Enzymatic desymmetrization of meso-2,3-bis(acetoxymethyl) and bis(hydroxymethyl) substituted hexachloronorbornadiene derivatives

Article abstract of DOI:10.1016/j.tetasy.2003.11.023

meso-Bis(acetoxymethyl)-1,4,5,6,7,7-hexachlorobicyclo[2.2.1]hepta-2, 5-diene and meso-bis(hydroxymethyl)-1,4,5,6,7,7-hexachlorobicyclo[2.2.1]hepta-2, 5-diene were transformed into chiral monoesters with 65-92% ee via enzymatic desymmetrization using various lipases. The absolute configuration was determined by transforming 2-acetoxymethyl-3-hydroxymethyl-1,4,5,6,7,7- hexachlorobicyclo[2.2.1]hepta-2,5-diene into the 2-acetoxymethyl-3- hydroxymethylbicyclo[2.2.1]hepta-2,5-diene of known absolute configuration.

Full text of DOI:10.1016/j.tetasy.2003.11.023

Tetrahedron:
Asymmetry
Tetrahedron: Asymmetry 15 (2004) 307–310
Enzymatic desymmetrization of meso-2,3-bis(acetoxymethyl) and
bis(hydroxymethyl) substituted hexachloronorbornadiene
derivatives
*
_
*
Cihangir Tanyeli, Timur Karada ꢀg and Idris Mecito ꢀg lu Akhmedov
Department of Chemistry, Middle East Technical University, 06531 Ankara, Turkey
Received 6 October 2003; revised 17 November 2003; accepted 20 November 2003
Abstract—meso-Bis(acetoxymethyl)-1,4,5,6,7,7-hexachlorobicyclo[2.2.1]hepta-2,5-diene and meso-bis(hydroxymethyl)-1,4,5,6,7,7-
hexachlorobicyclo[2.2.1]hepta-2,5-diene were transformed into chiral monoesters with 65–92% ee via enzymatic desymmetrization
using various lipases. The absolute configuration was determined by transforming 2-acetoxymethyl-3-hydroxymethyl-1,4,5,6,7,7-
hexachlorobicyclo[2.2.1]hepta-2,5-diene into the 2-acetoxymethyl-3-hydroxymethylbicyclo[2.2.1]hepta-2,5-diene of known absolute
configuration.
ꢀ
2003 Elsevier Ltd. All rights reserved.
1
. Introduction
Diels–Alder reaction of cyclopentadiene and acetylenic
7
aldehydes. Bis(acetoxymethyl) substituted norbornadi-
ene can be considered as a useful substrate for biologi-
Experimental studies on the syntheses of complex tar-
gets have resulted in the development of reactions,
which emphasize chemo-, regio- and stereoselectivity.
In defining strategies and reactions to construct complex
chiral molecules, in particular, high stereoselectivity is
required. In a wide variety of asymmetric methods,
enzymatic asymmetric hydrolysis has been a powerful
method in the development of strategies for the asym-
cally important compounds such as prostaglandins of
3a;8
1
the PGF series. In the literature, there are only a few
examples of enzymatic resolution of hexachlorinated
9
norbornene derivatives. Recently, we reported the
lipase and esterase-catalyzed resolution of (±)-2-hy-
droxymethylbicyclo[2.2.1]hepta-2,5-diene, (±)-2-hydroxy-
methyl-1,4,5,6,7,7-hexachlorobicyclo[2.2.1]hepta-2,5-
diene and (±)-2-acetoxymethylbicyclo[2.2.1]hepta-2,5-
diene, (±)-2-acetoxymethyl-1,4,5,6,7,7-hexachlorobicy-
2
metric synthesis of various natural products. In par-
ticular, hydrolase type enzymes are among those
enzymes most widely applied in organic synthesis. De-
symmetrization of meso-diesters using hydrolase type
enzymes is an important concept since it potentially
affords only one enantiomer in quantitative yield with-
10
clo[2.2.1]hepta-2,5-diene, respectively. In connection
to these biotransformations, during the course of enzy-
matic desymmetrization of meso-bis(acetoxymethyl)-
1,4,5,6,7,7-hexachlorobicyclo[2.2.1]hepta-2,5-diene 1 and
meso-bis(hydroxymethyl)-1,4,5,6,7,7-hexachlorobicyclo-
3
out wasting the other enantiomer.
