First example of hydrolytic kinetic resolution of acrylate of secondary alcohols by lipase Amano AK

Article abstract of DOI:10.1016/j.molcatb.2011.06.015

Lipase Amano AK is found to be extremely efficient catalyst for hydrolytic kinetic resolution of acrylates of secondary alcohols in aqueous phosphate buffer at pH 7.0. Both aliphatic and benzylic secondary alcohols show good to excellent E values.

Full text of DOI:10.1016/j.molcatb.2011.06.015

Journal of Molecular Catalysis B: Enzymatic 72 (2011) 270–275
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Journal of Molecular Catalysis B: Enzymatic
journal homepage: www.elsevier.com/locate/molcatb
First example of hydrolytic kinetic resolution of acrylate of secondary
alcohols by lipase Amano AK
Pranjal P. Bora, Ghanashyam Bez∗, Jasha Momo H. Anal
Department of Chemistry, North Eastern Hill University, Shillong-793022, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Lipase Amano AK is found to be extremely efficient catalyst for hydrolytic kinetic resolution of acrylates of
secondary alcohols in aqueous phosphate buffer at pH 7.0. Both aliphatic and benzylic secondary alcohols
show good to excellent E values.
Received 14 April 2011
Received in revised form 6 June 2011
Accepted 23 June 2011
© 2011 Elsevier B.V. All rights reserved.
Available online 13 July 2011
Keywords:
Lipase
Alcohol
Acrylates
Enantioselective
Aqueous
1. Introduction
with ␣,␤-unsaturated acid chlorides [6], or through enzymatic
kinetic resolution of acrylates of secondary alcohols (Scheme 1).
In recent years, enzymes [1] are finding huge applicability
in the manufacture of a wide range products, viz. drugs, agro-
pharmaceuticals, organic fine chemicals and plastics [2] because
of their easy commercial availability and high catalytic efficiency.
Among the enzymes, lipases are used very often in organic synthe-
sis because of their excellent selectivities. They catalyze hydrolysis,
esterification, trans-esterification including alcoholysis on a broad
range of substrates due to their ability to change their conforma-
tion depending on the substrate structure (induced fit enzyme) [3].
Especially, lipases are suited for the kinetic resolution of secondary
alcohols due to their exceptional stability and enantioselectivity
in both water and organic solvents, besides being environmentally
friendly.
The ␣,␤-unsaturated lactone [4] is one of the most important
functionalities present in a wide spectrum of naturally occurring
compounds that display diverse pharmacological properties, such
as antitumor, antimicrobial, and antifungal. The synthesis of ␣,␤-
unsaturated lactones can be achieved by ring closing metathesis
(RCM) of acrylates of secondary alcohol with unactivated olefin
terminal [5]. The stereoselectivity of the acrylate terminal can be
achieved in two pathways, viz. by esterification of chiral secondary
alcohol, derived from non-enzymatic stereoselective reactions,
While surfing the literature, we have observed that the
enzymatic esterification of olefin-tethered secondary alcohols to
synthesize enantiomerically pure ␣,␤-unsaturated ester is find-
ing scant attention, albeit being very promising. In spite of having
tremendous potential, there are only a few reports [7] on synthesis
of chiral ␣,␤-unsaturated esters by enzymatic trans- esterifica-
tion of racemic secondary alcohols with ␣,␤-unsaturated vinyl
esters. But, no report is available for enzymatic hydrolysis of ␣,␤-
unsaturated esters leading to chiral alcohol, unlike the enzymatic
hydrolysis of the acetate of secondary alcohols. It is a fact that
in most of the kinetically controlled enzymatic reactions, equilib-
rium shift towards the right with slightest change in the reaction
conditions. Therefore, both enzymatic esterification and hydroly-
sis are important pathways to achieve enantiomeric alcohol with
high ee-values. In order to develop an efficient method for the
synthesis enantiomerically pure acrylates and secondary alcohol,
we are reporting for the first time, the lipase Amano AK catalyzed
enzymatic kinetic hydrolysis of acrylates of secondary alcohols to
achieve good to excellent enantioselectivity.
2. Experimental
2.1. General
All reagents were commercially available and used without
further purification. Most of the alcohols were synthesized by
NaBH4 reduction of coommercially available ketones purchased
∗
Corresponding author.
E-mail addresses: bez@nehu.ac.in, ghanashyambez@yahoo.com (G. Bez).
