Highly efficient chemoenzymatic synthesis of methyl (R)-o-chloromandelate, a key intermediate for clopidogrel, via asymmetric reduction with recombinant Escherichia coli

Article abstract of DOI:10.1002/adsc.200800292

Methyl (R)-o-chloromandelate [(R)-1], which is an intermediate for a platelet aggregation inhibitor named clopidogrel, was obtained in >99% ee by the asymmetric reduction of methyl o-chlorobenzoylformate (2) with recombinant Escherichia coli overproducing

Full text of DOI:10.1002/adsc.200800292

FULL PAPERS
DOI: 10.1002/adsc.200800292
Highly Efficient Chemoenzymatic Synthesis of Methyl
R)-o-Chloromandelate, a Key Intermediate for Clopidogrel, via
Asymmetric Reduction with Recombinant Escherichia coli
(
a,
a
a
a,
Tadashi Ema, * Sayaka Ide, Nobuyasu Okita, and Takashi Sakai *
a
Division of Chemistry and Biochemistry, Graduate School of Natural Science and Technology, Okayama University,
Tsushima, Okayama 700-8530, Japan
Fax : (+81)-86-251-8092; e-mail: ema@cc.okayama-u.ac.jp
Received: May 12, 2008; Revised: June 25, 2008; Published online: August 19, 2008
Abstract: Methyl (R)-o-chloromandelate [(R)-1], optimum productivity as high as 178 g/L was attained
which is an intermediate for a platelet aggregation at 208C on a 2-gscale (1.0M). The optimized reac-
inhibitor named clopidogrel, was obtained in >99% tion could be scaled up easily to transform 20 gof 2
ee by the asymmetric reduction of methyl o-chloro- in 100 mL of buffer. Three synthetic methods for 2
benzoylformate (2) with recombinant Escherichia are compared.
coli overproducinga versatile carbonyl reductase. A
remarkable temperature effect on productivity was Keywords: asymmetric catalysis; biotransformations;
observed in the whole-cell reduction of 2, and the chemoenzymatic synthesis; enzyme catalysis
Introduction
lective hydroxynitrile lyases has also been used to
[
8,9]
access clopidogrel.
Amongthem, the direct asym-
Chemoenzymatic synthesis is becomingmore and
metric reduction of 2 is much safer, more straightfor-
more important from the viewpoint of green chemis- ward, and more advantageous because the asymmet-
try. An interdisciplinary field encompassingsynthetic ric center is generated in a step closer to the final
organic chemistry and biology will play a key role in product.
developingh hi gl y efficient and environmentally
benign synthetic routes. A synergic use of biotransfor- cally active alcohols are powerful synthetic tools.
Biocatalysts that can transform ketones into opti-
[1,2,10]
mation and organic synthesis, taking advantage of the We have been studyinga versatile carbonyl reductase
merits of each methodology, can realize a powerful called SCR capable of showingcatalytic activity for
[
1,2]
and secure production of a useful compound.
various ketones, such as a-chloro ketones, a-acetoxy
Clopidogrel is a platelet aggregation inhibitor ketones, a-keto esters, b-keto esters, g-keto esters,
widely administered to atherosclerotic patients with and b-diketones, and 13 out of 20 alcohols obtained
[
11]
the risk of a heart attack or stroke that are caused by had enantiomeric purities of >98% ee.
The gene
the formation of a clot in the blood. Worldwide sales encodingSCR has been cloned and expressed in E.
of Plavix (clopidogrel bisulfate) amounted to $6.4 bil- coli, and the asymmetric reduction of various ketones
[
3]
lion per year, which ranks second. The key enantio- with the recombinant E. coli cells has afforded 20 syn-
mer, methyl (R)-o-chloromandelate [(R)-1], can be thetically useful alcohols, 11 of which had enantiomer-
[
12]
prepared in several ways. (i) The corresponding( R)- ic purities of >98% ee. The gene encoding SCR is
[4]
carboxylic acid can be obtained by the fractional Gre2 (YOL151w) from Saccharomyces cerevisiae
crystallization of the racemic mixture or by the asym- (bakerꢀs yeast), and it has also been used by other re-
[
5]
[13]
metric reduction of the corresponding a-keto acid.
ii) The direct asymmetric reduction of the corre- Recently, we have succeeded in the highly efficient
spondingketone, methyl o-chlorobenzoylformate (2), asymmetric reduction of 2 usingthe recombinant E.
searchers for the purpose of biotransformations.
