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Synthesis of an OidiolactoneAnalogue from Abietic AcidPaulo M. Imamura a & Catarina dos Santos aa Instituto de Química, Universidade Estadual deCampinas, Campinas, São Paulo, BrazilPublished online: 16 Aug 2006.

To cite this article: Paulo M. Imamura & Catarina dos Santos (2005): Synthesis of anOidiolactone Analogue from Abietic Acid, Synthetic Communications: An InternationalJournal for Rapid Communication of Synthetic Organic Chemistry, 35:15, 2057-2065

To link to this article: http://dx.doi.org/10.1081/SCC-200066683

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Synthesis of an Oidiolactone Analoguefrom Abietic Acid

Paulo M. Imamura and Catarina dos Santos

Instituto de Quımica, Universidade Estadual de Campinas, Campinas,

Sao Paulo, Brazil

Abstract: A synthesis of a new analogue of homosesquiterpene oidiolactone is

described, starting from abietic acid.

Keywords: Abietic acid, oidiolacetone analogue

Oidiodendronic acid (1) and oidiodendrolide C (2) represent a new class of

metabolites isolated from extracts of the fungus Oidiodendron truncata[1,2]

that show potent antifungal activities against human pathogenic yeast

(Figure 1). Recently, for use in biological screening for this class of

compounds, Barrero et al.[3] synthesized compound 2 starting from the

natural diterpene trans-communic acid (3). To evaluate the biological activi-

ties resulting from structural modifications of 2, we envisioned the synthesis of

oidiolactone analogue 4 starting from polyoxgenated compound 6, readily

prepared from 5a in three steps.[4] Selective cleavage of the C12/C13 bond

was the key step for success in the synthesis of the target molecule.

The diester 7 was also obtained previously in a good yield through

oxidation of 6 with Jone’s reagent followed by treatment with diazomethane

(Scheme 1).[4] The Baeyer–Villiger reaction of 7 with mCPBA led, as

expected, to the migration of the more-substituted alkyl group C-15,[5] to

furnish isopropyl ester 8 in 42% yield.

Thus, the ozonolysis of the silyl-enol-ether prepared from the correspond-

ing ketone at C-13 seems to be an alternative to selectively cleave the

Received in the USA March 23, 2005

Address correspondence to Paulo M. Imamura, Instituto de Quımica, Universidade

Estadual de Campinas, UNICAMP C.P. 6154, 13084-971 Campinas, Sao Paulo, Brazil.

E-mail: imam@iqm.unicamp.br

Synthetic Communicationsw, 35: 2057–2065, 2005

Copyright # Taylor & Francis, Inc.

ISSN 0039-7911 print/1532-2432 online

DOI: 10.1081/SCC-200066683

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C12/C13 bond.[6] First, to selectively protect the aldehyde group, compound 6

was treated with ethylene glycol in an acidic medium (TsOH or camphorsul-

fonic acid), which only led to an intractable mixture of products. The reaction

of 6 with LDA/TMSCl at 2788C to directly prepare the corresponding silyl-

enol-ether also furnished a mixture of compounds from which, after silica-gel

column chromatography, an intramolecular aldol-dehydration product 9 was

isolated in 12% yield (Scheme 2).

To improve the yield of aldol product, different bases, such as sodium

ethoxide, potassium t-butoxide, and t-butyl lithium, were tried without any

success. After many attempts we found that the use of sodium methoxide in

methanol at 08C provided the best conditions to smoothly transform 6 to the

desired adduct 10 in 56% yield (Scheme 2), which was characterized by

analysis of IR and 1H and 13C NMR spectra. The stereochemistries at C-12

and C-14 were established through NOE experiments where irradiation of

H-7 (d 3.27) resulted in an enhancement of the signals of H-14 at d 3.99

(0.5%) and H-6 at d 1.75 (3.6%). Irradiation of H-14 showed an enhancement

of the signals of H-7 at d 3.27 (1%), H-12 at d 3.00 (0.2%), H-11b at d 1.48

(1%), and Me-20 at d 0.84 (0.5%) (Figure 2).

