Efficient kinetic bioresolution of 2-nitrocyclohexanol

Article abstract of DOI:10.1016/j.tetasy.2010.05.006

The kinetic bioresolution of 2-nitrocyclohexanol 1 was investigated by screening a range of hydrolases both for enantioselective transesterification and for enantioselective hydrolysis of the corresponding acetate. By appropriate choice of biocatalyst and conditions, both enantiomers of cis and trans 2-nitrocyclohexanol 1 can be accessed in enantiopure form.

Full text of DOI:10.1016/j.tetasy.2010.05.006

Tetrahedron: Asymmetry 21 (2010) 1011–1016
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Tetrahedron: Asymmetry
journal homepage: www.elsevier.com/locate/tetasy
Efficient kinetic bioresolution of 2-nitrocyclohexanol
Sinead E. Milner a, Maude Brossat b, Thomas S. Moody b, Curtis J. Elcoate a, Simon E. Lawrence a,
Anita R. Maguire c,
*
a Department of Chemistry, Analytical and Biological Chemistry Research Facility, University College Cork, Cork, Ireland
b Biocatalysis Group, Almac Sciences, David Keir Building, Stranmillis Road, Belfast, BT9 5AG, United Kingdom
c Department of Chemistry & School of Pharmacy, Analytical and Biological Chemistry Research Facility, University College Cork, Cork, Ireland
a r t i c l e i n f o
a b s t r a c t
Article history:
The kinetic bioresolution of 2-nitrocyclohexanol 1 was investigated by screening a range of hydrolases
both for enantioselective transesterification and for enantioselective hydrolysis of the corresponding ace-
tate. By appropriate choice of biocatalyst and conditions, both enantiomers of cis and trans 2-nitrocyclo-
hexanol 1 can be accessed in enantiopure form.
Received 4 May 2010
Accepted 11 May 2010
Available online 21 June 2010
Ó 2010 Elsevier Ltd. All rights reserved.
This paper is dedicated to the memory of Sir
Allen McClay and his commitment to the
enhancement of human health and science
from the island of Ireland.
1. Introduction
Four biocatalysts were examined in the study but only the re-
sults of Candida cylindracea were reported. Low yields of 2-nitrocy-
2-Nitro alcohols constitute an important class of organic mole-
cules as they are readily transformed into key synthetic intermedi-
clohexanol 1 were obtained with 20% of (S,S)-2-nitrocyclohexanol
1b following hydrolysis of the butyrate ester and 40% (R,R)-2-nitro-
cyclohexanol 1b. Enantioselectivity was high in the case of (R,R)-2-
nitrocyclohexanol 1b >98% ee. However, only 85% ee of the oppo-
site enantiomer (S,S)-2-nitrocyclohexanol 1b was achieved. While
this preliminary study had limited success, herein we report
potential access to all four enantiomers of 2-nitrocyclohexanol 1
via hydrolase-catalysed hydrolysis of 2-nitrocyclohexyl acetate 2
or hydrolase-catalysed transesterification of 2-nitrocyclohexanol
1 as shown in (Scheme 1).
