Rhodotorula minuta-mediated bioreduction of 1,2-diketones

Article abstract of DOI:10.3109/10242420903515445

The reduction of cyclic and acyclic 1,2-diketones was investigated by employing whole cells of the yeast Rhodotorula minuta as biocatalyst. The reactions showed a variable degree of regio- and enantioselectivity depending on the nature of the substrate. In the case of cyclic diketones, the reduction afforded a mixture of diastereomeric diols only. The reduction of acyclic diketones allowed production of both the hydroxy ketone and the diol, in a two-step reaction. The first step was highly regio- and stereoselective, affording the hydroxy ketone of (S)-configuration with high enantiomeric excess. After longer reaction times the corresponding (S,S)-diols were obtained in high yield and diastereomeric excess.

Full text of DOI:10.3109/10242420903515445

Biocatalysis and Biotransformation, March–April 2010; 28(2): 137–143
ORIGINAL ARTICLE
Rhodotorula minuta-mediated bioreduction of 1,2-diketones
LEANDRO N. MONSALVE1, PATRICIA CERRUTTI2, MIGUEL A. GALVAGNO2,3, &
ALICIA BALDESSARI1
1Departamento de Química Orgánica y UMYMFOR, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos
Aires, Buenos Aires, Argentina, 2Departamento de Ingeniería Química, Facultad de Ingeniería, Universidad de Buenos
Aires, Buenos Aires, Argentina, and 3IIB–Intech–CONICET–UNSAM, Buenos Aires, Argentina
Abstract
The reduction of cyclic and acyclic 1,2-diketones was investigated by employing whole cells of the yeast Rhodotorula minuta
as biocatalyst. The reactions showed a variable degree of regio- and enantioselectivity depending on the nature of the
substrate. In the case of cyclic diketones, the reduction afforded a mixture of diastereomeric diols only. The reduction of
acyclic diketones allowed production of both the hydroxy ketone and the diol, in a two-step reaction. The first step was
highly regio- and stereoselective, affording the hydroxy ketone of (S)-configuration with high enantiomeric excess. After
longer reaction times the corresponding (S,S)-diols were obtained in high yield and diastereomeric excess.
Keywords: 1,2-Diketones, bioreduction, Rhodotorula minuta
Introduction
1998), Ti, V and Zn halides (Clerici & Porta 1985;
Regioselective and stereoselective reactions have
been frequently used in the synthesis of biologically
active compounds or natural product precursors
(Hashimoto & Maruoka 2007; Mohr et al. 2008; Seki
2008). Among them, considerable effort has been
made to obtain hydroxy ketones and diols from
prochiral dicarbonyl derivatives or olefins (Bode
et al. 2006; Biradar et al. 2008; Neisius & Plietker
2008). It is well known that enantiomerically pure
A-hydroxy ketones are useful building blocks in the
synthesis of various pharmaceuticals and fine chem-
icals, such as inhibitors of B-amyloid protein produc-
tion (Wallace et al. 2003), antidepressant drugs (Fang
et al. 2000) or antitumor agents (Anisimov 2006).
However, their preparation is not always efficient
and generally requires use of a toxic transition metal
catalyst such as Rh, Ru, etc. (Ikariya & Blacker
2007). An approach to this class of compounds
involves the reduction of 1,2-diketones (Nakamura
et al. 1996) but it is not easy to control the regiose-
lectivity. In order to circumvent these problems, sev-
eral methods have been developed. For example, the
use of an electrochemical approach (Boutoute et al.
Hayakawa et al. 2000) and activated alkyl phosphines
(Zhang & Shi 2006) allowed production of A-hydroxy
ketones in good yield but no data about the stereo-
selectivity of the reactions has been reported.
Reduction of 1,2-diketones may be conducted
using biocatalysts (Nakamura et al. 2003; García-
Urdiales et al. 2005). Enantiopure diols and hydroxy
ketones have been produced biocatalytically by
employing alcohol dehydrogenases from various
sources (Stampfer et al. 2003; Kosjek et al. 2004).
Whole cells rather than isolated enzymes are used
preferentially to avoid enzyme purification and cofac-
tor addition or the requirement for an associate sys-
tem for cofactor regeneration, since such reactions
often require stoichiometric amounts of nicotin-
amide cofactors (Moore et al. 2007).