Dehydration of compound 10 was initially troublesome. Treatment of 10

under acidic conditions (p-TsOH or camphorsufonic acid) led to only an

intractable mixture of products, whereas from the reaction of 10 with MsCl

Figure 1. Structures of compounds 1–4.

Scheme 1.

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or TsCl, only the starting material was recovered. These results are probably

due to the steric hindrance and low access of the reagent to the hydroxyl group,

resulting from hydrogen bonding with the epoxide. Treatment of 10 with

thionyl chloride in pyridine furnished a 1:1 epimeric mixture of chloride 11

in 75% yield, together with diol-enone 12 in 8% yield. (Although

compound 11 showed only one spot on TLC eluted in several different

solvents, the 1H and 13C NMR spectra showed duplicated signals, indicating

Scheme 2. Reagents and conditions: a. LDA, TMSCl, THF, 2788C (12%);

b. MeO2Naþ/MeOH, rt (56%); c. SOCl2, Py, rt; d. (F3CCO)2O, CH2Cl2 (58%).

Figure 2. NOE experiments on compound 10.

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that it is an epimeric mixture of chlorides.) Compound 11 was obtained as

yellowish oil and the HREIMS gave a [Mþ.] at m/z 382.19327, corresponding

to the molecular formula C21H31ClO4 (calc. 382.19108). The HREIMS of

compound 12 gave a [Mþ.-H2O] at m/z 346.2247, corresponding to the

molecular formula C21H32O5-H2O (calc. 346.21441), and structure was

confirmed based on spectroscopic data analysis.

The desired product 9 was finally achieved in a moderate yield (58%)

when 10 were treated with trifluoroacetic anhydride in methylene chloride

in the presence of DMAP at 08C.

Next, ozonolysis of 9 followed by reductive treatment with Ph3P or with

NaBH4 led to only an unstable and complex mixture of products. Thus, we

decided to follow the sequence of reactions without any purification of the

intermediates as shown in Scheme 3. The purification of final crude product

using silica-gel column chromatography furnished the desired compound 3

in 17% overall yield.

Thus, the oidiolactone analogue 3 was prepared in eight steps from 5b, in

5.5% overall yield. None of synthesized compounds presented activity for

assay with Artemia salina.[7]

EXPERIMENTAL

General

Melting points were determined on a Mettler FP-52 installed on an Olympus

CBA-K microscope and are uncorrected. IR spectra were recorded on a Perkin

Elmer 1600 FTIR or on a BOMEM MB-100 instrument. 1H NMR and 13C

NMR spectra were recorded on a Bruker AC 300 spectrometer at 300 MHz

Scheme 3. Reagents and conditions: a. O3, CH2Cl2, 2788C; b. NaBH4, MeOH;

c. NaIO4, rt (17%, three steps).

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and 75 MHz, respectively, or on a Varian Inova 500 spectrometer at 500 MHz

and 125 MHz, respectively, with CDCl3 as solvent and TMS as internal

standard. High-resolution mass spectra were obtained on a VG Autospec-

Micromass. Optical rotations were measured with a Carl Zeiss photoelectric

polarimeter.

