Inversion of diastereoselectivity depending on substrate concentration in baker's yeast catalyzed reduction of σ-symmetrical 1,3-cyclopentadiones and 1,3-cyclohexadiones

Article abstract of DOI:10.1055/s-2006-949647

Inversion of diastereoselectivity caused by a change in substrate concentration was first observed in baker's yeast catalyzed reduction of σ-symmetrical 2,2-dialkylated cyclopentan-1,3-diones 1,2 and cyclohexan-1,3-dione 20. The selectivity altered by deg

Full text of DOI:10.1055/s-2006-949647

2176
LETTER
Inversion of Diastereoselectivity Depending on Substrate Concentration in
Baker’s Yeast Catalyzed Reduction of s-Symmetrical 1,3-Cyclopentadiones
and 1,3-Cyclohexadiones
Baker’s
Yeast
C
a
atalyzed
R
k
e
duction of
s
a
-Symmetr
i
h
cal 1, 3-Cycl
i
opentad
r
ione
s
o Katoh, Shinsuke Mizumoto, Masato Fudesaka, Yuki Nakashima, Tetsuya Kajimoto, Manabu Node*
Department of Pharmaceutical Manufacturing Chemistry, 21st Century COE Program, Kyoto Pharmaceutical University, Yamashina-ku,
Kyoto 607-8414, Japan
E-mail: node@mb.kyoto-phu.ac.jp
Received 16 May 2006
the C-2 position have been scarcely adopted as substrates
Abstract: Inversion of diastereoselectivity caused by a change in
in the asymmetric reduction using baker’s yeast. There-
substrate concentration was first observed in baker’s yeast cata-
fore, we embarked on study of the application of baker’s
lyzed reduction of s-symmetrical 2,2-dialkylated cyclopentan-1,3-
yeast catalyzed reduction to s-symmetrical derivatives of
diones 1,2 and cyclohexan-1,3-dione 20. The selectivity altered by
degrees depending on the substrate concentration from 8 mM to 40 cyclopentan-1,3-dione and cyclohexan-1,3-dione, which
mM. Meanwhile, application of the yeast-catalyzed reduction to the
hydrogenated compound (5) of 1 afforded a single diastereomer in
good yield when the reaction was conducted in high substrate
carried a long alkyl chain and an ester on the terminal car-
bon.
We started with the preparation of substrates 1–6 having
methyl and another alkyl group on the C-2 position of cy-
clopentan-1,3-dione. The substrates 1 and 2 having an eth-
ylene unit between the cyclic ketone and a,b-unsaturated
ester were synthesized in good overall yield by Michael
addition of carbanion generated from 2-methylcyclopen-
ta-1,3-dione (7) to acrolein, followed by Wittig reaction.
On the other hand, the substrates 3 and 4 having a methyl-
ene unit between the cyclic ketone and a,b-unsaturated es-
ter were synthesized in three steps, i.e., allylation of 7,
ozonolysis to afford aldehyde 8, and successive Wittig re-
action. Then, hydrogenation of the double bond of 1 and
3 afforded 5 and 6, respectively (Scheme 1).
concentration (40 mM).
Key words: baker’s yeast catalyzed asymmetric reduction, s-sym-
metrical cyclopentane-1,3-dione, substrate concentration
Asymmetric reductions with biocatalysts have been wide-
ly utilized to provide chiral synthons in organic synthesis
since the reaction can be conducted under mild condi-
tions, for example, in aqueous media and at moderate tem-
perature.1 Baker’s yeast is one of the best-used
biocatalysts among them mainly because of high potency
for the reduction of ketones and availability in large
amount.2
Next, the reduction of 1–6 with baker’s yeast (Sigma Co.
