Study of the enantioselectivity of the CAL-B-catalysed transesterification of α-substituted α-propylmethanols and α-substituted benzyl alcohols

Article abstract of DOI:10.1016/S0957-4166(01)00532-8

A study of the enantioselectivity exhibited by the lipase B from Candida antarctica in the transesterification of different α-substituted α-propylmethanols with vinyl acetate is shown. The best results are obtained when the large-sized (L) substituent of the alcohol is either a phenyl group or more especially a cyclohexyl group, although the reaction rates are lower than when linear or slightly branched groups are present. It is also found that ramification at the β-position of the L substituent has a deleterious effect on both lipase activity and enantioselectivity. Moreover, some α-substituted benzyl alcohols bearing medium-sized (M) substituents larger than an ethyl and smaller than a propyl group are resolved by means of this methodology with moderate-good enantioselectivities (E=46-57) and similar reaction rates.

Full text of DOI:10.1016/S0957-4166(01)00532-8

TETRAHEDRON:
ASYMMETRY
Pergamon
Tetrahedron: Asymmetry 12 (2001) 3047–3052
Study of the enantioselectivity of the CAL-B-catalysed
transesterification of a-substituted a-propylmethanols and
a-substituted benzyl alcohols
Eduardo Garc´ıa-Urdiales, Francisca Rebolledo and Vicente Gotor*
Departamento de Qu´ımica Orga´nica e Inorga´nica, Universidad de Oviedo, 33006 Oviedo, Spain
Received 6 November 2001; accepted 22 November 2001
Abstract—A study of the enantioselectivity exhibited by the lipase B from Candida antarctica in the transesterification of different
a-substituted a-propylmethanols with vinyl acetate is shown. The best results are obtained when the large-sized (L) substituent of
the alcohol is either a phenyl group or more especially a cyclohexyl group, although the reaction rates are lower than when linear
or slightly branched groups are present. It is also found that ramification at the b-position of the L substituent has a deleterious
effect on both lipase activity and enantioselectivity. Moreover, some a-substituted benzyl alcohols bearing medium-sized (M)
substituents larger than an ethyl and smaller than a propyl group are resolved by means of this methodology with moderate-good
enantioselectivities (E=46–57) and similar reaction rates. © 2002 Elsevier Science Ltd. All rights reserved.
1. Introduction
tivity (E=19).11 Moreover, this value is higher than the
one reported for the resolution of ( )-decan-4-ol (E=
10).8 Both substrates differ only in their L substituents,
which are made up of the same number of carbon
atoms. In order to shed light on the influence that the
different arrangements adopted by the L substituent
can have on both the activity and the enantioselectivity
of CAL-B. Herein, we wish to report our results con-
cerning the resolution of some a-substituted a-propyl-
methanols bearing a number of six carbon groups as
the L substituent. Likewise, we report the resolution of
a number of racemic a-substituted benzyl alcohols bear-
ing M substituents which are larger than an ethyl
group, in order to establish more accurate parameters
concerning the largest size of this substituent that can
be efficiently accepted by this lipase.
Lipases have been widely employed as catalysts for the
resolution of racemic secondary alcohols.1–3 Among
them, lipase B from Candida antarctica (CAL-B) has
proven to be a particularly efficient biocatalyst in these
processes,4,5 the stereochemical outcome of the reaction
being reliably predictable by Kazlauskas’ rule.6 More-
over, substrate mapping studies have shown the struc-
tural requirements that a secondary alcohol needs in
order to be successfully resolved by CAL-B. Thus,
alcohols bearing a medium-sized (M) substituent larger
than an ethyl group or a large-sized (L) substituent
smaller than an n-propyl group lead to poor enan-
tiomeric ratio (E)7 values. The same behaviour is
observed if the M substituent of the alcohol contains
chlorine or bromine atoms.8
However, there are reported examples in the literature
of highly selective CAL-B-catalysed resolutions of some
secondary alcohols which do not fulfil these require-
ments.9,10 In this sense, a previous study carried out in
our research group has shown that CAL-B catalyses the
resolution of ( )-1-phenylbutan-1-ol (M substituent
larger than an ethyl group) with moderate enantioselec-
2. Results and discussion
Transesterifications of alcohols ( )-1b–h (Table 1) were
carried out using lipase B from C. antarctica as catalyst
(Novozym 435), vinyl acetate as acylating agent and
1,4-dioxane as solvent. In order to avoid the competi-
tive enzymatic hydrolysis of the involved esters, all
reagents and solvents were dried prior to use, a nitro-
,
gen atmosphere was employed and 4 A molecular sieves
were added to ensure low water activity in the reaction
medium. For each transesterification, six aliquots were
* Corresponding author. Tel./fax: +34 985 10 34 48; e-mail: vgs@
sauron.quimica.uniovi.es
0957-4166/01/$ - see front matter © 2002 Elsevier Science Ltd. All rights reserved.
