Asymmetric reduction of enones with Synechococcus sp. PCC 7942

Article abstract of DOI:10.1016/j.tetasy.2004.04.024

Synechococcus sp. PCC 7942, a cyanobacterium, reduced both the endocyclic C-C double bond of s-trans enones and the exocyclic C-C double bond of s-cis enones with high enantioselectivity to afford the corresponding (S)-ketones under illumination.

Full text of DOI:10.1016/j.tetasy.2004.04.024

Tetrahedron:
Asymmetry
Tetrahedron: Asymmetry 15 (2004) 1677–1679
Asymmetric reduction of enones with Synechococcus sp. PCC 7942
Kei Shimoda,a,* Naoji Kubota,a Hiroki Hamada,b Misato Kajib and Toshifumi Hiratac
aDepartment of Pharmacology and Therapeutics, Faculty of Medicine, Oita University, 1-1 Hasama-machi, Oita 879-5593, Japan
bDepartment of Applied Science, Faculty of Science, Okayama University of Science, 1-1 Ridai-cho, Okayama 700-0005, Japan
cDepartment of Mathematical and Life Sciences, Graduate School of Science, Hiroshima University, 1-3-1 Kagamiyama,
Higashi-Hiroshima 739-8526, Japan
Received 24 March 2004; accepted 19 April 2004
Abstract—Synechococcus sp. PCC 7942, a cyanobacterium, reduced both the endocyclic C–C double bond of s-trans enones and the
exocyclic C–C double bond of s-cis enones with high enantioselectivity to afford the corresponding (S)-ketones under illumination.
ꢀ 2004 Elsevier Ltd. All rights reserved.
Optically active a-substituted ketones are versatile chiral
building blocks for asymmetric synthesis.1 Asymmetric
reduction of enones by living whole cells is very attractive
and useful for the practical preparation of a-chiral
ketones because of high enantioselectivity, no cofactor
requirement and ease of scaling up. Microorganisms and
plants capable of reducing s-trans enones to (R)-ketones
have been reported so far.2–4 However, a cell-mediated
process in which s-trans enones are reduced to (S)-ketones
is still unavailable. On the other hand, yeast-catalyzed
reduction of s-cis enones afforded (S)-ketones.4 Over the
course of developing a new cell-mediated reduction for
asymmetric induction, we investigated the asymmetric
reduction of enones by Synechococcus sp. PCC 7942.
O
O
O
O
R
2: R=Me
3: R=Et
1
5
6
4: R=n-Pr
O
O
O
O
R1
R2
9
10
11
7: R1=Me, R2=H
8: R1=H, R2=Me
R2
O
O
R3
R4
R1
First, s-trans enones 1–9 (10 mg each) with an endocyclic
C–C double bond were administered to 50 mL of a
suspension of Synechococcus sp. PCC 7942 cells (2 g)5;6
in 50 mM Na-phosphate buffer (pH 7.0) and incubated
at 25 ꢁC for 1 or 3 days under illumination.7 The yields
of the products were determined by GLC analyses.
Extraction from the cell broth with ether followed by
purification using column chromatography on silica gel
with pentane/ethyl acetate (95:5, v/v) gave the products.
It was found that the C–C double bonds of 1–3 were
reduced to give the corresponding (S)-ketones, as shown
in Table 1.8–11 The enantiomeric purities of the resulting
ketones were determined based on the peak area of the
corresponding enantiomers in the GLC analyses on CP
cyclodextrin b 236M-19.12 Enone 1 was the best sub-
14: R1,R2=O, R3=Me, R4=H
12
13
15: R1,R2=O, R3=Et, R
4=H
16: R ,R =O, R =n-Pr, R4=H
17: R11,R42=H, R23=OH, R3=Me
18: R1,R3=H, R2=OH, R4=Me
O
O
O
20
19
21
strate, allowing us to achieve the highest enantiomeric
excess (98% ee) and yield (>99%). In the case of 2, the
reduction of the C–C double bond of 2 was accompa-
nied by the formation of minor saturated (S)-alcohols 17
(>99% ee in 7% yield) and 18 (>99% ee in 2% yield).13–15
No reduction occurred in the case of 4, which had an
* Corresponding author. Tel.: +81-97-586-5606; fax: +81-97-586-5619;
e-mail: shimoda@med.oita-u.ac.jp
0957-4166/$ - see front matter ꢀ 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetasy.2004.04.024

