Field of Invention:
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-4yl)3 - [(3S)-3 -(4-fluorophenyl)-3-hydroxypropyl] 1
phenylazetidin-2-one (DEPA, formula III) through enzymatic kinetic resolution.
Background of the Invention:
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 Fig.l.
Ezetimibe (Formula II) (CAS. No. 163222-33-1), l-(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 US 5,767,115.
US 7320972 describes DEPA (Formula III) (3R, 4S) -4-(3,3'dihydroxybiphenyl 4yl) 3-
[(3S)-3-(4-fluorophenyl)-3-hydroxypropyl] l-phenylazetidin-2-one as a potent inhibitor
of cholesterol absorption.



Compound of formula I can be converted to either Ezetimibe (II) or DEP A (III) through
the process provided in US 6207822 and WO2006122216 respectively.
Prior art reveals that compound I has been synthesized by following methods:
1) Reduction of corresponding ketone (IV) by using borane as a reducing agent such
as Borane-dimethyl sulfide (as in US Pat. No. 6,207,822), Borane-tetrahydrofuran
complex (as in Tetrahedron Letters, 44 (2003) 801-804), or Borane diethylaniline

complex (as in Tetrahedron Letters, 48(2007) 2123-2125) in presence of chiral
catalyst such as (R)-l- methyl-3,3-diphenyltetahydro-3H-pyrrolo [l,2-c][l,3,2]
oxazaborole.
2) Compound T has also been synthesized by microbial reduction of ketone (IV) as
per the process provided in US Pat. No. 5,618,707.
However, most of the reported methods suffer from the following disadvantages
1) Boranes are highly reactive compounds and some are pyrophoric in
nature. Most of these are highly poisonous and require special handling
precautions, necessitating special operation procedure and higher
capital cost.
2) Boranes are volatile and flammable in nature.
3) Some boranes are reported to be unstable on storage, such as borane
tetrahydrofuran complex (THF ring opening) and also reported to be
explosive on prolonged storage.
4) Borane-dimethyl sulfide has an unpleasant odor and a fact not liked by
operation.
5) Enantiomeric purity is never exceed 95%, often requiring further
purification.
6) Efficiency of microbial reduction process for desired compound I is
low and required high dilution and hence not a practical process.
Further, any microbial process is associated with fermentation, which
needs special equipment such as sterile condition and environment. Use
of autoclave to sterilize the fermentation media, bioreactor, etc.
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.
Objects of the invention
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 enatiomeric 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.
Summary of invention
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.
Detailed description of the invention:
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.
Fig 1 shows the inventive process developed for synthesis of optically pure desired
compound I.
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
estrification of one enatiomer 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 enantioselectiove 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)
Example 1. Enzyme screening via enzymatic esterification of (R/S) 4-phenyl -3-[(5S)-5-
(4-fluorophenyl)-5-hydroxypentanoyl] -1,3 oxazolidin 2-one
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 300mg
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 US 6,207,822.
Retention time of compounds on Chiral HPLC
1) Compound I - 20.60 min
2) Compound V - 17.44 -and 20.60 min
3) Compound IV- 16.07 min
Chiral HPLC Condition
1) Column: Chiralcel ODH (4.6 X 250 mm)
3) Mobile Phase: n-hexane and ethanol (70:30), flow rate: 0.7 mi/min.; Detection
(UV): at210nm.
Compound VI: 1HNMR (200MHZ, CDC13):
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


Example 2: Effect of enzyme loading on enzymatic esterification of (R/S) 4-phenyl -3-
[(5S)-5-(4-fluorophenyl)-5-hydroxypentanoyl] -1,3 oxazolidin 2-one
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. Fig 2. gives effect of catalysts loading on the rate of reaction.
Example 3: Effect of different solvent on enantioselective enzymatic esterification of
(R/S) 4-phenyl ~3-[(5S)-5-(4-fluorophenyl)-5-hydroxypentanoyl] -1,3 oxazolidin 2-one
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
300mg 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


Example 4. Lipozyme TL IM catalyzed esterification of 4S-phenyl -3-[(5RS)-5-(4-
fluorophenyl)-5-hydroxypentanoyl] -1,3 oxazolidin 2-one
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 0.37gm (yield 74 %, 99% ee) of compound I, and
0.34 gm (yield 68 %, 99%ee) of compound of formula VI.

We claim:
1. 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.
2. The process as claimed in claim 1 wherein the esterification agent is vinyl acetate
3. The process as claimed in claim 1 wherein the Lipase enzyme is selected from the
group of Lipase AS, Lipase PS, Novozym 435, Lipozyme TL IM, or Lipozyme
RM IM
4. The process as claimed in claim 3 wherein the Lipase enzyme is Lipozyme TL
IM.
5. The process as claimed in claim 1 wherein the organic solvent is selected from
Toluene, diisopropyl ether or a mixture thereof.
6. The process as claimed in claim 1 wherein the esterification reaction is carried out
at 40°C.
7. The process as claimed in claim 1 wherein the isolation is carried out by column
chromatography or crystallization.

A process for synthesis of 4S-phenyl -3-[(5S)-5-(4-fiuorophenyl)-5-hydroxypentanoyl] -
1,3 oxazolidin 2-one comprising 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.