[
2.2.1]hepta-2,5-diene 3, screening reactions were first
The optically active norbornadienes are key intermedi-
ates in the synthesis of biologically active analogues of
done with various hydrolases (i.e., CCL, PPL, PL, PLE
and HLE) using substrate/enzyme ratios from 1:1 to
1:0.5. Among the hydrolases studied, PLE, CCL, PPL
and PL proved to be suitable for the desymmetrization
of these substrates. In particular, PL showed some
interesting enzyme- and substrate-dependant reversals
of enantioselectivity with the substrates meso-1 and
meso-3. The observed promising preliminary results
prompted us to undertake a thorough catalytic study.
PLE-, CCL- and PPL-catalyzed reactions of diester
substrate 1 and diol substrate 3 afforded half ester ())-
2a. In contrast to this, PL yielded monoester (+)-2b with
the diol substrate 3 whereas the same enzyme afforded
2 2
the prostaglandin endoperoxides PGH and PGG and
4
b-santalol used by Corey et al. and Ogasawara and
co-workers. Evans et al. has studied the synthesis of
5
optically active norbornadienes using a,b-unsaturated
N-acyloxazolidinones as chiral auxiliaries in Diels–Alder
6
reactions of cyclopentadiene. Yamamoto and
co-workers achieved the first enantioselective catalytic
*
Corresponding authors. Tel.: +90-312-210-3222; fax: +90-312-210-
280; e-mail addresses: tanyeli@metu.edu.tr; mecid@metu.edu.tr
1
0
957-4166/$ - see front matter ꢀ 2003 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetasy.2003.11.023

308
C. Tanyeli et al. / Tetrahedron: Asymmetry 15 (2004) 307–310
Cl
Cl
Cl
Cl Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
enzyme
enzyme
Cl
OH
OH
Cl
Cl
OAc
Cl
OH
Cl
OAc
or
OAc Cl
phosphate buffer
pH = 7
vinylacetate
Cl
OAc
Cl
OH
Cl
Cl
Cl
Cl
3
1
2a
2b
Scheme 1.
monoester ())-2a with diester substrate 1. CCL in par-
ticular, exhibited higher eeÕs and PL showed unusual
versatility and diversity in the enzymatic desymmetri-
zation of the hexachlorinated substrate.
tested afforded 2a with poor results in terms of enantio-
selectivity (entries 3 and 4). In order to improve the
enantiomeric excess, experimental conditions have been
tested in detail using various co-solvents such as iso-
propanol, MTBE and n-butanol in the case of CCL,
since it gives the best result in terms of enantioselectiv-
ity. No increase in the enantioselectivity was observed
(entries 5–7). The absolute configuration of the isolated
product ())-2a was determined by transforming it into
the corresponding (1S,4R)-())-4a by reaction with Na in
Herein, we describe the highly efficient resolution of the
meso-substrates 1 and 3 with PLE, CCL, PPL and PL
(
Scheme 1).
3a
liquid NH (Scheme 2).
3
2
. Results and discussion
Cl
Cl
Prochiral 1 was obtained in 85% chemical yield, using a
Diels–Alder reaction by heating a mixture of hexachlo-
rocyclopentadiene and 2-butyne-1,4-diol diacetate (1:2
Cl
Cl
OH
OH
Na/EtOH
liq. NH3
OAc
11
OAc
molar ratio) to 150 ꢁC for 8 h in a sealed tube.
Hydrolysis of prochiral 1 afforded 97% of the prochiral
Cl Cl
(
1S,4R)-(-)-2a
(1S,4R)-(-)-4a
11
substrate 3.
Scheme 2.