Ltd., Type II) was tried under normal conditions, i.e., 40
mM of the substrate was subjected to the reaction in an
aqueous medium containing 10% DMSO, and in the pres-
ence of sucrose in the same medium (Table 1). Addition
of sucrose tended to slightly increase the chemical yield
while an undesired effect was observed on the de of the
product (Table 1, entries 8–11), and the reactions of 3 and
4 that have one methylene between the cyclopentane ring
and the olefinic carbon proceeded in better yield with sat-
isfactory de than those of 1 and 2 having two methylene
groups. Herein, it is noteworthy that the reactions of 5 and
6 having no carbon–carbon double bond proceeded to
give satisfactory yield with excellent de (Table 1, entries
6 and 7).9 Moreover, it was found that the diastereoselec-
tivity of the products in the reaction of 1 was inverted
when the reduction was conducted in lower substrate con-
centration (8.0 mM; Table 1, entries 1, 2).10
During our study on the application of the yeast-catalyzed
reduction to s-symmetrical cyclic 1,3-diketones, which
afforded optically active cyclic 3-hydroxyketones, we en-
countered an interesting phenomenon that the diastereo-
meric ratio of products was inverted by changing the
concentration of a substrate in a couple of cases while
keeping Prelog’s rule where newly generated secondary
alcohols had the S-configuration.3 Here we would like to
report the details of this phenomenon.
Many studies on asymmetric reduction of 2,2-dialkylated
cyclohexan-1,3-diones have been published and some of
them reported practically excellent results,4–6 and it is
known that ratios of diastereomers obtained as products
varied depending on chemical properties of alkyl groups
on the C-2 quaternary carbon of the cyclohexan-1,3-di-
ones.7 However, almost nothing has been reported to date
on the reduction of 2,2-dialkylated cyclopentan-1,3-di-
ones with baker’s yeast, except for the reduction of 2,2-
dimethylcyclopentan-1,3-dione.8 Moreover, s-symmetri-
cal cyclohexan-1,3-diones carrying a long alkyl chain on
Fascinated by this phenomenon, the inversion of stereose-
lectivity depending on the substrate concentration, sub-
strates 2–4 were subjected to the enzymatic reduction in
two different concentrations, i.e., 40 mM and 8 mM of the
substrate in a medium (Table 2). The difference of sub-
strates affected the reactions; while the inversion of de oc-
curred on the substrate 2, only the decrease in the
SYNLETT 2006, No. 14, pp 2176–2182
0
1
.0
9
.2
0
0
6
Advanced online publication: 24.08.2006
DOI: 10.1055/s-2006-949647; Art ID: U05606ST
© Georg Thieme Verlag Stuttgart · New York

LETTER
Baker’s Yeast Catalyzed Reduction of s-Symmetrical 1,3-Cyclopentadiones
2177
O
O
a
d
CO2R
1: R = Me (85%)
CHO
O
O
76%
O
O
2: R = Et (94%)
O
O
7
b, c
d
CHO
CO2R
O
O
50%
3: R = Me (95%)
4: R = Et (94%)
8
O
O
O
O
e
e
1
3
CO2Me
CO2Me
5
97%
6
96%
Scheme 1 Reagents and conditions: (a) acrolein; (b) allyl bromide; (c) O3, then PPh3; (d) Ph3P=CHCO2R; (e) Pd/C, H2.
Table 1 Reduction of 1–6 with Baker’s Yeast
baker's yeast
O
OH
O
(3 g/mmol × 2)
1–6
+
CO2R
CO
H2O–DMSO
(10:1)
n
n
OH
b
a
30 °C, 48 h
9–14
Entry
Substratea
Sucroseb
Yield (%)
Product
n
2
2
2
1
1
2
1
2
2
1
1
R
a:b
1
1
1
2
3
4
5
6
1
2
3
4
–
–
–
–
–
–
–
+
+
+
+
37
30
30
72
70
57
68
42
27
81
73
9
9
Me
Me
Et
12:88d
89e:11
5:95
2c
3
10
11
12
13
14
9
4
Me
Et
16:84
19:81
1:99f
5
6
Me
Me
Me
Et
7
0:100g
26:74
22:78
21:79
19:81
8
9
10
11
12
10
Me
Et
11
a 40 mM.
b Sucrose (yeast × 2) g.