PII: S0957-4166(01)00532-8

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E. Garc´ıa-Urdiales et al. / Tetrahedron: Asymmetry 12 (2001) 3047–3052
Table 1. CAL-B-catalysed transesterification of alcohols (9)-1a–e
O
OH
OH
O
O
CALB
+
+
L
L
L
O
1,4-Dioxane
(±)-1a-e
(R)-2a-e
(S)-1a-e
Entry
Alcohol
L
t (h)
c (%)
E
1
2
3
4
5
(9)-1a
(9)-1b
(9)-1c
(9)-1d
(9)-1e
Ph
163
96
160 (96)
163
17.3
33.7
44.1 (33.9)
5.5
5.9
19.490.4
9.090.2
11.590.1
3.690.1
65.192.8
n-C6H13
i-C6H13
2-Ethylbutyl
Cyclohexyl
168
withdrawn at regular intervals and analysed by means
of chiral GC. Thus, the enantiomeric excesses of the
substrates 1 (e.e.s) and the products 2 (e.e.p) were
measured during all the process. For each transesterifi-
cation reaction four parameters were determined: E, c,
cFRE and cSRE.. Enantiomeric ratio (E) values were
calculated by fitting the e.e.s and e.e.p values to the
equation developed by Rakels et al.12 Conversion val-
ues (c) were determined from the e.e.s and e.e.p values
according to Sih et al.13 Finally, conversion values for
the fast- and slow-reacting enantiomers of the sub-
strates (cFRE and cSRE) were determined by means of
the degree of conversion (c) and the ratio of the peak
areas corresponding to each enantiomer of the product
2 measured for each aliquot.
M and the L substituents would be greater for alcohols
( )-1a,e than ( )-1b,c. This fact could account for the
lower E values obtained for the latter.
Kazlauskas’ rule has been traditionally translated into
an active site model for lipases consisting of two ‘pock-
ets’ of different size (Fig. 1).15–17 When a secondary
alcohol is resolved by a lipase, the fast-reacting enan-
tiomer binds to the active site in the manner shown in
Fig. 1. However, when the other enantiomer reacts with
the lipase, its large-sized substituent has to be accom-
modated in the smallest pocket (the stereoselectivity
pocket). Thus, the steric repulsions between this sub-
stituent and the stereoselectivity pocket account for the
lower reaction rate for this enantiomer. As the enan-
tiomeric ratio reflects the ratio of reactivity between the
fast- and the slow-reacting enantiomers of a racemic
mixture,7 the differences in the E values measured for
the transesterifications of alcohols ( )-1a–e could be
ascribed to different rates of conversion for their slow-
reacting enantiomers, their fast-reacting enantiomers or
both of them. For irreversible processes, the degree of
conversion is related to the reaction rate and so, to the
activation energy of the reaction. The degree of conver-
sion of each enantiomer of alcohols ( )-1a–e has to be
related to the energy of the diastereomeric transition
states that CAL-B forms with them. In Figs. 2 and 3,
the conversions of each enantiomer of alcohols ( )-1a–e
(cFRE and cSRE) are plotted against the reaction time.
