PROCESS RELATED IMPURITIES IN THE PREPARATION OF OLMESARTAN MEDOXOMIL: AN-ANTIHYPERTENSIVE DRUG

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1 Page2744 Indo American Journal of Pharmaceutical Research, 2015 ISS : PRCESS RELATED IMPURITIES I THE PREPARATI F LMESARTA MEDXMIL: A-ATIHYPERTESIVE DRUG Bommena Hanumantha Rao 1,2, Inti Venkata Subramanyeswara Rao 1, Vysyaraju Ravi Kanth 1, Korrapati Venkata Vara Prasadarao 1, K. Balamurali Krishna 2, Bethanabatla Syama Sundar * 2 1 Chemical Research and Development, Aurobindo Pharma Pvt Ltd, Survey o. 71& 72, Indrakaran Village, Sangareddy Mandal, Medak District, Telangana , India. 2 Department of Chemistry, Acharya agarjuna University, agarjuna agar, Guntur District, Andhra Pradesh , India. ARTICLE IF Article history Received 30/08/2015 Available online 30/09/2015 Keywords lmesartan Chloro Medoxomil, lmesartan Medoxomil Dimer, lmesartan Diol And Quaternary Salt Impurities. ABSTRACT lmesartan medoxomil is a prodrug within the class of angiotensin receptor antagonists, approved by the FDA for the treatment of hypertension. Present work describes the origin, synthesis and characterization of four process related novel impurities of olmesartan medoxomil viz. olmesartan chloro medoxomil, olmesartan medoxomil dimer, olmesartan diol and quaternary salt impurities. Corresponding author Dr. Bethanabatla Syama Sundar Department of Chemistry, Acharya agarjuna University. hbommena@gmail.com Please cite this article in press as Bommena Hanumantha Rao et al. Process Related Impurities in the Preparation of lmesartan medoxomil: An-antihypertensive Drug. Indo American Journal of Pharmaceutical Research.2015:5(09). Copy right 2015 This is an pen Access article distributed under the terms of the Indo American journal of Pharmaceutical Research, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

2 Page2745 Vol 5, Issue 09, Bommena Hanumantha Rao et al. ISS : ITRDUCTI In APIs, Impurities are the unwanted foreign materials which may originate from raw materials, develop during process development, and develop during formulation or upon aging of both API and formulated APIs to medicines. These related substances (impurities) in an active pharmaceutical ingredient (API) can have a momentous impact on the quality and safety of the drug products. ICH guidelines 1 also says that any impurities, which are forming at a level of 0.05% with respect to the API, should be identified, synthesized and characterized thoroughly. lmesartan medoxomil 1[Benicar, Sankyo pharma] is the newest agent in the class of angiotensin II receptor blockers 2,3 approved by the FDA for the treatment of hypertension 4 (Figure 1). The drug works by inhibiting the effects of angiotensin II, a potent vasoconstrictor and one of the key contributors to cardiovascular and renal disease. 5 H H 1 Figure 1. Chemical structure of olmesartan medoxomil (1). Recently we have reported a new process for the preparation 6 of 1 as shown in Scheme 1. In this process, we have noticed four new impurities. However to the extent that we are aware, the syntheses of these impurities were not reported so far. So we craving to discuss identification, synthesis and characterization of these impurities. H 2 H + Br H 3 4 H 6 (iii) H a 7 5 (iv) H H 1 Scheme 1: Synthesis of olmesartan medoxomil (1): DMAc, K 2 C 3, C, 12 h, 90% THF, C 2 H 5 H, H 2, 5 h, ah (iii) DMAc, ai (3% w/w), C, 10 h, 85% (iv) 75 % v/v Aq. AcH, C, 8 h, 76%.