ates, including 2-amino alcohols and
a-hydroxy carboxylic acids,
which are important chiral building blocks of many biologically ac-
tive natural and synthetic products.1–3 Access to enantiopure nitro
alcohols has been principally achieved via the asymmetric Henry
reaction. The first asymmetric synthesis of nitroalcohols via the
Henry reaction was reported in 1992 employing a chiral metal cat-
alyst,4 and there has been considerable development in this
approach.5
Despite the dramatic development of enantioselective synthesis
and chromatographic separation methods, bioresolution still re-
mains one of the most inexpensive and operationally simple meth-
ods for producing pure enantiomers on a large scale in the
chemical industry. Typically the reactions are carried out under
ambient and neutral conditions.6
The employment of a biocatalytic approach to the resolution of
2-nitro alcohols clearly has potential as hydrolase-catalysed ki-
netic resolutions have proved to be an efficient technique for the
preparation of enantiomerically enriched compounds of this type.7
By the appropriate choice of conditions and biocatalyst, access to
the various stereoisomers of secondary alcohols can often be
achieved with excellent enantiocontrol and across a wide range
of substrates.8
2. Results and discussion
2.1. Kinetic bioresolution
The hydrolase-mediated kinetic bioresolution of both cis-1a and
trans-2-nitrocyclohexanol-1b hasbeen explored. Thediastereomeric
2-nitrocyclohexanols were synthesised by sodium borohydride
reduction of 2-nitrocyclohexanone 3 followed by chromatographic
separation of the diastereomers ( )-1a and ( )-1b and 1-nitrocyclo-
hex-1-ene 4, (0.17:1:0.24, respectively) which forms as a byproduct
of this reduction, but is readily removed by chromatography (see
Scheme 2).
Racemic trans-2-nitrocyclohexyl acetate ( )-2b was prepared
by acetylation in acetic anhydride, pyridine and a catalytic amount
of dimethylaminopyridine (DMAP). However, the cis diastereomer
( )-2a required the use of acetyl chloride and an excess of DMAP.
Assignment of the relative stereochemistry of the diasteromeric
alcohols was enabled through comparison of the NMR data with
those reported in the literature10 and was confirmed by the
To the best of our knowledge, the sole report of hydrolase-med-
iated kinetic bioresolution of 2-nitrocycloalkanols involved the
kinetic resolution of trans-2-nitrocyclohexyl butyrate.9
* Corresponding author. Tel.: +353 21 4901693; fax: +353 21 4901770.
E-mail address: a.maguire@ucc.ie (A.R. Maguire).
0957-4166/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetasy.2010.05.006

1012
S. E. Milner et al. / Tetrahedron: Asymmetry 21 (2010) 1011–1016
OH
OH
NO2
NO2
OH
OAc
Lipase
Lipase
NO2
NO2
mediated
mediated
(1R,2R)-1a (1R,2S)-1a
OH OH
hydrolysis
trans-
esterification
NO2
NO2
2
1
(1R,2R)-2b
(1R,2S)-2b
Scheme 1. Potential access to all four enantiomers of 2-nitrocyclohexanol 1 via hydrolase-catalysed kinetic resolution.
O
OH
OH
NO2
NO2
NO2
NO2
NaBH4
EtOH, 0ºC
3
1b
1a
4
Ac2O
pyridine
AcCl
DMAP
OAc
OAc
NO2
NO2
2b
2a
Scheme 2. Preparation of racemic ( )-2-nitroalcohols 1 and racemic ( )-2-nitroacetates 2 employed in this study.
X-ray structure of (R,R)-trans-2-nitrocyclohexyl acetate (ꢀ)-2b.
Once the racemic starting materials were prepared a chiral HPLC
method was developed in order to determine the efficiency of
the hydrolase-catalysed reaction with a single injection shown in
(Fig. 1). Initially, experiments focused on the hydrolase-mediated
transesterification of the trans isomer ( )-1b and the results of
the study are summarised in (Table 1).
(<10%). However, the use of vinyl acetate as solvent and acyl donor
led to the desired kinetic resolution as summarised in (Table 1).
It is clearly seen in (Table 1) that the efficiency of the kinetic
resolution of ( )-1b varies enormously depending on the biocata-
lyst, which highlights the importance of screening a range of
hydrolases for a specific transformation. From this screening the
optimum biocatalysts for this biotransformation are Pseudomonas
fluorescens and immobilised Candida antarctica lipase B.
Based on the efficient resolution achieved in the transesterifica-
tion of the trans isomer ( )-1b, attention focused next on the cis
isomer ( )-1a employing the optimised conditions with ( )-1b,
that is, using vinyl acetate as solvent and acyl donor (Table 2).