2
.1. Enzymatic hydrolysis of prochiral substrate 1
2
.2. Esterification of prochiral substrate 3
Various lipases were tested with prochiral substrate 1
Table 1). The first bioconversion was performed using
PLE according to the following general procedure. To a
(
In prochiral ester hydrolysis studies, all enzymes used
afforded the (1S,4R)-())-2a. Related to this study, the
enzyme catalyzed acetyl transfer to meso-diol 3 with
CCL, PPL and PL was examined. The bioconversion of
meso-3 was performed by CCL according to the fol-
lowing general procedure. To a stirred solution of meso-
3 (500 mg) in vinyl acetate (5 mL), CCL (10 mg) was
added in one portion and the reaction mixture was
shaken at 20 ꢁC. The conversion was monitored by TLC.
After 21 h, the products were separated using flash col-
umn chromatography and compound (1S,4R)-())-2a
was isolated with 86% ee in 73% yield (entry 1 in Table
2). PPL gave the same compound (1S,4R)-())-2a as
above with 68% ee in 65% yield (entry 2). Among the
enzymes used in esterification of meso-3, PL afforded
stirred solution of 1 (500 mg) in phosphate buffer
(
pH 7.00, 50 mL), PLE (100 lL) was added in one por-
tion and the reaction mixture was stirred at 20 ꢁC in a
pH stat unit. The conversion was monitored by TLC.
After
,4,5,6,7,7-hexachlorobicyclo[2.2.1]hepta-2,5-diene 2a
was obtained with 65% ee in 48% chemical yield (entry
, Table 1). The next attempts involved substrate 1 using
24 h,
())-2-acetoxymethyl-3-hydroxymethyl-
1
1
CCL, PPL and PL under the same conditions as above.
CCL appeared to be the best enzyme tested, since ())-2-
acetoxymethyl-3-hydroxymethyl-1,4,5,6,7,7-hexachloro-
bicyclo[2.2.1]hepta-2,5-diene 2a was obtained with 92%
ee in 81% isolated yield (entry 2). All other enzymes
Table 1. Results of the enzyme-catalyzed hydrolysis of meso-1
a
20
b
Entry
Substrate
Enzyme
Solvent system
Time (h)
Monoester
Yield (%)
½aꢀD
Ee (%)
c
1
2
3
4
5
6
7
meso-1
meso-1
meso-1
meso-1
meso-1
meso-1
meso-1
PLE
CCL
PPL
PL
PB
PB
28
23
24
24
20
21
20
(1S,4R)-2a
(1S,4R)-2a
(1S,4R)-2a
(1S,4R)-2a
(1S,4R)-2a
(1S,4R)-2a
(1S,4R)-2a
48
81
78
83
79
85
80
)16.1
)22.8
)21.3
)21.8
)18.8
)19.5
)16.6
65
92
86
88
76
79
67
PB
PB
CCL
CCL
CCL
Isopropanol
MTBE
n-Butanol
a
b
c
Yields (%) are given as the isolated half esters.
Enantiomeric excess values are determined by the Chiralcel ODH chiral column HPLC analysis.
PB: phosphate buffer.

C. Tanyeli et al. / Tetrahedron: Asymmetry 15 (2004) 307–310
Table 2. Results of enzyme-catalyzed esterification of meso-3
309
a
20
b
Entry
Substrate
Enzyme
Solvent system
Time (h)
Monoester
Yield (%)
½aꢀD
Ee (%)
1
2
3
meso-3
meso-3
meso-3
CCL
PPL
PL
Vinyl acetate
Vinyl acetate
Vinyl acetate
21
24
24
(1S,4R)-2a
(1S,4R)-2a
(1R,4S)-2b
73
65
82
)21.3
)16.8
+20.8
86
68
84
a
Yields (%) are given as the isolated half esters.
Enantiomeric excess values are determined by the Chiralcel ODH chiral column HPLC analysis.
b
(1R,4S)-(+)-2b with 84% ee in 82% yield (entry 3). In
order to control the efficiency of the method applied in
from porcine pancreas) and PFL (lipase, from Pseudo-
monas fluorescens) were purchased from Aldrich.
the absolute configuration determination of (1S,4R)-())-
2
corresponding (1R,4S)-(+)-4b by reaction with Na in
liquid NH as above (Scheme 3).