1381-1177/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.molcatb.2011.06.015

P.P. Bora et al. / Journal of Molecular Catalysis B: Enzymatic 72 (2011) 270–275
271
2.2.4. 1-(3-Nitrophenyl) ethyl acrylate
Purification by column chromatography using hexane and ethyl
acetate in 9:1 ratio to achieve 1-(3-nitrophenyl)ethyl acrylate as
a colorless liquid (yield 75%). 1H NMR (400 MHz, CDCl3): ı 1.60
(d, J = 6.4 Hz, 3H) 5.88 (d, J = 10 Hz, 1H) 6.01 (q, J = 6.4 Hz, 1H), 6.15
(dd, J = 17.2 Hz, 10 Hz, 1H), 6.44 (d, J = 18 Hz, 1H), 7.52 (t, J = 8 Hz,
1H), 7.68 (d, J = 7.6 Hz, 1H), 8.14 (d, J = 8 Hz, 1H), 8.23 (s, 1H) ppm.
13C NMR (100 MHz, CDCl3): ı 22.4, 71.4, 121.1, 123.0, 128.3, 129.7,
131.8, 132.4, 143.9, 165.3 ppm.
Scheme 1.
2.2.5. 1-(4-Methyl phenyl)ethyl acrylate
Purification by column chromatography using hexane and ethyl
acetate in 9:1 ratio to achieve 1-(4-methylphenyl)ethyl acrylate as
a colorless liquid (yield 82%). 1H NMR (400 MHz, CDCl3): ı 1.52
(d, J = 6.8 Hz, 3H), 2.34 (s, 3H), 5.81 (dd, J = 10.4, 1.2 Hz,1H), 5.93
(q, J = 6.4 Hz, 1H), 6.17 (dd, J = 17.2, 10.4 Hz, 1H), 6.41 (dd, J = 17.6,
1.2 Hz, 1H), 7.164 (d, J = 8 Hz, 2H), 7.27 (d, J = 8 Hz, 2H) ppm. 13C
NMR (100 MHz, CDCl3): ı 21.1, 22.1, 72.4, 126.1, 128.8, 129.1, 130.7,
138.1, 165.5 ppm.
from Sigma Aldrich and acrylated with acryloyl chloride and
DBU/triethylamine as per literature procedure [6a]. The alcohol
derivatives for entry 6, 7 and 8 were synthesized by Grignard
reaction with their corresponding aldehydes. All acrylates were
characterized by 1H NMR, 13C NMR and IR spectroscopy. The IR
spectra were recorded on a Perkin Elmer spectrophotometer. 1H
NMR (400 MHz) and 13C NMR (100 MHz) spectra were obtained on
a Bruker AC-400 using CDCl3 as solvent and TMS as internal stan-
dard, unless otherwise stated. Optical rotations were measured on a
Perkin Elmer 341 polarimeter. HPLC analyses were performed on an
Waters M515 series equipped with a chiral column (Chiralcel AD-H
and Chiralcel OD-H), using mixtures of n-hexane/isopropyl alcohol
(IPA) as mobile phase, at 25 ◦C. For column chromatography, we
employed Merck silica gel 60–120 mesh.
2.2.6. 1-Phenylbutyl acrylate
Purification by column chromatography using hexane and ethyl
acetate in 12:1 ratio to achieve 1-phenylbutyl acrylate as a color-
less liquid (yield 73%). 1H NMR (400 MHz,CDCl3): ı 0.92 (t, J = 14.8,
7.2 Hz, 3H), 1.31 (m, 2H), 1.86 (m, 2H), 5.81 (t, J = 2.4 Hz, 1H), 5.83
(d, J = 0.8 Hz, 1H), 6.15 (dd, J = 21.2, 10.4 Hz, 1H), 6.41 (d, J = 21.6 Hz,
1H), 7.30 (m, 5H) ppm. 13C NMR (100 MHz, CDCl3): ı 13.8, 18.7,
38.4, 76.0, 126.4, 127.8, 128.4, 128.7, 130.7, 140.7, 165.5 ppm.
2.2. General procedure for the synthesis of acrylates
A mixture of the secondary alcohol (2 mmol) and triethylamine
(3 mmol) was dissolved in 20 mL dichloromethane and cooled to
0 ◦C. Then acryloyl chloride (5 mmol) was added drop wise to the
reaction mixture and allowed to stir overnight. Upon completion,
the reaction mixture was diluted with saturated NaHCO3 solution
and extracted with dichloromethane and aqueous NH4Cl solution,
dried over Na2SO4 and concentrated in a rotavapor. The residual oil
is purified by column chromatography (silica gel, EtOAc/Hexane).
