Enantioselective oxidative coupling of 2-naphthol derivatives catalyzed by Camellia sinensis cell culture

Article abstract of DOI:10.1016/S0040-4039(02)02089-0

Optically active 1,1′-binaphthyl-2,2′-diols were synthesized by oxidative coupling of 2-naphthols using Camellia sinensis cell culture as a catalytic system.

Full text of DOI:10.1016/S0040-4039(02)02089-0

TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 43 (2002) 8499–8501
Enantioselective oxidative coupling of 2-naphthol derivatives
catalyzed by Camellia sinensis cell culture
Masumi Takemoto,* Yuki Suzuki and Kiyoshi Tanaka
School of Pharmaceutical Sciences, University of Shizuoka, 52-1 Yada, Shizuoka 422-8526, Japan
Received 14 August 2002; revised 18 September 2002; accepted 20 September 2002
Abstract—Optically active 1,1%-binaphthyl-2,2%-diols were synthesized by oxidative coupling of 2-naphthols using Camellia sinensis
cell culture as a catalytic system. © 2002 Elsevier Science Ltd. All rights reserved.
1,1%-Binaphthalene derivatives have been widely used in
organic synthesis as chirality inducers for highly
stereoselective reactions.1 Enantiomerically pure
binaphthyl derivatives have been prepared by optical
resolution of racemic compounds,2 an intermolecular
Ullmann coupling,3 a nucleophilic aromatic substitu-
tion,4 an oxidative dimerization of 2-naphthols with
copper(II) amine complexes as oxidant5 or electrocata-
lytic oxidative coupling.6
Recently, we have found that Camellia sinensis cell
culture is an efficient source of peroxidase (POD)
enzymes. We have established C. sinensis cell culture
systems with high POD activity and applied them to the
oxidative coupling of dibenzylbutanolides with quanti-
tative yield.11 In this work, we would like to report our
investigation of enantioselective oxidative coupling of
2-naphthol derivatives by C. sinensis cell culture.
Oxidative coupling of 2-naphthol (1a) was first exam-
ined. The oxidative coupling reaction was performed at
25°C by three methods, that is: [A] with freely sus-
pended C. sinensis cell culture in B5 medium12 at pH
5.4 and in the stationary phase after 12 days of incuba-
tion in the presence of H2O2, [B] with immmobilized C.
sinensis cell culture (ICSC) in B5 medium in the absence
of foreign hydrogen peroxide or [C] with ICSC in
hexane in the absence of foreign hydrogen peroxide.
The results are summarized in Table 1.
Development of the usage of enzymes for oxidation
reactions aimed at green chemistry is significant these
days. Horseradish peroxidase (HRP) is a commercially
available metalloporphyrin enzyme and has been estab-
lished as an effective biocatalyst for organic and inor-
ganic oxidation reactions by using hydrogen peroxide
or hydroperoxides. Recently, this enzyme has once
again come into focus with the discovery of its remark-
able enantioselective reactions, viz., 1) enantioselective
oxidation of unsymmetrical sulfides to sulfoxides,7 2)
enantioselective reduction of racemic hydroperoxides to
alcohols8 and 3) enantioselective oxidation of 2-naph-
thols to 1,1%-binaphthyl-2,2%-diols.9 Sridhar et al.
reported a novel enantioselective oxidation of 2-naph-
thols to (R)-1,1%-binaphthyl-2,2%-diol catalyzed by HRP
(Y. 75%, 52% ee).9 Contrary to this report, Schreier et
al.10 published that the HRP is an effective but unselec-
tive biocatalyst for biaryl synthesis, where the oxidative
dimerization of 2-naphthol catalyzed by HRP to 1,1%-
binaphthyl-2,2%-diol resulted in 35% chemical yield with
<5% ee.
In the case of method A, the reactions were performed
under various H2O2 concentrations. Both optical and
chemical yields increased with increasing H2O2 content,
and maximum optical yield (59%) and chemical yield
(47%) were obtained with 0.5 mL of 30% H2O2 (entry
3). At 30% H2O2 contents of 1.0–6.0 mL, optical yields
and chemical yields decreased. The shortened reaction
time caused the better optical yields (entries 2–6), which
decreased for the longer time by more than 12 min.
Interestingly, (R)-1,1%-binaphthyl-2,2%-diol (2a) was pro-
duced as the sole product, which was isolated in 47%
yield after chromatographical purification. The enan-
tiomeric excess was determined to be 59% by HPLC
analysis using a chiral column and the absolute configu-
ration was assigned as R by comparison of the reten-
tion time of the authentic sample. In the case of
Keywords: asymmetric oxidative coupling; chiral binaphthol; cata-
lysts; enzymes and enzyme reaction.
* Corresponding
author.
Fax:
+81-54-264-5740;
e-mail:
takemoto@ys2.u-shizuoka-ken.ac.jp
0040-4039/02/$ - see front matter © 2002 Elsevier Science Ltd. All rights reserved.
PII: S0040-4039(02)02089-0

