Resolution of methylarylmethanols via oxidation with Nocardia corallina

Article abstract of DOI:10.1016/S0957-4166(01)00307-X

Ten different racemates of methylarylmethanols were subjected to whole cells of Nocardia corallina B-276 to give, via enantioselective oxidations, the corresponding ketone and the enantiomerically enriched secondary alcohol in moderate yields and excellent e.e.s. The configuration of the resulting alcohol is (R). This procedure permits a very good separation of the racemates of meta- and para-monosubstituted methylarylmethanols.

Full text of DOI:10.1016/S0957-4166(01)00307-X

TETRAHEDRON:
ASYMMETRY
Pergamon
Tetrahedron: Asymmetry 12 (2001) 1709–1712
Resolution of methylarylmethanols via oxidation with Nocardia
corallina
Herminia I. P e´ rez,* H e´ ctor Luna, Norberto Manjarrez and Aida Sol ´ı s
Universidad Aut o´ noma Metropolitana, Unidad Xochimilco, Depto. Sistemas Biol o´ gicos, A.P. 23/181 Mexico, DF Mexico
Received 30 April 2001; accepted 21 June 2001
Abstract—Ten different racemates of methylarylmethanols were subjected to whole cells of Nocardia corallina B-276 to give, via
enantioselective oxidations, the corresponding ketone and the enantiomerically enriched secondary alcohol in moderate yields and
excellent e.e.s. The configuration of the resulting alcohol is (R). This procedure permits a very good separation of the racemates
of meta- and para-monosubstituted methylarylmethanols. © 2001 Published by Elsevier Science Ltd.
1
. Introduction
and limitations of this methodology. Racemic methyl-
arylmethanols have been resolved in variable yields
through different approaches including dynamic kinetic
resolution with enzymes coupled with ruthenium-
Biotransformations of alcohols to ketones by isolated
enzymes and whole cell systems in asymmetric synthesis
are well established. However, there are fewer reports
of enantioselective enzymatic oxidation of alcohols1
than the enantioselective reduction of ketones.
Corynebacterium equi, Rhodococcus erythropilis, Bak-
er’s yeast, Bacillus stearothermophilus, and Yarrowia
11
catalysed racemization, asymmetric acylation with
12
twisted amides possessing axial chirality, by acylation
13
with planar-chiral derivative of DMAP, asymmetric
2
3
14
oxygenation catalysed by chiral ruthenium porphyrin,
4
5
by microbial deracemization with Geotrichum can-
6
lipolytica are microorganisms used in the enantioselec-
7
didum, or combined microbial oxidation/reduction
tive oxidation of sec-alcohols, producing variable yields
of the corresponding ketone and an enantiomerically
enriched alcohol. Microbial resolutions of racemic sec-
ondary carbinols provide approaches to enantiomeri-
cally pure chiral alcohols, which are interesting chiral
building blocks for the synthesis of natural products,
with Bacillus stearothermophilus and Yarrowia
5
lipolytica.
In asymmetric synthesis use of a microbial process with
whole cells would avoid the use of a chiral ligand,
which has to be readily available or easy recycled to be
6,7
pharmaceutical, and agricultural chemicals.
15
successfully exploited. Herein, we report an alterna-
tive approach to resolve racemic methylarylmethanols
via oxidation with Nocardia corallina B-276.
Recently, we reported that Nocardia corallina B-276
oxidises aldehydes, allylic and benzylic alcohols to car-
boxylic acids or ketones, respectively.
8,9
Then, we
extended our studies to the enantioselective oxidation
10
2. Results and discussion
of racemic benzhydrols as a useful procedure for
preparation of meta- and para-monosubstituted opti-
cally active diaryl carbinols in good yields and high
e.e.s.
When the racemate of methylphenylmethanol, 1, was
subjected to Nocardia corallina B-276 for 25 hours, we
observed an enantioselective oxidation of the (S)-alco-
hol (Scheme 1; Table 1, entry 1), the unreacted alcohol
obtained showed >99% e.e.
These applications of this microorganism in organic
chemistry encouraged us to extend the study to methyl-
arylmethanols and explore the effect of the structure in
microbial oxidation reactions, to determine the scope
A remarkable steric effect was observed for the ortho-
substituted methylarylmethanols (entries 2, 3, 12 and
1
3); even with extended reaction times, only conver-
*
0
Corresponding author. E-mail: hperez@cueyatl.uam.mx
sions of 2–7% to the ketones was observed and low e.e.s
957-4166/01/$ - see front matter © 2001 Published by Elsevier Science Ltd.
PII: S0957-4166(01)00307-X

