Lipase-catalyzed enantio- and regioselective transformation of 3-epi-shikimic acid derivatives as the key step for the entry of polyoxygenated carbacycles

Article abstract of DOI:10.1016/j.molcatb.2010.07.009

Candida antarctica lipase B (Novozym 435)-catalyzed transesterification on methyl (±)-3,4-di-O-acetyl-5-O-(tert-butyldimethyl)silyl-3-epi-shikimate worked highly regio- and enantioselective manner. Only (3R,4S,5S)-isomer reacted with an E value over 500,

Full text of DOI:10.1016/j.molcatb.2010.07.009

Journal of Molecular Catalysis B: Enzymatic 67 (2010) 78–84
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Journal of Molecular Catalysis B: Enzymatic
journal homepage: www.elsevier.com/locate/molcatb
Lipase-catalyzed enantio- and regioselective transformation of 3-epi-shikimic
acid derivatives as the key step for the entry of polyoxygenated carbacycles
Manabu Hamada, Toshinori Higashi, Mitsuru Shoji, Kazuo Umezawa, Takeshi Sugai∗
Department of Applied Chemistry and Faculty of Pharmacy, Keio University, 1-5-30, Shibakoen, Minato-ku, Tokyo 105-8512, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 10 June 2010
Received in revised form 16 July 2010
Accepted 20 July 2010
Available online 17 August 2010
Candida antarctica lipase
O-acetyl-5-O-(tert-butyldimethyl)silyl-3-epi-shikimate worked highly regio- and enantioselective
manner. Only (3R,4S,5S)-isomer reacted with an value over 500, exclusively on C-3 acetate.
The regio- and enantioselectivity were greatly affected by the substitution pattern on the
hydroxy groups. Towards polyoxygenated carbacycles, the above-mentioned highly selective trans-
formation enabled the subsequent stereoselective inversion and dihydroxylation, to give methyl
(3S,4R,5S)-3,4,5-triacetoxy-1-cyclohexenecarboxylate [antipode of naturally occurring methyl (−)-3,4,5-
tri-O-acetylshikimate], and methyl (1R,2S,3S,4R,5R)-3,4-diacetoxy-5-(tert-butyldimethyl)silyloxy-1,2-
dihydroxy-cyclohexanecarboxylate.
B (Novozym 435)-catalyzed transesterification on methyl ( )-3,4-di-
E
Keywords:
Lipase
Transesterification
Kinetic resolution
Regioselective transformation
© 2010 Elsevier B.V. All rights reserved.
1. Introduction
detection at 216 nm unless otherwise stated. Optical rotation val-
ues were recorded on a Jasco P-1010 polarimeter. Silica gel 60 N
Regioselective protection and deprotection of polyoxygenated
carbacycles are of much importance towards the synthetic trans-
formation to bioactive cyclohexanoids. Gotor and co-workers [1]
attempted Candida antarctica lipase B-catalyzed regioselective
acetylation on methyl ester of natural origin of 1a (Scheme 1). The
enzyme mainly worked on C-3 and C-5 hydroxy groups, monoac-
etates 1b and 1d were obtained in 45 and 37% yield, respectively. In
contrast, sterically hindered hydroxy group on C-4 was less reac-
tive and such acetylated product was obtained as low as 18% yield.
We turned our attention to similar, but the epimeric substrate,
methyl 3-epi-shikimate 2a [2]. Moreover, if a racemic mixture of
2a is applied to what, the difference of the reaction rates between
enantiomers (enantioselectivity) and the regioselectivity in each
enantiomer are very interesting.
(spherical, neutral, 63–210 ␮m, 37565-79) of Kanto Chemical Co.
was used for column chromatography. Preparative TLC was per-
formed with Merck Silica Gel 60 F254 plates (0.5 mm thickness, No.
1.05744).
2.1. C. antarctica lipase B-catalyzed acetylation of methyl
(3R*,4R*,5S*)-3,4,5-trihydroxy-1-cyclohexenecarboxylate (2a)
To a solution of ( )-2a (50.3 mg, 0.27 mmol) in vinyl acetate
(1.25 mL) was added C. antarctica lipase B (Novozym 435, 75 mg).
The mixture was stirred for 24 h at 30 ◦C. The reaction was mon-
itored by silica gel TLC (hexane/AcOEt = 1:2). After removal of
insoluble materials by filtration with a pad of Celite, the filtrate
was concentrated in vacuo to give a mixture of (3R,4R,5S)-2b
and (3S,4S,5R)-2c (total 65.0 mg). The conversion was determined
to be 100% by 1H NMR analysis of crude mixture. The residue
was purified by silica gel column chromatography (2 g). Elution
with hexane/AcOEt = 1:2 afforded (3R,4R,5S)-2b (12.0 mg, 19%) and
(3S,4S,5R)-2c (18.0 mg, 29%) as colorless oil.
2. Experimental
IR spectra were measured as thin films for oils or ATR for solid
on a Jeol FT-IR SPX60 spectrometer. 1H NMR and 13C NMR spectra
were measured in CDCl3 at 400 MHz and 100 MHz respectively, on a
VARIAN 400-MR spectrometer. HPLC data were recorded on Jasco
MD-2010 and SHIMADZU SPD-M20A multi-channel detectors by
(3R,4R,5S)-2b: [␣]D23–12 (c 0.60, CHCl3) [lit. [3] [␣]D +38 (c
1.07, CHCl3), for (3S,4S,5R)-2b]; 1H NMR: ı 2.15 (s, 3H, Ac),
2.39 (ddd, J2,6a = 2.2 Hz, J5,6a = 6.8 Hz, J6a,6b = 14.4 Hz, 1H, H6a), 2.83
(dd, J5,6b = 4.4 Hz, 1H, H6b), 3.67 (dd, J3,4 = 7.2 Hz, J4,5 = 10.0 Hz,
1H, H4), 3.75 (s, 3H, Me ester), 3.83 (ddd, 1H, H5), 5.40 (ddd,
J2,3 = 3.2 Hz, 1H, H3), 6.78 (dd, 1H, H2); 13C NMR: ı 21.1, 31.7,
52.2, 67.3, 69.5, 69.9, 75.0, 128.3, 137.2, 166.4, 172.2; IR: 3490,
∗
Corresponding author. Tel.: +81 3 5400 2665; fax: +81 3 5400 2665.