The reduction of different 1,2-diaryl-ethane-
diones with whole cells from various microorganisms
such as Saccharomyces cerevisiae (Besse et al. 1993),
Rhizopus oryzae (Demir et al. 2004), and more
recently Aspergillus oryzae, Fusarium roseum (Demir
et al. 2008) and Pichia glucozyma (Hoyos et al. 2008)
has been studied. Moreover, whole cells of the yeast
Correspondence: A. Baldessari, Departamento de Química Orgánica, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Pabellón
2 – Piso 3 – Ciudad Universitaria, C1428EGA Buenos Aires, Argentina. Tel/Fax: +54-11-4576-3385. E-mail: alib@qo.fcen.uba.ar
ISSN 1024-2422 print/ISSN 1029-2446 online © 2010 Informa UK Ltd. (Informa Healthcare, Taylor & Francis AS)
DOI: 10.3109/10242420903515445

138
L. N. Monsalve et al.
Rhodotorula spp. have been used in biotransforma-
tions performed in aqueous media (Yang et al. 2006)
and macroemulsions (Cinelli et al. 2006). In our
laboratory we have recently reported the application
of Rhodotorula minuta whole cells in the regio- and
stereoselective reduction of dialkyl esters of 2-oxo-
glutaric acid (Rustoy et al. 2008).
Now we have found that R.minuta cells also carry
out the reduction of 1,2-diketones. In the present
work we report the ability of these cells to produce
chiral A-hydroxy ketones and diols depending on the
structure of dicarbonyl substrate. Scheme 1 shows
the 1,2-diketones used as substrates in the biotrans-
formation.
film thickness 0.2 μm (80°C). Retention times in chi-
ral separations (min): 1a, 7.92; 1b, 11.30 (R,R), 11.42
(S,S); 1c, 10.94 (meso); 6b, 7.64 (R), 7.38 (S); 6c, 9.90
(S,S), 9.82 (R,R), 9.40 (meso); 7b, 9.84 (R), 9.91 (S);
7c, 13.73 (R,R), 13.81 (S,S), 14.03 (erythro diol); 8b,
17.43 (S), 17.52 (R); 8c, 18.22 (S,S), 18.36 (R,R),
18.54 and 18.70 (erythro diol). The absolute configu-
ration of products 1b, 6b–8b and 6c–8c was deter-
mined by comparison with the sign of the specific
rotation reported in literature (Hummel et al. 1989;
Besse et al. 1993; Boutoute et al. 1998). 1H NMR and
13C NMR spectra were recorded at 200 MHz with a
Bruker AC 200 NMR spectrometer (Bruker Biospin,
Billerica, MA, USA). Chemical shifts are reported in
units relative to tetramethylsilane set at Dꢁ0 ppm, and
coupling constants are given in Hz. EI-MS were
obtained at 70 eV withTRIO-2VG Masslab Shimadzu
QP-5000 (Shimadzu America Inc., Columbia, MD,
USA) and Finnigan TSQ70 mass spectrometers
(Thermo Electron Co., Boston, MA, USA), in m/z
(%). Elemental analysis was carried out with a Perkin-
Elmer 240 apparatus. Optical rotation measurements
of products were performed with Perkin-Elmer 343
instrument (Perkin Elmer,Waltham, MA, USA). Sol-
vents are indicated throughout.
Materials and methods
Substrates and analysis
All solvents and reagents were of reagent grade and
used without purification. Diketones 1a and 4a–8a
were available commercially from Sigma Aldrich
(Argentina SA). Sabouraud broth was purchased from
Merck KGaA (Darmstadt, Germany). For column
chromatography, Merck silica gel 60 (70–230 mesh)
was used. Microbial reductions were carried out with
a Sontec incubator shaker (Scientifica, Buenos Aires,
Argentina) at 33°C and 200 rpm.The courses of reac-
tions were followed by TLC on Merck silica gel 60F-
254 aluminum sheets (0.2 mm thickness). GLC
analysis for determination of percentage of conversion
was obtained on a Finnigan Focus GC instrument
(Thermo Electron Co., Boston, MA, USA), the capil-
lary column being HP-ULTRA-2 (Hewlett-Packard,
Newtown, PA, USA), 25 mꢀ0.2 mm, film thickness
0.2 μm (6 min at 80°C, 5°C/min, 150°C). GLC anal-
yses for determination of enantiomeric excess were
performed on the same apparatus, the capillary col-
umn being CHIRALDEX G-TA (Sigma-Aldrich
Argentina, Buenos Aires, Argentina) 40 mꢀ0.32 mm,
Chemical reduction
Substrates 1a and 4a–8a (1 mmol) were dissolved in
methanol (10 mL). Sodium borohydride (74 mg,
2 mmol) was added to the solution and the reaction
was stirred for 30 min. The solvent was evaporated
off; 10 mL methanol was added and then evapo-
rated. The mixture of products was separated by
column chromatography and used as standards for
chromatographic identification.