(
[
14]
is also promising. Although the Ru-catalyzed asym- coli as a versatile biocatalyst (Scheme 1). No bio-
metric hydrogenation of 2 and the corresponding transformations of 2 to 1 had been reported before.
ethyl ester has been done, (R)-1 and the correspond- Here we report the environmentally benign and prac-
ingethyl ester have been obtained, respectively, in
tical chemoenzymatic synthesis of the key intermedi-
0% ee and 76% ee at most. (iii) The asymmetric ate for clopidogrel, (R)-1, in detail.
hydrocyanation of o-chlorobenzaldehyde using R-se-
[6]
[7]
5
Adv. Synth. Catal. 2008, 350, 2039 – 2044
ꢁ 2008 Wiley-VCH VerlagGmbH & Co. KGaA, Weinheim
2039

Tadashi Ema et al.
FULL PAPERS
tography or distillation. The results are summarized
in Table 1.
When the reaction conditions previously optimized
[
12b]
for b-diketone were applied to 2,
hol (R)-1 was obtained in 76% yield with >99% ee
entry 1). We immediately tried to improve the effi-
the desired alco-
(
ciency of this biotransformation because of the indus-
trial utility of (R)-1 as a synthetic intermediate for
clopidogrel. What we did was to find the best reaction
temperature, at which the enzyme denaturation
caused by a large amount of substrate/product as well
as temperature is suppressed well, and at which the
asymmetric reduction of 2 proceeds smoothly, giving
the highest productivity of (R)-1. This workinghy-
pothesis turned out to be fine. Table 1 outlines how
Scheme 1. Asymmetric synthesis of (R)-1, a key intermedi-
ate for clopidogrel, by the asymmetric reduction of 2 with we optimized the productivity by changing the sub-
recombinant E. coli.
strate concentration and the reaction temperature.
When the reaction temperature decreased by 58C,
the conversion and isolated yield increased (entry 2),
Results and Discussion
which prompted us to double the substrate concentra-
tion. Even at the substrate concentration of 0.6 M, the
a-Keto ester 2 was prepared accordingto the litera-
conversion reached 94% (entry 3). Therefore, we fur-
[15]
ture,
and the whole-cell reduction of 2 was done ther increased the substrate concentration up to
with the E. coli strain coproducingSCR and GDH
1.0 M, which resulted in 90% conversion (entry 4). Fi-
glucose dehydrogenase) in the same way as reported nally, we further lowered the reaction temperature
(
[
12b]
previously (Scheme 1).
a-Keto ester 2 was added (entries 5 and 6) to find the best temperature giving
+
to a mixture of glucose, NADP , and E. coli wet cells the highest conversion at the same substrate concen-
in 0.1 M phosphate buffer. The mixture was stirred at tration. Thus, the whole-cell reduction of 1.0 M of 2
a regulated temperature for 24 h, during which 2 N at 208C gave 99% conversion and 1.78 g of isolated
NaOH was added to neutralize the solution acidified product (R)-1 (entry 5), which corresponds to the pro-
upon formation of gluconic acid. The product was ex- ductivity of 178 g/L (weight of isolated product per
tracted with EtOAc and purified by column chroma- liter of initial reaction volume). When the progress of
[a]
Table 1. Asymmetric reduction of 2 with recombinant E. coli.
+
[b]
[c]
[d]
Entry
[2]
[g·L ]
NADP [mg]
Cells [g]
T [8C]
C [%]
Yield [%]
ee [%]
À1
[g]
A
H
R
U
G
[M]
1
2
3
4
5
6
7
8
9
0.60
0.60
1.20
1.98
1.98
1.98
1.98
2.58
2.58
1.98
1.98
1.98
19.9
60
60
0.3
0.3
0.6
1.0
1.0
1.0
1.0
1.3
1.3
1.0
1.0
1.0
1.0
10
10
10
10
10
10
10
10
10
5
2
2
2
2
2
2
2
2
2
2
2
1
30
25
25
25
20
15
20
20
20
20
20
20
20
92
>99
94
90
99
86
>99
57
76
69
76
88
88
85
89
82
89
53
70
62
43
36
76
>99
>99
>99
>99
>99
>99
>99
>99
>99
>99
>99
>99
>99
120
198
198
198
198
258
258
198
198
198
199
[
[
e]
e]
10
11
12
13
0
10
100
47
42
98
20
[
a]
Conditions: 2 (quantity and concentration indicated above), wet cells of E. coli BL21(DE3) harboringpESCR and
pABGD (quantity indicated above), glucose (2 equiv. with respect to 2), NADP (quantity indicated above), 0.1 M phos-
A
H
R
U
G
+
phate buffer [pH 7.0, 10 mL except for entry 13 (100 mL)], 24 h.