As can be seen, cFRE and cSRE values considerably vary
with the L substituent of the substrates, thereby show-
2.1. Resolution of a-substituted a-propylmethanols
We first compared the result previously reported for the
resolution of ( )-1-phenylbutan-1-ol [( )-1a]11 with the
ones obtained for alcohols ( )-1b–e under the same
experimental conditions (Table 1). All substrates pos-
sess an L substituent made up of six carbon atoms and
in all cases, the enzyme follows Kazlauskas’ rule;
thereby esters (R)-2a–e were obtained as the major
enantiomers. As can be seen in Table 1, the reaction
rate and the enantioselectivity vary greatly according to
the structure of the L group. The presence of ramifica-
tion (branching) at the a- or b-positions of the L group
has a negative influence on the reaction rate. Thus, for
alcohols ( )-1b,c (entries 2 and 3) the degree of conver-
sion reached is higher than for alcohols ( )-1a (entry 1)
and, especially, ( )-1e (entry 5) and ( )-1d (entry 4).
With regard to the enantioselectivity, the higher values
are obtained with ( )-1a and ( )-1e (entries 1 and 5),
that is, with substrates bearing a conformationally rigid
L substituent. Again, ramification at the b-position in
( )-1d (entry 4) has a negative influence on the
enantioselectivity.
Phenyl and cyclohexyl rings have been described as
bulkier groups than the corresponding linear or slightly
branched aliphatic moieties made up of the same num-
ber of carbon atoms.14 According to Kazlauskas’ rule,
this would mean that the differences in size between the
Figure 1. Active site model for lipases derived from
Kazlauskas’ rule and applied to the resolution of racemic
secondary alcohols.

E. Garc´ıa-Urdiales et al. / Tetrahedron: Asymmetry 12 (2001) 3047–3052
3049
1e). This situation can be ascribed to the fact that both
pockets of the CAL-B active site can better accommo-
date the n-C6H13 and the i-C6H13 groups than the other
L substituents collected in Table 1, thus corroborating
the fact that linear or slightly branched substituents can
be regarded as less bulky groups than more branched
or cyclic moieties made up of the same number of
carbon atoms.
2.2. Resolution of a-substituted benzyl alcohols
Because ( )-1a is converted with moderate enantioselec-
tivity and conversion, we chose some benzyl alcohols,
( )-1f–h in order to investigate the influence of the M
substituent. The results obtained in the CAL-B-
catalysed transesterification of ( )-1f–h and that for
( )-1a11 are collected in Table 2. In all cases, the
enzyme follows Kazlauskas’ rule, esters (R)-2g and 2h
and (S)-2f being obtained as the major enantiomers.
Although CAL-B reacts at approximately the same rate
with all the substrates, the enantioselectivity exhibited
by the enzyme varied depending on the M substituent
of the alcohol. Thus, the E values decreased as follows:
( )-1g, 1h>( )-1f>( )-1a.
Figure 2. Degrees of conversion of the fast-reacting enan-
tiomers of alcohol’s 1a–f: (R)-1a (ꢀ), (R)-1b (ꢁ), (R)-1c (X),
(R)-1d (ꢂ) and (R)-1e (+).
For substrates ( )-1a and 1f–h, the L substituent is a
phenyl group. Taking into account the active site model
for lipases (Fig. 1), the larger the M substituent is, the
lower E values should be obtained. If we consider the
molecular volume of M as the criterion to estimate its
size, Kazlauskas’ rule can explain the different enan-
tioselectivity displayed by CAL-B during the resolution
of ( )-1a, 1f and 1h (Table 2, entries 1, 2 and 4).