The acrylates are characterized by 1H NMR, 13C NMR.
2.2.7. 1-(4-Bromophenyl)allyl acrylate
Purification by column chromatography using hexane and ethyl
acetate in 12:1 ratio to achieve 1-(4-bromophenyl)allyl acrylate as
a colorless liquid (yield 85%). 1H NMR (400 MHz, CDCl3): ı 5.25 (t,
J = 16.8 Hz, 2H), 5.83 (dd, J = 10.4, 1.2 Hz, 1H), 5.91–5.98 (m, 1H), 6.13
(dd, J = 17.2, 10.4 Hz, 1H), 6.24 (d, J = 5.6 Hz, 1H), 6.41 (dd, J = 17.2,
1.2 Hz, 1H), 7.21 (d, J = 8.4 Hz, 1H), 7.44 (d, J = 8.4 Hz, 1H) ppm. 13C
NMR (100 MHz, CDCl3): ı 75.6, 117.5, 122.2, 128.2, 128.9, 131.7,
135.6, 137.8, 165 ppm.
2.2.1. 1-Phenylethyl acrylate
2.2.8. 1-[(E)-2-Phenylvinyl]but-3-enyl acrylate
Purification by column chromatography using hexane and ethyl
acetate in 9:1 ratio to achieve 1-phenylethyl acrylate as a colorless
liquid (yield 79%). 1H NMR (400 MHz, CDCl3): ı 1.54 (d, J = 6.8 Hz,
3H), 5.78 (dd, J = 10.4 Hz, 1.6 Hz, 1H), 5.93 (q, J = 6.4 Hz, 1H), 6.11
(dd, J = 17.6 Hz, 10.4 Hz, 1H) 7.28 (m, 5H) ppm. 13C NMR (100 MHz,
CDCl3): ı 22.1, 72.7, 126.0, 127.9, 128.6, 130.7, 141.5, 165.4 ppm.
Purification by column chromatography using hexane and ethyl
acetate in 12:1 ratio to achieve 1-[(E)-2-phenylvinyl]but-3-enyl
acrylate as a colorless liquid (yield 66%). 1H NMR: ı 2.53 (m,
2H), 5.09–5.16 (m, 2H), 5.56 (q, J = 6.6 Hz, 1H), 5.75–5.85 (m, 2H),
6.11–6.21 (m, 2H), 6.43 (dd, J = 17.4, 1.4 Hz, 1H), 6.64 (d, J = 16.0 Hz,
1H), 7.24–7.39 (m, 5H) ppm. 13C NMR (100 MHz, CDCl3): ı 39.1,
73.9, 118.2, 126.6, 126.9, 128.0, 128.5, 128, 6, 130.8, 132,7, 133.0,
136.2, 165.4 ppm.
2.2.2. 1-(4-Methoxyphenyl)ethyl acrylate
Purification by column chromatography using hexane and ethyl
acetate in 9:1 ratio to achieve 1-(4-methoxyphenyl)ethyl acrylate
as a colorless liquid (yield 85%). 1H NMR (400 MHz, CDCl3): ı 1.35
(d, J = 6.4 Hz, 3H), 3.58 (s, 3H), 5.59 (dd, J = 10, 1.2 Hz, 1H), 5.72 (q,
J = 6.4 Hz, 1H), 5.91 (dd, J = 17.2, 10 Hz, 1H), 6.19 (dd, J = 17.6, 1.2 Hz,
1H), 6.70 (d, J = 8 Hz, 2H), 7.11 (d, J = 8.4 Hz, 2H) ppm; 13C NMR
(100 MHz, CDCl3): ı 22.0, 55.3, 113.8, 127.6, 128.8, 130.7, 133.6,
165.5 ppm.
2.2.9. Octan-2-yl acrylate
Purification by column chromatography using hexane and ethyl
acetate in 20:1 ratio to achieve octan-2-yl acrylate as a colorless
liquid (yield 86%). 1H NMR (400 MHz, CDCl3): ı 0.79 (t, J = 6 Hz,
3H), 1.09–1.60 (m, 13H), 4.85–4.93 (m, 1H), 5.71 (dd, J = 10, 1.2 Hz,
1H), 6.02 (dd, J = 17.2, 10.4 Hz, 1H), 6.3 (d, J = 16.8 Hz, 1H) ppm. 13
C
NMR (100 MHz, CDCl3): ı 14.0, 19.9, 22.5, 25.3, 29.1, 31.7, 35.8, 71.3,
129.1, 130.1, 165.9 ppm.
