Improvement of enantioselectivity in kinetic resolution of a primary alcohol through lipase-catalyzed transesterification by using a chiral acyl donor

Article abstract of DOI:10.1016/S0957-4166(00)00060-4

The enantioselectivity of the kinetic resolution of a primary alcohol which has a chiral center at the β-position of the hydroxyl group was substantially improved by employing a racemic mixture of a chiral acyl donor for enantioselective transesterification catalyzed by a lipase. The combination of the lipase, solvent, and acyl donor was also effective for the enantioselectivity. In addition, the important effect of the chirality of an acyl donor on kinetic resolution was investigated by using enantiomerically pure acyl donors. Here we demonstrate the effective kinetic resolution (E=98) of a primary alcohol, 2-phenyl-1-propanol, by using a racemic mixture of a chiral acyl donor, vinyl 3-phenylbutanoate. Copyright (C) 2000 Elsevier Science Ltd.

Full text of DOI:10.1016/S0957-4166(00)00060-4

Tetrahedron: Asymmetry 11 (2000) 1199±1210
Improvement of enantioselectivity in kinetic resolution of a
primary alcohol through lipase-catalyzed transesteri®cation
by using a chiral acyl donor
Keiji Hirose,* Hiroyuki Naka, Masashi Yano, Sozaburo Ohashi,
Koichiro Naemura and Yoshito Tobe
Department of Chemistry, Faculty of Engineering Science, Osaka University, Toyonaka, Osaka 560-8531, Japan
Received 28 December 1999; accepted 4 February 2000
Abstract
The enantioselectivity of the kinetic resolution of a primary alcohol which has a chiral center at the
b-position of the hydroxyl group was substantially improved by employing a racemic mixture of a chiral
acyl donor for enantioselective transesteri®cation catalyzed by a lipase. The combination of the lipase,
solvent, and acyl donor was also e€ective for the enantioselectivity. In addition, the important e€ect of the
chirality of an acyl donor on kinetic resolution was investigated by using enantiomerically pure acyl
donors. Here we demonstrate the e€ective kinetic resolution (E=98) of a primary alcohol, 2-phenyl-1-
propanol, by using a racemic mixture of a chiral acyl donor, vinyl 3-phenylbutanoate. # 2000 Elsevier
Science Ltd. All rights reserved.
1. Introduction
The importance of enzyme-catalyzed reactions has been well recognized during the last decade
as a promising method for the preparation of enantiomerically pure compounds.1 Particularly,
transesteri®cation catalyzed by lipases has become a popular method for the preparation of
enantiomerically pure secondary alcohols.2 However, the enantioselectivities of lipase-catalyzed
transesteri®cation of primary alcohols are relatively low, in most cases unsatisfactorily low so as
to preclude preparation of enantiomerically pure primary alcohols for synthetic purposes. In this
respect, it is desirable to devise measures to improve the enantioselectivity of the kinetic resolu-
tion of primary alcohols. Examples of the measures that have been taken in order to improve the
enantioselectivity of transesteri®cation gave: screening of enzymes, changing the solvent3 and/or
temperature,4 adding an additive,5 microwave irradiation,6 immobilization of enzyme on sup-
port,7 site-directed mutagenesis,8 and changing the acyl donors.9 We focused our attention on the
* Corresponding author. E-mail: hirose@chem.es.osaka-u.ac.jp
0957-4166/00/$ - see front matter # 2000 Elsevier Science Ltd. All rights reserved.
PII: S0957-4166(00)00060-4

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K. Hirose et al. / Tetrahedron: Asymmetry 11 (2000) 1199±1210
importance of the acylated enzyme which is the key intermediate for enzymatic reaction. The
steric environment of the acyl moiety in the acylated enzyme would be readily modi®ed by simply
employing di€erent acyl donors. The method to change the acyl donors could be considered as
active-site-directed transient chemical modi®cation of an enzyme,10 which might lead to an
improvement of the enantioselectivity for the kinetic resolution of primary alcohols. Indeed,
when the widely employed achiral and small acyl donor, isopropenyl acetate, was replaced by
methyl 3-phenylpropanoate 5, a moderate improvement of enantioselectivities was observed.11
Recently, the e€ect of an acyl donor which has an aromatic ring in the acyl moiety on the
enantioselectivity of lipase-catalyzed transesteri®cation of 2-phenyl-1-propanol 6 was reported.12
However, there seems to be no report on the use of a chiral acyl donor in the transesteri®cation
catalyzed by lipase for the resolution of primary alcohols.13 It is, therefore, interesting to investi-
gate the e€ect of a chiral acyl donor on the enantioselectivity of the transesteri®cation.