However, when alcohol ( )-1g (Table 2, entry 3) is
included the rule fails. The analysis of the degrees of
conversion obtained for each enantiomer of the sub-
strates (Figs. 4 and 5) reveals some characteristic of the
two pockets. As it is shown in Fig. 5 (S)-1a is converted
faster than the other (S)-enantiomers, which means that
the propyl moiety is the best accommodated group in
the largest pocket, probably due to a better steric
interaction. From Fig. 4, the order of accomodation in
the smallest pocket is deduced as follows: allyl (83
Figure 3. Degrees of conversion of the slow-reacting enan-
tiomers of alcohols 1a–f: (S)-1a (ꢀ), (S)-1b (ꢁ), (S)-1c (X),
(S)-1d (ꢂ) and (S)-1e (+).
ing that the structure of this substituent greatly affects
its interaction energy with the two pockets of the active
site of this lipase. More specifically, both enantiomers
of alcohols 1b and 1c react faster than the correspond-
ing enantiomers of the other alcohols tested (1a, 1d and
Table 2. CAL-B-catalysed transesterification of alcohols (9)-1a and 1f–h
3 b
c (%)a
E
V (A )
,
Entry
Alcohol
M
1
2
3
4
(9)-1a
(9)-1f
(9)-1g
(9)-1h
n-Propyl
Methoxymethyl
Allyl
17.3
17.4
23.1
20.6
19.490.4
45.893.9
55.190.7
56.590.8
90
78
83
66
Cyanomethyl
a Reaction time: 163 h.
b Values calculated with PC MODEL 5.13 (Serena Software, USA).

3050
E. Garc´ıa-Urdiales et al. / Tetrahedron: Asymmetry 12 (2001) 3047–3052
for lipase enantioselectivity derived from Kazlauskas’
rule and some limitations to it have been put forward.
Previous results concerning the resolution of ( )-1-
phenylbutan-1-ol11 led us to expect that solvent engi-
neering will allow acceleration of the rate of these
reactions, thus widening the range of substrates that
can be successfully resolved by this lipase for synthetic
applications.
4. Experimental
4.1. General
Lipase B from C. antarctica, Novozym 435, was a gift
from Novo Nordisk co. and was employed without any
previous treatment. All reagents were purchased from
Aldrich Chemie, Avocado or Janssen. ( )-Decan-4-ol
( )-1b, ( )-1-phenyl-2-methoxyethanol ( )-1f and ( )-3-
hydroxy-3-phenylpropanenitrile ( )-1h were obtained
by standard reduction (NaBH4, MeOH) of the corre-
sponding commercially available ketones. ( )-6-Ethyl-
octan-4-ol ( )-1d and ( )-1-phenylbut-3-en-1-ol ( )-1g
were prepared by addition of 2-ethylbutan-1-yl magne-
sium bromide to butanal and allyl magnesium bromide
to benzaldehyde, respectively. ( )-8-Methylnonan-4-ol
( )-1c was prepared by addition of n-propyl magne-
sium bromide to 5-methyl-N-methyl-N-methoxyhex-
anamide, which was obtained by addition of
N-methoxymethanamine to the 5-methylhexanoyl chlo-
Figure 4. Degree of conversion of the fast-reacting enan-
tiomers of alcohols 1a and 1f–h: (R)-1a (X), (S)-1f (ꢁ),
(R)-1g (ꢂ) and (R)-1h (ꢀ).
ride (5-methylhexanoic acid, oxalyl chloride, DMF(cat.)
,
THF). 1,4-Dioxane was distilled over sodium and
stored under nitrogen. Flash chromatography was per-
formed with Merck silica gel 60 (230–240 mesh). Opti-
cal rotations were measured by means of
a
Perkin–Elmer 1720-X FT IR spectrometer. Mass spec-
tra were recorded on a VG Autospec. 1H and 13C NMR
spectra were obtained with a Bruker DPX 300 (1H 300
MHz and 13C 75.5 MHz) spectrometer using TMS as
internal standard. CG analyses were performed in a
Hewlett–Packard 5890 Series II chromatograph
equipped with a FID detector, using the capillary
columns RtbDEXse (30 m×0.25 mm; Restek) and Chi-
raldex-BPH (30 m×0.25 mm; Astec) as chiral stationary
phases and nitrogen as carrier gas (110 kPa).
Figure 5. Degree of conversion of the slow-reacting enan-
tiomers of alcohols 1a and 1f–h: (R)-1a (X), (S)-1f (ꢁ),
(R)-1g (ꢂ) and (R)-1h (ꢀ).