2.2.3. 1-(4-Chlorophenyl) ethyl acrylate
Purification by column chromatography using hexane and ethyl
acetate in 9:1 ratio to achieve 1-(4-chlorophenyl)ethyl acrylate as
a colorless liquid (yield 88%). 1H NMR (400 MHz, CDCl3): 0.55 (d,
J = 6.8 Hz, 3H), 5.88 (dd, J = 27 Hz, 6.4 Hz, 1H), 5.84 (q, J = 6.4 Hz, 1H),
6.05 (dd, J = 17.2, 10.4 Hz, 1H), 6.34 (dd, J = 17.2, 0.8 Hz, 1H), 7.23
(m, 4H) ppm. 13C NMR (100 MHz, CDCl3): ı 22.1, 71.7, 127.5, 128.4,
128.5, 128.7, 131.0, 133.6, 140.1, 165.3 ppm.
2.2.10. Octan-3-yl acrylate
Purification by column chromatography using hexane and ethyl
acetate in 20:1 ratio to achieve octan-3-yl acrylate as a colorless
liquid (yield 81%). 1H NMR (400 MHz, CDCl3): ı 0.71–0.81 (m, 6H),
1.18 (m, 6H), 1.41–1.55 (m, 4H), 4.80 (m, 1H), 4.84 (dd, J = 10.4,
1.2 Hz, 1H), 6.02 (dd, J = 17.6, 10.4 Hz, 1H), 6.3 (dd, J = 17.6, 1.2 Hz,

272
P.P. Bora et al. / Journal of Molecular Catalysis B: Enzymatic 72 (2011) 270–275
1H) ppm; 13C NMR (100 MHz, CDCl3): ı 9.6, 14, 22.5, 24.9, 26.9,
31.5, 75.7, 129, 130.2, 166.1 ppm.
Chiralcel AD-H, n-hexane/2-propanol (95:5), 0.5 mL/min, 220 nm;
tR: (R) 14.53 min, (S) 16.38 min.
(R)-1-PHENYLBUTAN-1-OL: 82% ee. [␣]D20 =+59 (c 1.0, CHCl3).
HPLC analysis: Chiralcel AD-H, n-hexane/2-propanol (90:10),
0.5 mL/min, 220 nm; tR: (R) 10.94 min, (S) 12.04 min.
2.2.11. Hept-1-en-3-yl acrylate (3b)
Purification by column chromatography using hexane and ethyl
acetate in 20:1 ratio to achieve hept-1-en-3-yl acrylate (3b) as a
colorless liquid (yield 88%). 1H NMR (400 MHz, CDCl3): ı 0.82 (t,
J = 6.4 Hz, 3H), 1.18–1.3 (m, 4H), 1.52–1.63 (m, 2H), 5.08–5.26 (m,
3H), 5.69–5.78 (m, 2H), 6.06 (dd, J = 17.2, 10.4 Hz, 1H), 6.34 (dd,
J = 17.6, 1.6 Hz, 1H) ppm. 13C NMR ı (100 MHz, CDCl3): 13.9, 22.4,
27.2, 33.9, 75, 116.6, 128.8, 130.5, 136.5, 165.5 ppm.
(R)-1-(4-BROMOPHENYL)PROP-2-EN-1-OL:
94%
ee.
[␣]D20 = +46.4 (c 1.0, CHCl3) HPLC analysis: Chiralcel AD-H, n-
hexane/2-propanol (95:5), 0.5 mL/min, 254 nm; tR: (S) 10.15 min,
(R) 10.72 min.
(3R)-(1E)-PHENYLHEXA-1,5-DIEN-3-OL: 91% ee. [␣]D20 = +33.4 (c
1.0, CHCl3). HPLC analysis: Chiralcel AD-H, n-hexane/2-propanol
(95:5), 0.4 mL/min, 234 nm; tR: (R) 28.29 min, (S) 31.08 min.
(S)-OCTAN-2-OL: [␣]D20 = +7.0 (c 1.0, CHCl3) [9].
2.2.12. (R)-5-Butyl-2(5H)-furanone 3f
(S)-OCTAN-3-OL: [␣]D20 = +6.1 (c = 1, CHCl3) [lit. [10];
[␣]D20 = +9.15 (c 4.33, CHCl3)].
