Enantioselective reduction of bromo- and methoxy-acetophenone derivatives using carrot and celeriac enzymatic system

Article abstract of DOI:10.1016/j.tetasy.2004.05.033

The enantioselective reductions of the carbonyl group of bromo- and methoxy-acetophenones have been conducted using comminuted carrot (Daucus carota L.) and celeriac (Apium graveolens L., var. rapaceum) roots. (S)-(-)-1-(3-Methoxyphenyl)ethanol (100% yield, ee=100%) has been obtained by reduction of meta-methoxyacetophenone using carrot.

Full text of DOI:10.1016/j.tetasy.2004.05.033

Tetrahedron:
Asymmetry
Tetrahedron: Asymmetry 15 (2004) 1965–1967
Enantioselective reduction of bromo- and methoxy-acetophenone
derivatives using carrot and celeriac enzymatic system
Wanda K. Maczka and Agnieszka Mironowicz*
z
Department of Chemistry, Agricultural University, ul. Norwida 25, 50-375 Wrocław, Poland
Received 1 April 2004; accepted 25 May 2004
Available online
Abstract—The enantioselective reductions of the carbonyl group of bromo- and methoxy-acetophenones have been conducted using
comminuted carrot (Daucus carota L.) and celeriac (Apium graveolens L., var. rapaceum) roots. (S)-())-1-(3-Methoxyphenyl)ethanol
(
ꢀ
100% yield, ee ¼ 100%) has been obtained by reduction of meta-methoxyacetophenone using carrot.
2004 Elsevier Ltd. All rights reserved.
1. Introduction
This work is a continuation of our previous research
using these two biocatalysts.
16
Asymmetric syntheses of chiral alcohols have found
wide application in the production of drugs, agro-
chemicals, flavours and pigments. These alcohols may
be obtained by enantioselective reduction of prochiral
ketones. Among numerous methods of asymmetric
carbonyl group reduction that have been developed over
the last 25 years, biochemical methods using higher
2
. Results and discussion
Six acetophenone derivatives have been used as the
substrates for the biotransformations: ortho- 1, meta- 2
and para-methoxyacetophenone 3, and ortho- 4, meta- 5
and para-bromoacetophenone 6. The reduction of the
carbonyl group by the carrot’s and celeriac’s enzymatic
systems proceeded stereoselectively, following the Pre-
log’s rule, which resulted in formation of (S)-alcohols
predominantly (Scheme 1).
1
plants have been being widely used. Acetophenone is a
very interesting model xenobiotic substrate for bio-
reduction, because it may give rise to both enantiomers
of 1-phenylethanol. These compounds, as well as their
simple derivatives, have been effectively used as building
2–5
blocks for asymmetric synthesis of drugs.
It has been reported that reduction of a carbonyl group
may be performed using various plant biocatalysts in
O
OH
6;7
different forms: as suspension cell cultures, cell cul-
8
9;10
tures, immobilised plant cells and also as cuted fresh
fruits and vegetables.
11–15
X
X
1
- 6
1a - 6a
Our research has been focused on investigations as to
the influence of the two types of substituents (bromine
atom or methoxyl group) on the aromatic ring of ace-
tophenone on the efficiency and stereoselectivity of the
carbonyl group reduction. Comminuted roots of fresh
carrot (Daucus carota L.) and celeriac (Apium graveolens
L., var. rapaceum) have been employed as biocatalysts.
1, 1a: X = ortho-OMe
2
3
4
5
, 2a: X = meta-OMe
, 3a: X = para-OMe
, 4a: X = ortho-Br
, 5a: X = meta-Br
6, 6a: X = para-Br
Scheme 1.
*
0
Corresponding author. Tel.: +48-71-3205468; fax: +48-71-3284124;
e-mail: amiron@ozi.ar.wroc.pl
The results of bioreduction of substrates 1–6 are pre-
sented in Table 1.
957-4166/$ - see front matter ꢀ 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetasy.2004.05.033