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K. Shimoda et al. / Tetrahedron: Asymmetry 15 (2004) 1677–1679
Table 1. Reduction of enones by Synechococcus sp. PCC 7942
Substrates
Products
Reaction time
(day)
Conversion (%)a
Ee (%)
Configurationb
1
13
14
15
––
19
20
21
––
––
14
16
––
1
1
3
3
3
3
3
3
3
1
1
3
>99
86
17
0
98
85
83
––
80c
81c
86
––
––
71
72
––
S
2
S
3
S
4
––
S
5
>99
>99
15
0
6
S
7
S
8
––
––
S
9
0
10
11
12
82
7
S
0
––
a Percentage of the products in the reaction mixture on the basis of GLC analyses.
b Preferred configuration at the a-position to the carbonyl group of the products.
c Diastereomeric excess.
n-propyl group as the a-substituent. After three days
incubation, 5–7 were reduced to the corresponding (S)-
ketones 19–21. Synechococcus sp. PCC 7942 cells were
not able to reduce b-substituted substrates 8 and 9. The
results obtained here reveal that Synechococcus sp. PCC
7942 cells have (i) the ability of catalyzing enantioface
differentiating reduction of s-trans enones to afford (S)-
ketones and (ii) similar substrate specificity to micro-
organisms, which reduce s-trans enones if the substituent
at the b-position to the carbonyl group is hydrogen and
if the a-substituent is not too bulky.2;4
tion from Synechococcus sp. PCC 7942 are currently in
progress.
Acknowledgements
This work was supported in part by a Grant-in-Aid for
Scientific Research (No. 16790014) from the Ministry of
Education, Culture, Sports, Science and Technology,
Japan.
Next, s-cis enones 10 and 1116;17 with an exocyclic C–C
double bond were subjected to the same reduction sys-
tem. 10 was smoothly reduced to give (S)-ketone 14 in
82% yield, and the hydrogenation at the a-position
showed relatively low enantioselectivity (71% ee). Satu-
rated alcohols 17 (>99% ee) and 18 (>99% ee) were
formed as minor products in 7% yield (4:1). The
reduction of 11 gave (S)-ketone 16 with 72% ee in 7%
yield. On the other hand, substrate 12, which had both
endocyclic and exocyclic C–C double bonds was not
reduced by the cells probably due to the existence of the
b-methyl group. These results demonstrate that Syn-
echococcus sp. PCC 7942 cells have the same enantio-
selectivity in the reduction of s-cis enones as yeast.4
References and notes
1. Tomioka, K.; Koga, K. In Asymmetric Synthesis; Morri-
son, J. D., Ed.; Academic: New York, 1983; Vol. 2,
p 201.
2. (a) Kergomard, A.; Renard, M. F.; Veschambre, H.
Tetrahedron Lett. 1978, 5197; (b) Kergomard, A.; Renard,
M. F.; Veschambre, H. J. Org. Chem. 1982, 47, 792; (c)
Desrut, M.; Kergomard, A.; Renard, M. F.; Veschambre,
H. Biochem. Biophys. Res. Commun. 1983, 110, 908; (d)
Kergomard, A.; Renard, M. F.; Veschambre, H.; Cour-
tois, D.; Petiard, V. Phytochemistry 1988, 27, 407; (e)
Noma, Y.; Asakawa, Y. Phytochemistry 1992, 31, 2009; (f)
Takabe, K.; Hiyoshi, H.; Sawada, H.; Tanaka, M.;
Miyazaki, A.; Yamada, T.; Kitagiri, T.; Yoda, H. Tetra-
hedron: Asymmetry 1992, 3, 1399.
3. (a) Hirata, T.; Hamada, H.; Aoki, T.; Suga, T. Phyto-
chemistry 1982, 21, 2209; (b) Shimoda, K.; Hirata, T.
J. Mol. Catal. B: Enzym. 2000, 8, 255; (c) Hirata, T.;
Takarada, A.; Matsushima, A.; Kondo, Y.; Hamada, H.
Tetrahedron: Asymmetry 2004, 15, 15.
Thus, the asymmetric reductions of s-trans and s-cis
enones have been accomplished and optically active
a-substituted (S)-ketones have been prepared by using
Synechococcus sp. PCC 7942 as biocatalyst. It is worth
noting that this new biocatalyst has opposite enantio-
selectivity in the reduction of s-trans enones to other
microorganisms2;4 and plants3 and that each enantiomer
of the a-substituted ketones can be synthesized by
selective use of the whole cells. Recently, two enone
reductases have been isolated from Nicotiana tabacum;
s-trans enone reductase, which was responsible for the
reduction of the endocyclic C–C double bond and s-cis
enone reductase, which was capable of reducing the
exocyclic C–C double bond.18 In Synechococcus sp. PCC
7942 s-trans enone reductases with an opposite enantio-
selectivity to those from yeast and N. tabacum might
exist. Further investigations using the enzyme prepara-
4. Matsumoto, K.; Kawabata, Y.; Takahashi, J.; Fujita, Y.;
Hatanaka, M. Chem. Lett. 1998, 283.
5. The suspension cells of Synechococcus sp. PCC 7942 were
cultured in a 500 mL conical flask containing 300 mL of
BG-11 medium for 3 weeks under illumination (4000
lux).6 The grown cells were collected by centrifugation
at 5000 rpm for 10 min to give 2 g of wet cells.
6. Nakamura, K.; Yamanaka, R.; Tohi, K.; Hamada, H.
Tetrahedron Lett. 2000, 6799.
7. The conversion yields and enantiomeric purities of the
resulting ketones were drastically reduced when the
reactions occurred in the dark. For example, 1 was