Purification by column chromatography using hexane and ethyl
acetate in 12:1 ratio to achieve (R)-5-butyl-2(5H)-furanone (3f) as
a colorless liquid (yield 91%). 1H NMR (400 MHz, CDCl3): ı 0.84 (t,
J = 6.8 Hz, 3H), 1.25–1.4 (m, 4H), 1.55–1.74 (m, 2H), 4.96–5 (m, 1H),
6.03 (dd, J = 5.6, 2 Hz, 1H), 7.42 (dd, J = 5.6, 1.2 Hz, 1H) ppm. 13C NMR
(100 MHz, CDCl3): ı 13.8, 22.4, 27, 83.5, 121.4, 156.7, 173.3 ppm.
(S)-1-PHENYL ETHYL ACRYLATE: 87% ee. [␣]D20 = −48.6 (c 1.0,
CHCl3) HPLC analysis: Chiralcel AD-H, n-hexane/2-propanol (95:5),
0.5 mL/min, 254 nm; tR: (R) 9.72 min, (S) 9.25 min.
(S)-1-(4-METHOXYPHENYL)
ETHYL
ACRYLATE:
99%
ee.
[␣]D20 = −16.4 (c 0.5, CHCl3). Determination of the ee by HPLC
analysis: Chiralcel AD-H, n-hexane/2-propanol (98:2), 0.5 mL/min,
254 nm; tR (R) 12.98 min, (S) 17.89 min.
2.3. Preparation of phosphate buffer
(S)-1-(4-CHLOROPHENYL) ETHYL ACRYLATE: 79% ee. [␣]D20 = −68
(c 1.0, CHCl3). HPLC analysis: Chiralcel AD-H, n-hexane/2-propanol
(98:2), 0.5 mL/min, 254 nm; tR: (R) 11.56 min, (S) 9.76 min.
(-)-1-(3-NITROPHENYL) ETHYL ACRYLATE: 40% ee. [␣]D20 = −36.5
(c 1.0, CHCl3). HPLC analysis: Chiralcel AD-H, n-hexane/2-propanol
(98:2), 0.5 mL/min, 254 nm; tR: (R) 16.34 min, (S) 19.99 min.
(S)-1-(4-METHYLPHENYL) ETHYL ACRYLATE: 63% ee. [␣]D20 = −86
(c 1.0, CHCl3). HPLC analysis: Chiralcel AD-H, n-hexane/2-propanol
(95:5), 0.5 mL/min, 254 nm; tR: (R) 8.53 min, (S) 9.45 min.
(S)-1-PHENYL BUTYL ACRYLATE: 15% ee. [␣]D20 = −18.5 (c
1.0, CHCl3). HPLC analysis: Chiralcel AD-H, n-hexane/2-propanol
(98:2), 0.5 mL/min, 254 nm; tR: (R) 7.89 min, (S) 9.24 min.
One Buffer Tablet pH 7.0 containing chlorides, potassium phos-
phates and sodium phosphates, purchased from Fluka (Code no.
82561-1EA), was dissolved in milipore water in a 100 mL volu-
metric flask and made up to the 100 mL mark to prepare pH 7.0
phosphate buffer solution. The pH of the solution was ascertained
by digital pH meter (DP.505) and used for hydrolysis of acrylates in
the presence of lipases.
2.4. General procedure for lipase Amano AK catalyze hydrolysis of
acrylates
The racemic acrylates (0.1 g) was taken in 20 mL aqueous phos-
phate buffer and to it 0.05 g lipase Amano AK, from Pseudomonas
fluorescens; (Purchased from Sigma–Aldrich: CAS 9001-62-1; Item
code: 534730-50G; Batch # 07919JE; EC 232-619-9, WGK1) was
added. The mixture was stirred at room temperature and the
progress of the reaction was monitored from time to time by TLC.
The pH of the reaction mixture was monitored and no substantial
change in pH was observed due to formation of the acrylic acid
byproduct during the course of reaction. After almost 50% conver-
sion of the starting material (from TLC), the reaction mixture was
extracted with ethyl acetate (3× 10 mL), dried over Na2SO4 and
concentrated under vacuo. The resulting mixture was separated by
column chromatography using mixture ethyl acetate and hexane.
(1S)-1-(4-BROMOPHENYL)ALLYL
ACRYLATE:
98%
ee.
[␣]D20 = −45.0 (c 1.0, CHCl3). HPLC analysis: Chiralcel AD-H, n-
hexane/2-propanol (98:2), 0.5 mL/min, 254 nm; tR: (R) 20.93 min,
(S) 32.70 min.
(1S)-1-[(E)-2-PHENYLVINYL]BUT-3-ENYL ACRYLATE: 92% ee.