Enol carboxylate synthesis
2-Acetoxy-2-cyclohexenone (2a): 1,2-cyclohexane-
dione (180 mg, 1.6 mmol) was dissolved in a 1:1
(v/v) acetic anhydride–pyridine mixture (3 mL).The
resulting solution was shaken overnight at 33ºC and
200 rpm and poured into cold water (10 ml). Hydro-
chloric acid (20% v/v ) was added dropwise and,
once acid, the solution was extracted with ethyl ace-
tate (2ꢀ15 mL).The combined organic phases were
washed with water (3ꢀ10 mL), then dried and evap-
orated. 2a was obtained as colorless crystals (226
O
O
O
O
OR
O
O
O
2a: R = COCH3
4a
5a
1a
3a: R = CO(CH2)4CH3
O
O
O
1
mg, 92% yield). H NMR (CDCl3), D (ppm): 2.0–
2.2 (m, 2H); 2.2 (s, 3H); 2.4–2.6 (m, 4H); 6.55 (t,
1H). 13C NMR (CDCl3), D (ppm): 20.0, 22.2, 24.4,
37.6, 136.1, 144.9, 168.4, 191.5. EI-MS, m/z (rela-
tive intensity): 154 [Mꢂ] (14); 95 (100). Calc. for
C8H10O3: C, 62.33%; H, 6.47%. Found: C, 61.01%;
H, 6.47%.
O
O
O
6a
8a
7a
Scheme 1. 1,2-Diketones employed as substrates for microbial
reduction.

Bioreduction of 1,2-diketones 139
O
O
OH
OH
OR
O
OH
OH
(S)
(S)
(R)
(S)
Rhodotorula minuta
(RCO)2O / Py
+
1a
1b
1c
2a: R = COCH3
3a: R = CO(CH2)4CH3
Rhodotorula minuta
2-Hexanoyloxy-2-cyclohexenone
(3a):
As
10 min), washed twice with sterile deionized water
and centrifuged again. The pellets obtained were
used for the biotransformation experiments described
below.
described for 2a but using 1:1 (v/v) caproic anhy-
dride–pyridine mixture (3 mL). 3a was obtained as
colorless oil (255 mg, 76% yield). 1H NMR (CDCl3),
D (ppm): 0.85 (t, 3H); 1.2–1.4 (m, 4H); 1.64
(m, 2H); 1.9–2.1 (m, 4H); 2.3–2.6 (m, 4H); 6.55 (t,
1H). 13C NMR (CDCl3), D (ppm): 13.9, 20.0, 22.7,
24.4, 25.2, 30.2, 33.7, 37.6, 136.0, 144.9, 171.4,
191.5. EI-MS, m/z (relative intensity): 210 [Mꢂ] (12);
181 (7), 153 (20), 95 (100). Calc. for C12H18O3: C,
68.54%; H, 8.63%. Found: C, 67.10%; H, 8.89%.
General procedure for redution by R. minuta
Substrate (1 mmol) and glucose (50 mg) were added
to a suspension of yeast (0.5 to 8 g wet weight) in
the appropriate solvent (10 mL) and the resulting
mixture was incubated at 33ºC and shaken at 200
rpm in 25-mL sterile Erlenmeyer flasks stoppered
and sealed.Water incubations were performed using
sterile water alone. The course of reactions was fol-
lowed by TLC and GC. Aliquots (1 mL) were cen-
trifuged at 10 000g and the supernatants were
extracted with ethyl acetate (3ꢀ1 mL). The organic
phases were combined, dried over anhydrous
Na2SO4, evaporated and analyzed by GLC.
Microorganism
R. minuta strain was provided by Dr N. Refojo from
Laboratorio de Micología of the Instituto de Micro-
biologia Dr. C. Malbran (Buenos Aires, Argentina).
The strain is available to the public from the same
institute under the culture number 062693.
