Asymmetric synthesis of both enantiomers of secondary alcohols by reduction with a single microbe

Article abstract of DOI:10.1016/S0040-4039(02)00649-4

Both enantiomers of secondary alcohols were prepared by reduction of the corresponding ketones with a single microbe. Thus, reduction of aromatic ketones with Geotrichum candidum IFO 5767 afforded the corresponding (S)-alcohols in an excellent ee when amberlite XAD-7, a hydrophobic polymer, was added to the reaction system and the same microbe afforded (R)-alcohols also in an excellent ee when the reaction was conducted under aerobic conditions.

Full text of DOI:10.1016/S0040-4039(02)00649-4

TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 43 (2002) 3629–3631
Asymmetric synthesis of both enantiomers of secondary alcohols
by reduction with a single microbe
a,
a
b
b
Kaoru Nakamura, * Keishi Takenaka, Mikio Fujii and Yoshiteru Ida
a
Institute for Chemical Research, Kyoto University, Uji, Kyoto 611-0011, Japan
b
School of Pharmaceutical Science, Showa University, 1-5-8 Hatanodai, Shinagawa-ku, Tokyo 142-8555, Japan
Received 4 March 2002; revised 25 March 2002; accepted 29 March 2002
Abstract—Both enantiomers of secondary alcohols were prepared by reduction of the corresponding ketones with a single
microbe. Thus, reduction of aromatic ketones with Geotrichum candidum IFO 5767 afforded the corresponding (S)-alcohols in an
excellent ee when amberlite™ XAD-7, a hydrophobic polymer, was added to the reaction system and the same microbe afforded
(
R)-alcohols also in an excellent ee when the reaction was conducted under aerobic conditions. © 2002 Elsevier Science Ltd. All
rights reserved.
Enzymatic reductions are now recognized as a valuable
approach to the organic synthesis of optically active
chloroacetate inhibits the R-enzyme, both enantiomers,
(R)-hydroxy esters, and (S)-hydroxy esters could be
prepared selectively using these inhibitors.
1
–3
compounds.
Lots of optically active alcohols have
been prepared by enzymatic reduction. However, enzy-
matic reactions have a disadvantage: it is difficult to
obtain both enantiomers of an alcohol by using a single
biocatalyst. Since the number of available enzymes is
limited, it is usually impossible to find a suitable
enzyme for an unnatural substrate. In this report, we
would like to describe the enantioselective synthesis of
both enantiomers of alcohols with a single biocatalyst.
In fact, both enantiomers of b-hydroxy esters have been
prepared with high enantioselectivities by bakers’ yeast,
a single microbe, with the reduction–inhibition method.
However, this method can be applied only to b-hydroxy
esters. The synthesis of the other chiral alcohols with a
single microbe is still awaited. The inhibition method
has another disadvantage in that the use of an inhibitor
decreases the yield of the reduction of ketones, since the
inhibitor decreases the reducing activities of the
microbe. Therefore, the development of methods other
than those which use an inhibitor is strongly desired.
Here, we report the synthesis of both enantiomers of
simple alcohols with a single microbe.
Microbial whole cells have broader substrate specific-
ities than isolated alcohol dehydrogenases from the
same species. Furthermore, the use of microbial whole
cells has economical advantages since isolated dehydro-
genases require expensive coenzymes and a recycling
system. However, the stereoselectivities of microbial
reduction are usually low owing to the existence of
plural dehydrogenases which exhibit different stereose-
Synthesis of (S)-alcohol (Method A)
4–6
lectivities in the microbe. To increase the stereoselec-
tivity of microbial reduction, several methods have been
developed. For example, specific inhibitors such as
The stereoselectivities in the reduction of an aryl methyl
ketone with the resting cell of Geotrichum candidum
IFO 5767 were not satisfactory. For example, the
reduction of acetophenone (1a) afforded (R)-1-
phenylethanol ((R)-2a), with a 99% chemical yield in
6
7
methyl vinyl ketone, allyl alcohol and ethyl
6
chloroacetate change the stereochemical course of
yeast reduction of b-keto esters. Since methyl vinyl
ketone and allyl alcohol inhibit the S-enzymes (the
enzymes that afford (S)-alcohol on reduction) and ethyl
6
4% ee. Modification of the reaction conditions is
necessary to change the stereoselectivity to afford the
S)-alcohol. Previously, the synthesis of (S)-1-
(
arylethanols from aryl methyl ketones with G. candidum
IFO 4597, another species of Geotrichum, has been
Keywords: asymmetric reduction; microbial reduction; enantioselec-
tivity; hydrophobic polymer; stereochemical control.
8
reported using the acetone powder method, the
9
*
Corresponding author. Fax: +81-774-38-3201; e-mail: nakamura@
organic solvent method, and the hydrophobic polymer
10–12
scl.kyoto-u.ac.jp
method.
In the former two procedures, addition of
0
040-4039/02/$ - see front matter © 2002 Elsevier Science Ltd. All rights reserved.
PII: S0040-4039(02)00649-4