In this paper, we report improvement of the enantioselectivity of lipase-catalyzed transester-
i®cation of primary alcohol 6 by using chiral acyl donors, methyl 3-phenylbutanoate 1, vinyl 3-
phenylbutanoate 2 and methyl 2-phenylpropanoate 3, vinyl 2-phenylpropanoate 4, possessing a
stereocenter at the a- and b-positions of the carbonyl group, respectively, together with the e€ect
of chirality of acyl donor 1 and 2 on the enantioselectivity. Furthermore, the importance of a
combination between chiral acyl donors and lipases, Lipase QL from Alcaligenes sp., Lipase SL
from Pseudomonas cepacia, Lipase TL from Pseudomonas stutzeri, and Lipase UL from Rhizopus
sp., is also described.
2. Results and discussion
The substrate alcohol 2-phenyl-1-propanol 6 was chosen in order to compare the results with
previous studies using achiral acyl donors.14 Of the acyl donors, methyl esters (‹)-1 and (‹)-3
were prepared according to previously reported procedures.15 Vinyl esters (‹)-2 and (‹)-4 were
prepared by transesteri®cation with vinyl acetate catalyzed by mercury(II) acetate.16 The synthe-
ses of optically active acyl donors (R)-1, (S)-1, (R)-2 and (S)-2 were carried out by repeated
Lipase QL-catalyzed transesteri®cation using benzyl alcohol, as shown in Scheme 1. Thus, (‹)-1
was treated with benzyl alcohol in the presence of Lipase QL and the recovered starting material
was subjected to the same procedure to give (R)-1 enriched to 95% ee. On the other hand, the
product of the initial reaction 7 was treated with methanol in the presence of Lipase QL to a€ord
(S)-1 with 96% ee. Both (R)-1 and (S)-1 were converted to the corresponding vinyl esters (R)-2
and (S)-2 by hydrolysis followed by transesteri®cation catalyzed by Hg(OAc)2.

K. Hirose et al. / Tetrahedron: Asymmetry 11 (2000) 1199±1210
1201
Scheme 1. The syntheses of optically active chiral acyl donors 1 and 2
The enantioselective transesteri®cation of alcohol (‹)-6 with 2 mol equivalents of an acyl
donor was carried out in an organic solvent at 30ꢀC using lipase as a chiral catalyst. The progress
of the reaction was monitored by GLC, and the reactions were terminated by removal of the
enzyme by ®ltration. The recovered alcohol, recovered acyl donor and product esters were
separated by column chromatography on silica gel. The product esters were obtained as a mixture
of two diastereomers. The enantiomeric excesses (ees) of the recovered acyl donor and recovered
alcohol (eeS) were directly determined by HPLC using a chiral column detected by a UV detector
at 240 nm. The absolute con®guration of the recovered alcohol was con®rmed by comparison of
its speci®c rotation with that reported in the literature.17 The enantiomeric excesses of the
product esters were determined by HPLC using a chiral column for each diastereomer, and the
stereochemical assignment was established by comparison of the retention volumes with those of
authentic samples prepared independently. A representative result using (‹)-1 as an acylating
reagent is shown in Scheme 2.
Scheme 2. Representative kinetic resolution using a chiral acyl donor (‹)-1. The E values were calculated from the
enantiomeric excesses (ees and eep)18

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K. Hirose et al. / Tetrahedron: Asymmetry 11 (2000) 1199±1210
To compare the eciency of resolution, E values are generally used for enantioselective
reaction. In order to apply the concept of E values to the present reactions, in which the products
were obtained as mixtures of two diastereomeric esters, the enantiomeric excess of the alcohol
moiety in the product esters (eeP) was used in the equation described in the literature.18 When 1
or 2 was used as an acyl donor, the four components (R,R)-, (R,S)-, (S,S)- and (S,R)-8 were
separated e€ectively using the HPLC conditions described in the Experimental section. The eeP
was calculated based on the enantiomeric excesses of both of the diastereomeric product esters
and diastereomeric excesses of the product esters, which were obtained by HPLC using a chiral
column. When 3 or 4 was used as an acyl donor, the eeP wase obtained by the hydrolysis of the
mixture of diastereomeric product esters, because e€ective separation among the four compo-
nents of the product esters was not observed.
First, the e€ect of an acyl donor on enantioselectivity for transesteri®cation was investigated by
using esters 1 and 2 which have a methyl group on the b-position of the carbonyl group of 3-
phenylpropanoate 5. The results are shown in Table 1. For comparison, the result using achiral
acylating agent 5 is also listed in Table 1. The introduction of a methyl group does not seem to
a€ect the E values (entries 1 and 10), but the reaction required more time than that for 5. Since
the methyl group interferes with the transesteri®cation of both enantiomers of the substrate
alcohol (‹)-6, it is possible to control the reactivities by changing the reaction conditions.
Indeed, when hexane instead of diisopropyl ether was used as a solvent, substantial improvement
of selectivity (E=14) was observed together with reduction of the reaction time (entry 2).
Accordingly, the following investigations were carried out in hexane as a general solvent.