1
710
H. I. P e´ rez et al. / Tetrahedron: Asymmetry 12 (2001) 1709–1712
Scheme 1.
Table 1. Enantioselective oxidation of methlarylmethanols
Entry
Alcohol
G
Reaction time (h)
Ketone/unreacted alcohol
E.e. % (conf.)d
a
a
16
16
16
16
16
16
16
17
e
1
2
3
4
5
6
7
8
9
1
2
2
3
3
4
4
5
6
7
8
9
9
H
25
25
120
4
25
4
25
25
25
24
25
25
48
25
72/28
2/98
5/95
\99 (R)
a
a
2-Br
2-Br
3-Br
3-Br
3-Cl
3-Cl
4-Br
4-i-C H
4-OCH3
3-OC H
4
5
(R)
(R)
a
a
b
b
40/60
38 (R)
a
a
63/37
\99 (R)
a
a
43/57
22 (R)
a
b
67/33
\99 (R)
b
b
47/53
72 (R)
52/48b
91 (R)
b
3
7
b
b
17
10
11
12
13
14
50/50
\99 (R)
c
c
64/36
\99
6
5
a
a
e
e
e
2,3-diOCH3
2,3-diOCH3
3,4-diOCH3
4/96
7/93
3
4
(R)
(R)
a
a
b
10
61/39b
\99 (R)
a
b
c
Ratio and enantiomeric excess determined by GC on Chiraldex B-PH column.
Ratio and enantiomeric excess determined by GC on Chiraldex G-TA column.
1
Ratio and enantiomeric excess determined by H NMR, the e.e. by the a-CH
6
signal in the spectrum of the alcohols using (+)-[Eu(hfc) ] as a chiral
3
shift reagent.
d
e
Assignment of absolute configuration of the unreacted alcohol was carried out by comparison of the sign of the specific rotation with literature
data.
Assignment of absolute configuration of the unreacted alcohol was based on the assumption that R-enantiomers of sec-alcohols of this kind are
eluted before S-enantiomers on Chiraldex B-PH and G-TA columns.
were measured. In contrast, the meta- and para-substi-
tuted compounds showed the largest enantioselectivity
(c) The transformation seems to be independent of
electronic effects of the aromatic ring substituent.
(
entries 5, 7, 9, 10, 11 and 14), with e.e. values of >99%
in some cases.
With respect to the configuration of the enriched alco-
hol obtained by this procedure, comparison of the sign
Interestingly, the bulkier meta-phenoxy group (8, entry
16,17
of the specific rotation with literature data
allowed
1
1) gave the enantiomerically enriched alcohol after 25
assignment of the (R)-configuration to the alcohols 1,
hours in >99% e.e., similar to entries 5 and 7 with
halogen substituents (Br and Cl). It seems that the
meta-substituent did not show any electronic effect in
this biotransformation. For the para-substituted sub-
strates 5, 6, 7 (entries 8, 9 and 10), we obtained high
yields and excellent selectivity, but slightly lower enan-
tioselectivity than in our previous study with para-sub-
2
, 3, 4, 5 and 7. The assignment of (R)-configuration to
the alcohols 6, 9 and 10 was based on the assumption
that the (R)-enantiomer elutes before the (S)-enan-
tiomer from Chiraldex B-PH and G-TA columns.
18
Brunner used a similar argument using a Chirasil-L-
19
Val column with the urethane derivatives of sec-alco-
hols. These results are consistent with our previous
observations for the enantioselective oxidation with
1
0
stituted benzhydrols. These results demonstrate the
difficulty in predicting the steric requirements of the
enzymes involved in this biotransformation. However,
some generalities apply, i.e.:
10
Nocardia corallina B-276.
(
a) sec-alcohols, with meta- and para-substituted pat-
terns are transformed to the corresponding ketones
3. Conclusion
by Nocardia corallina B-276.
(b) ortho-substituted sec-alcohols are not trans-
We have extended this microbial resolution methodol-
formed.
ogy using Nocardia corallina to afford methylaryl-