E-mail address: sugai-tk@pha.keio.ac.jp (T. Sugai).
1381-1177/$ – see front matter © 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.molcatb.2010.07.009

M. Hamada et al. / Journal of Molecular Catalysis B: Enzymatic 67 (2010) 78–84
79
methoxybenzyl alcohol (2.33 mL, 18.7 mmol, 3.0 equiv.) were
added with stirring. The reaction was monitored by silica gel TLC
(hexane/AcOEt = 5:1). The mixture was stirred for 24 h at room
temperature, then the reaction was quenched by adding water.
The organic materials were extracted with AcOEt, and the com-
bined extracts were washed with brine, dried over Na2SO4, and
concentrated in vacuo. The residue was purified by silica gel col-
umn chromatography (100 g). Elution with hexane/AcOEt = 6:1
afforded ( )-2d (2.13 g, 81%) as colorless oil. 1H NMR: ı 0.11
[s, 6H, Si(CH3)2], 0.90 (s, 9H, tert-butyl), 2.20 (ddd, J2,6a = 2.8 Hz,
J5,6a = 4.8 Hz, J6a,6b = 14.8 Hz, 1H, H6a), 2.67 (ddd, J5,6b = 2.0 Hz,
J3,6b = 4.0 Hz, 1H, H6b), 3.67 (m, 2H, H3, H4), 3.72 (s, 3H, Me
ester), 3.78 (s, 3H, OCH3), 4.10 (ddd, J4,5 = 6.4 Hz, 1H, H5), 4.67 (d,
J = 11.2 Hz, 1H, Bn-CH), 4.74 (d, 1H, Bn-CH), 6.73 (dd, J2,3 = 2.4 Hz,
1H, H2), 6.86 (dd, J = 2.4, 6.8 Hz, 2H, Ar-H), 7.30 (d, 2H, Ar-H);
13C NMR: ı −4.76, −4.23, 18.0, 25.8, 33.0, 52.0, 55.3, 71.1, 72.1,
78.2, 113.8, 128.6, 129.5, 130.3, 137.0, 159.3, 166.5; IR: 3473,
3417, 2954, 2908, 2862, 1686, 1446, 1365, 1254, 1086, 1030 cm−1
.
Anal. Calcd for C22H34O6Si: C 62.53, H 8.11; found: C 62.71,
H 8.01.
Scheme 1. Reagents and conditions: (a) C. antarctica lipase B (Novozym 435), vinyl
acetate [45% for 1b, 18% for 1c and 37% for 1d].
2.4. Methyl (3R*,4S*,5S*)-5-(tert-butyldimethyl)silyloxy-3,4-
dihydroxy-1-cyclohexenecarboxylate
(2e)
3405, 3232, 2859, 1699, 1650, 1427, 1372, 1238, 1184, 1144, 1059,
999 cm−1. Its NMR spectra were identical with those reported
previously [3].
To
a mixture of 2d (2.05 g, 4.85 mmol), CH2Cl2 (40 mL),
and water (16 mL) was added 2,3-dichloro-5,6-dicyano-p-
benzoquinone (DDQ, 1.32 g, 5.82 mmol, 1.2 equiv.). The reaction
was monitored by silica gel TLC (hexane/AcOEt = 2:1). The mixture
was stirred for 12 h at 20 ◦C, then the reaction was quenched by
adding water. The aqueous layer was extracted with CHCl3, and
the combined extracts were washed with brine, dried over Na2SO4,
and concentrated in vacuo. The residue was purified by silica gel
column chromatography (40 g). Elution with hexane/AcOEt = 3:1
afforded ( )-2e (1.36 g, 93%) as colorless needles. mp 99.5–100 ◦C;
1H NMR: ı 0.10 [s, 6H, Si(CH3)2], 0.89 (s, 9H, tert-butyl), 2.23
(ddd, J2,6a = 2.8 Hz, J5,6a = 6.4 Hz, J6a,6b = 17.6 Hz, 1H, H6a), 2.69 (br
s, 2H, OH), 2.70 (ddd, J5,6b = 5.6 Hz, 1H, H6b), 3.55 (dd, J3,4 = 7.6 Hz,
J4,5 = 9.2 Hz, 1H, H4), 3.73 (s, 3H, Me ester), 3.74 (ddd, 1H, H5),
4.27 (ddd, J2,3 = 2.4 Hz, 1H, H3), 6.73 (dd, 1H, H2); 13C NMR: ı
−4.80, −4.32, 18.0, 25.8, 32.9, 52.0, 70.4, 71.2, 128.2, 138.0, 166.6;
IR: 3423, 2947, 2929, 2852, 1714, 1662, 1432, 1257, 1074, 1025,
985 cm−1. Anal. Calcd for C14H26O5Si: C 55.60, H 8.67; found: C
55.68, H 8.65.