Table 1
The e€ect of chirality of acyl donors 1 and 2 on E values for the kinetic resolution of primary alcohol
(‹)-6 using Lipase QLa)
As shown in entries 2 and 3, the E value obtained by using (‹)-1 is the same as that obtained
by using (S)-1. This result indicates that one of the enantiomers of acyl donor (S)-1 contributes
predominantly to determine the enantioselectivity of the transesteri®cation of 6 when the racemic
mixture of 1 is employed as an acyl donor. Acyl donor (R)-1 is practically inactive, or may act as
an inhibitor for this transesteri®cation, because longer reaction times were required when the

K. Hirose et al. / Tetrahedron: Asymmetry 11 (2000) 1199±1210
1203
racemic acyl donor was employed than in the case when (S)-1 was employed. The reaction did not
proceed when (R)-1 was used as an acyl donor (entry 4).
When vinyl ester 2 was used, the reaction became much faster than in the case of 1 (entries 5±7).
In addition, an improvement of the E value was observed. As in the case of 1, the S-enantiomer
of 2 plays a predominant role in the determination of reactivity and selectivity. Since (R)-2 gave a
low E value after a prolonged reaction time, and the use of (‹)-2 resulted in a longer reaction
time than when (S)-2 was used, the R-enantiomer may also act as an inhibitor of the reaction.
It is worth emphasizing here that the improvement of enantioselectivity was attained up to a
satisfactorily high level (E>20)19 with chiral acyl donor 2, and the extent of enantioselectivity for
the reaction with racemic acyl donor (‹)-2 (E=32) was comparable with that for the reaction
with optically active (S)-2 (E=30). Accordingly, an enantiomerically pure acyl donor is not
necessary for e€ective resolution.
The position of the stereogenic center in the acyl donor a€ected the reactivity and enantio-
selectivity of transesteri®cation reaction. The transesteri®cation results using esters 3 and 4 which
have a stereogenic center on the a-position of the carbonyl group of 3-phenylpropanoate 5 are
summarized in entries 8 and 9 in Table 1. When methyl ester 3 was used, the transesteri®cation
reaction did not proceed. When vinyl ester 4 was used, the reaction proceeded but the E value was
low.
Next, the e€ect of the enzyme was investigated using four lipases: Lipase QL, Lipase SL,
Lipase TL and Lipase UL. In all cases when Lipase UL or acyl donor 3 was employed, the
reactions did not proceed. Table 2 summarizes the results when isopropenyl acetate, 2 and 4 were
used as acyl donors. When isopropenyl acetate was employed, the reaction took place rapidly but
E values were small (around 1 to 3; entries 11±13). On the other hand, when chiral acyl donor
(‹)-2 was employed, the reaction took place relatively slowly and the enantioselectivities were
markedly improved (entries 14±16). When (‹)-4 was employed, the reaction proceeded more
slowly but the E values were not markedly improved (entries 17±19).
Table 2
The e€ect of lipase and acyl donor on kinetic resolutions of primary alcohol (‹)-6 using acyl donors
isopropenyl acetate (IPAc), (‹)-2 and (‹)-4 in hexane
Finally, the e€ect of solvent was investigated for the reaction with chiral acyl donor (‹)-2
using Lipase QL and SL as catalyst. The results are summarized in Table 3. For both lipases, the
reaction was the slowest in benzene and the fastest in diisopropyl ether. In contrast to the reaction

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K. Hirose et al. / Tetrahedron: Asymmetry 11 (2000) 1199±1210
Table 3
The solvent e€ect on E values of kinetic resolutions of primary alcohol (‹)-6 by Lipase QL- or SL-
catalyzed transesteri®cation with chiral acyl donor (‹)-2
using (‹)-1 as an acyl donor (entries 1 and 2 in Table 1), the enantioselectivity in the reaction
using diisopropyl ether was much better than that of the reaction in hexane. Thus, the best E value
(98) was obtained when the reaction was performed with Lipase SL in diisopropyl ether as solvent.
As mentioned above, the present results demonstrate that the combination of the acyl donor,
lipase and solvent is important to achieve high enantioselectivities. In particular, the use of acyl
donor 2, which has a stereogenic center at the b-position of the carbonyl group, resulted in a
dramatic improvement of enantioselectivity. Moreover, the con®guration of the acyl donor
a€ected the reactivity remarkably. One enantiomer of the acyl donor was practically inactive
towards this transesteri®cation so that it was not necessary to use an enantiomerically pure acyl
donor. The E value was improved up to 98 using a racemic mixture of acyl donor (‹)-2. In all
cases described in this article, the chirality of a fast-reacting substrate is unchanged; ( )-(S)-6
always reacts faster than (+)-(R)-6.
The enantioselectivities of lipase-catalyzed transesteri®cation might be caused by the diastereo-
meric interaction between the acylated lipase and substrate in the acylated enzyme±substrate
complex and/or by the intramolecular interaction of the tetrahedral intermediates in the transi-
tion state. A large acyl moiety makes the binding site more crowded than a smaller acyl moiety
does. Such spatial constraints for the fast- and slow-reacting substrates in the enzyme±substrate
complexes and/or following transition states might in¯uence the enantioselectivities. A full
explanation of the enantioselectivities of our results is not possible at this moment. Recently,
Hñ€ner and Norin reported the prediction of enantioselectivities using molecular modeling of a
lipase-catalyzed reaction.20 The molecular modeling of an acylated enzyme±substrate complex
and/or transition state might give an explanation of the enantioselectivities, including the position
of the stereogenic center, the chirality and all of the other structural relationships between a
substrate and an acyl moiety.