[␣]D20 = −48.6 (c 1.0, CHCl3) [lit. [11]; [␣]D20 = −50.6 (c 2.1,
CHCl3)]. HPLC analysis: Chiralcel AD-H, n-hexane/2-propanol
(98:2), 0.5 mL/min, 254 nm; tR: (R) 10.35 min, (S) 11.47 min.
(R)-2-OCTANYL ACRYLATE: [␣]D20 = −18 (c 1.0, CHCl3).
(R)–3-OCTANYL ACRYLATE: [␣]D20 = −14 (c 1.0, CHCl3).
2.5. Preparation of hept-1-en-3-yl acrylate, 3e
To an ice cold solution of (R)-3-hydroxyhept-1-ene, 3d (0.1 g,
0.88 mmol) and DBU (0.2 mL, 1.3 mmol) in dichloromethane
(15 mL), acryloyl chloride (0.17 mL, 2.2 mmol) was added dropwise
at 0 ◦C and allowed to stir for 12 h. Upon completion, the reaction
mixture was diluted with saturated aqueous NaHCO3 solution and
extracted with dichloromethane (30 mL ×3). The organic layer was
dried over anhydrous Na2SO4 and concentrated to get the crude
product, which was purified by column chromatography using 5%
ethyl acetate in hexane to achieve the product (0.143 g, 99%) as a
colorless liquid.
2.4.1. Specific rotation and HPLC data
(R)-PHENYLETHAN-1-OL: 90% ee. [␣]D20 = +38.5 (c 1.0, CHCl3)
[lit. [8]; [␣]D20 = + 48.6 (c 1.0, CH2Cl2)]. HPLC analysis: Chiralcel
OD-H, n-hexane/2-propanol (90:10), 0.5 mL/min, 217 nm; tR: (R)
11.08 min, (S) 12.50 min.
(R)-1-(4-METHOXYPHENYL)ETHAN-1-OL: 98% ee. [␣]D20 = + 48.5
(c 1.0, CHCl3) [lit. [8]; [␣]D20 = + 47.2 (c 1.0, CHCl3)]. HPLC analysis:
Chiralcel AD-H, n-hexane/2-propanol (95:5), 0.5 mL/min, 217 nm;
tR: (R) 21.97 min, (S) 32.34 min.
(R)-(4-CHOLROPHENY)LETHAN-1-OL: 87% ee. [␣]D20 = +47.1 (c
1.0, CHCl3) [lit. [8]; [␣]D20 = +46.1 (c 1.0, Et2O)]. HPLC analysis: Chi-
ralcel AD-H, n-hexane/2-propanol (90:10), 0.5 mL/min, 220 nm; tR:
(R) 28.79 min; (S) 40.89 min.
2.6. Synthesis of (R)-5-Butyl-2(5H)-furanone, 3f
To a solution of hept-1-en-3-yl acrylate, 3e (0.075 g, 0.45 mmol)
in dry dichloromethane (10 mL), Grubb’s catalyst 2nd generation
(0.019 g, 5 mol%) was added and allowed to stir at room tempera-
ture under nitrogen for 12 h. After completion of the reaction, the
solvent was removed under vacuum and the crude product was
immediately charged into silica gel column and eluted with ethyl
(+)-1-(3-NITROPHENYL)ETHAN-1-OL: 30% ee. [␣]D20 =+54.5 (c
1.0, CHCl3). HPLC analysis: Chiralcel AD-H, n-hexane/2-propanol
(95:5), 0.4 mL/min, 220 nm; tR:(R) 16.97 min; (S) 17.62 min.
(R)-1-(4-METHYLPHENYL)ETHAN-1-OL: 96% ee. [␣]D20 = +39.5 (c
1.0, CHCl3) [lit. [8]; [␣]D20 = +51.1 (c 1.0, CHCl3)]. HPLC analysis:

P.P. Bora et al. / Journal of Molecular Catalysis B: Enzymatic 72 (2011) 270–275
273
acetate and hexane mixture in 12:1 ratio to achieve the desired
product, 3f (0.057 g, 91%) as a colorless liquid.
3. Results and discussion
Since lipase Amano AK is finding a variety of applications in
organic synthesis, such as stereoselective trans-esterification for
resolution of alcohols and alcoholysis [12], we decided to carry out
enzymatic hydrolysis of ( )-1-phenyl ethyl acrylate in the pres-
ence of Lipase Amano AK at pH 7.0 in aqueous medium (Scheme 2).
