One-pot synthesis of (R)-1-(1-naphthyl)ethanol by stereoinversion using Candida parapsilosis

Article abstract of DOI:10.1016/j.tetlet.2013.04.051

(R)-1-(1-Naphthyl)ethanol is an essential chiral substrate for the synthesis of nonactin and dihydro-[1H]-quinoline-2-one derivatives. Stereoinversion of (S)-1-(1-naphthyl)ethanol to (R)-1-(1-naphthyl)ethanol by whole cell biocatalysis, using Candida parapsilosis, is reported here. Candida parapsilosis possesses a requisite redox system for the stereoinversion of secondary alcohol. The reaction conditions (temperature, time, pH, organic solvent, etc.) significantly influenced the stereoinversion process. Optimum conditions were found to be the reaction temperature of 30 C, a cellmass concentration of 200 mg/mL, pH 7 (phosphate buffer, 50 mM), a shaking speed of 200 rpm, and a 12 h reaction time. Under these optimum conditions, (R)-1-(1-naphthyl)ethanol was obtained in 100% ee_R and 88% yield.

Full text of DOI:10.1016/j.tetlet.2013.04.051

Tetrahedron Letters 54 (2013) 3274–3277
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Tetrahedron Letters
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One-pot synthesis of (R)-1-(1-naphthyl)ethanol by stereoinversion using
Candida parapsilosis
⇑
Suyog Madhav Amrutkar, Linga Banoth, Uttam Chand Banerjee
Biocatalysis Laboratory, Department of Pharmaceutical Technology, National Institute of Pharmaceutical Education and Research, Sector-67, S.A.S. Nagar 160062, Punjab, India
a r t i c l e i n f o
a b s t r a c t
Article history:
(R)-1-(1-Naphthyl)ethanol is an essential chiral substrate for the synthesis of nonactin and dihydro-[1H]-
quinoline-2-one derivatives. Stereoinversion of (S)-1-(1-naphthyl)ethanol to (R)-1-(1-naphthyl)ethanol
by whole cell biocatalysis, using Candida parapsilosis, is reported here. Candida parapsilosis possesses a
requisite redox system for the stereoinversion of secondary alcohol. The reaction conditions (tempera-
ture, time, pH, organic solvent, etc.) significantly influenced the stereoinversion process. Optimum con-
ditions were found to be the reaction temperature of 30 °C, a cellmass concentration of 200 mg/mL, pH 7
(phosphate buffer, 50 mM), a shaking speed of 200 rpm, and a 12 h reaction time. Under these optimum
conditions, (R)-1-(1-naphthyl)ethanol was obtained in 100% eeR and 88% yield.
Received 25 February 2013
Revised 10 April 2013
Accepted 12 April 2013
Available online 22 April 2013
Keywords:
Stereoinversion
Candida parapsilosis
(R)-1-(1-Naphthyl)ethanol
Biocatalysis
Ó 2013 Elsevier Ltd. All rights reserved.
Dihydro-[1H]-quinoline-2-one derivatives are retinoid X recep-
tor (RXR) agonists having a role in the treatment of dyslipidemia,
hypercholesteremia, and diabetes.1 (R)-1-(1-Naphthyl)ethanol is
a key chiral substrate used in the synthesis of dihydro-[1H]-quin-
oline-2-one derivatives.1 It is also used as a precursor for the syn-
thesis of nonactin used as antibiotic.2 Biocatalysis provides the
enantiopure secondary alcohols using various methods such as ki-
netic resolution by lipases,3 stereoselective oxidases,4 and
reductases.4a,5–9 The synthesis of enantiopure (S)-1-(1-naph-
thyl)ethanol has been reported by the kinetic resolution10 and dy-
namic kinetic resolution11 of racemic 1-(1-naphthyl)ethanol using
lipase.3a,b Enantiopure (S)-1-(1-naphthyl)ethanol has also been
produced by the asymmetric reduction of 1-acetonaphthone using
Baker’s yeast, Rhizopus arrhizus,9 Merulius tremellosus ono991,12
Daucus carota,13 Geotrichum candidum,14 and Candida vishwaa-
thii.5,15 Few racemic alcohols are cheaper or more readily available
than their prochiral ketones.16 For such cases the reduction of pro-
chiral ketones may not be suitable to obtain enantiopure secondary
alcohols.17 Stereoinversion of racemic alcohols remains the only
alternative to obtain 100% theoretical yield,18 as kinetic resolution
has a limitation of 50% yield.17,19 Stereoinversion and dynamic ki-
netic resolution are used for deracemization.18 Stereoinversion re-
quires two redox systems of opposite stereo-preferences.20 Any
one of the enantiomers from the racemic mixture undergoes ster-
eoselective oxidation into prochiral ketone while other enantiomer
remains unreacted. The prochiral ketone is then stereoselectively
reduced to another enantiomer. The theoretical yield of the desired
enantiomer can be attained to 100% by stereoinversion.18,21 It can
be carried out by isolated enzymes or by the whole cells of micro-
organisms.22 Biocatalysis using whole cells circumvents the isola-
tion and purification of relevant enzymes, and eliminates the
addition of cofactors.22 Stereoinversion using a few microorgan-
isms like Nocardia sp.,18 Geotrichum candidum23 has been reported
in the literature.4,24 Voluminous research is going on with Candida
parapsilosis as a putative organism for stereoinversion.25,26 Enan-
tiopure secondary alcohols,19 1,2-diols,20
a
-hydroxy esters,27 aro-
matic b-hydroxy esters,28 allylic alcohols,29 and propargylic
esters30 were obtained by stereoinversion. Here we report the opti-
mization conditions for the one-pot synthesis of (R)-1-(1-naph-
thyl)ethanol by stereoinversion using Candida parapsilosis
(Scheme 1).
Three different strains of Candida parapsilosis (Candida parapsi-
losis MTCC 1965, Candida parapsilosis MTCC 4448, and Candida par-
apsilosis MTCC 2511) were screened for the experiments.31,32
Stereoinversion of (S)-1-(1-naphthyl)ethanol to (R)-1-(1-naph-
thyl)ethanol was observed only with Candida parapsilosis MTCC
1965. HPLC analysis of the reaction mixture at different time inter-
vals showed the decline in the concentration of (S)-1-(1-naph-
thyl)ethanol with the concomitant increase in the concentration
of (R)-1-(1-naphthyl)ethanol. Intermediate occurrence of 1-aceto-
naphthone confirmed the mechanism is stereoinversion.
In stereoinversion, (S)-1-(1-naphthyl)ethanol is stereoselective-
ly oxidized to prochiral 1-acetonaphthone, and the synthesized 1-
acetonaphthone is then stereoselectively reduced to (R)-1-(1-
naphthyl)ethanol. The maximum percentage of enantiomeric ex-
cess and yield would be attained only when both the stereoselec-
tive oxidation, and the reduction operate efficiently in tandem.
⇑
Corresponding author. Tel.: +91 172 2214682/85x2142; fax: +91 172 2214692.
E-mail address: ucbanerjee@niper.ac.in (U.C. Banerjee).
0040-4039/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tetlet.2013.04.051