(3S,4S,5R)-2c: [␣]D23 +11 (c 0.90, CHCl3); 1H NMR: ı 2.13 (s, 3H,
Ac), 2.28 (ddd, J2,6a = 3.2 Hz, J5,6a = 10.0 Hz, J6a,6b = 17.6 Hz, 1H, H6a),
2.59 (br s, 1H, OH), 2.83 (dd, J5,6b = 6.0 Hz, 1H, H6b), 3.74 (s, 3H,
Me ester), 3.99 (ddd, J4,5 = 10.0 Hz, 1H, H5), 4.33 (ddd, J2,3 = 2.4 Hz,
J3,4 = 7.2 Hz, 1H, H3), 4.86 (dd, 1H, H4), 6.59 (dd, 1H, H2); 13C NMR: ı
21.1, 31.6, 52.2, 69.5, 74.8, 75.0, 130.5, 134.4, 166.0, 171.5; IR: 3406,
2354, 1714, 1655, 1431, 1371, 1228, 1061, 1026, 960 cm−1
.
2.2. Methyl (3R*,4R*,5R*)-5-(tert-butyldimethyl)silyloxy-
7-oxabicyclo[4.1.0]hept-1-en-1-carboxylate (3b)
To a solution of 3a (2.95 g, 17.3 mmol) in CH2Cl2 (20 mL) were
added tert-butyldimethylsilyl chloride (TBSCl, 3.13 g, 20.8 mmol,
1.2 equiv.) and imidazole (1.42 g, 20.8 mmol, 1.2 equiv.) with stir-
ring at 10 ◦C under argon atmosphere. The reaction was monitored
by silica gel TLC (hexane/AcOEt = 6:1). The mixture was stirred for
24 h, with gradually raising the reaction temperature to 25 ◦C, then
the reaction was quenched by adding saturated NH4Cl aqueous
solution. The organic materials were extracted with AcOEt several
times, and the combined extracts were washed with brine, dried
over Na2SO4, and concentrated in vacuo. The residue was purified
by silica gel column chromatography (100 g). Elution with hex-
ane/AcOEt = 7:1 afforded ( )-3b (4.73 g, 96%) as colorless oil. 1H
NMR: ı 0.06 (s, 3H, SiCH3), 0.08 (s, 3H, SiCH3), 0.84 (s, 9H, tert-butyl),
2.22 (ddd, J2,6a = 3.2 Hz, J5,6a = 4.8 Hz, J6a,6b = 17.2 Hz, 1H, H6a), 2.67
(ddd, J4,6b = 2.0 Hz, J5,6b = 2.4 Hz, 1H, H6b), 3.40 (ddd, J3,4 = 4.0 Hz,
J4,5 = 4.4 Hz, 1H, H4), 3.43 (dd, J2,3 = 4.0 Hz, 1H, H3), 3.74 (s, 3H, Me
ester), 4.50 (ddd, 1H, H5), 7.07 (dd, 1H, H2); 13C NMR: ı −4.8, 18.1,
25.7, 29.4, 46.7, 51.9, 56.4, 64.0, 131.0, 133.0, 166.6; IR: 2963, 2924,
2893, 2868, 1720, 1473, 1259, 1203, 1095 cm−1. Anal. Calcd for
C14H24O4Si: C 59.12, H 8.51; found: C 59.17, H 8.55.
2.5. C. antarctica lipase B-catalyzed acetylation of ( )-2e
In a similar manner as described for the acylation of ( )-2a, a
solution of ( )-2e (90.1 mg, 0.31 mmol) was treated with Novozym
435 (90 mg) in vinyl acetate (900 ␮L) to give (3R,4S,5S)-2f (51.0 mg,
48%, 75.4% ee) and (3S,4R,5R)-2e (30.2 mg, 34%, 77.6% ee) as color-
less oil.
(3R,4S,5S)-2f: [␣]D23–15.3 (c 1.45, CHCl3); 1H NMR: ı 0.10 (s,
6H, Si(CH3)2), 0.88 (s, 9H, tert-butyl), 2.10 (s, 3H, Ac), 2.23 (ddd,
J2,6a = 2.8 Hz, J5,6a = 10.4 Hz, J6a,6b = 17.6 Hz, 1H, H6a), 2.63 (br s,
1H, OH), 2.75 (ddd, J3,6b = 1.2 Hz, J5,6b = 5.2 Hz, 1H, H6b), 3.55 (dd,
J3,4 = 8.0 Hz, J4,5 = 10.0 Hz, 1H, H4), 3.72 (s, 3H, Me ester), 3.74
(ddd, 1H, H5), 4.27 (ddd, J2,3 = 2.4 Hz, 1H, H3), 6.73 (dd, 1H, H2);
13C NMR: ı −4.83, −4.31, 18.0, 21.0, 25.7, 32.9, 52.1, 70.8, 73.4,
74.5, 129.9, 134.9, 166.1, 170.6; IR: 2950, 2917, 2863, 1728, 1444,
1363, 1227, 1097, 968 cm−1. HPLC [column, Daicel CHIRALCEL®
AD-H, 0.46 cm × 25 cm; hexane/isopropyl alcohol = 70:1; flow
rate 0.5 mL/min]: tR (min) = 27.9 (87.7%), 33.4 (12.3%). The
authentic specimen of ( )-2f was prepared by the acetylation
of ( )-2e.
2.3. Methyl (3R*,4S*,5S*)-5-(tert-butyldimethyl)silyloxy
-4-hydroxy-3-(p-methoxy)benzyloxy-
1-cyclohexenecarboxylate (2d)
To
a solution of 3b (1.77 g, 6.22 mmol) in anhydrous
CH2Cl2 (18 mL), Yb(OTf)3 (0.39 g, 0.62 mmol, 0.1 equiv.) and p-

80
M. Hamada et al. / Journal of Molecular Catalysis B: Enzymatic 67 (2010) 78–84
(3S,4R,5R)-2e: [␣]D23–40.0 (c 1.50, CHCl3). HPLC [CHIRALCEL®
2.9. Methyl (3R*,4S*,5S*)-3,4-diacetoxy-
5-(tert-butyldimethyl)silyloxy-1-cyclohexenecarboxylate (2j)
AD-H, 0.46 cm × 25 cm; hexane/isopropyl alcohol = 15:1; flow rate
0.5 mL/min]: tR (min) = 22.3 (88.8%), 23.9 (11.2%).