3. Experimental
3.1. General
1H NMR spectra were recorded at 270 MHz on a JEOL JNM-MH-270 spectrometer for
solutions in CDCl3 with SiMe4 as an internal standard, and J values are given in hertz. Mass

K. Hirose et al. / Tetrahedron: Asymmetry 11 (2000) 1199±1210
1205
spectra were recorded with 3-nitrobenzyl alcohol as a matrix on a JEOL-DX-303-HF spectro-
meter. IR spectra were measured on JASCO FT/IR-410 spectrometer. UV and visible spectra
were measured on a HITACHI 260-10 spectrometer. Optical rotations were measured using a
1
1
JASCO DIP-40 polarimeter and [ꢀ]D values are given in units of 10 deg cm2 g . HPLC
analyses were carried out on a Shimadzu LC-6A using a chiral column CHIRAL PAK AD
(250Â4.6 mm) (Daicel) or a chiral column Opti-Pak XC (Waters), 250 mmÂ4.6 mm column. GLC
analyses were carried out on a Shimadzu GC 8A chromatograph using an SE-52 on Uniport HP
2 mÂ2.6 mm column. Lipase QL, Lipase SL, Lipase TL, and Lipase UL were supplied by Meito
Sangyo and used without further puri®cation. Diisopropyl ether, benzene, and hexane were
stocked on molecular sieves 4 A after drying on CaCl2 followed by distillation.
3.2. (‹)-Vinyl 3-phenylbutanoate 2
Mercury(II) acetate (242 mg, 0.80 mmol) was added to a solution of (‹)-3-phenylbutanoic acid
(10 g, 61 mmol) in freshly distilled vinyl acetate (31.5 g, 365 mmol). After stirring at room tem-
perature for 30 min, a mixture of 98% sulfuric acid and fuming sulfuric acid (20 ml, 59:41 v/v) was
added and the mixture was re¯uxed for 4 h with stirring. The reaction mixture was neutralized
with sodium acetate and extracted with ether. The extract was washed with saturated aqueous
NaCl solution and dried over anhydrous MgSO4. Chromatography on silica gel (hexane:ethyl
ether, 98:2, as eluent) gave (‹)-vinyl 3-phenylbutanoate 2 (5.5 g, 48%) as a colorless oil; IR
1
(neat) 1754, 1644, 1149 cm ; ꢁH (CDCl3) 1.32 (3H, d, J=6.9, CH3), 2.74±2.55 (2H, m, CH2),
3.37±3.25 (1H, m, CH), 4.54 (1H, dd, J=6.3, 1.6, (E)-vinyl CH2), 4.84 (1H, dd, J=11.7, 1.6, (Z)-
vinyl CH2), 7.33±7.18 (6H, m, ArH and vinyl CH).
3.3. (‹)-Vinyl 2-phenylpropanoate 4
Esteri®cation of (‹)-2-phenylpropanoic acid (5.8 g, 39 mmol) with mercury(II) acetate (154
mg, 0.50 mmol) in 20.0 g (232 mmol) of vinyl acetate was carried out as described for the
preparation of (‹)-2. Puri®cation by silica gel chromatography (hexane:ethyl ether, 98:2, as eluent)
1
a€orded 3.7 g (54%) of (‹)-4 as a colorless oil; IR (neat) 1751, 1645, 1150 cm ; ꢁH (CDCl3) 1.54
(3H, d, J=7.1, CH3), 3.78 (1H, q, J=7.1, CH), 4.55 (1H, dd, J=6.2, 1.6, (E)-vinyl CH2), 4.85
(1H, dd, J=14.0, 1.6, (Z)-vinyl CH2) and 7.24±7.36 (6H, m, ArH and vinyl CH).
3.4. Resolution of (‹)-1
A mixture of (‹)-1 (10.0 g, 56.1 mmol), Lipase QL (from Alcaligenes sp.) (3.0 g) and benzyl
alcohol (24.3 g, 0.255 mol) in diisopropyl ether (600 ml) was stirred for 14 days at 30ꢀC. The
reaction was terminated by the ®ltration of the enzyme at ca. 30% conversion monitored by
GLC. Then the volatile materials were evaporated under reduced pressure. The same reactions
by the same procedures were carried out three times. Distillation of the combined reaction
product (125 g) under reduced pressure (90±110ꢀC/38 mmHg) gave 97.1 g of a distillate A con-
sisting of benzyl alcohol, unreacted ( )-1 (31.5% ee by HPLC), and (+)-benzyl ester in a ratio of
82.2, 16.4 and 0.3%, respectively, by GLC. And the residue A (6.7 g) consisted of (+)-benzyl
ester and unreacted ( )-1 in a ratio of 94.2 and 5.8%, respectively, by GLC. A portion of the
distillate A (48.8 g), which contained about 8.0 g of ( )-1 and 40.1 g of benzyl alcohol, Lipase QL
(4.0 g) and diisopropyl ether (600 ml) was stirred for 16 days at 30ꢀC. The reaction was terminated

1206
K. Hirose et al. / Tetrahedron: Asymmetry 11 (2000) 1199±1210
by ®ltration of the enzyme and volatile materials were evaporated under reduced pressure. The
same reaction was carried out using the rest of the distillate A (48.3 g) under similar conditions.