c The reaction was carried out on 8 mM of substrate.
d 99% ee.
e 99% ee.11
f 97% ee.
g 98% ee.12
Synlett 2006, No. 14, 2176–2182 © Thieme Stuttgart · New York

2178
T. Katoh et al.
LETTER
O
9a
9b
CO2Me
baker's yeast
OH
(3 g/mmol×2)
1
+
100
H2O–DMSO (10:1)
30 °C, 48 h
OH
CO2Me
O
substrate/H2O
(mmol/L)
de
0
(%)
40
20
60
100
Figure 1
selectivity was observed with lower concentration of the Figure 2). On the other hand, the absolute configuration of
substrates 3 and 4.
9b was determined, after hydrogenation, on the basis of
identification with 13b.9 In addition, stereochemistry of
11b was confirmed in a similar way, i.e., conversion to
14b by hydrogenation and identification.9 Moreover,
Thus, dependency of the diastereoselectivity in the reduc-
tion of 1 was scrutinized and resulted in obtaining a
smooth sigmoid curve when the concentration of the sub-
strate was changed from 4 mM to 60 mM (Figure 1).
1
comparison of H NMR spectra between methyl esters
(11a,b) and ethyl esters (12a,b) could suggest the stere-
ochemistry of 12a and 12b, i.e., the signals assigned to the
methyl groups on the cyclopentanone ring in 11a and 12a
appeared in slightly lower field (0.05 ppm in both) than
those of 11b and 12b, respectively.
Unfortunately, we cannot explain the mechanism which
caused selectivity inversion of the products in the reduc-
tion of 1, and why the substrate 1 behaved in this way.
Finally, the absolute structure of the main product 9a was
determined by means of X-ray crystallography after de-
riving it to p-bromobenzoate (15), and the secondary alco-
hol and the quaternary carbon were determined to have
the S and R configurations, respectively (Scheme 2,
We next investigated whether this phenomenon was ob-
servable in s-symmetrical cyclohexan-1,3-dione or not.
The substrates examined in the reaction were synthesized
Table 2 Enzymatic Reduction of Substrates 2–4
OH
O
baker's yeast
(3 g/mmol × 2)
CO2R
2–4
CO2R
+
(
)
n
(
)
n
H2O–DMSO
(10:1)
O
OH
b
a
30 °C, 48 h
10–12
Entry
Substrate
Conc. (mM)
Yield (%)
Product
n
2
2
1
1
1
1
R
a:b
1
2
3
4
5
6
2
2
3
3
4
4
40
8
30
76
72
74
70
72
10
10
11
11
12
12
Et
5:95
Et
79:21
16:84
42:58
19:81
44:56
40
8
Me
Me
Et
40
8
Et
Synlett 2006, No. 14, 2176–2182 © Thieme Stuttgart · New York

LETTER
Baker’s Yeast Catalyzed Reduction of s-Symmetrical 1,3-Cyclopentadiones
2179
O
O
d
a
CHO
CO2R
O
O
17: R = Me (80%)
O
O
65%
18: R = Et (66%)
O
O
16
b
d
CHO
CO2R
O
O
52%
19: R = Me (88%)
20: R = Et (95%)
O
O
e
e
17, 18
CO2Me
19
CO2R
O
O
21: R = Me (99%)
22: R = Et (85%)
23: 97%
Scheme 2
As the result, such drastic inversion as in the case of 1 was
not observed; however, an inversion of diastereoselectiv-
ity in the product appeared in the reaction with 20
(Table 3, entries 7, 8).
The absolute configuration of the major product 24a in
entry 7 was determined by X-ray crystallography after de-
riving to p-bromobenzoate.13
In comparison with the reaction of 1,3-cyclopentadiones
5 and 6, 1,3-cyclohexandiones 21–23 were not converted
to a single product but to a mixture of diastereomers with
low selectivity in spite of a common structural feature,
that is, the absence of the carbon–carbon double bond
(Table 3, entries 9–11).