8500
M. Takemoto et al. / Tetrahedron Letters 43 (2002) 8499–8501
Table 1. Asymmetric oxidative coupling of 2-naphthol with C. sinensis cell culturea
Entry
Method
H2O2 (mL)
Time (h)
Yieldb (%)
%ee
Confignc
1
2
3
4
5
6
7
8
A
A
A
A
A
A
B
0
24
0
5
–
4
–
0.3% 1.0
30% 0.5
30% 1.0
30% 2.0
30% 6.0
0
0.2
0.2
0.2
0.2
0.2
24
R
R
R
R
R
R
R
47
40
31
10
6
59
30
24
15
32
22
C
0
24
16
a 50 mL.
b Isolated yields.
c Assignment by comparison with the authentic sample.
methods [B] and [C], 2a was given in the absence of
foreign hydrogen peroxide, but both chemical and opti-
cal yields were poor compared with the method of entry
3.
noteworthy that moderate to good ee values were
obtained for simple substrates such as 2-naphthol (CY
47%, OY 59%) that are difficult substrates for enan-
tioselective oxidative coupling reaction.5 Further studies
on enantioselective oxidative coupling are now in
progress.
According to the established procedure above, various
2-naphthol derivatives were subjected to oxidative cou-
pling reaction with C. sinensis cell culture. These results
are summarized in Table 2. Introduction of Br, OMe or
COOMe groups to the naphthalene ring decreased
enantioselectivity and chemical yield. To our surprise,
the coupling of 1b–d with C. sinensis cell culture yielded
2b–d with the opposite stereochemistry to that of 2a.
For a typical experiment, the suspension-cultured cells
which had originally been isolated from C. sinensis as
described in our previous papers were used.11,13–17 ICSC
were prepared according to the following procedure.
Freely suspended C. sinensis (4.6 g cells and 20 mL
broth) and 60 ml B5 medium in the stationary phase
after 12 days of incubation were mixed with 5% sodium
alginate solution (80 mL). The resultant mixture was
dropped into a 0.6% CaCl2 solution (1000 mL) and
rinsed with water to give ICSC. ICSC (including 7 g
In summary, a novel enantioselective oxidative coupling
of 2-naphthol derivatives by C. sinensis cell culture with
high POD activity can be achieved in this work. It is
Table 2. Asymmetric oxidative coupling of 2-naphthols with C. sinensis cell culture
Entry
Naphthol, 1
Method
H2O2 (mL)
Time (h)
Yield (%)a
% ee
Config.b
1
2
3
4
5
6
7
8
9
1b (R1=R3=H, R2=Br)
1b
1b
1c (R1=R2=H, R3=OCH3)
1c
1c
1d (R1=COOCH3, R2=R3=H)
1d
1d
A
B
C
A
B
C
A
B
C
30% 0.5
0
0
30% 0.5
0
0
30% 0.5
0
0
1
48
48
1
96
96
1
28
12
32
34
6
8
0
10
6
36
8
6
16
6
0
–
32
10
S
S
S
S
S
–
–
S
S
72
72
a Isolated yields.
b Assignment by comparison of optical rotations with the values in the literature. 2b,5a 2c,5d 2d.5d

M. Takemoto et al. / Tetrahedron Letters 43 (2002) 8499–8501
8501
cells and 30 mL broth) was added to freshly prepared
B5 medium (80 mL per flask) and was shaken on a
rotary shaker (110 rpm) in the dark at 25°C. A sub-
strate (35 mg) was added to the freely suspended plant
cell cultures (19 g cells and 80 mL broth), ICSC cells
(including 7 g cells and 30 mL broth) in 80 mL freshly
B5 medium or ICSC cells (including 7 g cells and 30
mL broth) in 20 mL hexane. After regular intervals of
incubation, the incubation mixture was filtered, the
filtered cells or immmobilized cells were washed with
AcOEt, and the filtrates were combined. The combined
mixture was extracted with AcOEt. The organic layer
was dried over anhydrous MgSO4. In the case of reac-
tion in hexane, homogenated cells were extracted with
AcOEt.
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Acknowledgements
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This work was partly supported by Grant-in-aid for
Scientific Research (C) from Japan Society for the
Promotion of Science (JSPS) (No. 12672057).
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