Distillation of the combined reaction mixture (97.0 g) under reduced pressure (106ꢀC/25 mmHg±
135ꢀC/5 mmHg) gave a distillate B (80.6 g) composed of benzyl alcohol (65 g) and unreacted
( )-1 (15 g, 66% ee by HPLC) and a residue B (6.0 g) composed of (+)-7 (5.4 g, 96% ee by
HPLC).
In order to obtain enantiomerically pure (R)-1, the same reaction was repeated using the
distillate B (80.7 g), Lipase QL (7.5 g) in the same solvent (700 ml) for 45 days at 30ꢀC. After a
similar work-up, distillation under reduced pressure (120±130ꢀC/25 mmHg) gave (R)-1 (11.5 g,
24
D
35% yield based on (‹)-1) as a colorless oil (95% ee by HPLC); ‰ꢀŠ
25.3 (c 1.07, CHCl3).
The combined residue A+B obtained from the distillations after the enzymatic reactions for
the synthesis of (R)-( )-1 described above was distilled again under reduced pressure (142±178ꢀC/
5 mmHg) to give (+)-benzyl 3-phenylbutanoate 7 (11.9 g) as a colorless oil. A mixture of (+)-7
(2.5 g, 9.8 mmol), methanol (1.3 g, 39.0 mmol), and Lipase QL (1.25 g) in diisopropyl ether (150
ml) was stirred for 13 days at 30ꢀC. The reaction was terminated by ®ltration and the volatile
materials were evaporated under reduced pressure. The same reactions were carried out twice by
the same procedures employing di€erent amounts (4.0 and 3.0 g, respectively) of the starting
material. All the reaction products were combined and puri®ed by distillation under reduced
pressure (130±139ꢀC/50 mmHg) followed by column chromatography on silica gel (hexane:ethyl
ether, 9:1, as eluent) to a€ord (S)-(+)-1 (5.5 g, 17% yield based on (‹)-1) as a colorless oil (96%
25
D
ee by HPLC); ‰ꢀŠ +29.6 (c 1.35, CHCl3).
3.5. (R)-( )-Vinyl 3-phenylbutanoate 2
To the solution of (R)-( )-1 (5.0 g, 28 mmol) in methanol (65 ml) was added 45% aqueous
KOH solution (61 ml), and the solution was stirred at room temperature for 14 h. The solvent
was evaporated under reduced pressure until its volume became 1/3. After acidi®cation of the
mixture with 6N hydrochloric acid, the mixture was extracted with ether. Chromatography on
22
D
silica gel (hexane:ethyl ether, 8:2, as eluent) gave (R)-( )-3-phenylbutanoic acid (3.2 g, 69%); ‰ꢀŠ
48.3 (c 1.07, benzene). Esteri®cation of ( )-3-phenylbutanoic acid (2.8 g, 17 mmol) with
mercury(II) acetate (68 mg, 0.21 mmol) in 9.5 g (110 mmol) of vinyl acetate was carried out as
described for the preparation of (‹)-2. Puri®cation by silica gel chromatography (hexane:ethyl
ether, 98:2, as eluent) a€orded 2.1 g (65%) of (R)-( )-vinyl 3-phenylbutanoate as a colorless oil
19.8 (c 1.01, CHCl3).
22
D
(93% ee); ‰ꢀŠ
3.6. (S)-(+)-Vinyl 3-phenylbutanoate 2
The reaction was carried out using the same procedure described for the preparation of (R)-
( )-vinyl 3-phenylbutanoate 2. To a solution of (S)-(+)-1 (3.0 g, 17 mmol) in methanol (65 ml)
was added 45% aqueous KOH solution (36 ml), and the solution was stirred at room temperature
for 2.5 h. The solvent was evaporated under reduced pressure until its volume became 1/3. After
acidi®cation of the mixture with 6N hydrochloric acid, the mixture was extracted with ether.
Chromatography on silica gel (hexane:ethyl ether, 8:2, as eluent) gave (S)-(+)-3-phenylbutanoic
22
acid (2.1 g, 75%); ‰ꢀŠ +52.2 (c 1.00, benzene). Esteri®cation of (+)-3-phenylbutanoic acid (1.9
D
g, 12 mmol) with mercury(II) acetate (48 mg, 0.25 mmol) in 7.5 g (87 mmol) of vinyl acetate was
carried out as described for the preparation of (‹)-2. Puri®cation by silica gel chromatography

K. Hirose et al. / Tetrahedron: Asymmetry 11 (2000) 1199±1210
1207
(hexane:ethyl ether, 98:2, as eluent) a€orded 1.2 g (53%) of (R)-( )-vinyl 3-phenylbutanoate as a
22
D
colorless oil (95% ee); ‰ꢀŠ +20.7 (c 1.08, CHCl3).