H. I. P e´ rez et al. / Tetrahedron: Asymmetry 12 (2001) 1709–1712
1711
methanols in moderate chemical yields, which are
4.3. Determination of the enantiomeric excess for the
methylarylmethanols
unoptimized with excellent e.e.s. However, the ortho-
derivatives were almost inert to these conditions, per-
haps due to steric hindrance. This behaviour is similar
to the microbial deracemization of similar alcohols with
(a) By GC. All e.e.s were determined by comparing the
GC data of the chiral products with those of the
corresponding racemic alcohols on the indicated Chi-
raldex column.
1
4
Geotrichum candidum. Nocardia corallina B-276 oxi-
dises allylic and benzylic alcohols, in contrast to
Yarrowia lipolytica, which is not able to oxidise
6
methylphenylmethanol.
Methylphenylmethanol, 1: B-PH column, 95°C, N , 1.0
2
mL/min. Racemic alcohols, t =33.52 min, t =34.21
R
S
min. Product from the enantioselective oxidation gave
tR=33.56 min, with >99% e.e.
4
. Experimental
.1. Materials and methods
Organism and growth. Nocardia corallina B-276
4
Methyl-(2-bromophenyl)methanol, 2: B-PH column,
1
30°C, N , 0.6 mL/min. Racemic alcohols, t =9.85
2
R
min, t =10.76 min. Product enrichment from the enan-
S
(
(
ATCC 31338) was grown at 28–30°C on agar plates
3 g beef extract/L; 5 g peptone/L; 15 g agar/L).
tioselective oxidation gave t =9.92 min and t =10.89
min with 4% e.e.
R
S
Incubation of liquid cultures was carried out in an
orbital shaker; broth compositions. Solution A: 0.05 g
FeSO ·7H O/L; 1.74 g K HPO /L; 2 g (NH ) SO /L;
Methyl-(3-bromophenyl)methanol, 3: B-PH column,
130°C, N , 0.8 mL/min. Racemic alcohols, t =55.65
4
2
2
4
4 2
4
2
R
1
g yeast extract/L. Solution B: 1.5 g MgSO /L. Solu-
min, t =56.30 min. Product from the enantioselective
4
S
tion C: 2 g glucose/L; each solution was sterilized
separately and later combined and the pH adjusted to
oxidation gave t =54.72 min, with >99% e.e.
R
8
.0 (±0.5). All substrates were prepared by conventional
Methyl-(3-chlorophenyl)methanol, 4: B-PH column,
120°C, N , 1.0 mL/min. Racemic alcohols, t =40.62
methods or purchased from Aldrich, Sigma or Janssen.
The methylarylmethanols and ketones were identified
by their infrared spectra (Perkin–Elmer Paragon 1000)
as liquid films or KBr discs, hydrogen nuclear magnetic
2
R
min, t =41.18 min. Product from the enantioselective
S
oxidation gave t =39.21 min, with >99% e.e.
R
1
resonance ( H NMR) (Br u¨ cker 500 MHz) and by TLC
Methyl-(4-bromophenyl)methanol, 5: G-TA column,
100°C, N , 0.6 mL/min. Racemic alcohols, t =26.22
on silica gel 60 GF254 Merck, and comparative analysis
with authentic samples. The specific rotations were
determined in a Perkin–Elmer 341 polarimeter. The GC
analysis was performed on a Hewlett Packard 6890 gas
chromatograph equipped with a flame ionization detec-
tor and a Chiraldex column B-PH (30 m) or G-TA (30
m).
2
R
min, t =28.93 min. Product enrichment from the enan-
S
tioselective oxidation gave t =26.53 min and t =30.59
R
S
min with 72% e.e.
Methyl-(4-isopropylphenyl)methanol, 6: G-TA column,
90°C, N , 0.5 mL/min. Racemic alcohols, t =21.44
2
R
min, t =22.28 min. Product enrichment from the enan-
S
4
4
.2. General procedure for biotransformations
tioselective oxidation gave t =21.11 min and t =22.79
R
S
min with 91% e.e.
.2.1. Preculture I. A 125 mL Erlenmeyer flask contain-
ing sterile culture medium (50 mL) was inoculated from
an agar plate (3 days old) and incubated at 28–30°C on
an orbital shaker (200 rpm) for 20–24 h.
Methyl-(4-methoxyphenyl)methanol, 7: G-TA column,
90°C, N , 0.6 mL/min. Racemic alcohols, t =36.60
2
R
min, t =37.44 min. Product from the enantioselective
S
oxidation gave t =34.35 min, with >99% e.e.
R
4.2.2. Preculture II. The content of Preculture I flask
was aseptically poured into a 250 mL Erlenmeyer flask
containing 100 mL of fresh sterile culture medium. The
flask was incubated at 28–30°C on an orbital shaker
Methyl-(2,3-dimethoxyphenyl)methanol,
9:
B-PH
column, 110°C, N , 0.6 mL/min. Racemic alcohols,
2
t =41.71 min, t =42.54 min. Product enrichment from
R
S
(
200 rpm) for 24 h.
the enantioselective oxidation gave t =42.46 min and
tS=43.18 min with 3% e.e.
R
4
.2.3. Biotransformation. Under aseptic conditions the
substrate (0.6 mmol) was added to the flask containing
Preculture II using 1 mL of N,N-dimethylformamide,
followed by the addition of n-octane (10 mL). The
mixture (161 mL final volume) was incubated at 28–
Methyl-(3,4-dimethoxyphenyl)methanol,
10:
G-TA
column, 110°C, N , 0.5 mL/min. Racemic alcohols,
2
t =47.71 min, t =49.27 min. Product from the enan-
R
S
tioselective oxidation gave t =48.07 min, with >99%
R
30°C on an orbital shaker (200 rpm). The progress of
e.e.
the biotransformation was monitored by TLC and
stopped at the time indicated in Table 1, then it was
saturated with NaCl and filtered through Celite; the
ketones and methylarylmethanols were extracted with
ethyl acetate (4×25 mL). The products were compared
1
(b) By H NMR. It was determined by comparing the
1
H NMR data of the chiral product with those of the
corresponding racemic alcohols in CDCl , using the
3
a-CH
6 signal in the spectra and (+)-[Eu(hfc) ] as a chiral
3
1
with authentic samples by H NMR, IR and TLC.
shift reagent.