Synthesis of 8

To a solution of 7[4] (62.0 mg, 0.16 mmol) in CH2Cl2 (10.0 mL) was added

mCPBA (55.0 mg, 0.32 mmol) and NaHCO3 (27.0 mg, 0.32 mmol) and the

mixture was refluxed for 36 h. After cooling and filtration of the reaction

mixture, the organic phase was washed with saturated solutions of NaHCO3

and of brine and dried with anhydrous MgSO4, and the solvent was

removed under reduced pressure. The residue was chromatographed on

silica gel (n-hexane–ethyl acetate 85:15) to give 8 (27.3 mg, 42%) as

colorless oil. [a]D20þ 22.38 (c ¼ 1.1, CHCl3); IR (film) nmax 3439, 2952,

1732, 1440, 753 cm21; 1H NMR (300 MHz) d 0.94 (s, 3H, H-20), 1.10

(m, Hax-1), 1.21 (d, J ¼ 7.1 Hz, 3H, H-15), 1.22 (s, 3H, H-19), 1.24

(d, J ¼ 7.1 Hz, 3H, H-16), 1.52 (m, 1H, H-9), 1.53 (m, 2H, H-2), 1.57

(m, 2H, H-3), 1.60 (m, 1H, Hax-11), 1.70 (m, 2H, H-6), 1.77 (m, 1H, H-5),

1.88 (m, 1H, Heq-1), 2.05 (m, 1H, Heq-11), 2.20 (m, 2H, H-12), 3.21

(m, 1H, H-7), 3.66 (s, 3H, H-21), 3.75 (s, 3H, H-22), 5.0 (sept, J ¼ 6.6 Hz,

1H, H-14); 13C NMR (75 MHz) d 14.6 (C-20), 16.9 (C-19), 17.9 (C-2), 19.5

(C-11), 21.7 (C-15 and C-16), 23.6 (C-6), 33.3 (C-12), 34.6 (C-10), 36.6

(C-3), 37.4 (C-1), 40.9 (C-12), 46.4 (C-4), 52.0 (C-21), 52.2 (C-22), 53.3

(C-9), 57.1 (C-7), 58.7 (C-8), 67.7 (C-14), 170.6 (C-13), 172.7 (C-17),

178.3 (C-18); HREIMS (Mþ.) calcd. for C22H34O7 410.23045, found

410.23036.

Synthesis of Compound 10 from 6

To an ice-cold solution of sodium methoxide, prepared from sodium (20.0 mg,

0.873 mmol) in dry methanol (2.0 mL) was added a solution of 6 (94.5 mg,

0.26 mmol) in dry methanol (2.0 mL). After stirring for 2 h, the reaction

mixture was neutralized by adding dropwise a solution of 5 molL21 HCl

and the solvent was removed under reduced pressure. The crude product

was dissolved in ethyl acetate (10.0 mL), which was washed with water

(10.0 mL) and dried with anhydrous MgSO4. The solvent was then removed

under reduced pressure. The residue was chromatographed on silica gel

(n-hexane–ethyl acetate 85:15) to give 10 (53.0 mg, 56%) as yellowish

crystals: mp 82.5–84.58C; [a]D20þ 25.08(c ¼ 1.6, CHCl3); IR (film) nmax

2952, 1728, 1436, 1389, 1247, 737 cm21; 1H NMR (500 MHz) d 0.84

(s, 3H, H-20), 1.10 (m, 1H, Hax-1), 1.13 (t, J ¼ 6.6 Hz, 6H, H-15, H-16),

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1.25 (s, 3H, H-19), 1.48 (m, 1H, Ha-11), 1.50 (m, 2H, H-2), 1.60 (m, 1H, Heq-1),

1.63 (m, 2H, H-3), 1.75 (m, 2H, H-6), 1.79 (m, 1H, Hb-11), 1.84 (m, 1H, H-9),

1.86 (m, 1H, H-5), 2.37 (d, J ¼ 7.8 Hz, OH), 2.79 (sept, J ¼ 7.0 Hz, H-14),

3.00 (m, 2H, H-12), 3.27 (s, 1H, H-7), 3.67 (s, 3H, H-21), 3.99 (dd,

J ¼ 14.8 Hz, 7.6 Hz, 1H, H-17); 13C NMR (125 MHz) d 15.4 (C-20), 17.3

(c-19), 17.5 (C-2), 17.9 (C-15 and C-16), 24.2 (C-11), 24.3 (C-6), 33.6

(C-10), 36.9 (C-4), 38.9 (C-1), 40.6 (C-5), 41.4 (C-14), 45.8 (C-4), 52.0

(C-21), 55.2 (C-9), 55.9 (C-12), 56.2 (C-7), 64.4 (C-8), 73.5 (C-17), 178.2

(C-18), 215.4 (C-13); MS m/z (%) 346 (Mþ., 1) 331 (21), 321 (37), 303 (28),

287 (17), 275 (48), 261 (15), 243 (54), 215 (52), 197 (30), 190 (24), 179 (55),

153 (38), 135 (28), 123 (47), 109 (90), 95 (21), 81 (25), 71 (100), 55 (27);

HREIMS (Mþ.- H2O) calcd. for C21H30O4 346.21441, found 346.22069.