3.7. Lipase-catalyzed acylation of alcohols
3.7.1. General procedure for lipase-catalyzed acylation
Entry 1ÐA mixture of (‹)-2-phenylpropanol 6 (400 mg, 2.9 mmol), (‹)-methyl 3-phenylbutanoate
1 (517 mg, 2.9 mmol) and Lipase QL (400 mg) in diisopropyl ether (20 ml) was stirred at 30ꢀC
and the progress of the reaction was monitored by GLC. After stirring for 189 h, the enzyme was
removed by ®ltration and the volatile materials were evaporated under reduced pressure. Silica gel
chromatography of the residue gave recovered substrate (R)-(+)-6 (26% ee) and the mixture of
product esters, (R)-2-phenyl-1-propyl (S)-3-phenylbutanoate (S,R)-8 (90% ee) and (S)-2-phenyl-1-
propyl (S)-3-phenylbutanoate (S,S)-8 (94% ee). The ee values of the recovered substrate (R)-(+)-
6, the acylated substrate (S,R)-8 and (S,S)-8, and the recovered acyl donor (R)-1 were determined by
HPLC using a chiral column. De values of acylated substrate (S,R)-8 and (S,S)-8 were 54% which
were estimated by the same chromatogram of HPLC. The analysis of HPLC was performed under
the following conditions; hexane:isopropyl alcohol (99:1) as eluent, Opti-Pak XC (Waters) as column,
0.2 ml/min as ¯ow rate, and 1,3,5-tri-tert-butylbenzene as inner standard at ambient temperature. The
capacity factors for (R,R)-, (R,S)-, (S,S)-, and (S,R)-8 were 2.08, 2.23, 3.73, and 4.40, respectively.
3.7.2. General procedure for the hydrolysis of product esters
A mixture of the product esters and 45% aqueous KOH solution (8.3 ml) in methanol (15 ml)
was stirred for 3 h under re¯ux. After concentration, the mixture was extracted with ether. The
combined organic layer was washed with saturated aqueous NaCl solution and dried over anhyd-
rous MgSO4. Evaporation of the solvent gave alcohol (S)-6. The original aqueous layer was
acidi®ed (pH 1) with concentrated HCl and extracted with ether. The organic layer was washed
with saturated aqueous NaCl solution and dried over anhydrous MgSO4. Evaporation of the
solvent gave an acyl moiety as carboxylic acid.
Entry 2ÐReaction of (‹)-6 (40 mg, 0.29 mmol), (‹)-1 (100 mg, 0.56 mmol) with Lipase QL
(150 mg) in hexane (40 ml) at 30ꢀC for 88 h gave (R)-6 (17 mg, 47% yield, 18% ee) and a mixture
of product esters (S,R)-8 and (S,S)-8 (17 mg, 21% yield). The ee values of (S,R)-8 and (S,S)-8
were 92 and 99%, respectively, and the diastereomeric excess of (S,S)-8 over (S,R)-8 was 84%.
The acyl donor (R)-1 (65 mg, 65% yield, 11% ee) was also recovered.
Entry 3ÐReaction of (‹)-6 (40 mg, 0.29 mmol), (S)-1 (100 mg, 0.56 mmol) with Lipase QL
(150 mg) in hexane (40 ml) at 30ꢀC for 69 h gave (R)-6 (18 mg, 47% yield, 35% ee) and a mixture
of (S,R)-8 and (S,S)-8 (14 mg, 17% yield). The ee values of the (S,R) and (S,S) product esters
were 85 and 99%, respectively, and the diastereomeric excess of (S,S)-8 over (S,R)-8 was 82%.
The acyl donor (S)-1 (75 mg, 75% yield, 99% ee) was also recovered.
Entry 4ÐReaction of (‹)-6 (40 mg, 0.29 mmol), (R)-1 (100 mg, 0.56 mmol) with Lipase QL
(150 mg) in hexane (40 ml) at 30ꢀC proceeded too slowly to be analyzed (3% conversion for 86 h).
There was practically no reaction.
Entry 5ÐReaction of (‹)-6 (107 mg, 0.79 mmol), (‹)-2 (300 mg, 1.58 mmol) with Lipase QL
(150 mg) in hexane (22 ml) at 30ꢀC for 15 h gave (R)-6 (35 mg, 33% yield, 87% ee) and a mixture
of (S,R)-8 and (S,S)-8 (112 mg, 51% yield). The ee values of (S,R)-8 and (S,S)-8 were 24 and
96%, respectively, and the diastereomeric excess of (S,S)-8 over (S,R)-8 was 80%. The acyl donor
(R)-1 (130 mg, 43% yield, 36% ee) was also recovered.

