Preparation of optically active 1-O-alkyl-3-O-arylsulfonyl-sn-grycerol derivatives: Substrate engineering in enzyme-mediated enantioselective hydrolysis

Article abstract of DOI:10.1055/s-0028-1083632

Lipase PS catalyzes the enantioselective hydrolysis of various 2-acetyl compounds of the 1-O-alkyl-3-O-arylsulfonyl-sn-glycerol derivatives to afford the corresponding optically active compounds. Changing the structure of the 1-O-alkyl and 3-O-arylsulfonyl groups affects both the reactivity and enantioselectivity. Finally, the E value of the reaction for 2-acetyl-3-O-3,5-dimethylbenzenesulfonyl-1-O-4-methoxybenzyl-sn-glycerol is greater than 200. Georg Thieme Verlag Stuttgart.

Full text of DOI:10.1055/s-0028-1083632

LETTER
2981
Preparation of Optically Active 1-O-Alkyl-3-O-arylsulfonyl-sn-glycerol
Derivatives: Substrate Engineering in Enzyme-Mediated Enantioselective
Hydrolysis
E
nzymatic Hydrol
a
ysis of
G
lyc
s
e
rol
D
eri
uvatives taka Shimada, Hiroshi Sato, Sachiyo Mochizuki, Kazutsugu Matsumoto*
Department of Chemistry, Meisei University, Hodokubo 2-1-1, Hino, Tokyo 191-8506, Japan
Fax +81(42)5917360; E-mail: mkazu@chem.meisei-u.ac.jp
Received 5 August 2008
We first examined the lipase-catalyzed hydrolysis of the
racemic 2-acetyl-3-O-tosyl-sn-glycerol derivatives ( )-1
bearing a suitable protecting group at the sn-1 position
(Table 1). The substrates were easily prepared from 2,2-
Abstract: Lipase PS catalyzes the enantioselective hydrolysis of
various 2-acetyl compounds of the 1-O-alkyl-3-O-arylsulfonyl-sn-
glycerol derivatives to afford the corresponding optically active
compounds. Changing the structure of the 1-O-alkyl and 3-O-aryl-
sulfonyl groups affects both the reactivity and enantioselectivity. dimethyl-4-hydroxymethyl-1,3-dioxolane by protection
and deprotection processes.6 In all cases, the enzymatic
reactions were performed using 4 mM of the substrates
with lipase PS (30 mg per 0.16 mmol of the substrate) in
0.1 M phosphate buffer (pH 6.5) containing 10% i-Pr2O
Finally, the E value of the reaction for 2-acetyl-3-O-3,5-dimethyl-
benzenesulfonyl-1-O-4-methoxybenzyl-sn-glycerol is greater than
200.
Key words: enantioselective hydrolyses, enzymes, kinetic resolu-
tion, glycerol derivatives, tosylates
for 24 hours at 30 °C. As shown in entry 1, we already
found that the R-enantiomer of ( )-1a with a benzyl group
(R = Bn) was selectively hydrolyzed to afford the almost
During the synthesis of natural and biologically active
compounds, optically active glycerol derivatives play sig-
nificant roles as useful chiral synthones. Moreover, the 1-
O-alkyl-sn-glycerol derivatives are direct precursors for
naturally occurring lipids with a broad spectrum of bio-
logical activities. Recently, the enzymatic reaction is one
of the practical and attractive methods used for the prepa-
ration of such optically active compounds.1 The hydro-
lase-mediated kinetic resolutions of the racemic 1,2-diol
monotosylate derivatives have also been developed as a
representative procedure.2–4 We have also accomplished
the practical preparation of various optically active 1,2-
diol monotosylates by enzymatic hydrolysis with lipase
PS (Burkholderia cepacia) from Amano Enzyme, Inc.,
and the methodical study of the substrate specificity.5 We
realized that the methodology was applicable to the prep-
aration of the optically active glycerol derivatives, al-
though the reactions did not always satisfactorily work in
terms of the enantioselectivity in some cases. In this pa-
per, we disclose the easy preparation of optically active
glycerol derivatives by enzymatic hydrolysis of the acetyl
compounds of the 1-O-alkyl-3-O-arylsulfonyl-sn-glycer-
ol derivatives. In particular, we focused on engineering
the structure of the 1-O-alkyl group, which could be easily
removed as the protecting group, and the arylsulfonyl part
as the leaving group in order to improve the enantioselec-
tivity for obtaining the useful chiral synthon with a high
ee, although both groups did not affect the structure of the
glycerol backbone.