To a solution of 2e (203 mg, 0.67 mmol) in pyridine (2 mL)
were added Ac2O (204 mg, 2.00 mmol, 3.0 equiv.) and 4-N,N-
dimethylaminopyridine (DMAP, 41.5 mg, 0.34 mmol, 0.5 equiv.)
under argon atmosphere. The reaction was monitored by silica gel
TLC (hexane/AcOEt = 5:1). The mixture was stirred for 2 h at room
temperature, then the reaction was quenched with adding water.
The organic materials were extracted with AcOEt, and the com-
bined extracts were washed with brine, dried over Na2SO4, and
concentrated in vacuo. The residue was purified by silica gel column
chromatography (12 g). Elution with hexane/AcOEt = 5:1 afforded
2.6. Methyl (3R*,4S*,5S*)-5-(tert-butyldimethyl)silyloxy-
3-(p-methoxy)benzyloxy-4-methoxy-
1-cyclohexenecarboxylate (2g)
To a solution of 2d (75.0 mg, 0.18 mmol) in anhydrous CH2Cl2
(3 mL), Proton Sponge® (91.3 mg, 0.43 mmol, 2.4 equiv.) and
Me3OBF4 (32.0 mg, 0.22 mmol, 1.2 equiv.) were added with stirring.
The reaction was monitored by silica gel TLC (hexane/AcOEt = 5:1).
The mixture was stirred for 14 h at 0 ◦C under argon atmosphere,
then the reaction was quenched by adding water. The organic mate-
rials were extracted with AcOEt, and the combined extracts were
washed with brine, dried over Na2SO4, and concentrated in vacuo.
The residue was purified by silica gel column chromatography
(4 g). Elution with hexane/AcOEt = 5:1 afforded ( )-2g (54.2 mg,
69%) as colorless oil. 1H NMR: ı 0.07 (s, 3H, SiCH3), 0.09 (s, 3H,
SiCH3), 0.89 (s, 9H, tert-butyl), 2.23 (ddd, J2,6a = 3.2 Hz, J5,6a = 9.6 Hz,
J6a,6b = 18.0 Hz, 1H, H6a), 2.65 (dd, J5,6b = 6.0 Hz,1H, H6b), 3.22 (dd,
J3,4 = 7.6 Hz, J4,5 = 9.6 Hz, 1H, H4), 3.60 (s, 3H, OCH3), 3.72 (s, 3H,
Me ester), 3.73 (ddd, 1H, H5), 3.79 (s, 3H, ArOCH3), 4.06 (ddd,
J2,3 = 2.4 Hz, 1H, H3), 4.64 (s, 2H, Bn-CH2), 6.72 (dd, 1H, H2), 6.87
(dd, J = 2.0, 6.8 Hz, 2H, Ar-H), 7.28 (d, 2H, Ar-H); 13C NMR: ı −4.84,
−4.63, 18.1, 25.8, 34.0, 51.9, 55.2, 61.1, 70.7, 71.4, 72.2, 79.4, 86.0,
113.7, 113.8, 129.4, 130.3, 132.0, 136.9, 159.1, 159.2, 166.6; IR:
(
)-2j (241 mg, 93%) as colorless oil. 1H NMR: ı 0.04 (s, 3H, SiCH3),
0.07 (s, 3H, SiCH3), 0.84 (s, 9H, tert-butyl), 2.03 (s, 3H, Ac), 2.04
(s, 3H, Ac), 2.34 (ddd, J2,6a = 3.2 Hz, J5,6a = 9.2 Hz, J6a,6b = 18.0 Hz,1H,
H6a), 2.68 (ddd, J3,6b = 1.2 Hz, J5,6b = 5.6 Hz, 1H, H6b), 3.74 (s, 3H, Me
ester), 3.91 (ddd, J4,5 = 9.6 Hz, 1H, H5), 5.11 (dd, J3,4 = 7.6 Hz, 1H, H4),
5.53 (ddd, J2,3 = 2.0 Hz, 1H, H3), 6.58 (dd, 1H, H2); 13C NMR: ı −5.00,
−4.69, 17.7, 20.8, 21.0, 25.5, 33.2, 52.1, 67.9, 71.5, 74.4, 130.2, 134.1,
165.9, 169.9, 170.3; IR: 2958, 2933, 2863, 2362, 1745, 1724, 1437,
1232, 1124, 1052, 1014 cm−1. Its 1H NMR spectra was identical with
that reported previously [5]. Anal. Calcd for C18H30O7Si: C 55.93, H
7.82; found: C 55.62, H 7.77.
2.10. C. antarctica lipase B-catalyzed transesterification of ( )-2j
A solution of 2j (186 mg, 0.48 mmol) in cyclopentanol (3.7 mL)
was added Novozym 435 (370 mg), and the mixture was stirred
for 24 h at 65 ◦C. After removal of insoluble materials by filtration
with the pad of Celite, the filtrate was concentrated in vacuo to
give a mixture of (3R,4S,5S)-2k and (3S,4R,5R)-2j (total 195 mg). The
conversion was determined by 1H NMR analysis of crude reaction
mixture. The residue was purified by silica gel column chromatog-
raphy (2 g). Elution with hexane/AcOEt = 4:3 afforded (3R,4S,5S)-2k
(60.3 mg, 38%, >99.9% ee) and (3S,4R,5R)-2j (89.0 mg, 48%, 90.4% ee)
as a colorless oil.
2941, 2858, 1714, 1605, 1522, 1444, 1246, 1068, 1034, 827 cm−1
This was employed for the next step without further purification.
.