Conversion determined by H NMR.
Isolated yield of (R)-1.
Determined by HPLC [Chiralpak AD-H, hexane/i-PrOH (9:1)].
[
[
[
[
b]
1
c]
d]
e]
CFE prepared from wet cells of E. coli BL21(DE3) harboringpESCR and pABGD (2 g) was used as a catalyst.
A
H
R
U
G
2040
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Adv. Synth. Catal. 2008, 350, 2039 – 2044

Highly Efficient Chemoenzymatic Synthesis of Methyl (R)-o-Chloromandelate
FULL PAPERS
Although other researchers had gained the highest
productivity at 208C in the whole-cell asymmetric re-
[
16]
duction of ethyl 4-chloroacetoacetate, the remark-
able temperature effect on productivity as described
above was beyond our expectation. We speculate that
loweringthe temperature led to a decrease in the mo-
bility of SCR by strengthening the intramolecular hy-
drogen bonds, which might suppress the protein dena-
turation caused by heat and/or a large amount of sub-
strate/product to retain the catalytic activity of SCR.
Apart from the mechanistic origin, the present whole-
cell reduction is quite promisingfrom a practical
viewpoint; only several examples of microbial reduc-
tion systems capable of giving productivity higher
[
1,2,10b,g,k,l,17–20]
than 100 g/L have been reported.
The result that (R)-1 was obtained in >99% ee
Table 1) was unexpected for the followingreason.
(
Although an analogous alcohol, ethyl (R)-mandelate
[
12b]
Figure 1. Time course of the bioreduction of 2. For the reac- [(R)-3], had been obtained in 92% ee before,
the
tion conditions, see entry 5 in Table 1. The reaction was
fact that the (R)-enantiomer of 3 was obtained could
not be explained well by a stereochemical trend we
1
monitored by H NMR.
[
11b]
had found.
Figure 2a illustrates the stereochemical
the reaction was monitored by NMR, the reaction trend observed for fifteen alcohols containinga car-
[
12b]
was almost complete (>99% conversion) in 9 h as bonyl group in the substituent.
shown in Figure 1. the fixation of the orientation of the ketone by hydro-
In the whole-cell reduction described above, the gen bonding followed by the attack of the b-face of
We have postulated
[
11b]
cells are not intact but permeabilized partially by ex- the carbonyl group by NADPH (Figure 2b).
The
posure to a large amount of substrate and by magnet- exception is (R)-3 as shown in Figure 2a. Because of
ic stirring. Nevertheless, the cell membrane can the irregular behavior of (R)-3, we could not predict
hinder the mass transfer. Indeed, the cell-free extract even whether the enantiomeric purity of 1 would be
(
CFE) prepared from 2 gof the recombinant E. coli higher or lower than that of 3. Although no consistent
gave >99% conversion under otherwise the same re- models are available at present, the molecular mecha-
action conditions (entry 7). Further comparison be-
tween the whole-cell reduction and the CFE reduc-
tion at a higher concentration (1.3 M) revealed that
the latter was superior to the former (entries 8 and 9).
The cell membrane therefore seems to retard the en-
zymatic reactions to some degree despite the facts
that the local concentrations of the enzymes (SCR
and GDH) in the cells are higher and that the en-
zymes in the cells are exposed to a lower amount of
substrate/product. Despite these results, we selected
the whole-cell reduction for further investigation be-
cause it is much more convenient than the CFE re-
duction.
Despite our efforts, all the attempts to further im-
prove the efficiency of the production of (R)-1 failed+.
For example, the decrease in the amount of NADP
or E. coli cells resulted in a decrease in conversion
(
entries 10, 11, and 12). We therefore concluded that
the reaction conditions indicated in entry 5 are the
best. We then scaled up the biotransformation by ten-
fold under the optimized reaction conditions
Figure 2. (a) A stereochemical trend observed for fifteen
carbonyl-containingalcohols obtained by the bioreduction.
The absolute configuration of (R)-3 was opposite to the ste-
(
entry 13), and the bioreduction of 20 gof 2 in
[12b]
100 mL of buffer at 208C for 24 h followed by distilla-
reochemical trend. Data taken from ref.
