Patent Application
20120028340
The invention relates to novel method for synthesis of optically pure (4S)-4-phenyl-3-[(5S)-5-(4-fluorophenyl)-5-hydroxypentanoyl]-1,3 oxazolidin 2-one, of formula I, an intermediate used for the synthesis of ezetimibe (formula II) and (3R,4S)-4-(3,3′dihydroxybiphenyl-4-yl)3-[(3S)-3-(4-fluorophenyl)-3-hydroxypropyl]1 phenylazetidin-2-one (DEPA, formula III) through enzymatic kinetic resolution.
This invention relates to the novel process for the chiral synthesis of ezetimibe and DEPA intermediate of Formula I, (4S)-4-phenyl-3-[(5S)-5-(4-fluorophenyl)-5-hydroxypentanoyl]-1,3 oxazolidin 2-one from the corresponding diastereoisomeric alcohols formula V. This is schematically represented in
Ezetimibe (Formula II) (CAS. No. 163222-33-1), 1-(4-fluorophenyl)-3(R)-[3-(4-fluorophenyl)-3(S)-hydroxypropyl]-4(S)-(4-hydroxyphenyl)-2-azetidinone), a potent and selective cholesterol absorption inhibitor is disclosed in U.S. Pat. No. 5,767,115.
U.S. Pat. No. 7,320,972 describes DEPA (Formula III) (3R,4S)-4-(3,3′dihydroxybiphenyl 4yl)3-[(3S)-3-(4-fluorophenyl)-3-hydroxypropyl]1-phenylazetidin-2-one as a potent inhibitor of cholesterol absorption.
Compound of formula I can be converted to either Ezetimibe (II) or DEPA (III) through the process provided in U.S. Pat. No. 6,207,822 and WO2006122216 respectively.
Prior art reveals that compound I has been synthesized by following methods:
However, most of the reported methods suffer from the following disadvantages
Non-chiral reduction of corresponding ketone (IV) to racemic hydroxy compounds V (Tetrahedron Letters, 44 (2003)), which is diastereoisomer and in-principle could be separated by crystallization. However, such separation is not simple and easy for the present case due to lower melting points of the individual isomers (39.7° C. for compound of formula I).
Summarizing it is evident that there is a need for development of an eco-friendly, hazard free, “green”, cost effective process for the synthesis of compound I. This invention provides that.
Thus the object of the present invention is to provide enzymatic kinetic resolutions of 4S-phenyl-3-[(5RS)-5-(4-fluorophenyl)-5-hydroxypentanoyl]-1,3 oxazolidin 2-one to obtain optically pure compound I with enantiomeric purity of at least about 98%.
Other object of the present invention is to provide an eco-friendly and hazard free process for the preparation of compound of formula I.
Another object of the present invention is to provide a process for the preparation of compound of formula I with better efficiency and selectivity.
A further object of the present invention is to provide an improved industrial process for the preparation of compound of formula I that produces minimum by-products.
The present invention provides a process for synthesis of 4S-phenyl-3-[(5S)-5-(4-fluorophenyl)-5-hydroxypentanoyl]-1,3 oxazolidin 2-one comprising of resolution of 4S-phenyl-3-[(5RS)-5-(4-fluorophenyl)-5-hydroxypentanoyl]-1,3 oxazolidin 2-one by selective esterification of 4S-phenyl-3-[(5R)-5-(4-fluorophenyl)-5-hydroxypentanoyl]-1,3 oxazolidin 2-one using appropriate esterification reagent in an organic solvent in presence of Lipase enzyme at a temperature ranging from 0° to 100° C., and further isolation.
The esterification agent used in the said process is vinyl acetate
Lipase enzyme used in the process of invention is selected from the group of Lipase AS, Lipase PS, Novozym 435, Lipozyme TL IM, or Lipozyme RM IM; more preferably it is Lipozyme TL IM.
Organic solvent used for the esterification reaction is selected from Toluene, diisopropyl ether or a mixture thereof.