2.7. Methyl (3R*,4S*,5S*)-5-(tert-butyldimethyl)silyloxy-
3-hydroxy-4-methoxy-1-cyclohexenecarboxylate (2h)
In a similar manner as described for the deprotection of ( )-
2d, treatment of ( )-2g (35.2 mg, 0.08 mmol) with DDQ (20.4 mg,
0.09 mmol, 1.2 equiv.) in CH2Cl2 (700 ␮L) and water (280 ␮L) gave
(
)-2h (25.5 mg, quant.) as a colorless oil. 1H NMR: ı 0.08 (s, 3H,
(3R,4S,5S)-2k: [␣]D +19.4 (c 0.75, CHCl3); 1H NMR: ı 0.08 (s,
23
SiCH3), 0.11 (s, 3H, SiCH3), 0.87 (s, 9H, tert-butyl), 2.23 (dddd,
J3,6a = 1.6 Hz, J2,6a = 2.0 Hz, J5,6a = 6.4 Hz, J6a,6b = 18.0 Hz, 1H, H6a),
2.54 (ddd, J3,6b = 2.0 Hz, J5,6b = 4.4 Hz, 1H, H6b), 2.82 (br s, 1H, OH),
3.36 (dd, J3,4 = 4.8 Hz, J4,5 = 6.4 Hz, 1H, H4), 3.49 (s, 3H, OCH3), 3.74
(s, 3H, Me ester), 4.12 (m, 2H, H3, H5), 6.86 (dd, 1H, H2); 13C NMR:
ı −5.04, −4.88, 18.0, 25.8, 30,7, 51.9, 59.2, 67.6, 68.4, 81.9, 127.6,
136.8, 167.2. Its NMR spectra were identical with those reported
previously [4].
3H, SiCH3), 0.09 (s, 3H, SiCH3), 0.86 (s, 9H, tert-butyl), 2.07 (s, 3H,
Ac), 2.41(ddd, J2,6a = 2.4 Hz, J5,6a = 6.0 Hz, J6a,6b = 18.0 Hz, 1H, H6a),
2.58 (ddd, J3,6b = 1.6 Hz, J5,6b = 4.8 Hz, 1H, H6b), 3.76 (s, 3H, Me ester),
4.08 (ddd, J4,5 = 7.2 Hz, 1H, H5), 4.19 (ddd, J4,5 = 4.8 Hz, 1H, H3),
4.92 (dd, 1H, H4), 6.84 (dd, 1H, H2); 13C NMR: ı −5.02, −4.83,
17.9, 21.1, 25.6, 31.3, 52.1, 67.0, 68.8, 75.4, 127.8, 136.8, 166.8,
171.0; IR: 2933, 2854, 2366, 2326, 1714, 1518, 1252, 1115, 1047,
1007 cm−1. Anal. Calcd for C16H28O6Si: C 55.79, H 8.19; found:
C 55.68, H 8.42. HPLC [CHIRALCEL® OD-H, 0.46 cm × 25 cm; hex-
ane/isopropyl alcohol = 30:1; flow rate 0.5 mL/min]: tR (min) = 30.0
(single peak). The retention time of the antipode was con-
firmed to be 24.0 min, by the analysis of an authentic specimen
of ( )-2k. This was prepared as follows: a solution of ( )-2d
(55.8 mg, 0.13 mmol) was treated with DMAP (7.2 mg, 0.07 mmol,
0.5 equiv.) and Ac2O (17.0 mg, 0.17 mmol, 1.2 equiv.) in pyri-
dine (200 ␮L) to give the acetate. Removal of (p-methoxy)benzyl
group provided ( )-2k (18.8 mg, 68% over two steps) as colorless
oil.
2.8. C. antarctica lipase B-catalyzed acetylation of ( )-2h
In a similar manner as described for the acetylation of ( )-
2a, treatment of ( )-2h (12.3 mg, 0.04 mmol) with Novozym 435
(20 mg) and vinyl acetate (200 ␮L) gave (3R,4S,5S)-2i (2.8 mg, 20%,
44.6% ee) and (3S,4R,5R)-2h (4.0 mg, 32%, 16.4% ee) as colorless
oil.
(3R,4S,5S)-2i: 1H NMR: ı 0.07 (s, 3H, SiCH3), 0.08 (s, 3H, SiCH3),
0.89 (s, 9H, tert-butyl), 2.10 (s, 3H, Ac), 2.29 (ddd, J2,6a = 2.8 Hz,
J5,6a = 8.4 Hz, J6a,6b = 18.0 Hz, 1H, H6a), 2.68 (ddd, J3,6b = 1.2 Hz,
J5,6b = 6.0 Hz, 1H, H6b), 3.27 (dd, J3,4 = 7.2 Hz, J4,5 = 8.8 Hz, 1H,
H4), 3.50 (s, 3H, OCH3), 3.73 (s, 3H, Me ester), 3.84 (ddd,
1H, H5), 5.39 (ddd, J2,3 = 2.0 Hz,1H, H3), 6.86 (dd, 1H, H2).
Its ee was determined by the HPLC analysis at the stage of
2h, after the hydrolysis of acetate. HPLC [CHIRALCEL® AD-
H, 0.46 cm × 25 cm; hexane/isopropyl alcohol = 50:1; flow rate
0.5 mL/min; detected at 220 nm]: tR (min) = 26.0 (27.7%), 36.7
(72.3%).
(3S,4R,5R)-2j: [␣]D +19.1 (c 1.55, CHCl3). HPLC [CHIRALCEL®
23
OD-H, 0.46 cm × 25 cm; hexane/isopropyl alcohol = 150:1; flowrate
0.5 mL/min]: tR (min) = 18.8 (4.8%), 22.7 (95.2%).