(b) A putative
tion gave 15 g of optically pure (R)-1 successfully bindingmode of a ketone bearinga carbonyl-containing
(
76% yield).
substituent.
Adv. Synth. Catal. 2008, 350, 2039 – 2044
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asc.wiley-vch.de
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Tadashi Ema et al.
FULL PAPERS
nism of enantioselectivity could be clarified by deter-
miningthe crystal structure of SCR in future.
Here we identified the factors responsible for the
highly enantioselective production of (R)-1 by exam-
iningthe enantiomeric purities of 4 and 5 obtained by
the whole-cell reduction of the correspondingke-
tones. As shown in Scheme 2, (R)-4 and (R)-5 were
Scheme 4. Preparation of 2 with the Grignard reagent.
philic attack of a Grignard reagent to dialkyl oxalate
forms a 1:1 adduct, which blocks the second attack of
[
21]
the reagent. In this particular case, 2 was isolated in
a good yield, although we needed to conduct the reac-
tion at a low temperature to suppress the formation
of benzyne generated from o-chlorophenylmagnesium
bromide. For comparison, we also examined another
synthetic method with the organolithium reagent
(
Scheme 5). Although the desired compound 2 was
isolated successfully, the yield was only modest. The
former method with the Grignard reagent (Scheme 4)
is therefore more economical and suitable for the syn-
thesis of 2.
Scheme 2. Asymmetric reduction of a-keto esters.
obtained in 96 and 99% ee, respectively. Clearly, the
presence of the chlorine atom and the replacement of
the ethyl group by the methyl group each contributed
to an enhancement of enantioselectivity, and the two
modifications led to the production of (R)-1 with
>
99% ee. In the bioreduction of a series of benzoyl
Scheme 5. Preparation of 2 with the organolithium reagent.
formate esters, the difference in the bulkiness of two
substituents seems to be much more important for
enantioselectivity than the hydrogen bond depicted in Conclusions
Figure 2b, and hence the most unbalanced one, 2, was
converted to the correspondingalcohol with the hi gh -
est % ee value.
A highly efficient chemoenzymatic method for methyl
(R)-o-chloromandelate [(R)-1] has been developed.
The present whole-cell reduction of a-keto ester 2 The asymmetric reduction of methyl o-chlorobenzoyl-
was so efficient that the chemical synthesis of 2 formate (2) with recombinant E. coli overproducinga
became a bottleneck. For the preparation of 2, we versatile carbonyl reductase, SCR, gave (R)-1 with
first employed the one-pot oxidation of methyl o- >99% ee. This is the first example of the direct asym-
chlorophenylacetate accordingto the literature
metric synthesis of (R)-1 with >99% ee. A remark-
[15]
(
Scheme 3). Although it is an excellent method, the able temperature effect on productivity was observed
productivity of 2 is not so high, and the reagents used in the whole-cell reduction of 2, and the optimum
are rather expensive. To make this chemoenzymatic productivity as high as 178 g/L was attained at 208C
synthesis of (R)-1 more successful, we searched for on a 2-gscale (1.0 M). This biotransformation could
other synthetic methods highly suitable for 2. We ex- be scaled up easily, and the bioreduction of 20 gof 2
amined various methods and finally found the in 100 mL of buffer at 208C for 24 h gave 15 g of opti-
Grignard reaction shown in Scheme 4. The reaction of cally pure (R)-1 successfully. The bioreduction of 2 is
o-chlorophenylmagnesium bromide prepared from o- a practical process, because the hydride source is glu-
bromochlorobenzene with dimethyl oxalate gave a- cose, which is the cheap biomass, and because the cat-
keto ester 2 selectively. It is known that the nucleo- alyst is E. coli, which can be multiplied easily and in-
expensively. Moreover, the bioreduction is performed
in an aqueous solution under air. Two synthetic meth-
ods giving a-keto ester 2 in good yields were found.
Although more experiments need to be done espe-
cially on a much larger scale, the present chemoenzy-
matic method has good potential for an industrial ap-
plication because of the pharmaceutical value of the
Scheme 3. Preparation of 2 by the one-pot oxidation.
downstream product, clopidogrel.
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Highly Efficient Chemoenzymatic Synthesis of Methyl (R)-o-Chloromandelate
FULL PAPERS
Experimental Section
evaporation, brine was added, and the product was extract-
ed with EtOAc. The organic layer was dried over MgSO4
and concentrated. The product was purified by basic alumi-
na column chromatography (hexane/EtOAc, 10:1–0:1) to
General
[7]
Methyl o-chlorobenzoylformate (2) was prepared according
afford ethyl o-chlorobenzoylformate as a pale yellow oil;
[15]
1
to the literature. Methyl benzoylformate was purchased.