3
a, the isolated product (+)-2b was transformed into the
4.1. Synthesis of meso-bis(acetoxymethyl)-1,4,5,6,7,7-
hexachlorobicyclo[2.2.1]hepta-2,5-diene 1
3a
A mixture of 2-butyne-1,4-diol diacetate (3.40 g, 20
mmol) and hexachlorocyclopentadiene (2.73 g, 10 mmol)
containing few crystals of hydroquinone was sealed
under vacuum in a thick-walled Pyrex tube. The mixture
was heated 8 h at 150 ꢁC. The crude product was purified
by flash column chromatography to afford meso-1
Cl
Cl
Cl
Cl
OAc
OH
Na/EtOH
liq. NH3
OAc
OH
Cl Cl
1R,4S)-(+)-2b
(
EtOAc/hexane, 1:5) (3.76 g, 85% yield). Mp: 54 ꢁC
11 1
(
(1R,4S)-(+)-4b
(lit., mp: 54–55 ꢁC). H NMR: d 2.01 (s, 6H, O
4
(
2 3
CCH ),
.79 (d, 2H, AB system CH H OAc, J ¼ 13 Hz), 4.88
a
b
Scheme 3.
13
d, 2H, AB system CH
a
H
b
OAc, J ¼ 13 Hz). C NMR:
d 21.4, 57.1, 85.2, 114.1, 137.6, 143.5, 170.3. IR (KBr):
ꢁ
1
1
726, 1680, 750 cm . Anal. Calcd for C Cl H O
13
6
10
4
(442.94): C, 35.25; Cl, 48.02; H, 2.28. Found: C, 35.21;
Cl, 48.04; H, 2.27.
3. Conclusion
In this study, we have shown that the two enantiomers
of half ester 2a and 2b could be obtained through
enzymatic desymmetrization of prochiral substrates 1
and 3. Among the enzymes used in both hydrolysis and
esterification conditions, CCL showed the best enantio-
selectivity. The two enantiomers 2a and 2b were
obtained only with PL by a hydrolysis and an esterifi-
cation, respectively. The absolute configuration of both
2a and 2b were determined by transforming them into
the corresponding nonchlorinated norbornadiene
derivatives with Na in liquid NH . Commercially
3
available and inexpensive enzymes, in particular, CCL
and PL used in catalytic levels, renders the process very
attractive for large scale preparations.
4.2. Synthesis of meso-bis(hydroxymethyl)-1,4,5,6,7,7-
hexachlorobicyclo[2.2.1]hepta-2,5-diene 3
A mixture of meso-1 (2.00 g, 4.5 mmol), concd HCl
(0.25 mL) and methanol (10 mL) was stirred for 3 h at
reflux. The reaction vessel was cooled down to 25 ꢁC and
diluted with EtOAc (25 mL), extracted with saturated
NaHCO
3
(3 · 50 mL) and brine (2 · 50 mL), dried over
MgSO and evaporated under reduced pressure. The
4
crude product was purified by flash column chroma-
tography to afford meso-3 (EtOAc/hexane, 2:3) (1.57 g,
1
1
1
9
7% yield). Mp: 155 ꢁC (lit., mp: 155–156 ꢁC).
NMR: d 2.10–2.15 (br s, 2H, OH), 4.34 (d, 2H, AB
system CH
OH, J ¼ 14 Hz), 4.50 (d, 2H, AB system
CH
OH, J ¼ 14 Hz). C NMR: d 54.9, 84.7, 112.7,
36.8, 143.2. IR (KBr): 3410, 3425, 1630, 745 cm .
Anal. Calcd for C Cl (358.87): C, 30.12; Cl, 59.27;
H
a
H
b
1
3
a
H
b
ꢁ
1
1
4. Experimental
9
6 6 2
H O
H, 1.69. Found: C, 30.12; Cl, 59.24; H, 1.67.