3
630
K. Nakamura et al. / Tetrahedron Letters 43 (2002) 3629–3631
secondary alcohols such as 2-propanol and cyclopen-
tanol increases the chemical yield and changes the
selectivity of the reduction toward affording the (S)-
alcohols. The last procedure did not need an additive to
change the stereochemical course of the reduction.
Synthesis of (R)-alcohol (Method B)
Previously, (R)-1-arylethanols were obtained with G.
candidum IFO 5767 from the corresponding racemic
alcohols using the stereoinversion method.
13,14
Since
stereoinversion is thought to be conducted with plural
enzymes—one enzyme oxidizes the (S)-alcohol to the
ketone and the other reduces the ketone to the (R)-
alcohol—enhancement of oxidation should increase the
(R)-enantioselectivity of the product in reduction. G.
candidum IFO 4597 is known to oxidize only the (S)-
To obtain (S)-alcohol preferentially, we chose the
1
0
hydrophobic polymer method, which was effective for
reduction using G. candidum IFO 4597. We assumed
that reduction with G. candidum IFO 5767 could also
be controlled by the addition of the polymer. Thus, G.
candidum IFO 5767 was cultivated in a glycerol medium
for 24 h, and the cells were obtained by filtration. The
cells (15 g wet wt.) were added to a mixture of a ketone
9
alcohol, not the (R)-alcohol. We assumed that G.
candidum IFO 5767 also has similar enzymes. Although
the reduction afforded both enantiomers of the alcohol
(the reduction of 1a: ee=64%), the yield of the (R)-
alcohol is thought to have increased when the reaction
was conducted under moderately aerobic conditions.
The cells (20 g wet wt.) and a ketone (200 mg) were
added into a Sakaguchi flask containing water (100 ml),
and shaken at 130 rpm for 1 day at 30°C. The usual
work up afforded the corresponding (R)-alcohol. For
example, (R)-2a was obtained with a 99% chemical
yield in over 99% ee by the reduction of 1a. The other
ketones, 1b–1f were also reduced using the same
method and afforded the (R)-alcohols in excellent ee
except for the reduction of 1c. The reduction of ketones
(
300 mg) and XAD-7 (18 g) in water (90 ml), and the
mixture was shaken at 130 rpm for 1 day at 30°C under
a nitrogen atmosphere. The usual work up afforded the
corresponding (S)-alcohol as expected. For example,
the reduction of acetophenone (1a) gave (S)-
phenylethanol ((S)-2a) in >99% ee with a 98% chemical
yield. The effectiveness of the hydrophobic polymer
XAD-7 is noteworthy when the result is compared with
that without the polymer. The hydrophobic polymer
change the stereochemical course of the reduction from
6
4% ee (R) to >99% ee (S) toward affording the
(
S)-alcohol. Results are listed in Table 1.
a
Table 1. Asymmetric reduction of ketones with G. candidum IFO5767
Substrate
Method A
Isolated (%)
Method B
Isolated (%)
Yield (%)
Ee (%)
Config.
Yield (%)
Ee (%)
Config.
1a
1b
1c
1d
1e
1f
98
\99
96
\99
99
74
92
90
88
77
79
\99
92
\99
99
98
99
S
S
S
S
S
S
99
\99
61
\99
\99
98
73
99
56
82
89
60
\99
98
85
95
99
R
R
R
R
R
R
\99
\99
a
The chemical yield, the ee and the absolute configurations were determined by GLC analysis.
1
4
14
Method A: 1a: [h]D −57.0° (c=1.00, CHCl ), (lit. [h]D +53.5° (c=1.13, CHCl ), 99% ee (R)), 1b: [h] −35.3° (c=1.00, CHCl ), (lit. [h]D +39.6°
3
3
D
3
1
4
3 D 6 6 6 6 D
(
c=1.24, CHCl ), >99% ee (R)), 1c: [h] +21.0° (c=1.02, C H ), (lit. [h]D −21.1 (c=1.00, C H ), 99% ee (R)), 1d: [h] −2.8° (c=1.50, EtOH)
and +28.9° (c=1.10, CHCl ), (lit. [h]D +2.8° (c=0.58, EtOH), 97% ee (R)), 1e: [h] −24.5° (c=0.50, CHCl ), (lit. [h]D +24.5° (c=0.31,
1
4
14
3
D
3
1
4
CHCl )), 98% ee (R)), 1f: [h]D −44.9° (c=0.99, MeOH), (lit. [h]D +44.9° (c=0.94, MeOH), 100% ee (R)). Method B: 1a: [h]D +56.8° (c=1.01,
3
CHCl ), 1b: [h] +37.6° (c=1.24, CHCl ), 1c: [h]D −18.3° (c=0.99, C H ), 1d: [h] −27.8° (c=0.96, CHCl ), 1e: [h]D +24.7° (c=0.31, CHCl3),
3
D
3
6
6
D
3
1
f: [h]D +44.9° (c=0.98, MeOH).

K. Nakamura et al. / Tetrahedron Letters 43 (2002) 3629–3631
3631
by G. candidum IFO 5767 under aerobic conditions
gives (R)-alcohols with high yields and high ee (85–
XAD-7, is highly suitable for the practical synthesis of
optically active secondary alcohols.
>99%), as shown in Table 1.
References
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IFO 5767 gives the (S)- and (R)-enantiomers with
excellent ee for both conditions. In a previous study of
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change the air conditions and to include the addition of
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