In general the efficiency of the transformation of ( )-1a is high-
er than that of the trans isomer ( )-1b and again by appropriate
choice of biocatalyst it is possible to obtain the alcohol (1S,2R)-
1a and acetate (1R,2S)-2a in enantiopure form.
(S, S)-1b
(R, R)-2b
III
Preparative scale transacetylation of ( )-trans-2-nitrocyclohex-
anol 1b (2.94 mmol) was then performed with P. fluorescens which
led to a 50% conversion after 28 h with the production of both
enantiomers in >99% ee (Fig. 1). The enantiopure acetate (1R,2R)-
2b was produced in 49% yield after column chromatography and
the alcohol (1S,2S)-1b was produced in 48% yield.
A crystal structure determined the absolute configuration of the
trans-2-nitrocyclohexyl acetate 2b isolated from the scale up to be
(1R,2R)-2b as expected10 (see Fig. 2).
II
I
( )-1b
( )-2b
( )-1a
Figure 1. HPLC traces I: A racemic mixture of ( )-trans-2-nitrocyclohexylacetate 2b
and trans and cis-2-nitrocyclohexanol ( )-1a and ( )-1b, respectively. II: Enantio-
pure (R,R)-trans-2-nitrocyclohexyl acetate (-)-2b and III: Enantiopure (S,S)-trans-2-
nitrocyclohexanol (+)-1b (conditions in experimental Section 4.2).
The large scale transesterification of cis-2-nitrocyclohexanol
( )-1a was next performed. Excellent enantioselectivity (>99% ee)
was achieved in the production of both the acetate (1R,2S)-2a
and the alcohol (1S,2R)-1a. However, upon separation of the enan-
tioenriched products on silica gel, decomposition of the cis acetate
(1R,2S)-2a to 1-nitrocyclohex-1-ene 4 was observed and neither 1a
nor 2a could be isolated analytically pure. Therefore, while the
absolute stereochemistry of 1a and 2a has not been confirmed it
A number of hydrolase-catalysed acetylation conditions were
examined employing a range of solvents, (ethyl acetate, tert-
butylmethyl ether) and acyl donors, (vinyl acetate, ethyl acetate,
vinyl benzoate, vinyl propionate, vinyl butyrate and isopropenyl
acetate) with negligible conversions in each case. When one equiv-
alent of vinyl acetate was employed as acyl donor with tert-
butylmethyl ether as solvent, limited conversions were observed

S. E. Milner et al. / Tetrahedron: Asymmetry 21 (2010) 1011–1016
1013
Table 1
Hydrolase-mediated transesterification of ( )-trans-2-nitrocyclohexanol 1b in vinyl acetate
OH
OAc
OH
NO2
NO2
NO2
Lipase
Vinyl acetate
º
20 C, 24 h
( )-1b
(1R,2R)-2b
(1S,2S)-1b
Enzyme strain
Conversiona (%)
2b (1R,2R) % ee
1b (1S,2S) % ee
E
Candida cylindracea C1
Candida cylindracea C2
Rhizopus oryzae
45
26
0
>98
—
—
80
—
—
244
—
—
Alcaligenes spp.
37
39
59
7
98
>98
69
—
53
46
89
—
168
156
15
Pseudomonas cepacia
Pseudomonas stutzeri
Rhizopus spp.
—
Rhizopus niveus
0
—
—
—
Aspergillus niger
0
—
—
—
Alcaligenes spp.
Pseudomonas cepacia P2
Mucor javanicus
50
8
2
>98
>98
—
91
6
—
>400
105
—
Penicillium camembertii
Pseudomonas fluorescens
Mucor meihei
Candida antarctica (lipase B)
Porcine pancrease II (Aldrich)
Pig liver esterase
0
—
—
—
50
17
49
Trace
0
>98
>98
>98
—
>98
32
98
—
>400
272
>400
—
—
—
—
a
Conversions were determined by 1H NMR spectroscopy of the crude products.