1
H NMR spectra were recorded in CDCl on Bruker
3
Spectrospin Avance DPX 400 spectrometer. Chemical
shifts are given in ppm downfield from tetramethylsi-
lane. IR spectra were obtained from a Perkin–Elmer
Model 1600 series FT-IR spectrometer and are reported
4.3. General procedure for enzymatic hydrolysis of 1
To a stirred solution of 500 mg meso-1 in 50 mL pH 7.00
phosphate buffer, 100 lL PLE (or 10 mg of lipase) was
added in one portion and the reaction mixture was
stirred at 20 ꢁC in a pH stat unit. The conversion
was monitored by TLC. The reaction mixture was ex-
ꢁ
1
in cm . Optical rotations were measured in CHCl
3
solution in a 1 dm cell using a Bellingham & Stanley P20
polarimeter at 20 ꢁC. Elemental analyses were per-
formed on a LECO 932. PLE (pig liver esterase) and PL
(
lipase, Pseudomonas species) were purchased from
Sigma as a suspension in ammonium sulfate solution
3.2 mol/L) and as a powder, respectively. CCL (lipase,
Type VII, from Candida rugosa), PPL (lipase, Type II,
4
tracted with ethyl acetate, dried over MgSO and con-
centrated under reduced pressure. The product (1S,4R)-
())-2a was purified by flash column chromatography
(
2
D
0
1
(EtOAc/hexane, 1:5). ½aꢀ ¼ )22.8 (c, 4.17, MeOH). H

310
C. Tanyeli et al. / Tetrahedron: Asymmetry 15 (2004) 307–310
NMR: d 1.99 (s, 3H, O
OH), 4.29 (d, 1H, AB system CH
2
CCH
3
), 2.71–2.76 (br s, 1H,
OH, J ¼ 15 Hz),
.53 (d, 1H, AB system CH H OH, J ¼ 15 Hz), 4.61 (d,
20 min. The resultant mixture was stirred for additional
20 min and then solid NH Cl was added in small por-
tions until the solution turned to be colourless. NH was
a
H
b
4
4
2
a
b
3
H, AB system CH
OAc, J ¼ 13 Hz). C NMR: d 21.5,
7.2, 57.7, 85.2, 85.3, 113.7, 137.4, 137.7, 139.0, 148.2,
a
H
b
OAc, J ¼ 13 Hz), 5.12 (d, 2H,
2
removed by passing N through the mixture and ice
13
AB system CH
a
H
b
water was added. The resultant mixture was acidified
with 2 N HCl and extracted with ether (3 · 50 mL).
5
1
ꢁ
1
71.9. IR (neat): 3300, 1730, 1681, 1433, 751 cm . Anal.
(400.90): C, 32.96; Cl, 53.06; H,
.01. Found: C, 32.95; Cl, 53.07; H, 2.03.
Organic phase was washed with saturated NaHCO
3
Calcd for C11Cl
2
6
H
8
O
3
(3 · 50 mL), brine (2 · 50 mL) and dried over MgSO
4
and evaporated under reduced pressure. The crude
product was purified by flash column chromatography
to 20 afford (1R,4S)-(+)-4b (EtOAc/hexane, 1:5).
½aꢀ ¼ +17.8 (c 2, CH Cl ) (0.39 g, 81% yield).
4
.4. General procedure for enzymatic acetylation of 3
D
2
2
To a stirred solution of 500 mg meso-3 in 5 mL vinyl
acetate, 10 mg of CCL (or lipase) was added in one
portion and the reaction mixture was stirred at 20 ꢁC
Acknowledgements
(
TLC monitoring). The reaction mixture was filtered
and vinyl acetate was evaporated under reduced pres-
sure. The product (1S,4R)-())-2a or (1R,4S)-(+)-2b were
purified by flash column chromatography (EtOAc/hex-
We thank the Turkish Scientific and Technical Research
Council for a grant [no. TBAG-2244(102T169)] and
Turkish State Planning Organization for a grant (no.
BAP-07-02-DPT-2002 K120540-04).
20
ane, 1:5). (1R,4S)-(+)-2b: ½aꢀ ¼ +20.8 (c, 0.83, MeOH).