The process of invention is carried out more preferably at 40° C.
The isolation of desired compound I is carried out by column chromatography or crystallization.
The present invention is directed towards the method for preparation of enantiomerically pure 4S-phenyl-3-[(5S)-5-(4-fluorophenyl)-5-hydroxypentanoyl]-1,3 oxazolidin 2-one (I). The method of the present invention involves a kinetic resolution of 4S-phenyl-3-[(5SR)-5-(4-fluorophenyl)-5-hydroxypentanoyl]-1,3 oxazolidin 2-one (VI) by selective acetylation of one isomer in presence of lipase.
Interestingly, the present inventors found that 4S-phenyl-3-[(5R)-5-(4-fluorophenyl)-5-hydroxypentanoyl]-1,3 oxazolidin 2-one (the undesired enantiomer) specifically undergoes the acetylation reaction to give compound of formula VI and the desired compound (I) remains un-reacted. Compound of formula I is easily separated from compound of formula VI by column chromatography or through crystallization by derivatization of the desired alcohol moiety.
The process consists of reaction of vinyl acetate with compound of formula V in organic solvent in presence of specified lipase to yield a mixture containing compound I with high yield and high % ee, and undesired isomer is acetylated to give VI. The resulting mixture of alcohol of formula I and acetate of formula VI after usual work-up is purified to individual compounds by column/flash chromatography.
Such enantioselective acetylation reaction of racemic hydroxy compound in presence of lipase is well documented (Hydrolases in organic synthesis, ed Bornscheuer and Kazlauskas, Wiley VCH verlag GmbH & Co, 2006, pp 61-183). However, apriori, it is difficult to predict required enzyme, solvent, temperature and turnover number of catalyst i.e. lipase.
The resulting hydroxy compound (Formula I) which is enantiomerically enriched undergoes further reaction to yield the desired essentially enantiomerically pure Ezitimibe (II) and DEPA (III). Compound VI can be reused in enzymatic resolution after subsequent racemization via ester hydrolysis and oxidation to obtain compound IV through known chemical methods, thereby improving overall yield.
The enzyme (or Biocatalyst) may be any protein that will catalyze the enatioselective esterification of one enantiomer to yield the ester of hydroxy compound. Useful enzymes for enantioselectively esterification of hydroxy compound to ester of hydroxy compound may thus include hydrolases, including lipases. Such enzyme may be obtained from a variety of natural sources, including animal organs and microorganisms.
As described hereinafter useful enzymes for the enantioselective conversion of the hydroxy compound to ester of undesired hydroxy compound include lipases obtained from various biological sources (Table 1). Preferably such lipases include enzyme derived from the microorganism Termomyces lanuginosus, such as available from Novozyme A/S.
The reaction mixture may comprise a single phase or may comprise multiple phases. For example, the enantioselective hydrolysis may be carried out in two phases system comprised of solid phase, which contains the enzyme, and an solvent, which contains the initially racemic substrate, the undesired optically active ester and the desired optically active hydroxy compound I.
The amounts of the racemic substrate (Formula V) and the biocatalyst used in the enantioselective hydrolysis will depend on, the properties of the recemic substrate and enzyme. Reaction may generally employ an enzyme loading of about 10% to about 100% and in many cases, may employ an enzyme loading of about 10 to 50% (W/V)
The enantioselective esterification may be carried out over wide range of temperature. For example, the reaction may be carried out at temperature of about 25° C. to a 50° C., but typically carried out at 40° C. Such temperatures generally permit substantially full conversion e.g, 95 to 99% of the one enantiomer in a reasonable period of time e.g. 72 to 120 h without deactivating the enzyme. Enzyme can be reused, and generally the turn-over of immobilized enzyme is high.
The enantioselective esterification may be carried out in different solvents. For example, the reaction may be carried in solvent such as toluene, diisopropyl ether (DIPE), cyclohexane, n-heptane, n-hexane and THF. Preferentially aromatic solvent such as toluene is preferred,
Activated ester used in enantioselective esterification may be consisting of vinyl acetate.