Table 2
Hydrolase-mediated transesterification of ( )-cis-2-nitrocyclohexanol 1a in vinyl acetate
OH
OAc
OH
NO2
NO2
NO2
Lipase
Vinyl acetate
20 ºC, 24 h
( )-1a
1a
(1S,2R)-
(1R,2S)-2a
Enzyme strain
Conversiona (%)
2a (1R,2S) % ee
1a (1S,2R) % ee
E
Candida cylindracea C1
Candida cylindracea C2
Pseudomonas cepacia P1
Pseudomonas stutzeri
Rhizopus niveus
81
3
13
53
0
>98
—
>98
>98
—
>98
—
16
>98
—
>400
—
232
>400
—
Alcaligenes spp.
Pseudomonas cepacia
Mucor javanicus
47
14
0
>98
—
—
88
—
—
>400
—
—
Penicillium camembertii
Pseudomonas fluorescens
0
50
—
>98
—
>98
—
>400
a
Conversions were determined by 1H NMR spectroscopy of the crude products.
has been assigned by analogy to the results obtained with the
trans-1b isomer and is consistent with the expected stereochemi-
cal outcome.
The alternative approach of the hydrolase-mediated hydroly-
sis of the trans acetate 2b was next explored using the series
of hydrolases, the results of which are summarised in
(Table 3).
Efficient kinetic bioresolution in the hydrolysis is observed with
a number of hydrolases C. cylindracea C1, Pseudomonas stutzeri,
Alcaligenes spp. and Pseudomonas cepacia P2. With the less efficient
biocatalysts, in most instances, the alcohol formed has high enan-
tiopurity, but the acetate is recovered with poor enantioselectivity,
due to the limited extent of reaction. However, with two of the bio-
catalysts C. cylindracea C2 and Aspergillus niger the hydrolysis pro-
ceeds with poor stereocontrol, with the alcohol 1b recovered with
poor enantiopurity.
Figure 2. Crystal structure of (1R,2R)-trans-2-nitrocyclohexyl acetate (ꢀ)-2b.
Atomic displacement ellipsoids are drawn at the 30% probability level.

1014
S. E. Milner et al. / Tetrahedron: Asymmetry 21 (2010) 1011–1016
Table 3
Hydrolase-mediated hydrolysis of ( )-trans-2-nitrocyclohexanol 1b in phosphate buffer
OAc
OAc
OH
NO2
NO2
NO2
Lipase
Phosphate
Buffer pH 7
-1b
2b
(1S,2S)-
(1R,2R)
( )-2b
Enzyme strain
Conversiona (%)
Acetate-2b (1S,2S) % ee
Alcohol-1b (1R,2R) % ee
E
Candida cylindracea C1
Candida cylindracea C2
Rhizopus oryzae
52
72
3
>98
100
—
91
45
—
158
16
—
Alcaligenes spp.
48
47
50
4
88
88
96
—
93
99
92
—
80
>400
94
Pseudomonas cepacia P1
Pseudomonas stutzeri
Rhizopus spp.
—
Rhizopus niveus
2
—
—
—
Aspergillus niger
Alcaligenes spp.
65
53
51
>1
15
13
22
44
49
99
99
—
16
11
26
75
26
97
99
—
89
85
99
97
2.6
>400
>400
—
20
13
Pseudomonas cepacia P2
Penicillium camembertii
Mucor meihei
Porcine pancrease II
Porcine pancrease II
Pig liver esterase
256
148
a
Conversions were determined by 1H NMR spectroscopy of the crude products.
4. Experimental
4.1. General procedures
A Bruker Avance 300 MHz NMR spectrometer was used to re-
cord 1H (300 MHz) NMR spectra. 1H (400 MHz) NMR spectra were
recorded on a Bruker Avance 400 MHz NMR spectrometer. All
spectra were recorded at room temperature (ꢁ20 °C) in deuterated
chloroform (CDCl3) unless otherwise stated using tetramethylsil-
ane (TMS) as an internal standard. Melting points are uncorrected.