Yeast cells previously grown in Sabouraud broth
plus 0.3% w/v yeast extract at 28ºC and 160 rpm
were inoculated in 8.33ꢀ volume Erlenmeyer flasks
containing the same medium to initial OD of 0.025
at 630 nm. Cultures thus prepared were incubated at
28ºC for 48 h in a rotary shaker at 160 rpm. Then,
cells were harvested by centrifugation (10 000g for
The conversions were determined by GLC by
comparing the retention time of the product obtained
with that of the diketone (1a–8a) and standard com-
pounds: hydroxy ketone (6b–8b) or diols (1b, 1c, 6c,
7c and 8c). After the indicated time, ethyl acetate was
added (10 mL) and the contents of the flask were
centrifuged. The supernatants were removed and,
Table I. Bioreduction of 1,2-cyclohexanedione 1a and 1,2-cyclohexanedione enol esters 2a and 3a by Rhodotorula minuta whole cells.
Products
1b
1c
% yielda
Entry
Substrate
Solvent
Time (h)
% yielda
% ee
1
2
3
4
5
6
7
8
1a
1a
1a
1a
1a
1a
1a
1a
2a
2a
3a
3a
water
glycerol
hexane
toluene
water–hexaneb
water–isooctaneb
water–tolueneb
water–ethyl acetateb
water
24
24
24
24
24
24
24
24
2
19
4
8
58
61
54
56
55
57
57
53
57
56
–
74
14
50
23
67
50
24
25
57
57
5
9
17
13
7
7
9
40
42
2
10
11
12
water
water
water
24
2
24
32
57
64
Reaction conditions are described in the Materials and methods section; biomass (g)/substrate (mmol) ratioꢁ4:1.
aIsolated yield.
Ratioꢁ1:1 (v/v).

140
L. N. Monsalve et al.
O
OH
OH
R
R
R. minuta
R
R. minuta
(S)
(S)
(S)
Me
Me
Me
O
O
OH
ꢀꢁ: R = Me
ꢂꢁ: R = Et
ꢃꢁ: R = Ph
ꢀꢄ: R = Me
ꢂꢄ: R = Et
ꢃꢄ: R = Ph
ꢀꢅ: R = Me
ꢂꢅ: R = Et
ꢃꢅ: R = Ph
fore 1b is (S,S)-1,2-cyclohexanediol and 1c is (S,R)-
1,2-cyclohexanediol (see scheme in Table I).
when applied, water phases were extracted with ethyl
acetate (3ꢀ10 mL).The organic phase was separated,
dried over anhydrous Na2SO4, filtered and concen-
trated. The products were purified by flash chroma-
tography (eluant: hexane–ethyl acetate, 2:1 to 1:1
v/v). All experiments were performed in duplicate.
The identity of isolated compounds was determined
by 1H NMR, 13C NMR and MS, and the percentage
enantiomeric excess (% ee) was determined by chiral
GLC. Yields of isolated compounds 1b, 1c and 6b,
6c, 7b, 7c and 8b, 8c obtained by reduction using R.
minuta cells are reported in Tables I and II.
Yeast cells were active in water and, to a lesser
extent, in organic or biphasic systems. As experi-
ments using water as solvent gave the best conver-
sions, we optimized the biomass/substrate ratio by
following reactions with diverse biomass loading at
different times (Figure 1).
The best results were achieved using a biomass
ratio of 4 g of fresh cells over 1 mmol of substrate.
Under these reaction conditions a conversion of 100%
was observed, yielding meso-1,2-cyclohexanediol
(1c) (74%) and (S,S)-1,2-cyclohexanediol (1b) (19%,
58% ee) (Table I, entry 1). According to previous
work on microbial reduction of 1,2-cyclohexanedione,
Results and discussion
A series of cyclic and acyclic 1,2-diketones were sub-
mitted to reduction by fresh cells from R. minuta as
the source of reductase activity.The results are shown
in Tables I and II.
HO OH
R2
R1
O
We began studying the behavior of cyclic
ketones and used 1,2-cyclohexanedione 1a as model
substrate. Table I (entries 1–8) shows the results
obtained in the yeast reduction of 1a in various solvent
systems, such as water, glycerol, hexane, toluene and
1:1 (v/v) biphasic mixtures of water–hexane, water–
toluene, water–isooctane and water–ethyl acetate.
In every case, 1,2-cyclohexanediol was obtained
as a mixture of cis and trans isomers. Most of the
trans isomer 1b had the configuration (S,S); there-
O
O
O
R2
R2
R2
- H2O
+ H2O
R1
R1
R1
OH
OH
OH
O
R1
Table II. Bioreduction of acyclic A-diketones 6a, 7a and 8a with
Rhodotorula minuta whole cells.