Synthesis of 11 and 12

To a solution of 10 (97.9 mg, 0.27 mmol) in dry pyridine (0.3 mL) at 08C was

added thionyl chloride (200mL, 1.68 mmol). After the mixture had been

stirred for 2 h, a few drops of iced water were carefully added and the

solution was diluted with ethyl acetate (30.0 mL). The organic phase was

washed with 10% NaHCO3, 5% HCl, and brine, and dried with anhydrous

MgSO4. The solvent was removed under reduced pressure. The residue was

chromatographed on silica gel (n-hexane–ethyl acetate 85:15) to give a

C-14 (1:1) epimeric mixture of chloride 11 and the enone 12.

Compound 11 (72.9 mg, 75%) was a yellowish oil: Rf: 0.27 (n-hexane–

ethyl acetate 7:3); IR (film) nmax 2969, 1723, 1469, 1434, 1251, 1192, 1155,

737, 703 cm21; 1H NMR (300 MHz) d 0.79 and 0.82 (s, 3H, H-20) 1.06

(m, 1H, Hax-1), 1.10 (d, 3H, J ¼ 7.0 Hz, H-15), 1.12 (d, 3H, J ¼ 7.0 Hz,

H-16), 1.23 (s, 3H, H-19), 1.46 (m, 2H, H-2), 1.48 (m, 1H, Hax-11), 1.58

(m, 1H, Heq-1), 1.62 (m, 2H, H-3), 1.66 (m, 1H, H-6), 1.69 (m, 1H, Heq-11),

1.84 (m, 1H, H-5), 1.90 (bs, 1H, H-9), 2.66 and 2.70 (sept, J ¼ 7.1 Hz, 1H,

H-14), 3.32 (m, 1H, H-12), 3.40 (m, 1H, H-7), 4.81 and 4.95 (d, 1H,

J ¼ 9.2 Hz, 1H, H-17); 13C NMR (75 MHz) d 15.5 and 15.6 (C-20), 17.4

and 17.5 (C-19), 17.6 (C-2), 17.6 (C-15), 17.7 (C-16), 24.2 (C-11), 24.4 and

25.5 (C-6), 33.5 and 33.6 (C-10), 36.8 (C-3), 38.9 and 39.1 (C-1), 39.8 and

40.0 (C-5), 41.0 and 41.4 (C-14), 45.8 and 45.9 (C-4), 52.0 and 52.1

(C-12), 52.3 (C-21), 53.0 (C-9), 54.4 and 55.2 (C-7), 62.1 and 62.2 (C-8),

74.4 and 75.3 (C-17), 178.2 and 178.3 (C-18), 213.5 and 213.14 (C-13);

HREIMS (Mþ.) calcd. for C21H31ClO4 382.19108, found 382.19327.

Compound 12 (7.7 mg, 8 %) was a yellowish oil; Rf: 0.36 (n-hexane–

ethyl acetate 7:3); [a]D20 217.08 (c ¼ 0.9, CHCl3); IV (film) nmax 3448, 2984,

1721, 1650, 1458, 1389, 1249, 1141, 738 cm21; 1H NMR (300 MHz) d 0.64

(s, 3H, H-20), 1.06 (m, 1H, Hax-1), 1.12 (s, 3H, H-15), 1.13 (s, 3H, H-16),

1.19 (s, 3H, H-19), 1.52 (m, 2H, H-2), 1.60 (m, 2H, H-3), 1.62 (m, 1H,

Heq-1), 1.71 (m, 2H, H-6), 2.00 (m, 1H, H-5), 2.10 (d, J ¼ 5.9 Hz, 1H,

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H-9), 2.20 (s, 1H, OH), 2.46 (d, J ¼ 17.1 Hz, 1H, Hax-11), 2.81 (ddd, J ¼ 17.1,