In conclusion, we have found an interesting phenomenon
that the diastereoselectivity of the product in the reduction
of 1 was inverted depending on the concentration of the
substrate. Moreover, it was found that the baker’s yeast
catalyzed reduction of 5 that have no carbon–carbon dou-
ble bond on the side-chain afforded a single diastereomer
in satisfactory yield.
Figure 2
Our finding will provide a promising method for the syn-
thesis of many biologically active compounds and natu-
rally occurring compounds, and disclosed an important
issue of the substrate concentration in baker’s yeast cata-
lyzed reaction as well as in other enzymatic reactions.
as the substrates 1–6. Namely, elongation of a propional-
dehyde or an acetaldehyde group from the C-2 position of
cyclohexan-1,3-dione (16) was attained by Michael addi-
tion of acrolein and allylation followed by ozonolysis, re-
spectively. Successive Wittig reaction of the aldehyde Further studies on the relationship between freshness of
afforded 17–20, of which the hydrogenation on Pd/C the baker’s yeast and the potency of the inversion in
yielded 21–23 (Scheme 3).
diastereoselectivity10 as well as those on the application of
the baker’s yeast catalyzed reduction for the synthesis of
naturally occurring bioactive compounds are in progress.
Baker’s yeast (Sigma, Type II) catalyzed asymmetric re-
ductions of 17–20 were attained under the conditions of
low and high substrate concentrations (Table 3).
Synlett 2006, No. 14, 2176–2182 © Thieme Stuttgart · New York

2180
T. Katoh et al.
LETTER
O
O
O
O
d
a
CHO
CO2R
17: R = Me (80%)
O
O
65%
18: R = Et (66%)
O
O
16
b
d
CHO
CO2R
O
O
52%
19: R = Me (88%)
20: R = Et (95%)
O
O
e
e
17, 18
CO2Me
19
CO2R
O
O
21: R = Me (99%)
22: R = Et (85%)
23
97%
a: acrolein, b: allyl bromide, c: O3, then PPh3, d: Ph3P=CHCO2R, e: Pd-C/H2
Scheme 3 Reagents and conditions: (a) acrolein; (b) allyl bromide; (c) O3, then PPh3; (d) Ph3P=CHCO2R; (e) Pd/C, H2.
Table 3 Baker’s Yeast Catalyzed Asymmetric Reductions of 17–23
O
OH
baker's yeast
(3 g/mmol × 2)
17–23
CO2R
+
CO2R
(
)
n
H2O–DMSO
(10:1)
(
)
n
OH
O
a
b
30 °C, 48 h
24–30
Entry
Substrate
Conc. (mM)
Yield (%)
Product
n
2
2
2
2
1
1
1
1
2
2
1
R
a:b
1
2
17
17
18
18
19
19
20
20
21
22
23
40
8
67
72
26
60
35
55
71
74
68
70
58
24
24
25
25
26
26
27
27
28
29
30
Me
Me
Et
94:6
93:7
3
40
8
84:16
86:14
50:50
49:51
30:70
66:34
70:30
72:28
61:39
4
Et
5
40
8
Me
Me
Et
6
7
40
8
8
Et
9
40
40
40
Me
Et
10
11
Me
Synlett 2006, No. 14, 2176–2182 © Thieme Stuttgart · New York

LETTER
Baker’s Yeast Catalyzed Reduction of s-Symmetrical 1,3-Cyclopentadiones
2181
Acknowledgment
O
5-bromonicotinic
acid, EDC, DMAP
Br
This research was financially supported in part by Frontier Research
Program and the 21st Century Center of Excellence Program ‘De-
velopment of Drug Discovery Frontier Integrated from Tradition to
Proteome’ of the Ministry of Education, Culture, Sport and Techno-
logy, Japan.
O
13b
MeO2C
CH2Cl2
r.t., 20 h
99%
S
O
S
N
Scheme 4
References and Notes
(1) See, for example: Wong, C.-H.; Whitesides, G. M. Enzymes
in Synthetic Organic Chemistry, In Tetrahedron Organic
Chemistry Series, Vol. 12; Baldwin, J. E.; Magnus, P. D.,
Eds.; Pergamon Press: Oxford, 1994.