Although, the acrylate did not dissolve in water, we were excited
to see that enzymatic hydrolysis does take place under this con-
dition. The reaction was monitored by TLC and stopped after 30 h,
Scheme 2.
when approximately 50% consumption of the starting material was
observed. The reaction mixture was extracted with ethyl acetate
(15 mL ×3), dried (over Na2SO4), concentrated under vacuum and
separated by column chromatography. HPLC analysis using Chiral-
cel AD-H column with 10% isopropanol in hexane as eluent showed
Table 1
Hydrolytic kinetic resolution of racemic acrylates
.
Entry
1
Substrate
Time (h) %
30
yielda (A/B)
38/42
% ee of Ab
% ee of Bb
E-valuec
Configurationd (A/B)
90
87
52
R/S
2
32
47/36
98
99
>500
R/S
3
4
5
32
45
34
40/44
39/44
44/40
87
30
96
79
40
63
35
3
R/S
ND
R/S
94
6
7
62
6
31/47
45/46
45/42
82
94
91
15
98
92
12
R/S
R/S
R/S
>100
70
8
9
40
72
80
42/43
42/45
ND
ND
ND
ND
ND
ND
S/R
S/R
10
a
Isolated yield, after purification by column chromatography.
Enatiomeric excess was determined by HPLC with Chiralcel OD-H and AD-H columns.
b
c
E = ln[(1 − eeS)/(1 + eeS/eeP)]/ln[(1 + eeS)/(1 + eeS/eeP)].
d
Absolute stereochemistry of the alcohols were determined by comparing the sign of optical rotation the alcohols in the literature [8–11]. ND = not determined.

274
P.P. Bora et al. / Journal of Molecular Catalysis B: Enzymatic 72 (2011) 270–275
Scheme 3. Reagent and conditions: (a) acrolyl chloride, DBU, 99%; (b) lipase Amano AK, phosphate buffer (pH 7.0), 3 days, 48%; (c) 2nd generation Grubb’s catalyst, N2
atmosphere, 12 h, 91%.
excellent enantiomeric excess (87% ee) for the acrylate and the
alcohol (90% ee). Comparison of specific rotations of the both the
acrylate and the alcohol with literature report [8] led us to con-
clude that the acrylate has S-configuration, while the alcohol has
the opposite, i.e. the R-configuration.
the substrates having vinylic alcohol moiety react comparatively
faster and showed good enantioselectivity as evident from entry
7 and 8 in Table 1. The acrylate of allylic secondary alcohol,
1-(4-bromophenyl)-prop-2-en-1-ol (entry 7, Table 1) underwent
enzymatic hydrolysis in the presence of Lipase Amano AK at pH 7.0
in aqueous phosphate buffer to give excellent selectivity for both
the alcohol (94% ee) and the acrylate (98% ee). It is interesting to
note that when the acrylate is flanked by two ꢀ-systems (entry 8,
Table 1), hydrolysis is very fast (6 h) under our reaction conditions
and gave very good enantioselectivities for both the alcohol (91%
ee) and the acrylate (92% ee).
Since the enzyme enantioselectivity, E for this particular conver-
sion was moderate (E = 52) in comparison to hydrolysis of acetate
(E > 300) of the same alcohol [13], we set out to screen other
lipases at our disposal in order to compare their reactivity and
enzyme selectivity with lipase Amano AK and study the effect of
water–acetonitrile mixture (9:1) on the reaction profile. It was
observed that for ( )-1-phenyl ethyl acrylate, the reaction in water-
acetonitrile mixture (9:1) solvent gave higher yield (43%) of the
hydrolyzed product, i.e. 1-phenethyl alcohol. But enantioselectiv-
ity of the alcohol got reduced substantially in water–acetonitrile
medium (10% ee) in comparison to water medium (Table 1). In the
hydrolysis of phenylethyl acrylate in water medium using lipase
Amano PS, 50% conversion of the starting material was not achieved
even after 120 h and gave only 25% isolated yield with 20% ee. In the
cases of Candida rugosa lipase and Aspergillus niger lipase, continu-
ous stirring of the reaction mixture for 144 h were not enough for
50% conversion of the starting material under similar conditions
and the selectivities of the isolated alcohol were not apprecia-
ble either, 5% ee and 18% ee respectively. In water–acetonitrile
medium, no appreciable incremental changes in reactivity and
selectivity were observed for all the aforesaid lipases in the hydrol-
ysis of ( )-1-phenyl ethyl acrylate. When the same reaction was
carried out with the lipases, such as Mucor javanicus lipase (entry 4)
and PPL (entry 6), they were found not selective under our reaction
conditions.