D
4.5. Dechlorination of (1S,4R)-())-2-acetoxymethyl-3-
hydroxymethyl-1,4,5,6,7,7-hexachlorobicyclo[2.2.1]-
References and notes
hepta-2,5-diene (1S,4R)-())-2a
1
2
. Trost, B. M. Science 1985, 227, 908.
. (a) Eichberger, G.; Penn, G.; Faber, K.; Griengl, H.
Tetrahedron Lett. 1986, 27, 2843; (b) Oberhauser, T.;
Bodenteich, M.; Faber, K.; Penn, G.; Griengl, H. Tetra-
hedron 1987, 3931.
To a stirred solution of metallic sodium (2.05 g,
8
(
9.5 mmol) in liquid NH3 (80 mL), (1S,4R)-())-2a
1.46 g, 3.64 mmol) in absolute EtOH/ether (25 mL, 1:1
ratio) was added dropwise under argon atmosphere over
3
. (a) Muchow, G.; Brunel, J. M.; Maffei, M.; Buono, G.
J. Org. Chem. 1995, 60, 852; (b) Ranchoux, M.; Brunel, J.
M.; Iacazio, G.; Buono, G. Tetrahedron: Asymmetry 1998,
9, 581; (c) Kashima, Y.; Liu, J.; Takenami, S.; Niwayama,
S. Tetrahedron: Asymmetry 2002, 13, 953.
2
2
0 min. The resultant mixture was stirred for additional
0 min and then solid NH Cl was added in small por-
was
4
tions until the solution turned to be colourless. NH
3
removed by passing N through the mixture and ice
2
water was added. The resultant mixture was acidified
with 2 M HCl and extracted with ether (3 · 50 mL).
4. Corey, E. J.; Shibasaki, M.; Nicolaou, K. C.; Malmsten,
C. L.; Samuelsson, B. Tetrahedron Lett. 1976, 737.
5
6
7
. Takano, S.; Kubodera, N.; Ogasawara, K. J. Org. Chem.
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Organic phase was washed with saturated NaHCO
(
3
1
3 · 50 mL), brine (2 · 50 mL), and dried over MgSO
4
and evaporated under reduced pressure. The crude
product was purified by flash column chromatography
to 20 afford (1S,4R)-())-4a (EtOAc/hexane, 1:5).
1
½
aꢀ ¼ )19.8 (c 2, CH
2
Cl
2
) (0.61 g, 86% yield). All H
NMR, C NMR and IR data are in accordance with
D
8. (a) Mitra, A. The Synthesis of Prostaglandins; John Wiley:
New York, 1977; (b) Roberts, S. M.; Scheinmann, F. New
Synthetic Routes to Prostaglandins and Thromboxanes;
Academic: London, 1982; (c) Apsimon, J. In The Total
Synthesis of Natural Products; John Wiley: New York,
13
3a
the literature data.
1
983; Vol. 5, p 249.
4
hydroxymethyl-1,4,5,6,7,7-hexachlorobicyclo[2.2.1]-
hepta-2,5-diene (1R,4S)-(+)-2b
.6. Dechlorination of (1R,4S)-())-2-acetoxymethyl-3-
9
. (a) Berger, B.; Rabiller, C. G.; K o€ nigsberger, K.; Faber,
K.; Griengl, H. Tetrahedron: Asymmetry 1990, 1, 541; (b)
Lapis, A. A. M.; Kreutz, O. C.; Pohlmann, A. R.; Costa,
V. E. U. Tetrahedron: Asymmetry 2001, 12, 557.
_
To a stirred solution of metallic sodium (2.05 g,
1
0. Tanyeli, C.; Cßelikel, G.; Akhmedov, I. M. Tetrahedron:
8
9.5 mmol) in liquid NH
1.00 g, 2.50 mmol) in absolute EtOH/ether (25 mL, 1:1
ratio) was added dropwise under argon atmosphere over
3
(80 mL), (1R,4S)-(+)-2b
Asymmetry 2001, 12, 2305.
11. Hoch, P. E.; Clegg, J. M. J. Am. Chem. Soc. 1959, 81,
5413.
(