S. M. Amrutkar et al. / Tetrahedron Letters 54 (2013) 3274–3277
3275
H3C
OH
H3C
OH
H3C
OH
(R)-1-(1-naphthyl)ethanol
S-specific alcohol
R-specific carbonyl
dehydrogenase
reductase
H3C
O
(RS)-1-(1-naphthyl)ethanol
(R)-1-(1-naphthyl)ethanol
1-Acetonaphthone
Scheme 1. Stereoinversion of (S)-1-(1-naphthyl)ethanol by the whole cells of Candida parapsilosis.
Different reaction conditions were studied to attain the optimum
stereoinversion. For optimization studies, one condition was chan-
ged at a time, while others were kept constant. Optimum condition
in one step was used for the subsequent studies.
remained the same, while the percentage yield of (R)-1-(1-naph-
thyl)ethanol started decreasing. It may be due to a drastic decline
in the stereoselective reductase activity of C. parapsilosis at alkaline
pH. At pH 7, the maximum enantiomeric excess (100% eeR) and
yield (88%) of (R)-1-(1-naphthyl)ethanol were observed.
Temperature affects the rate of reaction, the stability of the bio-
catalyst, the enantioselectivity of the catalyst,15 and the solubility
of the substrate and its products.8 In stereoinversion, two enzyme
systems are being used in tandem. Temperature may hamper the
activity of either one or both of the enzymes. The enantiomeric ex-
cess values (% eeR) did not change with the increasing of tempera-
ture up to 35 °C, thereafter, the values decreased drastically (Table
1). Maximum percentage yield of (R)-1-(1-naphthyl)ethanol was
87% at 30 °C, and decreased thereafter. Hence, for all the subse-
quent reactions, 30 °C was used as the optimum reaction
temperature.
Reaction progress was monitored by analyzing the reaction
mixture at different time intervals.21,30 Concentration of (R)-1-(1-
naphthyl)ethanol increased with the concurrent decrease of (S)-
1-(1-naphthyl)ethanol concentration in the reaction mixture. For-
mation of intermediate prochiral ketone with the advent of stere-
oinversion was observed (Fig. 1). At 12 h, there was a maximum
percentage eeR, and a maximum percentage yield of (R)-1-(1-naph-
thyl)ethanol (Table 2). All the subsequent reactions were run for
12 h.pH alters the ionic state of the enzyme protein molecule,
therefore pH plays an important role in its reactivity.8,33 For stere-
oinversion, the effect of pH on the activity of either oxidase or
reductase, or both would be important. The oxidoreductase system
of C. parapsilosis showed a change in the conversion with respect to
pH. To determine the optimum pH for the stereoinversion reaction,
the reaction was performed at different pHs (50 mM) using citrate
buffer for a pH range 3–6, phosphate buffer for a pH range 7–8 and
Tris–HCl for a pH range 9–10. It is evident from Figure 2 that with
the increasing reaction pH, both the enantiomeric excess and the
yield increased. Maximum percentage eeR and percentage yield
were obtained at pH 7. From pH 7 onwards, the percentage eeR
To increase the substrate solubility both polar and non polar or-
ganic solvents were selected. Water miscible organic solvents were
thought to aid in the solubility by the phenomenon of co-solvency,
however water immiscible organic solvents aid by forming a bi-
phasic reaction mixture. Different organic solvents of varying LogP
values were selected to study the effect of organic solvents on bio-
catalytic stereoinversion.7,15 It was observed that in most of the
cases, both the stereoselective oxidation and the reduction were
severely affected. Among these, percentage ee was better with
1,4-dioxane, hexane, and dimethyl sulphoxide. The reactions were
carried out with a 2% (v/v) organic solvent. The maximum stereo-
inversion >99% (eeR) was obtained in hexane with a 55.78 percent-
age yield of (R)-1-(1-naphthyl)ethanol (Table 3). Whole cell
biocatalysis in organic solvent has a limitation due to the toxic ef-
fect of the solvent on enzyme activity. Kansal et al. studied the ef-
fect of organic solvent on the activity of ketone reductase from
Candida viswanathii and found that there is no direct correlation
between solvent polarity (LogP) and enzyme activity.15 Similar re-
sults were obtained while studying stereoinversion of (S)-1-(1-
naphthyl)ethanol to (R)-1-(1-naphthyl)ethanol by C. parapsilosis.
The higher values of enantiomeric excess with hexane, DMSO,
and dioxane might be due the absorption of these organic solvents
inside the membrane leading to a change in membrane fluidity and
ease in substrate uptake resulting in activity retention, while the
other solvents might have deactivated reductase enzyme. Reten-
tion of enzyme activity in DMSO and hexane was also reported
by Zhu et al. during the asymmetric reduction of aryl ketones by
Pyrococcus furiosus.7 The results of stereoinversion in organic sol-
vents were found to be inferior to those in an aqueous system. Sig-
nificant conversion to ketone compared to eeR in the presence of
organic solvents was observed. This indicates that organic solvents
have a detrimental effect on the activity of reductase.
Table 1
In conclusion, Candida parapsilosis MTCC 1965 contains oxidore-
ductase system for stereoinversion. Reaction conditions were opti-
mized for the stereoinversion of (S)-1-(1-naphthyl)ethanol to (R)-
1-(1-naphthyl)ethanol. In the present study, about 100 percentage
eeR of (R)-1-(1-naphthyl)ethanol with 88 percentage yield was
achieved at the optimum reaction condition. The yield may be in-
creased by the further manipulation of reaction conditions. Similar
oxidoreductase activity was not detected in other two organisms of
the same species. The oxidoreductase system seems to be very
Effect of temperature on the stereoinversion of (S)-1-(1-naphthyl)ethanol to
(R)-1-(1-naphthyl)ethanol by the whole cells of Candida parapsilosis
Temperature (°C)
% eeR
% Yield
25
30
35
40
45
100
100
100
22
67
87
55
49
49
9