3
3
3
,
,
,
A )>cyanomethyl (66 A )>methoxymethyl (78 A ) and
3
,
propyl (90 A ), which evidence that the steric repulsions
are not the only interactions responsible for CAL-B
enantioselectivity. In this sense, the distinct ability of
the M substituents to adopt different conformations in
the active site of the enzyme and the existence of
electronic interactions could also play a key role during
CAL-B enantiorecognition process. The traditional
model, which only takes into account steric interactions
on the basis of the size of the substituents, is inappro-
priate to explain CAL-B enantioselectivity towards
these types of alcohols.
4.2. Typical procedure for the enzymatic
transesterification of alcohols ( )-1b–h
To a solution of the corresponding alcohol (1.0 mmol)
in 1,4-dioxane (10 mL), vinyl acetate (3.0 mmol),
molecular sieves (250 mg) and CAL-B (200 mg) were
added. The resulting mixture was shaken at 30°C and
250 rpm for the time shown in Table 1. Six aliquots (10
mL) were withdrawn at regular intervals and analysed
through chiral GC. For each enzymatic reaction a
control experiment without enzyme was carried out and
no non-enzymatic reaction was detected through GC
analysis. For transesterifications of alcohols ( )-1b, 1c
and 1f–h, after the reaction time shown in Table 1
(entries 2 and 3) and Table 2 (entries 2–4) the enzyme
and the molecular sieves were filtered off and washed
with dichloromethane and the organic solvents were
3. Conclusions
We have shown that lipase B from C. antarctica can be
an efficient catalyst for the resolution of secondary
alcohols bearing medium-sized substituents larger than
an ethyl group but smaller than an n-propyl group.
Results have been discussed on the basis of the model

E. Garc´ıa-Urdiales et al. / Tetrahedron: Asymmetry 12 (2001) 3047–3052
3051
evaporated. Flash chromatography of the residue (elu-
ent: dichloromethane/hexane gradient) yielded the cor-
4.3. Determination of the enantiomeric excesses
responding substrates and products.
The e.e. of alcohols 1b–h and esters 2b–h were deter-
mined by means of chiral GC. Only for the case of
compounds 1c, 1d, 1g and 2e direct analyses were not
possible. Thus, alcohols 1c and 1d were transformed
into their propanoyl ester derivatives (O-Prp-1c, 1d),
alcohol 1f into its trifluoroacetyl derivative (O-TFA-1f)
and ester 2e into its corresponding alcohol (1e) prior to
analysis. Conditions are as follows. 1b: RtbDEXse,
80°C, 30 min hold, 80–120°C, 2°C/min, 10 min hold,
tR1 (R)=46.3 min, tR2 (S)=47.1 min, Rs 1.0; O-Prp-
1c: Chiraldex-BPH, 50°C, 5 min hold, 50–100°C, 1°C/
min, 30 min hold, tR1 (S)=36.9 min, tR2 (R)=37.6
min, Rs 1.2; O-Prp-1d: Chiraldex-BPH, 50°C, 5 min
hold, 50–100°C, 1°C/min, 10 min hold, tR1 (S)=32.5
min, tR2 (R)=33.3 min, Rs 1.9; 1e: RtbDEXse, 100°C,
25 min hold, tR1 (S)=18.9 min, tR2 (R)=20.6 min, Rs
2.1; O-TFA-1f: RtbDEXse, 80°C, 20 min hold, 80–
120°C, 2°C/min, 30 min hold, tR1 (R)=32.0 min, tR2
(S)=32.4 min, Rs 1.0; 1g: RtbDEXse, 80°C, 5 min
hold, 80–150°C, 2°C/min, 10 min hold, tR1 (S)=34.3
min, tR2 (R)=34.6 min, Rs 1.8; 1h: RtbDEXse, 170°C,
17 min hold, tR1 (R)=13.6 min, tR2 (S)=14.5 min, Rs
3.9; 2b: RtbDEXse, 80°C, 30 min hold, 80–120°C,
2°C/min, 10 min hold, tR1 (S)=47.8 min, tR2 (R)=48.3
min, Rs 0.8; 2c: Chiraldex-BPH, 50°C, 5 min hold,
50–100°C, 1°C/min, 30 min hold, tR1 (S)=30.4 min,
tR2 (R)=31.2 min, Rs 1.2; 2d: Chiraldex-BPH, 50°C, 5
min hold, 50–100°C, 1°C/min, 10 min hold, tR1 (S)=
26.7 min, tR2 (R)=27.8 min, Rs 2.1; 2f: RtbDEXse,
80°C, 20 min hold, 80–120°C, 2°C/min, 30 min hold,
tR1 (R)=50.5 min, tR2 (S)=51.5 min, Rs 1.7; 2g:
RtbDEXse, 80°C, 5 min hold, 80–150°C, 2°C/min, 10
min hold, tR1 (S)=32.0 min, tR2 (R)=32.6 min, Rs
2.3; 2h: RtbDEXse, 170°C, 17 min hold, tR1 (S)=9.7
min, tR2 (R)=9.9 min, Rs 1.7.