O
Products
HO
2-Hydroxy
ketone
R2
1,2-Diol
Entry Substrate Time (h) % yielda % ee % yielda % ee
1
2
3
4
5
6
7
6a
6a
7a
7a
8a
8a
8a
2
24
2
24
2
6b (39)
–
7b (53)
–
8b (82)
8b (5)
8b (5)
99
–
97
–
99
97
93
6c (58)
6c (91)
7c (44)
7c (88)
8c (15)
8c (82)
8c (81)
33
85
40
77
95
95
95
O
O
O
OH
24
48
Reaction conditions are described in the Materials and methods
section; biomass (g)/substrate (mmol) ratioꢁ4:1.
aIsolated yield.
Scheme 2. 1,2-Diketones tautomeric forms in aqueous medium

Bioreduction of 1,2-diketones 141
100
90
80
70
60
50
40
30
20
10
0
2 hours
4 hours
24 hours
24 hours
4 hours
0.5
1
2 hours
2
4
ꢊꢉꢃꢋꢌꢈꢈꢁꢍ ꢎ
8
Figure 1. Time/biomass/conversion plot for the reduction products of 1,2-cyclohexanedione 1a in water; reaction performed under
standard conditions.
the reaction was not chemoselective and the forma-
tion of the 1,2-hydroxy ketone intermediate was not
observed. The enzymatic pathway for 1,2-diketone
reduction has been investigated using Baker’s yeast
and it seems that the 1,2-hydroxy ketone is reduced
much faster than the diketone, therefore it cannot be
detected (Besse et al. 1993).
In aqueous medium 1,2-diketones may exist
under three forms in equilibrium, as shown in
Scheme 2. The enolic form is predominant in the
case of cyclic A-diones such as 1,2-cyclohexane-
dione (Segretario et al. 1986) and it has been
reported that the presence of nucleophiles in the
substrate can lead to deactivation of reductase activ-
ity of the enzyme via complexation of the essential
Zn2ꢂ ion in the active site (Fries et al. 1979). In
order to avoid the possible deactivation of the
reductase and to obtain 2-hydroxycyclohexanone,
we decided to try the reduction of an enol ester of
1,2-cyclohexanedione.
In order to evaluate the influence of the length
in the acid moiety of the ester group in the R. minuta
reduction, we prepared two enol esters: 1,2-cyclo-
hexanedione enol acetate 2a and 1,2-cyclohexane-
dione enol hexanoate 3a. Compounds 2a and 3a are
not commercially available, so we synthesized them
by treatment of the diketone 1a with the correspond-
ing acid anhydride and pyridine. Both products were
obtained in very good yield and were identified by
spectroscopic methods.
Subsequently, the reduction of 2a and 3a was per-
formed using whole cells of R. minuta. The results at
2 h and 24 h of reaction are depicted in Table I
(entries 9–12). Unfortunately we could not obtain the
desired hydroxycyclohexanone either with the enol
acetate 2a or enol hexanoate 3a.The microbial reduc-
tion again afforded a mixture of the diasteromeric
diols: meso-1,2-cyclohexanediol 1c and (S,S)-1,2-cy-
clohexanediol 1b in a ratio 1:1 from 2a and 2:1 from
3a, respectively. It is evident that the reaction did not
show any regioselectivity.The fact that 2a and 1a gave
the same results might suggest that the hydrolysis of
the enol ester occurred prior to reduction of the car-
bonyl group, as previously observed with microbial
reactions on cyclic ketone enol esters (Kume & Ohta
1992). Moreover, although the reaction with enol
hexanoate 3a afforded the same products, the reac-
tion was slower than with 1a, perhaps due to the steric
hindrance caused by the hexanoyl group.
In order to study the effect of substitution in the
microbial reduction we decided to test two other
cyclic 1,2-diketones:3-methyl-1,2-cyclohexanedione
4a and 3-methyl-1,2-cyclopentanedione 5a. Biore-
duction of these substrates is a challenging job
because the complete reduction of the dione system
to the diols would lead to the generation of up to
three new stereocenters (Scheme 3).
As with 1,2-cyclohexandione 1a, these cyclic
diketones remain predominantly in their enolic form.
