ISSN: 0973-4945; CODEN ECJHAO
E-Journal of Chemistry
http://www.e-journals.net 2010, 7(3), 844-848
Detection, Isolation and Characterization of Principal
Synthetic Route Indicative Impurity in Lansoprazole
K.S.V SRINIVAS*, K MUKKANTI,
R BUCHI REDDY§ and P SRINIVASULU
*Analytical Development Laboratory,
Inogent Laboratories Private Limited, No. 28A, IDA,
Nacharam, Hyderabad, 500 076, India. §Research & Development Laboratory,
Inogent Laboratories Private Limited, No. 28A, IDA,
Nacharam, Hyderabad, 500 076, India.
Centre for Environment,
JNT University, Kukatpally, Hyderabad, 500 072, India.
Received 1 April 2009; Accepted 1 June 2009
Abstract: An unknown impurity in lansoprazole (2-[[[3-methyl-4-(2, 2,
2-trifluoroethoxy)-2-pyridyl] methyl] sulfinyl] benzimidazole) was
detected by HPLC and was identified as des-(trifluoroethoxy)
lansoprazole, an principal synthetic route indicative impurity of
lansoprazole. Lansoprazole was subjected to different ICH prescribed
stress conditions like hydrolysis, oxidation, photolysis and thermal
degradation conditions to enrich the impurity. The impurity was enriched
by using acid catalytic degradation, isolated by using preparative HPLC
and characterized (FTIR, MS and NMR). Limit of Detection (LOD) and
Limit of Quantification (LOQ) are found to be 0.014% and 0.035%
respectively.
Keywords: Impurity, Isolation, Characterisation, Preparative HPLC, Degradation.
Introduction
Lansoprazole (1) (Figure 1), a substituted benzimidazole, 2-[[[3-methyl-4-(2,2,2-
trifluoroethoxy)-2-pyridyl] methyl] sulfinyl] benzimidazole, a compound that inhibits gastric
acid secretion. Lansoprazole is in a class of drugs called proton pump inhibitors (PPI)
which block the production of acid by the stomach. Proton pump inhibitors are used for the
Detection, Isolation and Characterization 845
treatment of conditions such as ulcers, gastroesophageal reflux disease (GERD) and
Zollinger-Ellison Syndrome that are caused by stomach acid. Lansoprazole, like other
proton-pump inhibitors, blocks the enzyme in the wall of the stomach that produces acid. By
blocking the enzyme, the production of acid is decreased, and this allows the stomach and
esophagus to heal. The recemic mixture of the lansoprazole was introduced as a therapeutic
agent under the trade name of Prevacid1® (TAP Pharmaceutical Products Inc.)
Here, we report the structural characterization of the unknown impurity (5) (Figure 1).
Figure 1. Structures of lansoprazole and impurities.
The different analytical techniques reported so far for the determination of this drug
along with corresponding impurities by UV-Visible spectrophotometry2. Several HPLC
methods involving assay and a LC–MS/MS method for the determination of impurities and
degradation products of lansoprazole have been published3-5
.
The lansoprazole sample containing 0.09% of unknown impurity at 0.52 RRT was
observed when the sample was analysed by using chromatographic conditions published in
the USP monograph for lansoprazole6. As per regulatory guidelines, the pharmaceutical
studies using a sample of the isolated impurities can be considered for safety assessment. It
is therefore, essential to isolate and characterize unidentified impurities present in the drug
sample7. Forced degradation studies were conducted to enrich this impurity and were formed
under acid hydrolytic conditions along with other known impurities. The acid degraded
sample was taken for the isolation of unknown impurity by using preparative HPLC and the
isolated impurity was charecterised by using LC-MS, NMR and IR .To the best of our
knowledge, the impurity detected at 0.52 RRT was published for first time.
Chromatogram
Ab
sorb
ance
, A
U
Time, min
Time, min
Ab
sorb
ance
, A
U
Time, min
Ab
sorb
ance
, A
U
846 K.S.V SRINIVAS et al.
Figure 2. Typical chromatograms of lansoprazole (a) Spiked with all impurities (b) Under
acid hydrolytic conditions and (c) Isolated impurity 1.
(a)
(b)
(c)
Detection, Isolation and Characterization 847
Experimental
HPLC grade acetonitrile, HPLC grade triethylamine (TEA) and HPLC grade ortho
phosphoric acid were purchased from Merck (Darmstadt, Germany).
Instrumentation
The HPLC system was equipped with quaternary gradient pumps with auto sampler and auto
injector (Model Alliance 2695, Make Waters USA ) connected with photo diode array
detector (PDA Model 2996, Make Waters USA) controlled with Empower
software(Make Waters , USA).
The preparative HPLC system was equipped Prep LC controller with binary gradient
pumps with Waters fraction collector (model 2767, Make Waters USA) and with photo
diode array detector (PDA Model 2996, Make Waters USA) controlled with Empower 2
software (Make Waters, USA).
Positive ion ESI-MS was performed on 6310 ion-trap mass spectrometer (Agilent, USA)
equipped with an ESI source. Sample solutions were introduced into the ion source at a flow
rate of 4 Lm−1
, capillary voltage 3.8 kV, drying gas temperature 250 ◦C, drying gas flow rate
5 Lm−1
and nebulizer pressure 14 psi nitrogen was used as both nebulizing gas and drying gas.