4.2.1. (R)-Decan-4-yl acetate (R)-2b. Colourless liquid;
yield, 90% (34% c); [h]D22 +4.7 (c 0.82, CHCl3, 74% e.e.);
1
IR (neat) 1740 cm−1; H NMR (CDCl3) l (ppm) 0.88
(m, 6H, 2CH3), 1.26 (m, 10H, 5CH2), 1.49 (m, 4H,
2CH2), 2.03 (s, 3H, CH3), 4.87 (m, 1H, CH); 13C NMR
(CDCl3) l (ppm) 13.9 (CH3), 14.0 (CH3), 18.5 (CH2),
21.2 (CH3), 22.5 (CH2), 25.2 (CH2), 29.1 (CH2), 31.7
(CH2), 34.1 (CH2), 36.2 (CH2), 74.1 (CH), 170.9 (CꢀO);
MS (70 eV) m/z (%) 157 (18), 140 (56), 115 (80), 97
(80), 43 (100).
4.2.2. (R)-2-Methylnonan-6-yl acetate (R)-2c. Colour-
less liquid; yield, 85% (44% c); [h]2D1 +5.9 (c 1.07,
CHCl3, 73% e.e.); IR (neat) 1740 cm−1; 1H NMR
3
(CDCl3) l (ppm) 0.85 (d, 6H, JHH=6.5 Hz, 2CH3),
3
0.90 (t, 3H, JHH=7.5 Hz, CH3), 1.16 (m, 2H, CH2),
1.30 (m, 4H, 2 CH2), 1.49 (m, 5H, 2 CH2, CH), 2.03 (s,
3H, CH3), 4.87 (m, 1H, CH); 13C NMR (CDCl3) l
(ppm) 13.9 (CH3), 18.5 (CH2), 21.2 (CH3), 22.4 (CH3),
22.5 (CH3), 23.0 (CH2), 27.8 (CH), 34.3 (CH2), 36.2
(CH2), 38.7 (CH2), 74.1 (CH), 170.9 (CꢀO); MS (70 eV)
m/z (%) 157 (7), 140 (17), 115 (53), 97 (67), 43 (100).
4.2.3. (S)-1-Phenyl-2-methoxyethyl acetate (S)-2f.
Colourless liquid; yield, 92% (17% c); [h]2D2 +84.2 (c
1.19, CHCl3, 95% e.e.); IR (neat) 1739 cm−1; H NMR
1
(CDCl3) l (ppm) 2.13 (s, 3H, CH3), 3.40 (s, 3H, CH3),
3.56 (dd, 1H, 2JHH=10.9 Hz, 3JHH=3.9 Hz, CHH),
3.73 (dd, 1H, 2JHH=10.9 Hz, 3JHH=8.0 Hz, CHH),
3
3
5.97 (dd, 1H, JHH=8.0 Hz, JHH=3.9 Hz, CH), 7.35
(m, 5H, Ph); 13C NMR (CDCl3) l (ppm) 21.2 (CH3),
59.1 (CH3), 74.2 (CH), 75.2 (CH2), 126.6 (CH), 128.2
(CH), 128.4 (CH), 137.4 (C), 170.2 (CꢀO); MS (70 eV)
m/z (%) 162 (40), 149 (100).