E. coli BL21(DE3) cells harboringpESCR and pABGD
were grown as reported previously.
yield: 1.42 g(44%). H NMR (CDCl , 600 MHz): d=1.41 (t,
3
ACHTREUNG
J=7.5 Hz, 3H), 4.43 (q, J=7.5 Hz, 2H), 7.40–7.46 (m, 2H),
[12b]
+
NADP was pur-
7
1
1
3
.53 (ddd, J=8.1, 7.8, 1.8 Hz, 1H), 7.77 (dd, J=7.8, 1.8 Hz,
1
3
chased from Oriental Yeast. Silica gel and basic alumina
column chromatography was performed using Fuji Silysia
BW-127 ZH (100–270 mesh) and Merck aluminum oxide 90
active basic (0.063–0.200 mm), respectively. Thin layer chro-
matography (TLC) was performed on Merck silica gel 60
H); C NMR (CDCl , 150 MHz): d=13.9, 62.8, 127.2,
3
30.5, 131.6, 133.3, 133.9, 134.3, 163.1, 186.6; IR (film): v=
À1
071, 2988, 1732, 1699, 1589, 1198, 1065, 1018, 760 cm .
The whole-cell reduction of ethyl o-chlorobenzoylformate
was performed at 308C on a 3.0-mmol scale as described
2
D
2
F254
.
above. Isolated yield: 93%. [a] : À149.0 (c 1.0, CHCl ),
3
[24]
25
D
9
9% ee, (R) {lit. [a] : À45.0 (c 4.0, CHCl ), 62% ee, (R)};
3
HPLC: Chiralcel OD-H, hexane/i-PrOH (20:1), flow rate
Typical Procedure for the Whole-Cell Asymmetric
À1
1
.0 mLmin , detection 254 nm, (S) 12.3 min, (R) 14.6 min;
H NMR (CDCl , 600 MHz): d=1.22 (t, J=6.9 Hz, 3H),
Reduction of 2 to give Methyl (R)-o-
1
3
Chloromandelate [(R)-1]
A
C
H
T
R
E
U
N
G
3
.56 (d, J=5.1 Hz, 1H), 4.18–4.30 (m, 2H), 5.55 (d, J=
+
To a mixture of glucose (3.60 g, 20.0 mmol), NADP (10 mg,
2 mmol), and E. coli BL21(DE3) cells harboringpESCR
and pABGD (2.0 g) in 0.1M phosphate buffer (pH 7.0,
0 mL) was added methyl o-chlorobenzoylformate (2)
1.98 g, 10.0 mmol). The mixture was stirred in a water bath
5.1 Hz, 1H), 7.27–7.30 (m, 2H), 7.38–7.41 (m, 2H);
1
3
1
A
H
R
U
G
C NMR (CDCl , 150 MHz): d=14.0, 62.5, 70.4, 127.1,
3
128.8, 129.7, 129.9, 133.6, 136.1, 173.2; IR (film): v=3468,
À1
1
(
3067, 2984, 1732, 1217, 1090, 756 cm .
at 20 8C for 24 h, duringwhich 2 N NaOH was added to
neutralize the solution acidified by the progress of the reac-
tion. Solid NaCl (5.5 g) was added, and the product was ex-
tracted with EtOAc (3”25 mL), where centrifugation
Preparation of CFE for the Asymmetric Reduction of
2
(
3,200 rpm, 10 min) was conducted to promote the phase
E. coli BL21
2.0 g) in 0.1 M phosphate buffer (pH 7.0, 5 mL) were lysed
by sonication for 1 min in an ice bath (”10). Centrifugation
20,000 rpm, 48C, 30 min) gave a cell-free extract (CFE) as
the supernatant. The precipitate was suspended in the phos-
phate buffer (5 mL), and centrifugation (20,000 rpm, 48C,
A
H
R
U
G
separation. The combined organic layers were dried over
MgSO , filtered, and concentrated under reduced pressure.
Purification by silica gel column chromatography (hexane/
EtOAc, 10:1) gave methyl (R)-o-chloromandelate [(R)-1] as
(
4
(
1
9
a colorless oil; yield: 1.78 g(89%). [ a] : À178.3 (c 1.3,
D
[22]
22
CHCl ), >99% ee, (R) {lit. [a] : À146.3 (c 1.05, CHCl ),
3
D
3
1
0 min) gave a CFE. The CFE solutions were combined and
8
0.8% ee, (R)}; HPLC: Chiralpak AD-H (Daicel Chemical
used for the asymmetric reduction of 2. The CFE reduction
of 2 was conducted as described for the whole-cell reduction
of 2.