(2) (a) Sih, C. J. Angew. Chem., Int. Ed. Engl. 1984, 23, 570.
(b) Sih, C. J. Angew. Chem., Int. Ed. Engl. 1989, 28, 695.
(c) Whitesides, G. M.; Wong, C.-H. Angew. Chem., Int. Ed.
Engl. 1985, 24, 617. (d) Jones, J. B. Tetrahedron 1986, 42,
3351.
(3) Prelog, V. Pure Appl. Chem. 1968, 9, 119.
(4) (a) Brooks, D. W.; Mazdiyanski, H.; Grothaus, P. G. J. Org.
Chem. 1987, 52, 3223. (b) Brooks, D. W.; Grothaus, P. G.;
Irwin, W. L. J. Org. Chem. 1982, 47, 2820.
(5) (a) Kitahara, T.; Miyake, M.; Kido, M.; Mori, K.
Tetrahedron: Asymmetry 1990, 1, 775. (b) Mori, K.;
Fujiwhara, M. Tetrahedron 1988, 44, 343. (c) Mori, K.;
Mori, H. Org. Synth. 1990, 68, 56. (d) Fuhshuku, K.; Funa,
N.; Akeboshi, T.; Ohta, H.; Hosomi, H.; Ohba, S.; Sugai, T.
J. Org. Chem. 2000, 65, 129.
(6) (a) Iwamoto, M.; Kawada, H.; Tanaka, T.; Nakada, M.
Tetrahedron Lett. 2003, 44, 7239. (b) Watanabe, H.;
Iwamoto, M.; Nakada, M. J. Org. Chem. 2005, 70, 4652.
(c) Wei, Z.-L.; Li, Z. Y.; Lin, G.-Q. Tetrahedron:
Asymmetry 2001, 12, 229. (d) Wei, Z.-L.; Li, Z.-Y.; Lin, G.-
Q. Synthesis 2000, 1673. (e) Inoue, T.; Hosomi, K.; Araki,
M.; Nishide, K.; Node, M. Tetrahedron: Asymmetry 1995, 6,
31.
Figure 3
O
Br
5-bromonicotinic
O
acid, EDC, DMAP
14b
MeO2C
S
S
CH2Cl2
r.t., 20 h
96%
N
O
(7) Gramatica, P.; Manitto, P.; Monti, D.; Speranta, G.
Tetrahedron 1988, 44, 1299.
(8) (a) Brooks, D. W.; Grothaus, P. G.; Irwin, W. L. J. Org.
Chem. 1982, 47, 2820. (b) Not only baker’s yeast but also
Saccharomyces cerevisiae (brewing yeast), Bacillus
thuringiensis afforded excellent results: (c) Kosmol, H.;
Kieslish, K.; Vossing, R.; Koch, H. J.; Petzoldt, K.; Gibian,
H. Justus Liebigs Ann. Chem. 1967, 701, 198. (d) Dai, W.
M.; Zhou, W. S. Tetrahedron 1985, 41, 4475.
Scheme 5
(9) The stereochemistry of 13b (Scheme 4, Figure 3) and 14b
(Scheme 5, Figure 4) was confirmed by X-ray
crystallography after deriving to bromonicotinates.
Compound 13b: colorless oil. 1H NMR (400 MHz, CDCl3):
d = 0.98 (s, 3 H), 1.24–1.35 (m, 1 H), 1.39–1.72 (m, 5 H),
1.92–2.00 (m, 1 H), 2.05 (br s, 1 H), 2.15–2.24 (m, 1 H),
2.26–2.37 (m, 3 H), 2.43–2.52 (m, 1 H), 3.67 (s, 3 H), 4.11
(br s, 1 H). 13C NMR (100 MHz, CDCl3): d = 19.2, 23.0,
25.3, 27.8, 29.2, 33.4, 33.9, 51.6, 53.2, 77.2, 174.3, 220.8.