We performed the reduction employing R. minuta

142
L. N. Monsalve et al.
OH
O
OH
*
Reduction
O
O
HO
*
*
C
C
H
C
H2
H2
2 n
n
n
n = 2,3
Scheme 3. Generation of asymmetric centers in the reduction of 4a and 5a.
cells under the same experimental conditions for the
bioreduction of 1,2-cyclohexanedione. In this case
the cells were not active and no reduction products
were obtained from the substituted diketones 4a and
5a. In general, yeast alcohol dehydrogenase has very
narrow substrate specificity and accepts only small
carbonyl compounds. As a consequence, it seems
reasonable that acyclic ketones bearing bulky groups
or substituted cyclic ketones are excluded as sub-
strates. Our results support the suggestion that the
catalytic pocket of yeast alcohol dehydrogenase is
not big enough to achieve the reduction of enol
esters or cyclic 1,2-diketones substituted in the posi-
tion 3 (Ramaswamy et al. 1994; Trivic´ & Leskovac
2000).
Finally, we tried R. minuta in the reduction of
acyclic 1,2-diketones: 2,3-butanedione 6a, 2,3-pen-
tanedione 7a and 3-phenyl-2,3-propanedione 8a.
The biotransformation was carried out following the
same procedure described for the reduction of cyclic
diketones. It can be observed in Table II that these
diketones were readily bioreduced. After 2 h of incu-
bation a mixture of the corresponding 2-hydroxy
ketone and diol was detected for the diketones 6a
(ratio 2:3) and 7a (ratio about 1:1) (Table II, entries
1 and 3). A higher proportion of the hydroxy ketone
was observed using 3-phenyl-2,3-propanedione 8a
as substrate where the ratio of hydroxy ketone to diol
increased to 5:1 (Table II, entry 5). In all cases, the
reduction was highly regio- and stereoselective and
the hydroxy ketone corresponding to the reduction
of the less hindered carbonyl group was obtained as
the only product.The microbial reduction of 6a with
R. minuta is particularly interesting compared with
the results obtained with other microorganisms.
Some of them show less regioselectivity (Boutoute
et al. 1998); in others it is not possible to stop the
reaction at the hydroxy ketone and the diol is pro-
duced (Edegger et al. 2006).
At longer reaction times the second reduction step
occurred, showing a moderate to high stereoselectivity,
since the (S)-enantiomer of each hydroxy ketone (6b,
7b and 8b) was reduced further to yield the corre-
sponding (S,S)-1,2-diol (6c, 7c and 8c, respectively)
(Table II entries 2, 4 and 6).
According to early reports on microbial reduction
of 7c, depending on the microbial source, the con-
figuration of 7c can be preferentially (S,S) as with
our results (Boutoute et al. 1998) or the diastere-
omer (S,R) as with S.cerevisiae and Rhodococcus ruber
(Edegger et al. 2006), where further reduction of the
remaining carbonyl group yields the corresponding
diol predominantly in the anti-configuration.
It is interesting to observe that the diastereomeric
excess for (S,S)-diols increased with reaction time,
suggesting the participation of multiple enzymatic
pathways with different rates in the reduction of the
diketones.
Conclusions
We have described the bioreduction of various dike-
tones as a convenient methodology to obtain hydroxy
ketones and diols. The reactions showed a variable
degree of regio- and enantioselectivity depending on
the substrate. In the case of cyclic diketones, the reduc-
tion afforded a mixture of diastereomeric diols only,
and the hydroxy ketone was not obtained as an inter-
mediate from the reduction of only one carbonyl group
in the diketone. Similar results were obtained using
the enol esters of 1,2-cyclohexanedione as substrates.
The reduction of acyclic diketones allowed both
hydroxy ketone and diol to be obtained, in a two-step
reaction. The first step was highly regio- and stereose-
lective, affording the expected hydroxy ketone of (S)-
configuration with high enantiomeric excess. After
longer reaction times the corresponding (S,S)-diols
were obtained in high yield and diastereomeric excess.
The enantiomeric excess was very good in the
three products (6b, 7b and 8b) with values between
97 and 99%. In the case of the bioreduction of 8a it
was observed that longer reaction times did not
change the stereoselective behavior of the biocatalyst
(Table II, entries 6 and 7). The configuration of the
new chiral center in the hydroxy ketones 6b, 7b and
8b is (S), following Prelog’s rule.
Acknowledgements
We thank UBA (X089 (2004-2007) and X010
(2008-2010), ANPCyT (PICT 2005 06-32735) for
partial financial support. A.B. and M.A.G. are
Research Members of CONICET. The authors

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Declaration of interest: The authors report no
conflicts of interest. The authors alone are respon-
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January 2010.