optically pure (S)-1a as the remaining substrate and the re-
sulting (R)-2a.5,7 However, the enantioselectivity was
moderate (E value = 22)8 and lower than that in the case
of the substrate bearing a methyl group (R = Me), which
could not be easily deprotected under mild conditions (E
value = 292).5 Interestingly, changing the R group drasti-
cally affected both the reactivity and the enantioselectivi-
ty. The enzyme catalyzed the hydrolysis of ( )-1b bearing
a benzyloxymethyl group (R = BOM) with a higher enan-
tioselectivity (conv. = 0.51, E value = 127) to afford (S)-
1b with a 98% ee and (R)-2b with a 93% ee in 46% and
52% yields, respectively (entry 2), although the conver-
sion was lower than that in the case of 1a. Furthermore,
the hydrolysis of the substrate ( )-1c bearing a 4-
methoxybenzyl group (R = PMB) gave the best result (en-
try 3). The E value was up to 145 (conv. = 0.52), and both
enantiomers with high ee were obtained; (S)-1c with a
99% ee and (R)-2c with a 93% ee. In these cases, we as-
sumed that the hydrolysis of the S-enantiomers could be
very slow due to the interaction between the enzyme and
the oxygen atom of the R groups, thus this phenomenon
could lead to lower conversions and higher enantioselec-
tivities. On the other hand, the substrate ( )-1d bearing a
tert-butyldimethylsilyl group (R = TBS) was also hydro-
lyzed to give the corresponding (R)-2d (entry 4). Howev-
er, the ee of the resulting 2d was very low (12% ee), and
the substrate 1d was decomposed under the stated reaction
conditions.
When the benzyl group is fixed as the R substituent, we
can operate by changing the acyl and arylsulfonyl parts in
order to improve the enantioselectivity. Because triglycer-
ides of the higher fatty acids are the original substrates of
the lipase, the longer-chain acyl group could be better for
the enzymatic hydrolysis. However, using a longer-chain
SYNLETT 2008, No. 19, pp 2981–2984
x
x
.x
x
.2
0
0
8
Advanced online publication: 12.11.2008
DOI: 10.1055/s-0028-1083632; Art ID: U08108ST
© Georg Thieme Verlag Stuttgart · New York

2982
Y. Shimada et al.
LETTER
Table 1 Enantioselective Hydrolysis of 2-O-Acetyl-1-O-alkyl-3-O-tosyl-sn-glycerol [( )-1]a
OAc
OAc
OH
lipase PS
+
TsO
OR
TsO
OR TsO
OR
buffer–i-Pr2O
30 °C
( )-1
(S)-1
(R)-2
Entry
R
(S)-1
(R)-2
Conv.b
E valuec
Yield (%)
ee (%)
99.6
98
Yield (%)
ee (%)
59
1d
2
a
b
c
Bn
29
46
45
0
58
52
52
27
0.63
0.51
0.52
–
22
127
145
–
BOM
93
3
PMB
TBS
99
93
4
d
–
12
a Unless otherwise noted, the reaction was performed using ( )-1 (4 mM) with lipase PS in 0.1 M phosphate buffer (pH 6.5) containing 10%
i-Pr2O for 48 h at 30 °C.
b Calculated using ee(1)/[ee(1) + ee(2)].
c Calculated using ln{[1 – conv.][1 – ee(1)]}/ln{[1 – conv.][1 + ee(1)]}.
d We already reported these results in ref. 5.