1H and
13C NMR spectra were acquired Varian with autosampler version 2.2 C at 305 K.
The hydrogen and carbon chemical shifts are referred to the internal tetramethylsilane
(TMS). The coupling constants are expressed in Hertz.
The IR spectra were recorded in the solid state as KBr dispersion medium using Perkin-
Elmer Spectrum One FT IR spectrophotometer.
Isolation of the destrifuoro ethoxy impurity
Acid catalytic conditions
Sample was dissolved in 0.1N HCl and stirred for 30 minutes at 60 oC. The degraded sample
was subjected for preparative HPLC and isolated the impurity. The impurity (5) was
enriched to 17%.
Chromatographic conditions for preparative HPLC
The chromatographic separation was achieved on an Gemini C18 (Phenomenex, USA),
150 mm × 30 .0 mm, 5 µ semi preparative column using a mobile phase containing mixture
of water and acetonitrile (70 :30, v/v). The flow rate of the mobile phase was 20.0 mL min-1. The
column temperature was maintained at 25 ◦C and the wavelength was monitored at 285 nm. The
injection volume was 1000 µL. The test concentration for the analysis was 50 mg mL-1
. The
standard and the test dilutions were prepared in the mobile phase.
Isolation of the impurity The collected fractions from preparative HPLC were subjected to distillation for 60 min. to
remove the solvent and then crystallized by using lyophilizer.
Results and Discussion
The solid crystallized compound was analyzed by HPLC and the HPLC purity was found to
be 98.1%. The impurity was then characterized by using LC-MS, NMR and IR.
The +ve ES-MS spectrum of the impurity showed peaks at m/z 272.2 and 543.2
corresponding to the adduct ions (M+H)+ and (2M+H)+. Further the −ve ES-MS spectrum
showed peaks at m/z 270 corresponding to (M−H)−. The adduct ions confirm the molecular
ion of the impurity (5) to be m/z 271. The DEPT spectra displayed one negative signal due to
848 K.S.V SRINIVAS et al.
one methylene group and five positive peaks due to the presence of one methyl group and
the rest are due to the methine groups (all in aromatic). IR spectrum displayed characteristic
absorptions at 3061(Aromatic C-H stretching), 2967(Aliphatic C-H stretching), 1560
(Aromatic C=C, C=N stretching), 1433 (Aliphatic C-H bonding), 1267 (C-N
stretching),1022 (S=O stretching) and 748 cm-1
(Aromatic C-H stretching). Presence of
signals at 2.37 ppm (3H) and 4.89 ppm (2H) in 1H NMR spectrum was attributed to methyl
and methylene groups respectively. Other signal at 7.29, 7.47, 7.66 and 8.26 ppm attributed
to aromatic protons (Table.1). Limit of detection (LOD) and Limit of quantification (LOQ)
of the impurity was found to be 0.014% and 0.035% respectively.
Table 1. 1H and
13C NMR, MS and IR assignments for des-(trifluoroethoxy) lansoprazole.
Position 1H ppm/J 13
C MS IR
1 3H 2.37/s 15.19
2 -- -- 139.3
3 1H 7.47/m 116.0
4 1H 7.66/m 123.7
5 1H 8.26/d 132.3
6 -- -- 151.8
7 2H 4.89/s 60.2
8 -- -- 153.0
9 -- -- 123.2
10 -- -- 123.2
11 1H 7.66/m 143.7
12 1H 7.29/m 147.2
13 1H 7.29/m 147.2
14 1H 7.66/m 143.7
+ve ES-MS :
272.2 (M+H)+
543.2 (2M+H)+
-ve ES-MS:
270 (M-H)-
3061: Aromatic C-H
stretching
2967: Aliphatic C-H
stretching
1560: Aromatic C=C, C=N
stretching
1433 : Aliphatic C-H
bonding
1267 : C-N stretching
1022 : S=O stretching
748 : Aromatic C-H
stretching
Based on the above spectral data the molecular formula for impurity (5) could be
C14H13N3OS and the corresponding structure was characterized as 2-((3-methylpyridin-2-
yl)methylsulfinyl)-1H-benzo[d]imidazole.
References
1. Prevacid (Lansoprazole), Drug description, Pharmacology, Pharmacokinetics, Studies
Metabolism, http://www.rxlist.com/prevacid-drug.htm#cp. Accessed on March 2010.
2. Karljikovic-Rajic K, Novovic D, Marinkovic V and Agbaba D, J Pharm Biomed
Anal., 2003, 32,1019-1027.
3. El-Sherif Z A, Osman Mohamed A, El-Bardicy M G and El-Tarras M F, Chem Pharm
Bull., 2006, 54, 814-818.
4. DellaGreca M, Iesce M R, Previtera L, Rubino M, Temussi F and Brigante M,
Chemosphere, 2006, 63(7), 1087-1093.
5. Selenka J, Duff S, He J, Li K, Sunthankar P and Ding X, Aapspharmsci Abstracts,
AM_2007, AAPS2007-003647.PDF.
6. The United States Pharmacopoeia 30, Monographs: Monographs: Lansoprazole, 1229, 2007.
7. ICH, Draft Revised Guidance on Impurities in New Drug Substances Q3A (R2),
International Conference on Harmonisation, IFPMA, Geneva, 2006.
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