K. Shimoda et al. / Tetrahedron: Asymmetry 15 (2004) 1677–1679
1679
reduced to 13 with 70% ee in 42% yield after one day’s
incubation in the dark.
and 12.9 min; (S)- and (R)-16, 27.7 and 27.9 min; (S)- and
(R)-21, 50.1 and 51.9 min.
25
D
25
D
8. Product 13: ½aꢀ
¼
þ114:9 (c 0.52, CHCl3) {lit.9
13. Product 17: ½aꢀ ¼ þ51:2 (c 0.4, MeOH) {lit.14
25
½aꢀ ¼ ꢁ110:5 for (R)-enantiomer}; 14 converted from 2:
20
D
25
D
½aꢀ ¼ þ42:9}; 18: ½aꢀ ¼ þ25:7 (c 0.2, MeOH)
D
20
CD ½hꢀ ¼ þ887 (c 0.75, MeOH) {lit.10 ½hꢀ ¼ ꢁ987 for
{lit.14 ½aꢀ ¼ þ24:3}. The enantiomeric purities of 17
288
288
D
(R)-enantiomer}; 14 from 10: CD ½hꢀ ¼ þ701 (c 0.68,
and 18 were determined by 1H NMR analyses of the
corresponding MTPA esters as described previously.15 In
the cases of the other substrates, saturated alcohols were
not obtained during the incubation time examined.
14. Backstrom, R.; Sjoberg, B. Ark. Kemi. 1967, 26, 549.
15. Hirata, T.; Izumi, S.; Akita, K.; Yoshida, H.; Gotoh, S.
Tetrahedron: Asymmetry 1993, 4, 1465.
288
MeOH); 15: CD ½hꢀ ¼ þ1914 (c 0.32, MeOH) {lit.11
288
½hꢀ ¼ þ2200}; 16: CD ½hꢀ ¼ þ1860 (c 0.15, MeOH)
288
288
{lit.11 ½hꢀ ¼ þ2480}; 21: CD ½hꢀ ¼ þ995 (c 0.14,
288
288
MeOH).
9. Partridge, J. J.; Chada, N. K.; Vskokovic, M. R. J. Am.
Chem. Soc. 1973, 95, 532.
10. Cheer, C. J.; Djerassi, C. Tetrahedron Lett. 1976,
3877.
11. Meyers, A. I.; Williams, D. R.; Erickson, G. W.; White, S.;
Druelinger, M. J. Am. Chem. Soc. 1981, 193, 3081.
12. Conditions for capillary GLC analysis: column, CP
16. The configuration of 11 at the propylidene site was
assigned to be E based on the 1H NMR data. The
chemical shift of the olefin proton signal comparatively
shifted downfield to d 6.61 (1H, tt, J ¼ 7:4 and 2.1 Hz) due
to the placement of this proton in the deshielding region of
the neighbouring carbonyl group.17.
17. Crandall, J. K.; Arrington, J. P.; Hen, J. J. Am. Chem.
Soc. 1967, 89, 6208.
18. Tang, Y. X.; Suga, T. Phytochemistry 1992, 31,
2599.
cyclodextrin
b 236M-19 (0.25 mm · 25 m); injection,
180 ꢁC; detector, 180 ꢁC; oven, 100 ꢁC; carrier gas, N2
(50 mL minꢁ1). Retention times for the products in the
GLC were as follows: (S)- and (R)-13, 10.5 and 11.4 min;
(S)- and (R)-14, 11.8 and 12.8 min; (S)- and (R)-15, 12.7