3 Page2746 Vol 5, Issue 09, Bommena Hanumantha Rao et al. ISS : Even though, few authors have reported various possible process related impurities 7,8,9,10,11,12 of 1, the fact that there is some less data available to understand the complete impurity profile of olmesartan medoxomil (1). So, we have determined to synthesize all the possible impurities of 1 so that we can evaluate the extent of contamination of these impurities in 1. For the first time, during o u r process development of 1, we have observed t h e s e impurities in HPLC chromatograms. Some of them are carryover impurities from the raw materials and remaining are generated during process development. In LC-MS, apart from the molecular ion peak of 1, four more peaks with distinct molecular ions a r e observed. Based on these molecular ion peaks, we have envisaged the following four structures from 8 to 11, as shown in Figure 2. H CH H 3 3 C H H H H H 8 9 H H H H H H Figure 2. Related substances of olmesartan medoxomil (1). A comprehensive study has been undertaken to identify these impurities. Initially the impurities masses were evaluated by LC-MS and later confirmed by synthesizing them. The synthesized impurities structures have been established based on spectroscopic 1 techniques such as H MR, IR and mass spectroscopy. MATERIALS AD METHDS All reagents and solvents employed were of commercial grade and were used as such, unless otherwise specified. Reaction flasks were oven-dried at 200 C, flame-dried, and flushed with dry nitrogen prior to use. All moisture and air-sensitive reactions were carried out under an atmosphere of dry nitrogen. TLC was performed on Kieselgel 60 F254 silica-coated aluminum plates (Merck) and visualized by UV light ( = 254 nm) or by spraying with a solution of KMn4. rganic extracts were dried over anhydrous a 2 S 4. Flash chromatography was performed using Kieselgel 60 brand silica gel ( mesh). The melting points were determined in an instrument and were uncorrected. The IR spectra were obtained on a icolet 380 FT-IR instrument (neat for liquids and as KBr pellets for solids), HPLC (Agilent Technologies, 1200 series). MR spectra were recorded with a Varian 300 MHz Mercury Plus Spectrometer at 300 MHz (1H). Chemical shifts were given in ppm relative to trimethylsilane (TMS). Mass spectra were recorded on Waters quattro premier XE triple quadrupole spectrometer using either electron spray ionization (ESI) or atmospheric pressure chemical ionization (APCI) technique. Experimental/ Methodology Preparation of olmesartan chloro medoxomil (8): 4,5-Bis(chloromethyl)-1,3-dioxolen-2-one (13): To a solution of 4-chloromethyl-5- methyl-1, 3-dioxolen-2-one (6, 50 g, mol) in dichloromethane (500 ml) added sulfuryl chloride (45.5 g, mol), iodine (1 g) at C. Stirred the content at C for 1 h. Distilled off the dichloromethane completely under vacuum at 40 C resulted 4,5-Bis(chloromethyl)-1,3-dioxolen-2-one (13, 36 g) in 80% yield 99% purity by GC. 1 H MR (300 MHz, CD3 ): δ (ppm); 4.42 (s, 4H), m/z [GC-MS (QP-5050A)]-EI:182, 184, 186[(MH) + ]; C 5 H 4 C1 2 3.

4 Page2747 Vol 5, Issue 09, Bommena Hanumantha Rao et al. ISS : Preparation of olmesartan chloro medoxomil (8): To a solution of 5 (20 g, mol) in, Dimethylacetamide (60 ml) added compound 13 (3.8 g, mol), ai (0.6 g, 3% w/w) at C. Heated the contents to C and stirred for 24 h). To the reaction mass added dichloromethane (200 ml) followed by DM water (100 ml at C. Stirred the contents for 10 min and separated the aqueous layer. The resulted organic layer was washed with DM water (100 ml) followed by 10% aqueous sodium chloride solution (100 ml). The resulted organic layer was concentrated at 40 C under reduced pressure. The formed residue mass was suspended in 75% aqueous acetic acid (100 ml), stirred for 12 hat C. Filtered the byproduct (trityl alcohol), through hyflo bed, washed the wet cake with 75% aqueous acetic acid (20 ml). Filtrate was suspended in a mixture of dichloromethane (200 ml) and DM water (100 ml). Aqueous layer was separated and organic layer was concentrated and isolated the product 8 by column chromatography on silica gel (60x120 mesh) using mobile