Optical rotations were measured on a Perkin–Elmer 141 polarime-
ter at 589 nm in a 10-cm cell; concentrations (c) are expressed in g/
100 mL. ½a t
ꢂ
D is the specific rotation of a compound and is expressed
in units of 10ꢀ1 deg cm2 gꢀ1. All hydrolases used for these biotrans-
formations were obtained from Almac Sciences. All reagents are
analytical grade and purchased from Sigma–Aldrich chemical
company.
4.2. Chiral HPLC analysis
Enantiomeric purity of 1 and 2 was determined by chiral HPLC
analysis on a Chiralcel OJ-H column (5 ꢃ 250 mm) purchased from
Daicel Chemical Industries, Japan. Mobile phase was 1% isopropa-
nol in hexane; flow rate 0.9 mL/min; detection wavelength
209.8 nm. HPLC analysis was performed on a Waters alliance
2690 separations module with a PDA detector. All solvents em-
ployed were of HPLC grade.
Figure 3. Plot of E-value versus hydrolase for 1a, 1b and 2a.
Interestingly, while there is some similarity in the profiles of the
efficiency of the kinetic resolution of each of the biocatalysts
(Fig. 3) in the transesterification and hydrolysis processes there
are also significant variations. For example, use of P. stutzeri leads
to very efficient kinetic resolution in the transesterification of cis-
2-nitrocyclohexanol ( )-1a but under the same conditions the res-
olution of trans-2-nitrocyclohexanol ( )-1b, is very limited.
4.3. Experimental procedures
4.3.1. Nitrocyclohexanol 1a and 1b9
3. Conclusion
2-Nitrocyclohexanone 3 (5.00 g, 0.035 mol) in ethanol (50 mL)
was added dropwise over 10 min to a stirred suspension of NaBH4
(1.32 g, 0.035 mol) in ethanol (150 mL) at 0 °C under nitrogen and
stirring was continued for 5 h at 0 °C. The ice bath was removed
and 10% HCl was added to adjust to pH 1. The solution was concen-
trated in vacuo and the resulting residue was partitioned between
water (50 mL) and dichloromethane (50 mL). The aqueous phase
was extracted with dichloromethane (3 ꢃ 30 mL) and the
Efficient kinetic bioresolution of both cis and trans-2-nitrocyclo-
hexanol 1a and 1b, respectively, can be achieved through ester
hydrolysis or hydrolase-mediated transesterification. Through the
appropriate selection of biocatalyst, three of the four isomers
(1R,2R)-1b, (1S,2S)-1b and (1S,2R)-1b were obtained directly, while
hydrolysis of (1R,2S)-2a would potentially lead to (1R,2S)-1b
although this is complicated by competing elimination.

S. E. Milner et al. / Tetrahedron: Asymmetry 21 (2010) 1011–1016
1015
combinedorganiclayerswere washedwith brine, dried(MgSO4)and
concentrated in vacuo to give a crude mixture (3.89 g) of nitroalco-
hols 1a, 1b and nitrocyclohexene 4 (0.17:1:0.24, respectively) as a
yellow oil. Purification by column chromatography using a (3–
25%) ethyl acetate hexane gradient as eluant gave 1-nitrocyclohex-
1-ene 4 as a yellow oil (490 mg, 11%); dH (400 MHz, CDCl3) 1.60–
1.67 (2H, sym m), 1.74–1.82 (2H, sym m), 2.30–2.38 (2H, sym m),
2.54–2.61 (2H, sym m), 7.31–7.35 (1H, sym m). (less polar) ( )-cis-
2-nitrocyclohexanol 1a (520 mg, 10%); dH (300 MHz, CDCl3) 1.19–
2.31 (8H, m), 2.57 (1H, d, J 3.9), 4.34–4.41 (1H, m), 4.51 (1H, br s)
and ( )-trans-2-nitrocyclohexanol 1b (2.54 g, 50%); dH (300 MHz,
CDCl3) 1.12–1.46 (3H, m), 1.70–1.89 (3H, m), 2.04–2.17 (1H, m),
2.25–2.40 (1H, m), 2.85 (1H, br s), 4.06 (br s), 4.18–4.42 (1H, m).
shaken at 750 rpm for 24 h at room temperature and 40 °C for 3 h.