1966
W. K. Maczka, A. Mironowicz / Tetrahedron: Asymmetry 15 (2004) 1965–1967
z
Table 1. Results of bioreductions of 1–6 with carrot and celeriac
3.3. Biotransformation conditions
Substrate
Entry
Ketone conversion
%)/ee of (S)-OH (%)
(
Healthy vegetable roots were comminuted (cuted) using
an electric mixer for 2 min and 20 mL of vegetable pulp
Carrot
11/78
Celeriac
(
1.0–1.5 g of dry wt, 100 ꢁC, 24 h) was placed in Erlen-
mayer flasks with 50 mL of 0.1 M phosphate buffer
pH ¼ 6.2 (celeriac), pH ¼ 6.5 (carrot)]. This pulp with
0–30 mg of the substrate dissolved in 0.5 mL acetone
1
2
3
4
5
6
(o-OMe)
(m-OMe)
(p-OMe)
(o-Br)
1
2
10/87
[
2
3
4
100/100
12/88
8/100
54/91
41/95
100/98
10/87
27/100
40/86
30/88
was shaken for 48 h. The course of biotransformation
was controlled by means of TLC and GC. Biotrans-
formed mixtures were extracted with CHCl . The
3
enantiomeric composition of product mixture was
established by GC by application of chiral columns. All
substrates in the buffer solution were stable under these
conditions.
5
6
7
8
(m-Br)
9
1
0
(p-Br)
11
3.4. Analytical methods
12
The ratios of substrates conversion and configurations of the resulting
alcohols were determined by GC analysis of crude extracts.
GC: Hewlett-Packard 5890, FID, carrier gas––H
2
2
at
mL/min, using following Chrompack WCOT capillary
columns: Chirasil-Dex CB (25 m · 0.25 mm · 0.25 lm)
for 1, 1a (column temp 120 ꢁC/1 min; gradient 2 ꢁC/min
to 140 ꢁC, gradient 30 ꢁC/min to 200 ꢁC–2 min; injector
temp 200 ꢁC, detector temp 250 ꢁC); for 2, 2a (column
temp 120 ꢁC/1 min; gradient 2 ꢁC/min to 150 ꢁC, gradient
The results obtained show that the presence of a sub-
stituent at the meta-position, no matter whether it is
electron-withdrawing or electron-donating, gives rise to
the highest yields of substrates 2 and 5 using both the
biocatalysts described (entries 3, 4 and 9, 10). This
observation is in accordance with the results of the
bioreduction of meta-methoxyacetophenone by means
3
0 ꢁC/min to 200 ꢁC–2 min; injector temp 200 ꢁC, detec-
tor temp 250 ꢁC); for 3, 3a (column temp 119 ꢁC/1 min;
gradient 0.2 ꢁC/min to 125 ꢁC, gradient 30 ꢁC/min to
17
2
2
1
00 ꢁC–2 min; injector temp 200 ꢁC, detector temp
50 ꢁC); for 4, 4a (column temp 130 ꢁC/1 min; gradient
ꢁC/min to 146 ꢁC, gradient 30 ꢁC/min to 200 ꢁC–2 min;
of Rhizopus arrhizus cultures, acetone powder of
Geotrichum candidum and fresh root of carrot, in the
case of replacing the oxygen atom in the methoxyl group
18
19
injector temp 200 ꢁC, detector temp 250 ꢁC); for 5, 5a
with the selenium one.
(
1
column temp 126 ꢁC/1 min; gradient 0.3 ꢁC/min to
33 ꢁC, gradient 30 ꢁC/min to 200 ꢁC–2 min; injector
As far as the para-substituted acetophenone derivatives
are concerned (entries 5, 6, 11 and 12), we have observed
that reduction of the substrate containing a bromine
atom 6 by means of both biocatalysts proceeds three
times faster than for the methoxy-substituted ketone 3,
which is in accordance with the results reported by
temp 200 ꢁC, detector temp 250 ꢁC); for 6, 6a (column
temp 135 ꢁC/1 min; gradient 0.5 ꢁC/min to 144 ꢁC, gra-
dient 30 ꢁC/min to 200 ꢁC–2 min; injector temp 200 ꢁC,
detector temp 250 ꢁC); TLC: silica gel 60 F pre-coated
254
aluminium sheets (layer thickness 0.2 mm, Merck) with
n-hexane–acetone (5:1) for 1–3 and 1a–3a and n-hexane–
acetone (7:1) for 4–6 and 4a–6a.
10
18
Akakabe et al. and Nakamura and Matsuda. The
highest enantiomeric excess of the alcohols was observed
when meta-methoxyacetophenone 2 (entries 3 and 4)
and ortho-bromoacetophenone 4 (entries 7 and 8) were
subjected to the reduction. The results obtained indicate
that both the enantioselectivity and efficiency of the
reduction of bromo- and methoxy-substituted acetoph-
enone derivatives by means of carrot’s and celeriac’s
enzymatic systems depends mainly on the substituent
location. The influence of a substituent nature is less
important.
Acknowledgements
We thank the State Committee for Scientific Research
(KBN) for support (Grant No. 3 PO6 030 24).
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