5.9 and 2.53 Hz, 1H, Heq-11), 3.23 (sept, J ¼ 7.1 Hz, 1H, H-14), 3.70 (s, 3H,

H-21), 4.35 (dd, J ¼ 11.0 and 9.5 Hz, 1H, H-7), 6.92 (d, J ¼ 2.6 Hz, 1H,

H-17); 13C NMR (75 MHz) d 15.8 (C-20), 17.1 (C-19), 17.3 (C-2), 18.6

(C-15), 19.4 (C-16), 31.8 (C-11), 33.2 (C-6), 36.4 (C-14), 36.8 (C-3), 36.8

(C-10), 38.8 (C-1), 46.5 (C-5), 46.8 (C-4), 52.3 (C-21), 60.8 (C-9), 66.9

(C-7), 87.2 (C-8), 140.7 (C-17), 148.2 (C-12), 178.5 (C-18), 203.6 (C-13);

HREIMS (Mþ-H2O) calcd for C21H32O5-H2O 346.21441; found 346.2247.

Synthesis of Compound 9

To a solution of 10 (835.5 mg, 2.30 mmol) in anhydrous CH2Cl2 (3.0 mL) at

08C under nitrogen atmosphere was added triethylamine (890mL, 6.0 mmol)

and a solution of DMAP (catalyst) in anhydrous CH2Cl2 (4.0 mL), followed

by careful addition of a solution of trifluoroacetic anhydride (536mL,

3.1 mmol) in anhydrous CH2Cl2 (0.6 mL). After 15 min the ice bath was

removed, the reaction mixture was stirred at room temperature for 24 h, and

then water (1.0 mL) and a saturated solution of Na2CO3 (1.0 ml) were

added. The reaction mixture was extracted with ethyl acetate (3 � 10.0 mL)

and dried with anhydrous MgSO4, and the solvent was removed under

reduced pressure. The residue was chromatographed on silica gel (n-hexane–

ethyl acetate 85:15) to give 9 (463.4 mg, 58%) as yellowish crystals:

mp 72.5–74.58C; [a]D20þ 86.98 (c ¼ 0.9, CHCl3); IR (film) nmax 2969,

1723, 1669, 1455, 1386, 1255, 1196, 737 cm21; 1H NMR (500 MHz) d 0.77

(s, 3H, H-20), 0.90 (m, 1H, Hax-1), 1.10 (d, J ¼ 7.0 Hz, 3 H, H-15), 1.13

(d, J ¼ 7.0 Hz, 3H, H-16), 1.24 (s, 3H, H-19), 1.48 (m, 1H, H-9), 1.50

(m, 2H, H-2), 1.67 (m, 2H, H-6), 1.73 (m, 1H, H-5), 1.84 (m, 1H, Heq-1),

1.86 (m, 1H, H-5), 2.05 (dd, J ¼ 9.8, 4.9 Hz, 1H, H-9), 2.47 (ddd, J ¼ 18.0,

9.8, 1.8 Hz, 1H, Hax-11), 2.77 (ddd, J ¼ 18.0, 4.9, 1.8 Hz, 1H, Heq-11), 3.16

(sept, J ¼ 6.7 Hz, 1H, H-14), 3.46 (t, J ¼ 1.53 Hz, 1H, H-7), 3.67 (m, 3H,

H-21), 6.23 (t, J ¼ 1.8 Hz, 1H, H-17); 13C NMR (125 MHz) d 13.9 (C-18),

17.3 (C-19), 17.6 (C-2), 19.0 (C-15), 19.3 (C-16), 25.0 (C-6), 30.0 (C-11),

33.8 (C-10), 36.6 (C-14), 37.0 (C-3), 39.2 (C-1), 40.2 (C-5), 46.1 (C-4),

51.2 (C-9), 52.12 (C-21), 59.0 (C-7), 70.5 (C-8), 140.0 (C-17), 147.9

(C-12), 178.3 (C-18), 202.6 (C-13); MS m/z (%) 346 (58), 317 (38), 257

(32), 195 (34), 194 (34), 179 (71), 135 (100), 107 (28), 84 (29), 71 (34), 55

(35); HREIMS (Mþ.) calcd. for C21H30O4 346.21441, found 346.21458.