The solution was filtered and concentrated in vacuo. The sample
was analysed by 1H NMR spectroscopy, reconcentrated and dis-
solved in a mixture of hexane:iso-propyl alcohol (90:10 HPLC
grade) and enantioselectivity determined by chiral HPLC. Enantio-
meric excess was only determined for conversions above 10%. The
results of the screening are summarised in (Table 2).
4.3.6. Hydrolase-mediated hydrolysis of ( )-trans-2-
nitrocyclohexylacetate 2b
A standard solution of ( )-trans-2-nitrocyclohexylacetate 2b
(320 mg, 1.70 mmol) in tert-butylmethyl ether (4 mL) was pre-
pared and aliquots (250 lL, 0.42 M, 0.10 mmol of 2b) were dis-
pensed between 16 test tubes. Phosphate buffer (1 mL) at pH 7
and a spatula tip of enzyme (ꢁ5-10 mg) were added to each test
tube which was then sealed and shaken at 750 rpm for 24 h at
room temperature. Diethyl ether (1 mL) was added and the layers
were separated. The organic layer was filtered and concentrated in
vacuo. The crude product was analysed by 1H NMR spectroscopy,
reconcentrated and dissolved in a mixture of hexane:iso-propyl
alcohol (90:10 HPLC grade) and enantioselectivity determined by
chiral HPLC. The results of the screening are summarised in
(Table 3).
4.3.2. ( )-cis-2-Nitrocyclohexyl acetate 2a11
( )-cis-2-Nitrocyclohexanol 1a (1.00 g, 6.88 mmol) and acetyl
chloride (5.0 mL, 0.07 mol) were stirred in CH2Cl2 (35 mL) under
nitrogen and N,N-dimethylaminopyridine (1.2 mg, 10.32 mmol)
was added and stirring was continued at room temperature for
12 h. Aqueous NaHCO3 (satd, 20 mL) was added and the mixture
was transferred to a separation funnel. The aqueous phase was ex-
tracted with dichloromethane (3 ꢃ 20 mL) and the combined or-
ganic layers were washed with brine, dried (MgSO4) and
concentrated in vacuo to give a crude acetate 2a (0.90 g, 70%) dH
NMR (300 MHz, CDCl3) 1.30–1.45 (1H, m), 1.49–1.66 (3H, m),
1.89–2.00 (1H, m), 2.08 (3H, s), 2.11–2.19 (3H, m), 4.42–4.49 (1H,
m), 5.56–5.61 (1H, m). (7% trans acetate 2b was observed in the
product). Purification was not possible due to the partial formation
of the elimination product 4 on exposure to silica gel.
4.3.7. Preparative scale transesterification of ( )-trans-2-
nitrocyclohexanol 1b
P. fluorescens (80 mg) was added to ( )-trans-2-nitrocyclohexa-
nol (830 mg, 5.71 mmol) in vinyl acetate (10 mL) and this was sha-
ken at 750 rpm for 28 h at room temperature. The solution was
filtered through a pad of Celite and the mother liquor concentrated
in vacuo to produce a clear oil (932 mg). Purification by column
chromatography using (3–25%) ethyl acetate in hexane gradient as
eluant gave acetate (1R,2R)-2b as a white crystalline solid; mp 41–
4.3.3. ( )-trans-2-Nitrocyclohexyl acetate 2b11
N,N-Dimethylaminopyridine (12.9 mg, 0.10 mmol) was added
to a stirring solution of ( )-trans-2-nitrocyclohexanol 1b (1.54 g,
10.6 mmol), acetic anhydride (7.0 mL) and pyridine (3.5 mL) in
dichoromethane (35 mL). The mixture was stirred at room temper-
ature for 20 h under nitrogen. Aqueous NaHCO3 (satd) (20 mL) was
added to quench the reaction. The solution was transferred to a
separating funnel and washed with aqueous CuSO4 (satd), water,
aqueous NaHCO3 (satd) and brine (30 mL each) and dried over
MgSO4. The resultant solution was concentrated in vacuo to pro-
duce the acetate 2b as a white crystalline solid; mp 40–42 °C,
(1.65 g, 83%). dH (300 MHz, CDCl3) 1.26–1.55 (3H, m), 1.75–1.94
(3H, m), 2.01 (3H, s), 2.17–2.28 (1H, m), 2.32–2.42 (1H, m), 4.46–
4.57 (1H, m), 5.17–5.26 (1H, ddd appears as a dt, J 4.8, 10.5).