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K. Hirose et al. / Tetrahedron: Asymmetry 11 (2000) 1199±1210
Entry 6ÐReaction of (‹)-6 (107 mg, 0.79 mmol), (S)-2 (300 mg, 1.58 mmol) with Lipase QL
(150 mg) in hexane (22 ml) at 30ꢀC for 1 h gave (R)-6 (45 mg, 42% yield, 99% ee) and a mixture
of (S,R)-8 and (S,S)-8 (130 mg, 58% yield). The ee values of (S,R)-8 and (S,S)-8 were 99 and
99%, respectively, and the diastereomeric excess of (S,S)-8 over (S,R)-8 was 72%. The acyl donor
(S)-1 (130 mg, 43% yield, 92% ee) was also recovered.
Entry 7ÐReaction of (‹)-6 (107 mg, 0.79 mmol), (R)-2 (300 mg, 1.58 mmol) with Lipase QL
(150 mg) in hexane (22 ml) at 30ꢀC for 41 h gave (R)-6 (42 mg, 39% yield, 19% ee) and a mixture
of (S,R)-8 and (S,S)-8 (69 mg, 31% yield). The ee values of (R,S)-8 and (R,R)-8 were 99 and 38%,
respectively, and the diastereomeric excess of (R,R)-8 over (R,S)-8 was 31%. The acyl donor (R)-
1 (211 mg, 1.11 mmol, 70% yield, 99% ee) was also recovered.
Entry 8ÐReaction of (‹)-6 (107 mg, 0.79 mmol), (‹)-3 (300 mg, 1.58 mmol) with Lipase QL
(150 mg) in hexane (22 ml) at 30ꢀC did not proceed.
Entry 9ÐReaction of (‹)-6 (116 mg, 0.85 mmol), (‹)-4 (300 mg, 1.70 mmol) with Lipase QL
(160 mg) in hexane (23 ml) at 30ꢀC for 10 h gave (R)-6 (69 mg, 60% yield, 2% ee), recovered acyl
donor (R)-4 (184 mg, 61% yield) and a mixture of product esters (83 mg, 36% yield), which was
hydrolyzed by the procedures described in General procedure for the hydrolysis of product esters.
The enantiomeric excess of alcohol (S)-6 was 4% as determined by HPLC using a chiral column.
Entry 10ÐReaction of (‹)-6 (400 mg, 2.9 mmol), methyl 3-phenylpropanoate 5 (3.1 g, 17.4
mmol) with Lipase QL (400 mg) in diisopropyl ether (20 ml) for 2.5 h followed by silica gel
chromatography of the products gave (+)-(R)-6 (40% ee), [ꢀ]D +3.0 (c 1.43, MeOH) and (S)-
( )-2-phenylpropanol 3-phenylpropanoate (62% ee), [ꢀ]D 6.3 (c 1.07, CHCl3), which was
hydrolyzed by the procedures described in General procedure for the hydrolysis of product esters.
The enantiomeric excess of alcohol (S)-6 was 62% as determined by HPLC using a chiral column.
Entry 11ÐReaction of (‹)-6 (200 mg, 1.47 mmol), isopropenyl acetate (300 mg, 2.99 mmol)
with Lipase QL (200 mg) in hexane (90 ml) at 30ꢀC for 3 h gave (R)-6 (73 mg, 37% yield, 8% ee)
and the product ester (S)-2-phenyl-1-propyl acetate (110 mg, 42% yield), which was hydrolyzed
by the procedures described in General procedure for the hydrolysis of product esters. The
enantiomeric excess of alcohol (S)-6 was 6% as determined by HPLC using a chiral column.
Entry 12ÐReaction of (‹)-6 (200 mg, 1.47 mmol), isopropenyl acetate (300 mg, 2.99 mmol)
with Lipase SL (200 mg) in hexane (90 ml) at 30ꢀC for 9 h gave (R)-6 (87 mg, 44% yield, 45% ee)
and the product ester (S)-2-phenyl-1-propyl acetate (65 mg, 25% yield), which was hydrolyzed by
the procedures described in General procedure for the hydrolysis of product esters. The enantio-
meric excess of alcohol (S)-6 was 37% as determined by HPLC using a chiral column.
Entry 13ÐReaction of (‹)-6 (200 mg, 1.47 mmol), isopropenyl acetate (300 mg, 2.99 mmol)
with Lipase TL (200 mg) in hexane (90 ml) at 30ꢀC for 4 h gave (R)-6 (66 mg, 33% yield, 4% ee)
and the product ester (S)-2-phenyl-1-propyl acetate (120 mg, 46% yield), which was hydrolyzed
by the procedures described in General procedure for the hydrolysis of product esters. The
enantiomeric excess of alcohol (S)-6 was 3% as determined by HPLC using a chiral column.
Entry 14ÐIdentical to entry 5.