3276
S. M. Amrutkar et al. / Tetrahedron Letters 54 (2013) 3274–3277
Figure 1. HPLC chromatograms for stereoinversion of (S)-1-(1-naphthyl)ethanol to (R)-1-(1-naphthyl)ethanol by the whole cells of Candida parapsilosis. (A) 0 h, (B) 6 h, (C)
9 h, (d) 12 h.
Table 3
Table 2
Effect of organic solvent on the stereoinversion of (S)-1-(1-naphthyl)ethanol
to (R)-1-(1-naphthyl)ethanol by the whole cells of Candida parapsilosis
Course of stereoinversion of (S)-1-(1-naphthyl)ethanol to (R)-1-
(1-naphthyl)ethanol by the whole cells of Candida parapsilosis
Solvent
% eeR
% Yield
Time (h)
% eeR
% Yield
Dioxane
Ethanol
Hexane
2-Propanol
Pyridine
100
8
100
20
1
52
49
56
48
26
48
50
0
3
6
9
12
0.14
1
63
89
100
50
51
66
83
88
Toluene
Dimethyl sulphoxide
12
100
specific. This may be a very good technique for obtaining 100%
pure alcohol from the racemic mixture.
Acknowledgments
We are grateful to the financial support by the Department of
Biotechnology and Council of Scientific and Industrial Research,
Govt. of India.
Supplementary data
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.tetlet.2013.
04.051.
References and notes
Figure 2. Effect of pH on the stereoinversion of (S)-1-(1-naphthyl)ethanol to (R)-1-
(1-naphthyl)ethanol by the whole cells of Candida parapsilosis.
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