2.11. Methyl
(3R*,4R*,5S*)-3,4,5-triacetoxy-1-cyclohexenecarboxylate (2l)
To a solution of 3a (320 mg, 1.88 mmol) in THF (2 mL) were
added water (1 mL) and trifluoroacetic acid (300 ␮L). After stirring
for 40 h at room temperature, the mixture was concentrated in
(3S,4R,5R)-2h: HPLC: tR (min) = 26.0 (58.2%), 36.7 (41.8%).

M. Hamada et al. / Journal of Molecular Catalysis B: Enzymatic 67 (2010) 78–84
81
vacuo, and the residue was dissolved in pyridine (2 mL). To the
mixture were added Ac2O (1.15 g, 11.3 mmol, 6.0 equiv.) and DMAP
(24.4 mg, 0.20 mmol, 0.1 equiv.). The reaction was monitored by
silica gel TLC (hexane/AcOEt = 4:1). The mixture was stirred for 4 h
at room temperature, then the reaction was quenched with water.
The organic materials were extracted with AcOEt, and the com-
bined extracts were washed with brine, dried over Na2SO4, and
concentrated in vacuo. The residue was purified by silica gel column
chromatography (30 g). Elution with hexane/AcOEt = 4:1 afforded
−4.87, 17.9, 20.9, 25.6, 31.3, 52.1, 65.9, 66.9, 70.2, 131.0, 133.2,
166.5, 170.0, 170.1; IR: 3419, 2952, 2345, 1718, 1446, 1375, 1238,
1041, 927, 843 cm−1. Its 1H NMR spectrum was identical with that
reported previously [5].
2.14. Methyl (3S,4R,5S)-3,4,5-triacetoxy-
1-cyclohexenecarboxylate (1f)
(
)-2l (334 mg, 56%) as colorless oil. 1H NMR: ı 2.00 (s, 3H, Ac), 2.01
To a solution of 1e (35.2 mg, 0.09 mmol) in THF (1 mL) were
added acetic acid (13.2 mg, 0.22 mmol 2.4 equiv.) and tetra-n-
butylammonium fluoride (TBAF, 1 M solution in THF, 11 ␮L,
0.11 mmol, 1.2 equiv.). The mixture was stirred for 40 h at 20 ◦C,
then the reaction was quenched with water. The organic materi-
als were extracted with AcOEt, and the combined extracts were
washed with brine, dried over Na2SO4, and concentrated in vacuo.
The residue was purified by silica gel column chromatography (2 g).
Elution with hexane/AcOEt = 3:1 afforded diacetate (11.2 mg) as
colorless oil. This residue was employed for next step without fur-
ther purification.
(s, 3H, Ac), 2.02 (s, 3H, Ac), 2.37 (ddd, J2,6a = 2.8 Hz, J5,6a = 9.2 Hz,
J6a,6b = 18.0 Hz, 1H, H6a), 2.94 (dd, J5,6b = 6.0 Hz, 1H, H6b), 3.71 (s,
3H, Me ester), 5.11 (ddd, J4,5 = 9.2 Hz, 1H, H5), 5.25 (dd, J3,4 = 7.6 Hz,
1H, H4), 5.55 (ddd, J2,3 = 2.4 Hz, 1H, H3), 6.62 (dd, 1H, H2); 13C NMR:
ı 20.7, 20.8, 29.3, 52.3, 68.3, 70.9, 71.3, 129.7, 133.9, 165.5, 169.9,
170.0, 170.1; IR: 2962, 2362, 1734, 1708, 1437, 1363, 1227, 1039,
968 cm−1. Anal. Calcd for C14H18O8: C 53.50, H 5.77; found: C 53.73,
H 5.79.
2.12. C. antarctica lipase B-catalyzed transesterification of ( )-2l
This was dissolved in pyridine (300 ␮L) were added Ac2O
(4.6 mg, 0.45 mmol, 1.2 equiv.) and DMAP (2.3 mg, 0.20 mmol,
0.5 equiv.). The reaction was monitored by silica gel TLC (hex-
ane/AcOEt = 2:1). The mixture was stirred for 2 h at room
temperature, and the reaction was quenched with water. The
organic materials were extracted with AcOEt, and the combined
extracts were washed with brine, dried over Na2SO4, and con-
centrated in vacuo. The residue was purified by preparative TLC
with hexane/AcOEt = 2:1 to afford 1f (10.2 mg, 36% over two steps)
In a similar manner as described for the transesterification of
)-2j, a solution of ( )-2l (150 mg, 0.48 mmol) was treated with
Novozym 435 (300 mg) in cyclopentanol (3 mL) to give (3R,4R,5S)-
2m and (3S,4S,5R)-2n (70.8 mg) and (3S,4S,5R)-2l (50.8 mg, 34%,
56.8% ee) as colorless oil.
(
Through 1H NMR measurement of the mixture of 2m and 2n,
the following signals were assigned for each component, respec-
tively. (3R,4S,5S)-2m: ı 2.03 (s, 3H, Ac), 2.09 (s, 3H, Ac), 2.39
(ddd, J2,6a = 2.8 Hz, J5,6a = 8.8 Hz, J6a,6b = 17.6 Hz, 1H, H6a), 2.89 (ddd,
J3,6b = 1.2 Hz, J5,6b = 5.6 Hz, 1H, H6b), 3.74 (s, 3H, Me ester), 4.40
(ddd, J2,3 = 3.2 Hz, J3,4 = 6.8 Hz, 1H, H3), 5.02 (dd, J4,5 = 10.0 Hz, 1H,
H4), 5.12 (ddd, 1H, H5), 6.78 (dd, 1H, H2); (3S,4S,5R)-2n: ı 2.05
(s, 3H, Ac), 2.09 (s, 3H, Ac), 2.36 (ddd, J2,6a = 3.2 Hz, J5,6a = 9.6 Hz,
J6a,6b = 18.0 Hz, 1H, H6a), 2.94 (ddd, J3,6b = 1.2 Hz, J5,6b = 5.2 Hz, 1H,
H6b), 3.74 (s, 3H, Me ester), 3.93 (ddd, J4,5 = 9.6 Hz, 1H, H5), 5.06
(dd, J3,4 = 7.6 Hz, 1H, H4), 5.56 (ddd, J2,3 = 2.8 Hz, 1H, H3), 6.78 (dd,
1H, H2).