1
712
H. I. P e´ rez et al. / Tetrahedron: Asymmetry 12 (2001) 1709–1712
Methyl-(3-phenoxyphenyl)methanol, 8: a-CH
.83 ppm, the signal shifted to 6.20 and 6.14 ppm. The
product had >99% e.e.
6
signal at
6. Fantin, G.; Fogagnolo, M.; Medici, A.; Pedrini, P.;
Fontana, S. Tetrahedron: Asymmetry 2000, 11, 2367–
2373.
4
7. Nakamura, K.; Inoue, Y.; Matsuda, T.; Ohno, A. Tetra-
hedron Lett. 1995, 36, 6263–6266.
Acknowledgements
8. P e´ rez, H. I.; Luna, H.; Manjarrez, N.; Sol ´ı s, A.; Nu n˜ ez,
M. A. Biotechnol. Lett. 1999, 21, 855–859.
9
. P e´ rez, H. I.; Luna, H.; Maldonado, L. A.; Sandoval, H.;
Manjarrez, N.; Sol ´ı s, A.; S a´ nchez, R. Biotechnol. Lett.
1998, 20, 77–79.
We thank the financial support of Consejo Nacional de
Ciencia y Tecnolog ´ı a (CONACyT), M e´ xico, Grant
Num. 28543N. We also thank Ms Atilano Gutierrez for
10. P e´ rez, H. I.; Luna, H.; Manjarrez, N.; Sol ´ı s, A.; Nu n˜ ez,
M. A. Tetrahedron: Asymmetry 2000, 11, 4263–4268.
11. Koh, J. H.; Jung, H. M.; Kim, M. J.; Park, J. Tetra-
hedron Lett. 1999, 40, 6281–6284.
1
the
H NMR spectra and chiral shift reagent
experiments.
12. Yamada, S.; Katsumata, H. J. Org. Chem. 1999, 64,
9365–9373.
References
. Davies, H. G.; Green, R. H.; Kelly, D. R.; Roberts, S. M.
13. Ruble, J. C.; Tweddell, J.; Fu, G. C. J. Org. Chem. 1998,
63, 2794–2795.
1
Biotransformation in Preparative Organic Chemistry; Aca-
demic Press: London, 1989; pp. 157–219.
. Ohta, H.; Kato, Y.; Tsuchihashi, G. I. J. Org. Chem.
14. Gross, Z.; Ini, S. Org. Lett. 1999, 1, 2077–2080.
15. Bae, S. J.; Kim, S. W.; Hyeon, T.; Kim, B. M. Chem.
Commun. 2000, 31–32.
2
3
4
5
1
987, 52, 2735–2739.
16. Nakamura, K.; Matsuda, T. J. Org. Chem. 1998, 63,
8957–8964.
17. Huang, W. S.; Hu, Q. S.; Pu, L. J. Org. Chem. 1999, 64,
7940–7956.
18. Brunner, H.; K u¨ rzinger, A. J. J. Organomet. Chem. 1988,
346, 413–424.
19. Frank, H.; Nicholson, G. J.; Bayer, E. J. Chromatogr.
1978, 146, 197–206.
. Shimizu, S.; Hattori, S.; Hata, H.; Yamada, H. Appl.
Environ. Microbiol. 1987, 53, 519–522.
. Fantin, G.; Fogagnolo, M.; Medici, A.; Pedrini, P.; Poli,
S.; Sinigaglia, M. Tetrahedron Lett. 1993, 34, 883–884.
. Fantin, G.; Fogagnolo, M.; Giovannini, P. P.; Medici,
A.; Pedrini, P. Tetrahedron: Asymmetry 1995, 6, 3047–
3
053.
.