43 °C, ½a 2D0
¼ ꢀ40:65 (c 1.0, CH2Cl2), >98% ee, (520 mg, 97%) and
ꢂ
(1S,2S)-1b ½a 2D0
ꢂ
¼ þ48:6 (c 1.0, CH2Cl2), >98% ee, lit.9
½
a 2D0
ꢂ
¼ þ43:3
(c 1.0, CH2Cl2) 85% ee, (400 mg, 96%). 1H NMR spectra were identical
to those of the racemic materials previously prepared.
A sample of (1R,2R)-2b was recrystallised from a dichlorometh-
ane hexane (50:50) mixture. X-ray diffraction measurements for
2b were made on a Bruker APEX II DUO diffractometer using
graphite-monochromatised MoKa radiation (k = 0.71073 Å) and
cooled with an Oxford Cryosystems COBRA fitted with a N2 gener-
ator. All calculations were made using the APEX2 software,12,13 and
the diagrams prepared using PLATON.14 Crystallographic data
(excluding structure factors) for the structure in this paper have
been deposited with the Cambridge Crystallographic Data Centre
as supplementary publication numbers CCDC No. 771829. Copies
of the data can be obtained, free of charge, on application to CCDC,
12 Union Road, Cambridge, CB2 1EZ, UK [fax: +44(0)-1223-336033
or e-mail: deposit@ccdc.cam.ac.uk].
4.3.4. Hydrolase-mediated transesterification of ( )-trans-2-
nitrocyclohexanol 1b with vinyl acetate as solvent and acyl
donor
A
standard solution of ( )-trans-2-nitrocyclohexanol 1b
(360 mg, 2.48 mmol) in vinyl acetate (18 mL) was prepared and
aliquots (1 mL, 0.14 M, 0.13 mmol of 1b) were dispensed into 18
test tubes. A spatula tip of enzyme (ꢁ5-10 mg) was added, shaken
at 750 rpm for 24 h at room temperature and 40 °C for a further
3 h. The solution was filtered and concentrated in vacuo. The sam-
ple was analysed by 1H NMR spectroscopy, reconcentrated and dis-
solved in a mixture of hexane:iso-propyl alcohol (90:10 HPLC
grade) and enantioselectivity determined by chiral HPLC. The re-
sults of the screening are summarised in (Table 1).
Acknowledgements
This work was carried out with the financial support of IRCSET
and Pfizer. Nuala Maguire and Tom O’ Mahony are acknowledged
for their technical assistance.
References
4.3.5. Hydrolase-mediated transesterification of ( )-cis-2-
nitrocyclohexanol 1a with vinyl acetate as both acyl donor and
solvent
A standard solution of ( )-cis-2-Nitrocyclohexanol 1a (200 mg,
1.37 mmol) in vinyl acetate (10 mL) was prepared and aliquots
(1 mL, 0.14 M, 0.13 mmol of 1a) were dispensed into 10 test tubes.
A spatula tip of each enzyme (ꢁ5–10 mg) was added and this was
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