phase -ethyl acetate: hexanes (1:1) as white crystalline solid (5.9 g, 25%) with 99% Purity by HPLC. 1 H MR (300 MHz, DMS-d6 ): δ (ppm); 0.87 (t, 3H), 1.47 (s, 6H), 1.57 (m, 2H), 2.57 (t, 2H), 4.82 (s, 2H), 5.19 (s, 3H), 5.42 (s, 2H), 6.86 (d, 2H), 7.03 (d, 2H), (m, 4H), 16.2 (brs, 1H); m/z: 593.2[(MH) + ]; 595.2[(MH) + ]. C 29 H 29 C Preparation of olmesartan medoxomil dimer (9): To a solution of 5 (40 g, mol) in, Dimethylacetamide (60 ml) added 13 (3.8 g, mol), ai (4.2 g, mol) at C. Heated the content to C and stirred for 24 h. Added dichloromethane (200 ml), DM water (100 ml)to the reaction mass at C, aqueous layer was separated. The resulted organic layer was washed with DM water (50 ml) followed by 10% aqueous sodium chloride solution (50 ml). The resulted organic layer was concentrated at 40 C under vacuum, affords trityl olmesartan medoxomil dimer (15, 28 g, 68%) as pale brown solid. 1 H MR (500 MHz, DMS-d6 ): δ (ppm); 0.75 (t, 6H), 1.46 (s, 12H), 1.49 (m, 4H), 2.37 (t, 4H), 5.04 (s, 4H), 5.17 (s, 2H), 5.29 (s, 4H), (m, 46H); m/z: 1488, 1489 [(MH) + ]; C 91 H Suspended compound 15 (25 g, mol) in 75% v/v aqueous acetic acid (125 ml) and stirred for 12 h a t C. The formed byproduct (trityl alcohol) was filtered, washed with 75% v/v aqueous acetic acid ( 20 ml). Filtrate was suspended in a mixture of dichloromethane and DM water, separated the aqueous layer. rganic layer was washed with saturated sodium bicarbonate solution. Aqueous layer was separated and organic layer was concentrated completely, affords olmesartan medoxomil dimer (9, 6.4g, 38%) as pale brown solid. 1 H MR (300 MHz, DMS-d6 ): δ (ppm); 0.87 (t, 6H), 1.44 (s, 12H), 1.57 (m, 4H), 2.57 (m, 4H), 5.13 (s, 6H), 5.37 (s, 4H), 6.80 (d, 4H), 6.99 (d, 4H), (m, 8H); m/z: [(MH) + ]; C 53 H Preparation of olmesartan diol impurity (10): To a solution of compound 4 (25 g, mol) in THF (500 ml) added 2 molar THF solution of methyl magnesium bromide (105 g, mol) at ambient temperature. The contents were stirred for 1 h. Quenched the reaction mass by added Conc.H (25 ml) at C. Aqueous layer was separated from the reaction mass, concentrated organic layer at 40 C. The resulting mass was mixed with dichloromethane (200 ml) and DM water (200 ml). The resulted organic layer was concentrated at 40 C under reduced pressure. The compound 22 was isolated by column chromatography on silica gel using 1:1 mixture of ethyl acetate and hexanes as yellow oil mass (13 g, 52%). 1 H MR (500 MHz, DMS-d 6): δ (ppm); 0.70 (t, 3H), 1.28 (s, 6H), 1.47 (m, 2H), 1.54 (s, 6H), 2.15 (t, 2H), 6.21 (s, 1H), 5.14 (s, 2H), 6.22 (s, 1H), (m, 23H); m/z : 703.3[(MH) + ].C 26 H The oil mass (12 g, mol) was suspended in 75% aqueous acetic acid (40 ml), stirred for 24 h at C. The byproduct was filtered through hyflo bed, washed with 75% aqueous acetic acid (12 ml). Filtrate was suspended in a mixture of dichloromethane (120 ml) and DM water (120 ml). Aqueous layer was separated and organic layer was concentrated at 40 C under reduced pressure, yielded product 10 as a white crystalline solid (7 g, 90%). 1 H MR (500 MHz, DMS-d6 ): δ (ppm); 0.83 (t, 3H), 1.35 (s, 6H), 1.52 (m, 8H), 2.29 (t, 2 H), 5.23 (s, 2H), 6.21 (s, 1H), 6.77 (d, 2H), 7.06 (d, 2H), 7.09 (s, 1H), (m, 4H); m/z: 461.2[(MH) + ].C 26 H Preparation of quaternary salt impurity(11): Sparged, -dimethylamine gas into solution of 3 (25 g, 0.045mol) in,-dimethylacetamide (500 ml) at C for 3 h. Raised the temperature of content to C. Maintained at the same temperature for more 2 h and cooled the reaction mass to C. The resulted solution was concentrated at C under reduced pressure. The resulted oil mass contains trityl quaternary salt impurity was suspended in 75% aqueous acetic acid (100 ml) at C, stirred for 8 h. Added ethyl acetate (250 ml) and DM water (250 ml) to the reaction mass, separated the aqueous layer. The organic layer was concentrated and isolated the quaternary salt impurity 11 through column chromatography on silica gel (60x120 mesh) using 1:1 ethyl acetate and hexanes, as white crystalline solid (19 g, 80%). 1 H MR (300 MHz, CD3 ): δ (ppm); 2.67(s, 6H), 4.46 (s, 4H), (m, 46H); m/z: [(M) + ]; C 30 H 29 9.