À1
Industries), hexane/i-PrOH (9:1), flow rate 0.5 mLmin , de-
tection 254 nm, (S) 20.3 min, (R) 22.7 min; H NMR
1
(CDCl , 600 MHz): d=3.56 (d, J=5.4 Hz, 1H), 3.78 (s, 3H),
3
5
2
1
3
.57 (d, J=5.4 Hz, 1H), 7.28–7.29 (m, 2H), 7.39–7.40 (m,
13
H); C NMR (CDCl , 150 MHz): d=53.2, 70.3, 127.2,
3
28.8, 129.8, 130.0, 133.5, 135.9, 173.7; IR (film): v=3454, Preparation of Methyl o-Chlorobenzoylformate (2)
À1
003, 2955, 1744, 1441, 1223, 1090, 756 cm .
using the Grignard Reagent
A solution of o-bromochlorobenzene (1.24 g, 6.48 mmol) in
Methyl (R)-Mandelate [(R)-4]
dry THF (8 mL) was added dropwise to a mixture of Mg
(0.163 g, 6.71 mmol) and I (1 piece) in dry THF (2 mL) at
10–158C over 0.5 h under N . To the Grignard reagent thus
prepared was added a solution of dimethyl oxalate (0.503 g,
4.26 mmol) in dry THF (10 mL) and dry Et O (10 mL) at
The whole-cell reduction of methyl benzoylformate was per-
2
formed at 308C on a 3.0-mmol scale as described above. Iso-
2
2
3
lated yield 72%. [a] : À130.8 (c 1.0, MeOH), 96% ee, (R)
D
[
23]
20
D
{
lit. [a] : À124.8 (c 0.8, MeOH), 86% ee, (R)}; GC: CP-
2
cyclodextrin-b-2,3,6-M-19 (Chrompack, ø 0.25 mm”25 m),
À708C via syringe. After the mixture had been stirred at
À708C for 1 h, the reaction was quenched with 10% HCl.
The product was extracted with EtOAc, and the organic
injector 3008C, column 1008C, detector 2508C, (R) 77.8 min,
1
(
S) 83.6 min; H NMR (CDCl , 600 MHz): d=3.42 (d, J=
3
5
.4 Hz, 1H), 3.77 (s, 3H), 5.18 (d, J=5.4 Hz, 1H), 7.34–7.43
layer was dried over MgSO and concentrated. Purification
4
13
(m, 5H); C NMR (CDCl , 150 MHz): d=53.1, 72.9, 126.6,
by silica gel column chromatography (hexane/EtOAc, 10:1)
3
1
1
28.5, 128.6, 138.2, 174.1; IR (KBr): v=3443, 3032, 2955,
740, 1435, 1209, 1096, 739 cm .
gave methyl o-chlorobenzoylformate (2) as a pale yellow
À1
1
oil; yield: 626 mg(74%). H NMR (CDCl
, 600 MHz): d=
3
3
.96 (s, 3H), 7.42 (ddd, J=7.8, 7.2, 1.2 Hz, 1H), 7.45 (dd,
J=7.8, 1.2 Hz, 1H), 7.54 (ddd, J=7.8, 7.2, 1.8 Hz, 1H), 7.77
Ethyl (R)-o-Chloromandelate [(R)-5]
1
3
(
dd, J=7.8, 1.8 Hz, 1H); C NMR (CDCl , 150 MHz): d=
3
A solution of methyl o-chlorobenzoylformate (2) (3.01 g,
53.3, 127.3, 130.5, 131.6, 133.2, 133.9, 134.4, 163.4, 186.2; IR
1
5.2 mmol) and H SO (0.6 mL) in EtOH (380 mL) was
(film): v=3013, 2955, 1740, 1701, 1589, 1435, 1254, 1207,
2
4
À1
heated at reflux for 4 d. After removal of EtOH by rotary
1065, 1007, 760 cm .
Adv. Synth. Catal. 2008, 350, 2039 – 2044
ꢁ 2008 Wiley-VCH VerlagGmbH & Co. KGaA, Weinheim
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2043

Tadashi Ema et al.
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2
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Adv. Synth. Catal. 2008, 350, 2039 – 2044