Synthesis of Oidiolactone Analogue 4

A stream of ozone was passed through a stirred solution of 9 (110 mg,

2.90 mmol) in dry CH2Cl2 (20.0 mL) at –788C until a blue color persisted.

The excess of ozone was then removed by passing nitrogen through the

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mixture and the solvent was removed under reduced pressure. The residue was

dissolved in dry methanol (10.0 mL) and cooled to 08C, and NaBH4

(329.0 mg, 7.8 mmol) was added. Next, the ice bath was removed to allow

the temperature of the reaction mixture rise to room temperature. After

stirring for 3 h, the solvent was removed under reduced pressure and the

residue was dissolved in ethyl acetate (30 mL). The organic phase was

washed with brine and dried with anhydrous MgSO4, the solvent was

removed under reduced pressure, and the crude product was filtered through

a silica-gel pad (CH2Cl2–MeOH, 94:6). After removing the solvent, the

residue was dissolved in methanol (10.0 mL), and NaIO4 (40.0 mg,

0.19 mmol) was added. The reaction mixture was stirred at room temperature

for 15 h, and then the solvent was removed under reduced pressure. The

residue was dissolved in water (3.0 mL), acidified with 5% HCl to pH 4,

and extracted with EtOAc (3 � 20.0 mL). It was washed with brine and

dried with anhydrous MgSO4. The solvent was removed under reduced

pressure. The residue was chromatographed on silica gel (n-hexane–ethyl

acetate 85:15) to give 4 (15 mg, 17%) as yellowish oil. [a]D20þ11.58

(c ¼ 0.7, CHCl3); IR (film) nmax 3436, 2932, 1454, 1724, 1460, 1238, 1045,

735 cm21; 1H NMR (300 MHz) d 0.91 (s, 3H, H-16), 1,00 (m, 1H, Hax-1),

1.25 (s, 3H, H-15), 1,52 (m, 2H, H-2), 1.69 (m, 2H, H-3), 1.74 (m, 1H, Heq-1),

1.80 (m, 1H, Heq-6), 1.93 (dd, J ¼ 12.0, 6.3 Hz, 1H, H-5), 1.98 (dd,

J ¼ 11.0, 6.2 Hz, 1H, H-9), 2.43 (dd, J ¼ 15.0, 11.0 Hz, 1H, Hax-11), 2.64

(dd, J ¼ 15.0, 6.2 Hz, 1H, Heq-11), 3.20 (s, 1 H, H-7), 3.67 (s, 3H, H-17),

3.98 (d, J ¼ 12.8 Hz, 1H, Heq-13), 4.27 (d, J ¼ 12.8 Hz, 1H, Hax-13); 13C

NMR (75 MHz) d 14.8 (C-16), 17.4 (C-15), 17.6 (C-2), 24.0 (C-6), 28.9

(C-11), 34.0 (C-10), 36.6 (C-3), 37.8 (C-1), 39.2 (C-5), 46.0 (C-4), 46.4

(C-9), 52.1 (C-17), 55.7 (C-7), 56.4 (C-8), 71.9 (C-13), 172.3 (C-12), 177.6

(C-14); HREIMS (Mþ.) calcd. for C17H24O5 308.16237, found 308.16224.

ACKNOWLEDGMENTS

We are grateful to FAPESP for financial support and to Harima do Parana

Industria Quımica Ltd. and Especialidades Quımicas Parana S.A. for

providing Pinus elliottii’s resin. C. S. acknowledges CNPq for a fellowship.

We also thank C. H. Collins for reading this paper and L. H. B. Baptistella

for helpful discussions.

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