acyl group leads to an increase in the molecular weight of lectivity (E value = 30), and the conversion was lower
the substrates. We then decided that this method was not than that in the case of 1a (Table 2, entry 1). Interestingly,
good for the practical synthesis, and next became interest- the substrate bearing a methyl group at the meta position
ed in the structure of the arylsulfonyl group. In previous [( )-3c, Ar = 3-MeC6H4] was hydrolyzed with a higher
reports, little attention has been paid to the structure of the enantioselectivity (E value = 60) to afford the almost op-
arylsulfonyl group because this was merely a kind of leav- tically pure (S)-3c, while a methyl substitution at the ortho
ing group. However, we expected that the substitution pat- position [( )-3b, Ar = 2-MeC6H4] did not improve the
tern on the aryl group could affect the reactivity in a enantioselectivity (entries 2 and 3). Based on these obser-
similar manner as in the case of the alkyl part, although vations, we assumed that a methyl group at the meta posi-
the aryl group could be remote from the active center of tion on the benzene ring could play an important role in
the enzyme. We then carried out the enzymatic hydrolyses the enzymatic distinction of the stereochemistry. As ex-
of the substrates with various arylsulfonyl groups, and pected, the highest enantioselective hydrolysis of the ( )-
these results are summarized in Table 2.9
3d with a 3,5-dimethylphenyl group (Ar = 3,5-Me2C6H3),
which had two methyl groups at the meta positions, for 24
hours at 30 °C smoothly proceeded (conv. = 0.49) to af-
Changing Ar to a phenyl group [( )-3a], which has no
substitution on the ring, slightly improved the enantiose-
Table 2 Enantioselective Hydrolysis of 2-O-Acetyl-1-O-benzyl-3-O-arylsulfonyl-sn-glycerol [( )-3]a
O
S
OAc
O
S
OAc
O
S
OH
lipase PS
+
Ar
O
OBn
Ar
O
OBn
Ar
O
OBn
buffer–i-Pr2O
O
O
O
( )-3
(S)-3
(R)-4
Entry
Ar
Ph
Time (h)
Temp (°C) (S)-3
Yield (%) ee (%)
(R)-4
Conv.
E value
Yield (%) ee (%)
1
2
3
4
5
6
7
8
9
a
b
c
24
24
24
24
48
24
24
24
48
30
30
30
30
30
10
20
40
30
28
47
39
42
44
69
46
39
52
82
74
40
43
58
48
53
25
50
40
43
89
80
81
96
88
93
87
82
82
0.52
0.48
0.55
0.49
0.53
0.22
0.51
0.52
0.47
30
20
2-MeC6H4
3-MeC6H4
3,5-Me2C6H3
99.7
93
60
d
168
>106
33
>99.8
26
87
42
88
29
e
2,4,6-Me3C6H2
73
22
a Unless otherwise noted, the reaction was performed using ( )-3 (4 mM) with lipase PS in 0.1 M phosphate buffer (pH 6.5) containing 10% i-Pr2O.
Synlett 2008, No. 19, 2981–2984 © Thieme Stuttgart · New York

LETTER
Enzymatic Hydrolysis of Glycerol Derivatives
2983
ford (S)-3d with a 93% ee and (R)-4d with a 96% ee, and we have successfully shown that engineering the structure
the E value was up to 168 (entry 4). Successive treatment of the protecting and leaving groups was a very important
of (S)-3d and (R)-4d with K2CO3 in MeOH resulted in technique for the enzymatic reaction in a manner similar
both enantiomers of the useful chiral synthons (R)- and to that for typical organic reactions.
(S)-benzyloxy-1,2-epoxypropane (5), respectively, with-
out any racemization (Scheme 1).10 A 48-hour reaction
Acknowledgment
gave the optically pure (S)-3d (entry 5). It is noteworthy
We thank Professor Tomoya Machinami (Meisei University) for
helpful discussion and Material Science Research Center (Meisei
University) for NMR analysis.
that lowering and raising the reaction temperature de-
creased the enantioselectivities (entries 6–8), and the re-
sults were not inconsistent with our previous report.5 We
also examined the enzymatic esterification of ( )-3d with
lipase PS-C Amano II, vinyl acetate, and Et3N in i-Pr2O
for 24 hours at 30 °C according to the modified procedure
reported by Boaz et al.3d Although the esterification pro-
ceeded, the reactivity (conv. = 0.34) and enantioselectivi-
ty (E value = 19) were lower than those obtained by our
hydrolysis version. On the other hand, the substitution of
a 2,4,6-trimethyl group on the benzene ring [( )-3e,
Ar = 2,4,6-Me3C6H2] did not improve the E value, but de-
creased the reactivity (entry 9).