4.4. Determination of the absolute configuration
The absolute configuration of alcohols 1f and 1g was
determined by comparison of the sign of their optical
rotations with the data published in the literature for
their (R)-enantiomers.18,19 The absolute configuration
of alcohol 1h was determined by comparison of the
elution times of their peaks in the GC chromatogram
with those published for both enantiomers of this com-
pound.20 Finally, the absolute configuration of esters
2b–e was assigned assuming that the enzyme followed
Kazlauskas’ rule6 during the transesterfication pro-
cesses. This assumption is in accordance with the fact
that the elution times of the peaks corresponding to the
major enantiomers of esters 2b–d and the one published
for ester 2a9 are always higher than the ones corre-
sponding to the minor enantiomers of these esters, no
matter which stationary phase is employed.
4.2.4. (R)-1-Phenylbut-3-en-1-yl acetate (R)-2g. Colour-
less liquid; yield, 87% (23% c); [h]2D2 +58.4 (c 0.81,
CHCl3, 95% e.e.); IR (neat) 1739 cm−1; 1H NMR
(CDCl3) l (ppm) 2.08 (s, 3H, CH3), 2.60 (m, 2H, CH2),
5.07 (m, 2H, CH2), 5.71 (m, 1H, CH), 5.81 (dd, 1H,
3
3JHH=6.3 Hz, JHH=7.7 Hz, CH), 7.34 (m, 5H, Ph);
13C NMR (CDCl3) l (ppm) 21.2 (CH3), 40.7 (CH2),
75.0 (CH), 118.0 (CH2), 126.4 (CH), 127.9 (CH), 128.3
(CH), 133.2 (CH), 139.9 (C), 170.2 (CꢀO); MS (70 eV)
m/z (%) 190 (M+, <1), 149 (80), 107 (100).
4.2.5. (R)-2-Cyano-1-phenylethyl acetate (R)-2h. White
solid; yield, 94% (21% c); mp 123–124°C; [h]2D2 +71.7 (c
1
1.21, CHCl3, 95% e.e.); IR (neat) 2252, 1739 cm−1; H
NMR (CDCl3) l (ppm) 2.16 (s, 3H, CH3), 2.91 (dd,
2
3
2H, JHH=1.0 Hz, JHH=6.2 Hz, CH2), 5.98 (dd, 1H,
3JHH=6.3 Hz, JHH=6.0 Hz, CH), 7.40 (m, 5H, Ph);
3
13C NMR (CDCl3) l (ppm) 20.9 (CH3), 25.5 (CH2),
70.4 (CH), 116.0 (CN), 126.0 (CH), 128.9 (CH), 129.1
(CH), 137.1 (C), 169.5 (CꢀO); MS (70 eV) m/z (%) 189
(M+, 55), 162 (59), 149 (38), 147 (74), 130 (48), 120 (53),
107 (100).
Acknowledgements
We are grateful to the MCYT (Project BIO 98-0770)
for financial support, to Novo Nordisk Co. for the

3052
E. Garc´ıa-Urdiales et al. / Tetrahedron: Asymmetry 12 (2001) 3047–3052
generous gift of lipase B from C. antarctica. E.G.-U.
thanks MEC for a predoctoral fellowship.
9. Liu, H.-L.; Hoff, B. H.; Anthonsen, T. J. Chem. Soc.,
Perkin Trans. 1 2000, 1767–1769.
10. Pchelka, B. K.; Loupy, A.; Plenkiewicz, J.; Blanco, L.
Tetrahedron: Asymmetry 2000, 11, 2719–2732.
11. Garc´ıa-Urdiales, E.; Rebolledo, F.; Gotor, V. Adv. Synth.
Catal. 2001, 343, 646–654.
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