After the completion of reaction, desired hydroxy compound of formula I and ester of undesired enantiomer (VI) is separated out by column chromatography using silica gel as stationary phase and cyclohexane:ethyl acetate (1:1) as a mobile phase.
The present invention is illustrated in more detail by referring to the following Examples, which are not to be construed as limiting the scope of the invention.
Enzymatic screening reactions were performed in an HLC Termomixer. All enzymes used in the screening plate were obtained from commercial enzyme suppliers including Amano (Japan) and Novozyme (Denmark)
Enzyme screening was carried out in HLC parallel thermomixer, which consist of 14 chambers to carry out individual reaction in 10 ml vial (called as individual reactors). Each individual reactor was charged with 3 ml toluene, 100 mg of substrate, and 300 mg of vinyl acetate and stirred at room temperature for 15 min. In each reactor different type of lipases (50% w/w of substrate) was added to initiate reaction. The resulting mixture was stirred at 40° C. for 120 h. reaction was monitor with chiral HPLC for enantioselectivity of Lipases. Retention time of compound I matched with standard sample prepared by known method as provided in U.S. Pat. No. 6,207,822.
Compound VI: 1HNMR (200 MHz, CDCl3):
δ 7.15-7.42 (m, 7H), 7.00 (t, 2H), 5.7 (t, 1H), 5.4 (dd, 1H), 4.68 (t 1H), 4.27 (dd 1H), 2.93 (dt 2H), 2.1 (m, 3H), 1.58-1.80 (m, 4H) ppm
Effect of enzyme loading was carried out in HLC parallel thermomixer, which consist of 14 chambers to carry out individual reaction in 10 ml vial (called as individual reactors). Each individual reactor was charged with 3 ml toluene, 100 mg of substrate, and 300 mg of vinyl acetate and stirred at room temperature for 15 min. In each reactor different % w/w of Lipozyme TL IM lipase was added to initiate reaction. The resulting mixture was stirred at 40° C. for 120 h. reaction was monitor with chiral HPLC for enantioselectivity of Lipases.
Effect of enzyme loading was carried out in HLC parallel thermomixer, which consist of 14 chambers to carry out individual reaction in 10 ml vial (called as individual reactors). Each individual reactor was charged with 3 ml of solvent, 100 mg of substrate, and 300 mg of vinyl acetate and stirred at room temperature for 15 min. In each reactor of Lipozyme TL IM lipase was added to initiate reaction. The resulting mixture was stirred at 40° C. for 120 h. reaction was monitor with chiral HPLC for enantioselectivity of Lipases. Table 3. Effect of different solvent on enantioselectivity
4S-phenyl-3-[(5RS)-5-(4-fluorophenyl)-5-hydroxypentanoyl]-1,3 oxazolidin 2-one (1 gm), 3 ml. toluene and 3 g of vinyl acetate were stirred at room temperature for 15 min at an ambient temperature in a HLC thermomixer. The reaction mixture was heated to 40° C. and 300 mg of Lipozyme TL IM (Thermomyces lanuginosus) were added to it. Progress of the reaction was monitored using chiral HPLC. After complete conversion of unwanted 4S-phenyl-3-[(5R)-5-(4-fluorophenyl)-5-hydroxypentanoyl]-1,3 oxazolidin 2-one to the Compound VI, reaction was filtered to remove the enzyme. Filtrate was concentrated under vacuum to remove toluene to give crude product, which on column chromatography over silica gel gives 0.37 gm (yield 74%, 99% ee) of compound I, and 0.34 gm (yield 68%, 99% ee) of compound of formula VI.
| Number | Date | Country | Kind |
|---|---|---|---|
| 577/KOL/2009 | Apr 2009 | IN | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/IN10/00224 | 4/5/2010 | WO | 00 | 10/20/2011 |
