not discuss the non-obviousness determination.276

b. Most Common Salt Form Used for Known Active Found Obvious in Obviousness-Type Double Patenting Analysis

On the other hand, in Eli Lilly & Co. v. Barr Labs., Inc.,277 the court held that non-statutory type double patenting was not avoided where the first patent claimed the use of the compound fluoxetine or pharmaceutically acceptable salts thereof to treat anxiety, and the second patent claimed the use of fluoxetine hydrochloride salt to inhibit the uptake of serotonin.278 The Federal Circuit held that the later claim was invalid for double patenting on anticipation grounds because the administration of fluoxetine to treat anxiety claimed in the first patent inherently inhibited the uptake of serotonin as claimed in the second patent. The second patent merely claimed the mechanism of action of fluoxetine that resulted in the treatment of anxiety.

The Federal Circuit also found that the second claim’s limitation to the particular hydrochloride salt of fluoxetine did not provide a patentable distinction over the first claim, stating “[a] person of ordinary skill in the art would have recognized that fluoxetine hydrochloride is a pharmaceutically-acceptable salt of fluoxetine. In fact, hydrochloride salts are the most common pharmaceutically acceptable salts of basic drugs, and hence are obvious compounds. See, e.g., The Merck Index of Chemicals and Drugs (Paul G. Stecher et al. eds., 7th ed. 1960).279 The Federal Circuit did not refer to any argument concerning whether there was a reasonable expectation of success.

276 Pfizer, 457 F.3d at 1291-92.277 Eli Lilly & Co. v. Barr Labs., Inc., 251 F.3d 955, 969 (Fed. Cir. 2001).278 Id. at 969.279 Id. See also Berge, supra note 242, which also reports that hydrochloride was the most commonly

used acid to make salts of active base compounds, it having been used in over 42.9% of salts that were approved by the FDA, far more than any other acid.

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