5 Page2748 Vol 5, Issue 09, Bommena Hanumantha Rao et al. ISS : RESULTS AD DISCUSSI 4-Chloromethyl-5-methyl-1,3-dioxol-2-one (6) is one of the key raw materials used in the preparation of olmesartan medoxomil (1) and is prepared by known method 13 as shown in Scheme Scheme 2: Preparation of 4- chloromethyl-5-methyl-1,3-dioxol-2-one (6). Reagents and reaction conditions: 12, DCM, S 2 2, 90 C, 1 h, 80%. The prepared 6 was analyzed by GC-MS, and found 13 is only the predominant reactive impurity in 6 in about 0.2 to 0.5%. Compound 13 was prepared by reacting compound 6 with sulfuryl chloride and catalytic iodine in dichloromethane with 80% yield as shown in Scheme Scheme 3: Preparation of 4,5-Bis(chloromethyl)-1,3-dioxolen-2-one (13). Reagents and reaction conditions: S 2 2 / I 2, C, 1 h, 80%. Impurity olmesartan chloro medoxomil ( 8) is one of the critical impurities and is prepared as per the Scheme 4. This impurity was originating during the preparation of trityl olmesartan medoxomil (7). Impurity 8 was prepared from the reaction of impurity 13 with trityl olmesartan sodium salt (5) in,-dimethylacetamide in presence of 3% w/w sodium iodide yielded trityl olmesartan chloro medoxomil (14), which on in-situ detritylation obtained olmesartan chloro medoxomil (8) in 25% yield. The molecular weight of 9 is So there is a need of calculating relative response factor with respect to olmesartan medoxomil (1).

6 Page2749 Vol 5, Issue 09, Bommena Hanumantha Rao et al. ISS : H a + H H H 8 Scheme 4: Preparation of olmesartan chloro medoxomil (8). Reagents and reaction conditions: DMAc, KI (3% w/w), C, 24 h 75% v/v Aqueous acetic acid, C, 8 h, 25%. B y the reaction of 5 with 0.5 mole equivalent of 4, 5 - Bis (chloromethyl) -1, 3 dioxolen 2 - one (13) in, - Dimethylacetamide with one mole equivalent sodium iodide resulted trityl olmesartan medoxomil dimer (15), which on detritylation with 75% v/v aqueous acetic acid achieved olmesartan medoxomil dimer (9) as shown in Scheme 5. H a + CH H 3 3 C H H CH H 3 3 C H H H H 9 Scheme 5: Preparation of olmesartan medoxomil dimer (9). Reagents and reaction conditions: DMAc, KI, C, 24 h 75% v/v Aqueous acetic acid, C, 8 h, 60%.

7 Page2750 Vol 5, Issue 09, Bommena Hanumantha Rao et al. ISS : lmesartan diol impurity (17) is originated from the preparation of 2 4 and is inturn prepared by the Grignard reaction on imidazole diethyl ester (16) with 6 mole equivalents of methyl magnesium bromide and as a consequence the impurity imidazole diol (17) was observed in 0.5 to 1% in compound 2. CH 3 CH 3 H 16 H 2 H CH 3 H H H 17 Scheme 6: Preparation of imidazole ethyl ester derivative (2). Imidazole diol impurity carry through the synthesis of 1 resulted impurity 10. Impurity imidazole diol (17) was on Grignard reaction with methyl magnesium bromide in a mixture of toluene and THF, resulted trityl olmesartan diol impurity (18). This was on detritylation resulted olmesartan diol impurity (10) as shown in Scheme 7. H 2 H + Br 4 H H H H H Scheme 7: Preparation of olmesartan diol impurity (10). Reagents and reaction conditions: DMAc, K 2 C 3, C, 24 h, 90% 75% v/v Aqueous acetic acid, C, 8 h, 90%. Coming to the fourth impurity 11, is known as quaternary salt impurity, it is originated from, - dimethylamine (DMA). Because of longer reaction times of preparation of 4 by using strong bases like sodium hydroxide or potassium hydroxide or sodium hydride in,-dimethylacetamide (DMAc) or,-dimethylformamide (DMF), some of the solvent was hydrolyzed and generated DMA as a by-product. The formed DMA on reaction with bromo methyl biphenyl trityl tetrazole (3) resulted trityl quaternary salt impurity (19) as shown in Scheme 8. This was on trityl de-protection with aq. acetic acid yielded quaternary salt impurity (11). Br Br H Ph 3 C Ph 3 C H H Scheme 8: Preparation of quaternary salt impurity (11). Reagents and reaction conditions: DMA, DMAc, C, 5 h 75% v/v Aqueous acetic acid, C, 8 h, 80%.