Compound 14b: colorless oil. 1H NMR (400 MHz, CDCl3):
d = 0.97, (s, 3 H), 1.44–1.73 (m, 4 H), 2.00–2.07 (m, 1 H),
2.12–2.22 (m, 1 H), 2.27–2.37 (m, 2 H), 2.42–2.53 (m, 2 H),
3.14 (br s, 1 H), 3.69 (s, 3 H), 4.21 (br dt, J = 4.4, 2.2 Hz, 1
H). 13C NMR (100 MHz, CDCl3): d = 18.7, 18.9, 27.2, 29.2,
33.1, 34.0, 51.9, 53.8, 76.8, 175.1, 221.3.
(10) In order to obtain high reproducibility in the reaction with
8 mM substrate, newly opened baker’s yeast must be used.
If long-term-stored yeast (longer than ca. 6 months at 4 °C)
is used in the reaction, a reduced de is observed. The repro-
duced results were obtained with baker’s yeast (Sigma, type
II, lot. No. 125K0062).
Figure 4
Synlett 2006, No. 14, 2176–2182 © Thieme Stuttgart · New York

2182
T. Katoh et al.
LETTER
Compound 9a: colorless oil. 1H NMR (400 MHz, CDCl3):
d = 1.03 (s, 3 H), 1.51–1.64 (m, 2 H), 1.76 (br s, 1 H), 1.84–
1.93 (m, 1 H), 2.16–2.31 (m, 4 H), 2.44–2.52 (m, 1 H), 3.72
(s, 3 H), 4.17–4.20 (m, 1 H), 5.83 (td, J = 1.6, 15.7 Hz, 1 H),
6.92 (td, J = 6.8, 15.7 Hz, 1 H). 13C NMR (100 MHz,
CDCl3): d = 14.7, 26.8, 27.9, 33.3, 34.9, 51.5, 52.6, 75.8,
121.2, 148.7, 166.9, 219.6.
(11) Chiral HPLC analysis of 9b was performed with a Shimadzu
LC-10A Liquid Chromatograph series using a SHISEIDO
Ceramospher Chiral RU-1 (0.46 f × 250 mm). Two
enantiomers of 9b were detected at the retention time of 10.7
and 11.7 min by eluting with MeOH, flow rate: 0.5 mL/min,
at 50 °C. The enantiomer predominantly obtained in the
reaction (entry 1, Table 1) appeared at 11.7 min. Meanwhile,
two enantiomers of 9a were detected using Daicel
CHIRALCEL OJ-H (0.46 f × 250 mm) at 43.2 and 47.5 min
by eluting with a mixed solvent of n-hexane and 2-PrOH
(9:1), flow rate: 0.5 mL/min, at 25 °C. The predominant
enantiomer in the reaction (entry 2, Table 1) was detected at
47.5 min.
Compound 9b: colorless oil. 1H NMR (400 MHz, CDCl3):
d = 1.02 (s, 3 H), 1.67–1.76 (m, 3 H), 1.90–1.97 (m, 1 H),
2.18–2.35 (m, 4 H), 2.44–2.53 (m, 1 H), 3.72 (s, 3 H), 4.13
(br dt, J = 3.7, 4.1 Hz, 1 H), 5.86 (td, J = 1.6, 15.7 Hz), 6.99
(td, J = 6.8, 15.7 Hz, 1 H). 13C NMR (100 MHz, CDCl3):
d = 19.2, 26.7, 28.2, 28.4, 33.9, 51.4, 52.7, 77.3, 121.0,
149.2, 167.1, 220.0.
(12) Chiral HPLC analyses of 13b and 14b were performed with
Daicel CHIRALCEL OD-H (n-hexane–i-PrOH = 96:4).
(13) Katoh, T.; Mizumoto, S.; Fudesaka, M.; Takeo, M.;
Kajimoto, T.; Node, M. Tetrahedron: Asymmetry 2006, in
press.
Synlett 2006, No. 14, 2176–2182 © Thieme Stuttgart · New York