23
as colorless oil. [␣]D +180 (c 0.52, CHCl3) [lit. [6] [␣]D–174 (c
1.07, CHCl3), for (3R,4S,5R)-1f]; 1H NMR: ı 2.03 (s, 3H, Ac), 2.05
(s, 3H, Ac), 2.06 (s, 3H, Ac), 2.41 (ddd, J2,6a = 2.0 Hz, J5,6a = 5.2 Hz,
J6a,6b = 18.0 Hz, 1H, H6a), 2.58 (ddd, J3,6b = 1.6 Hz, J5,6b = 4.8 Hz, 1H,
H6b), 3.75 (s, 3H, Me ester), 5.25 (dd, J3,4 = 4.8 Hz, J4,5 = 8.0 Hz,
1H, H4), 5.27 (ddd, 1H, H5), 5.71 (ddd, J2,3 = 3.6 Hz, 1H, H3), 6.74
(dd, 1H, H2); 13C NMR: ı 20.7, 20.8, 21.0, 52.2, 66.0, 66.8, 67.7,
131.2, 132.7, 165.9, 169.9, 170.0; IR: 1745, 1714, 1439, 1371, 1216,
1036 cm−1. Its NMR spectra were identical with those reported
previously [6].
(3S,4S,5R)-2l: [␣]D +28.3 (c 2.50, CHCl3). HPLC [CHIRALCEL®
23
AD-H, 0.46 cm × 25 cm; hexane/isopropyl alcohol = 30:1; flow rate
0.5 mL/min]: tR (min) = 20.6 (21.6%), 21.9 (78.4%).
2.15. Methyl (1R,2S,3S,4R,5R)-3,4-diacetoxy-
5-(tert-butyldimethyl)silyloxy-1,2-dihydroxy-
cyclohexanecarboxylate (5a)
2.13. Methyl (3S,4S,5S)-3,4-diacetoxy-
5-(tert-butyldimethylsilyloxy)-1-cyclohexenecarboxylate (1e)
Diacetate 2j (259.4 mg, 0.67 mmol) was dissolved in tert-
BuOH (1.3 mL) and H2O (1.3 mL). To this, K2OsO2(OH)4 (12.5 mg,
0.034 mmol, 0.05 equiv.) and N-methylmorpholine N-oxide (NMO,
102.2 mg, 0.87 mmol 1.3 equiv.) were added with stirring. The reac-
tion was monitored by silica gel TLC (hexane/AcOEt = 2:1). The
mixture was stirred for 2 h at 40 ◦C, then the reaction was quenched
with water. The organic materials were extracted with AcOEt,
and the combined extracts were washed with saturated aqueous
Na2S2O3, brine, dried over Na2SO4, and concentrated in vacuo.
The residue was purified by silica gel column chromatography
(10 g). Elution with hexane/AcOEt = 2:1 afforded 5a (249.4 mg, 89%)
as white solid. mp 59.5–60.5 ◦C; 1H NMR: ı 0.02 (s, 3H, SiCH3),
0.03 (s, 3H, SiCH3), 0.82 (s, 9H, tert-butyl), 1.88 (dd, J5,6a = 10.8 Hz,
J6a,6b = 13.6 Hz, 1H, H6a), 1.96 (dd, J5,6b = 5.2 Hz, 1H, H6b), 2.02 (s, 3H,
Ac), 2.05 (s, 3H, Ac), 3.59 (br s, 1H, OH), 3.83 (s, 3H, Me ester), 3.92
(d, J2,3 = 9.6 Hz, 1H, H2), 4.02 (ddd, J4,5 = 9.2 Hz, 1H, H5), 5.02 (dd,
J3,4 = 9.8 Hz, 1H, H4), 5.10 (dd, 1H, H3); 13C NMR: ı −4.95, −4.68,
17.8, 20.8, 21.0, 25.5, 39.2, 53.6, 67.7, 73.6, 74.0, 75.1, 169.8, 171.5,
To a solution of 2k (50.0 mg, 0.14 mmol) in anhydrous CH2Cl2
(420 ␮L) were added Et3N (44.6 mg, 0.44 mmol, 3.1 equiv.) and
MsCl (65.6 mg, 0.44 mmol, 3.1 equiv.) under argon atmosphere,
and stirred for 10 min at 0 ◦C. The reaction was quenched with
water, and the organic materials were extracted with AcOEt. The
combined extracts were washed with brine, dried over Na2SO4,
and concentrated in vacuo. The residue was dissolved in toluene
(500 ␮L) and to that were added 18-crown-6 (73.9 mg, 0.18 mmol,
1.3 equiv.) and CsOAc (84.5 mg, 0.44 mmol, 3.1 equiv.) at 10 ◦C
under argon atmosphere. The mixture was stirred for 48 h at 25 ◦C,
then the reaction was quenched with water. The organic materi-
als were extracted with AcOEt, and the combined extracts were
washed with brine, dried over Na2SO4, and concentrated in vacuo.
The residue was purified by silica gel column chromatography (2 g).