8 Page2751 Vol 5, Issue 09, Bommena Hanumantha Rao et al. ISS : CCLUSI In this article we reported synthesis, characterization of four novel related substances of olmesartan medoxomil, an antihypertensive drug. Authors Statements Competing Interests The authors declare no conflict of interest. REFERECES 1. ''International conference on harmonization (ICH) Guidelines'' Q3A (R) Impurities in ew Drug Substances, February Fukuda M., Yamanaka T., Mizuno M., ''Angiotensin II type 1 receptor blocker, lmesartan restores nocturnal blood pressure decline by enhancing daytime natriuresis,'' J hypertension 2008, 26(3), Suga Kurikawa M., S. Kuroda, K.Yamada, and H. Ishikawa, "An angiotensin II type receptor antagonist, olmesartan medoxomil, improves experimental liver fibrosis by suppression of proliferation and collangen synthesis in activated hepatic stellate cells," British J Pharmacology 2003, 139(6), Yanagisawa YH., Kanazaki AT., "onpeptide angiotensin II receptor antagonists: synthesis, biological activities, and structure- activity relationships of imidazole-5-carboxylic acids bearing alkyl, alkenyl, and hydroxyalkyl substituents at the 4-position and their related compounds,'' J Med Chem 1996, 39(1), Gardner SF., Franks, and Ann AM., "lmesartan medoxomil: the seventh angiotensin receptor antagonist, Pharmacotherapy 2003, 37(1), Korrapati Venkata Vara Prasadarao; Koilpillai Joseph Prabahar; Inti Venkata Subramanyeswararao; Bommena Hanumantharao; Vysyaraju Ravikanth; Meenakshisunderam Sivakumaran. Indian Patent. Appl. (2013), I 2010CH02167 A 7. Babu KS., Reddy MS., Tagore AR., Reddy GS., Sebastian S., Varma MS., Anand RV., Efficient synthesis of olmesartan medoxomil, an antihypertensive drug. Syn. Commun.2009, 39(2), Babu KS., Tagore AR., Reddy GS., Venkateswarlu G., Reddy PP., Anand RV., Synthesis of related substances of olmesartan medoxomil, an antihypertensive drug. ARKIVC 2010, Pati H., Lahiri S., Sabbam RK., Vangala VB. Ramalingam B., Hiriyanna SG., Bose P. A convenient and practical synthesis of olmesartan medoxomil methyl ether. J. Heterocyclic Chem. 2008, 45(3), Venkanna G., Madhusudhan G., Mukkanti K., Sankar A., Kumar SY., arayana GV., Synthesis and characterization of process related impurities of an antihypertensive drug olmesartan medoxomil. Journal of chemistry 2013, 5I6459, 8 pp. 11. Pai andini R., Sawant Seema S., S y n t h e s i s o f o l me s a r t a n a c i d i mp u r i t y o f o l me s a r t a n m e d o x o mi l, a n a n t i h yp e r t e n s i v e d r u g. Rasayan Journal of Chemistry 2013, 6(3), Srimurugan PS., Suresh B., Babu SG., Hiriyana H., Pati., "Unusual Detritylation of Tritylated Tetrazole in Sartan Molecules" Chemical and Pharmaceutical Bulletin 2008, 56(3), Shiji I., Yasushi T., Ryoichi H., Fumio S., Koji I., Goro T., AA convenient and practical preparation of 4-chloromethyl-5-methyl- 1,3-dioxol-2one. Chemical and Pharmaceutical Bulletin. 1988, 36(1),