Entry 15ÐReaction of (‹)-6 (107 mg, 0.79 mmol), (‹)-2 (300 mg, 1.58 mmol) with Lipase SL
(150 mg) in hexane (22 ml) at 30ꢀC for 40 h gave (R)-6 (30 mg, 28% yield, 93% ee) and a mixture
of product esters (S,R)-8 and (S,S)-8 (116 mg, 52% yield). The ee values of (S,R)-8 and (S,S)-8
were 46 and 95%, respectively, and the diastereomeric excess of (S,S)-8 over (S,R)-8 was 84%.
The acyl donor (R)-1 (126 mg, 42% yield, 40% ee) was also recovered.
Entry 16ÐReaction of (‹)-6 (107 mg, 0.79 mmol), (‹)-2 (300 mg, 1.58 mmol) with Lipase TL
(150 mg) in hexane (22 ml) at 30ꢀC for 2 h gave (R)-6 (33 mg, 31% yield, 45% ee) and a mixture

K. Hirose et al. / Tetrahedron: Asymmetry 11 (2000) 1199±1210
1209
of product esters (S,R)-8 and (S,S)-8 (110 mg, 49% yield). The ee values of (S,R)-8 and (S,S)-8
were 85 and 98%, respectively, and the diastereomeric excess of (S,S)-8 over (S,R)-8 was 40%.
The acyl donor (R)-1 (184 mg, 61% yield, 36% ee) was also recovered.
Entry 17ÐIdentical to entry 9.
Entry 18ÐReaction of (‹)-6 (116 mg, 0.85 mmol), (‹)-4 (300 mg, 1.70 mmol) with Lipase SL
(160 mg) in hexane (23 ml) at 30ꢀC for 10 h gave (R)-6 (43 mg, 37% yield, 47% ee), recovered
(R)-4 (195 mg, 65% yield) and a mixture of product esters (80 mg, 35% yield), which was
hydrolyzed with the procedures described in General procedure for the hydrolysis of product esters. The
optical purity of alcohol (S)-6 was 73% ee which was determined by HPLC using a chiral column.
Entry 19ÐReaction of (‹)-6 (116 mg, 0.85 mmol), (‹)-4 (300 mg, 1.70 mmol) with Lipase TL
(160 mg) in hexane (23 ml) at 30ꢀC for 77 h gave (R)-6 (50 mg, 43% yield, 7% ee), recovered (R)-
4 (181 mg, 60% yield) and a mixture of product esters (56 mg, 25% yield), which was hydrolyzed
with the procedures described in General procedure for the hydrolysis of product esters. The optical
purity of alcohol (S)-6 was 26% ee which was determined by HPLC using a chiral column.
Entry 20 ÐReaction of (‹)-6 (36 mg, 0.26 mmol), (‹)-2 (100 mg, 0.53 mmol) with Lipase QL
(50 mg) in benzene (8 ml) at 30ꢀC for 26 h gave (R)-6 (18 mg, 50% yield, 51% ee) and a mixture
of (S,R)-8 and (S,S)-8 (30 mg, 41% yield). The ee values of (S,R)-8 and (S,S)-8 were 33 and 96%,
respectively, and the diastereomeric excess of (S,S)-8 over (S,R)-8 was 85%. The acyl donor (R)-1
(42 mg, 42% yield, 36% ee) was also recovered.
Entry 21ÐIdentical to entry 5.
Entry 22ÐReaction of (‹)-6 (36 mg, 0.26 mmol), (‹)-2 (100 mg, 0.53 mmol) with Lipase QL
(50 mg) in diisopropyl ether (8 ml) at 30ꢀC for 2 h gave (R)-6 (16 mg, 45% yield, 98% ee) and a
mixture of (S,R)-8 and (S,S)-8 (41 mg, 45% yield). The ee values of (S,R)-8 and (S,S)-8 were 72%
and 99%, respectively, and the diastereomeric excess of (S,S)-8 over (S,R)-8 was 84%. The acyl
donor (R)-1 (48 mg, 0.25 mmol, 49% yield, 36% ee) was also recovered.
Entry 23ÐReaction of (‹)-6 (36 mg, 0.26 mmol), (‹)-2 (100 mg, 0.53 mmol) with Lipase QL
(50 mg) in benzene (8 ml) at 30ꢀC did not proceed.
Entry 24ÐIdentical to entry 15.
Entry 25ÐReaction of (‹)-6 (36 mg, 0.26 mmol), (‹)-2 (100 mg, 0.53 mmol) with Lipase SL
(50 mg) in diisopropyl ether (8 ml) at 30ꢀC for 1.5 h gave (R)-6 (11 mg, 31% yield, 85% ee) and a
mixture of (S,R)-8 and (S,S)-8 (29 mg, 39% yield). The ee values of (S,R)-8 and (S,S)-8 were 48
and 99%, respectively, and the diastereomeric excess of (S,S)-8 over (S,R)-8 was 94%. The acyl
donor (R)-1 (59 mg, 60% yield, 36% ee) was also recovered.
Acknowledgements
The authors thank Meito Sangyo Co. Ltd, for kindly providing the lipases. This work was
partially supported by a Grant-in-Aid for Scienti®c Research from the Ministry of Education,
Science and Culture of Japan.
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