References and Notes
(1) For recent reviews, see: (a) Bornscheuer, U. T.; Kazlauskas,
R. J. Hydrolases in Organic Synthesis; Wiley-VCH:
Weinheim, 1999. (b) Bommarius, A. S.; Riebel, B. R.
Biocatalysis; Wiley-VCH: Weinheim, 2004. (c) Faber, K.
Biotransformations in Organic Chemistry: A Textbook, 5th
ed.; Springer: Berlin, 2004. (d) Ghanem, A.; Aboul-Enein,
H. Y. Chirality 2004, 17, 1. (e) Garcia-Uradiales, E.;
Alfonso, I.; Gotor, V. Chem. Rev. 2005, 105, 313.
(f) Bornscheuer, U. T. Trends and Challenges in Enzyme
Technology; Springer: Berlin, 2005. (g) Fogassy, E.;
Nógrádi, M.; Kozma, D.; Egri, G.; Pálovics, E.; Kiss, V.
Org. Biomol. Chem. 2006, 4, 3011. (h) Gadler, P.; Faber, K.
Trends Biotechnol. 2007, 25, 83. (i) Ghanem, A.
O
S
OAc
K2CO3
O
O
O
OBn
OBn
OBn
OBn
MeOH
91%
O
Tetrahedron 2007, 63, 1721. (j) Gotor, V.; Alfonso, I.;
Garcia-Urdiales, E. Asymmetric Organic Synthesis with
Enzymes; Wiley-VCH: Weinheim, 2008.
(S)-3d
(R)-5
(S)-5
O
S
OH
(2) For enzymatic hydrolysis of acyl derivatives of 1,2-diol
monotosylates in an aqueous media, see: (a)Hamaguchi,S.;
Ohashi, T.; Watanabe, K. Agric. Biol. Chem. 1986, 50, 375.
(b) Hamaguchi, S.; Ohashi, T.; Watanabe, K. Agric. Biol.
Chem. 1986, 50, 1629. (c) Hamaguchi, S.; Katayama, K.;
Ohashi, T.; Watanabe, K. JP 62158250, 1987.
K2CO3
O
MeOH
91%
O
(R)-4d
Scheme 1
(d) Hamaguchi, S.; Kobayashi, M.; Katayama, K.; Ohashi,
T.; Watanabe, K. JP 62209049, 1987. (e) Kobayashi, M.;
Hamaguchi, S.; Katayama, K.; Ohashi, T.; Watanabe, K. JP
62212382, 1987. (f) Pederson, R. L.; Liu, K. K.-C.; Rutan,
J. F.; Chen, L.; Wong, C.-H. J. Org. Chem. 1990, 55, 4897.
(g) Chen, C.-S.; Liu, Y.-C.; Marsella, M. J. Chem. Soc.,
Perkin Trans. 1 1990, 2559.
Finally, we examined the enzymatic reaction of the race-
mic 2-acetyl-3-O-3,5-dimethylbenzenesulfonyl-1-O-4-
methoxybenzyl-sn-glycerol [( )-6] bearing the substitu-
tions, which produced the excellent result mentioned
above (Scheme 2). As expected, the reaction for 24 hours
at 30 °C smoothly proceeded with the highest enantiose-
lectivity to afford the corresponding (S)-6 with a 99% ee
and (R)-7 with a 96% ee in 37% and 48% isolated yields,
respectively (conv. = 0.51, E value = 259), and we did not
detect any byproducts.11 We postulated that the structure
of the PMB and 3,5-dimethylphenyl groups could precise-
ly fit the enzyme active site.
(3) For enzymatic esterification of 1,2-diol monotosylates in
organic solvent, see: (a) Chen, C.-S.; Liu, Y.-C.
Tetrahedron Lett. 1989, 30, 7165. (b) Chênevert, R.;
Gagnon, R. J. Org. Chem. 1993, 58, 1054. (c) Neagu, C.;
Hase, T. Tetrahedron Lett. 1993, 34, 1629. (d) Boaz, N. W.;
Zimmerman, R. L. Tetrahedron: Asymmetry 1994, 5, 153.