We sought to examine lipase Amano AK catalyzed hydroly-
sis of acrylates for some saturated aliphatic alcohols to explore
the versatility of this method. The acrylates of 2-octanol and 3-
octanol were giving (S)-alcohol upon treatment with lipase under
similar hydrolytic reaction conditions. The (S)-configuration of 2-
octanol and 3-octanol were confirmed by comparimg the sign of
specific rotation of reported in the literature [9,10], while the (R)-
configuration of acrylates were assigned by comparing the sign
of rotation of corresponding (S)-alcohols. Moreover, hydrolysis of
these acrylates took comparatively longer time than benzylic alco-
hols, which might be due to greater hydrophobicity of those esters
that comparatively hinders their entry to the enzyme reaction site.
Here too, the acrylate of octan-2-ol (entry 9, Table 1) reacted faster
(72 h for approximately 50% conversion) that the acrylate of octan-
3-ol (entry 10). For the acrylate of allylic secondary alcohol, 3b
we observed the preference for hydrolysis of (R)-acrylate in spite
having aliphatic chain (Scheme 3). The configuration of the alco-
hol, 3d was confirmed by synthesizing (R)-5-Butyl-2(5H)-furanone
3f, the penultimate precursor to (R)-(+)-trans-Whisky lactone, 3
(Scheme 3) and comparing the sign of specific rotation. The syn-
thesis started with acrylation of the allylic alcohol, 3a with acryloyl
chloride and DBU to achieve the acrylate, 3b followed by hydrolytic
kinetic resolution in aqueous medium at pH 7.0 (using phosphate
buffer) to get 3c (48% yield; [␣]D20 = +9.8 (c= 1.5, CHCl3) and 3d (45%
yield). Acrylation of 3d followed by RCM reaction using Grubb’s 2nd
generation catalyst led to 3f {[␣]D20 = −101.0 (c = 2.0, CHCl3); lit.
[11]; [␣]D20 = −112.0 (c 1.57, MeOH)}, the penultimate precursor
of (R)-(+)-trans-whisky lactone.
As lipase is known to sustain temperature as high as 70 ◦C, we
sought to study the effect of temperature on selectivity of Amano
AK under hydrolytic conditions. Ironically, increase of temperature
showed adverse effect on enantioselectivity. When temperature
was enhanced to 30 ◦C, 50% conversion of ( )-1-phenyl ethyl acry-
late took almost similar time, but the enantioselectivity of the
hydrolyzed product dropped down to 57% ee. At 35 ◦C, the reaction
time could be reduced to 16 h for 50% conversion, but ended up
with only 19% ee of the resulting alcohol. Further increase of tem-
perature to 40 ◦C resulted in no selectivity, although it took only
10 h for 50% conversion of ester.
4. Conclusion
Having standardize all the reaction parameters, we explored
the reactivity and selectivity pattern in other benzylic alcohols
(Table 1, entry 2–6)) and they were found to have reasonably high
enantioselectivity except 1-(3-nitrophenyl) ethanol (entry 4), in
which case poor enantioselectivity (E = 3) was observed. Never-
theless, the introduction of longer chain in the benzylic alcohol
(entry 6, Table 1) might have affected the efficiency of the catalyst
system as evident from the poor conversion to alcohol even after
62 h, albeit giving reasonably good %ee of the alcohol. Interestingly,
In conclusion, we have for the first time reported that acrylates
of secondary alcohols efficiently undergoes hydrolytic kinetic res-
olution in the presence of lipase Amano AK, in that case, in the
presence of lipase to generate enantiomerically pure secondary
alcohols and their acrylates with very good E-values. The method
works extremely well for benzylic and other secondary alcohols.
The method may find useful applications for the synthesis of ␣,␤-
unsaturated lactones.

P.P. Bora et al. / Journal of Molecular Catalysis B: Enzymatic 72 (2011) 270–275
275
Acknowledgments
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Thanks are due to UGC, New Delhi [(Grant No. 31–54/2005 (SR)],
CSIR, New Delhi [Grant No. 01(1992)/05/EMR-II] and DST, New
Delhi [Grant No. SR/S1/OC-25/2007] for providing financial sup-
ports to carry out this work. Thanks are also due to Prof. Abu T Khan,
IIT Guwahati, India and Dr Dongkupar Syiem, Dept of Biochemistry,
NEHU, Shillong for providing the HPLC facility.
(c) P. Gupta, S.V. Naidu, P. Kumar, Tetrahedron Lett. 46 (2005) 6571–6573;
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Appendix A. Supplementary data
Supplementary data associated with this article can be found, in
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