(e) Boaz, N. W.; Falling, S. N.; Moore, M. K. Synlett 2005,
1615. (f) For enzymatic hydrolysis in organic solvent, see
ref. 3c. For enzymatic alcoholysis in organic solvent, see
refs. 3a and 2g.
In summary, we have developed a simple and efficient
preparation of optically active 1-O-alkyl-3-O-arylsulfo-
nyl-sn-glycerol derivatives, which are useful chiral syn-
thons, by the enzyme-mediated hydrolysis. In particular,
(4) For enantioselective decomposition of 1,2-diol
monotosylate by microorganisms, see: Saito, Y.; Nakamura,
T. JP 10057096, 1998.
O
S
OAc
O
S
OAc
O
S
OH
lipase PS
+
O
OPMB
O
OPMB
O
OPMB
buffer–i-Pr2O
24 h, 30 °C
O
O
O
( )-6
(S)-6
28%, 99% ee
(R)-7
50%, 96% ee
conv. = 0.51
E value = 259
Scheme 2
Synlett 2008, No. 19, 2981–2984 © Thieme Stuttgart · New York

2984
Y. Shimada et al.
LETTER
(9) The substrate with a mesyl group was quite unstable and
decomposed under the enzymatic reaction conditions.
(10) Compound (R)-5: [a]D30 +1.89 (c 0.90, CHCl3; 93% ee).
Compound (S)-5: [a]D21 –1.81 (c 0.83, CHCl3; 95% ee); lit.14
[a]D21 +1.79 (c 5.02, CHCl3; R form).
(11) To a 200 mL Erlenmeyer flask containing ( )-6 (72.3 mg,
0.17 mmol; sub. concd, ca. 4 mM) were added of i-Pr2O (4
mL), 0.1 M phosphate buffer (40 mL, pH 6.5), and lipase PS
(30 mg). After the mixture was incubated for 24 h at 30 °C,
the products were extracted with EtOAc and purified by
flash column chromatography on SiO2 (eluent: hexane–
EtOAc, 4:1) to afford (S)-6 (26.4 mg, 37%, 99% ee) and (R)-
7 (31.5 mg, 48%, 96% ee).
(12) Martinelli, M. J.; Vaidyanathan, R.; Pawlak, J. M.; Nayyar,
N. K.; Dhokte, U. P.; Doecke, C. W.; Zollars, L. M. H.;
Moher, E. D.; Khau, V. V.; Kosmrlj, B. J. Am. Chem. Soc.
2002, 124, 3578.
(5) Shimada, Y.; Sato, H.; Minowa, S.; Matsumoto, K. Synlett
2008, 367.
(6) The racemic alcohols ( )-2, except for 2d, as the precursor
of the substrates were prepared in three steps: 1) protection
of the hydroxyl group of 2,2-dimethyl-4-hydroxymethyl-
1,3-dioxolane, 2) 2 M aq HCl–THF, 3) TsCl, Bu2SnO, Et3N–
CH2Cl2.12 In all cases, the resulting ( )-2 contained the
regioisomers, 3-acetyl-2-O-tosyl-sn-glycerol ( )-7, as the
minor product. After the enzymatic acylation of the mixture
using porcine pancreas lipase (PPL, Sigma), the pure ( )-2
was obtained. The details will be reported separately. On the
other hand, ( )-2d was prepared from the coupling of ( )-
glycidol with TsOH, followed by selective protection of the
primary hydroxyl group with TBS.
(7) The absolute configuration of 2a {[a]D25 –4.19 (c 2.49,
C6H6) (59% ee)} was confirmed by comparing the obtained
optical rotation value with the reported value: lit.13 [a]D
–6.70 (c 10, C6H6; R form).
25
(13) Byun, H.-S.; Bittman, R. Tetrahedron Lett. 1989, 30, 2751.
(14) Takano, S.; Goto, E.; Hirama, M.; Ogasawara, K.
Heterocycles 1981, 16, 381.
(8) Chen, C.-S.; Fujimoto, Y.; Girdaukas, G.; Sih, C. J. J. Am.
Chem. Soc. 1982, 104, 7294.
Synlett 2008, No. 19, 2981–2984 © Thieme Stuttgart · New York