Elution with hexane/AcOEt = 5:1 afforded 1e (35.2 mg, 65% over two
steps) as colorless oil. 1H NMR: ı 0.07 (s, 3H, SiCH3), 0.08 (s, 3H,
SiCH3), 0.86 (s, 9H, tert-butyl), 2.02 (s, 3H, Ac), 2.05 (s, 3H, Ac),
2.32 (ddd, J2,6a = 1.6 Hz, J5,6a = 4.8 Hz, J6a,6b = 18.4 Hz, 1H, H6a), 2.65
(ddd, J3,6b = 2.0 Hz, J5,6b = 4.4 Hz, 1H, H6b), 3.75 (s, 3H, Me ester),
4.14 (ddd, J4,5 = 6.8 Hz, 1H, H5), 5.08 (dd, J3,4 = 4.0 Hz, 1H, H4), 5.75
(ddd, J2,3 = 3.6 Hz, 1H, H3), 6.69 (dd, 1H, H2); 13C NMR: ı −4.96,
173.9; IR: 2954, 2860, 2368, 2324, 1736, 1517, 1240, 1039 cm−1
.
Anal. Calcd for C18H32O9Si: C 51.41, H 7.67; found: C 51.64,
H 7.56.

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M. Hamada et al. / Journal of Molecular Catalysis B: Enzymatic 67 (2010) 78–84
2.16. Methyl (1R,2S,3S,4R,5R)-2,3,4,5-tetraacetoxy-
1-hydroxycyclohexanecarboxylate (5b)
To a solution of 5a (68.6 mg, 0.15 mmol) in THF (700 ␮L) were
added acetic acid (18 mg, 0.30 mmol, 2 equiv.) and TBAF (1 M in
THF, 300 ␮L, 0.30 mmol, 2 equiv.). The mixture was stirred for 2 d at
room temperature, then the reaction was quenched with water. The
organic materials were extracted with AcOEt, and the combined
extracts were washed with brine, dried over Na2SO4, and concen-
trated in vacuo. The residue was treated with pyridine (100 ␮L)
and Ac2O (35 ␮L, 0.33 mmol, 2.2 equiv.) for 12 h at room temper-
ature to afford 5b (32.0 mg, 55%) as white solid. mp 141–142 ◦C;
1H NMR: ı 1.96 (s, 3H, Ac), 1.98 (s, 3H, Ac), 1.99 (s, 3H, Ac), 2.00
(s, 3H, Ac), 2.06 (ddd, J2,6a = 2.4 Hz, J5,6a = 4.8 Hz, J6a,6b = 13.6 Hz, 1H,
H6a), 2.27 (dd, J5,6b = 4.8 Hz, 1H, H6b), 3.54 (br s, 1H, OH), 3.73 (s,
3H, Me ester), 5.25 (m, 3H), 5.43 (dd, J = 9.6 Hz, J = 10.0 Hz, 1H);
13C NMR: ı 20.4, 20.5, 20.6, 20.8, 34.6, 53.6, 68.6, 70.6, 72.8, 73.6,
169.4, 169.6, 169.7, 169.9, 172.2; IR: 3469, 1741, 1380, 1230, 1034,
956 cm−1. This was employed for the next step without further
purification.
Scheme 2. Reagents and conditions: (a) Novozym 435, vinyl acetate [19% for
(3R,4R,5S)-2b and 29% for (3S,4S,5R)-2c].
3. Results and discussion
Our first attempt was the acetylation of methyl ( )-3-epi-
shikimate 2a (Scheme 2). In contrast to methyl shikimate 1a, an
equimolar formation of C-3 acetate 2b and C-4 acetate 2c was
observed. The acetylation on C-3 hydroxy group proceeded to give
2b in an enantioselective manner. By comparison of the sign of
optical rotation with a known data [3], the reaction occurred pre-
dominantly for the formation of (3R,4R,5S)-isomer.
From the synthetic points of view, the differentiation of two
hydroxy group in diols 2b and 2c are desirable. Since the hydroxy
groups on C-5 in both enantiomers were inert, the introduction
of TBS group on that position was considered prior to the lipase-
catalyzed reaction.
The preparation of the substrate was shown in Scheme 3. The
hydroxy group in literally known racemic epoxide 3 [9] was pro-
tected as TBS ether in a conventional manner. For the hydrolysis of
epoxy ring, the strong acid such as TFA was not available due to the
acid-labile property of TBS ether in this particular case. The forma-
tion of PMB ether on an exclusive allylic position was successful by
2.17. Methyl (3R,4S,5S,6R)-3,4,5,6-tetraacetoxy-
1-cyclohexenecarboxylate (6)
To
a solution of 5b (29.2 mg, 0.075 mmol) in anhydrous
CH2Cl2 (600 ␮L) was added Martin’s sulfurane (75.7 mg, 0.11 mmol,
1.5 equiv.). The mixture was stirred for 4 h at room temperature,
then the reaction was quenched with water. The organic materi-
als were extracted with AcOEt, and the combined extracts were
washed with brine, dried over Na2SO4, and concentrated in vacuo.
The residue was purified by silica gel column chromatography (2 g).
Elution with hexane/AcOEt = 3:1 affored 6 (25.0 mg, 90%) as color-
less needles. mp 121–122 ◦C [lit. [7] mp 122–124 ◦C]; [␣]D23–39.5
(c 1.25, CHCl3) [lit. [7] [␣]D +23 (c 0.68, CHCl3), for (2S,3R,4R,5S)-6];
1H NMR: ı 1.99 (s, 3H, Ac), 2.01 (s, 3H, Ac), 2.02 (s, 3H, Ac), 2.06 (s,
3H, Ac), 3.74 (s, 3H, Me ester), 5.29 (dd, J2,3 = 7.6 Hz, J3,4 = 10.4 Hz,
1H, H4), 5.30 (dd, J4,5 = 10.4 Hz, 1H, H4), 5.66 (dd, J2,6 = 2.0 Hz, 1H,
H6), 5.99 (dd, J5,6 = 2.8 Hz, 1H, H3), 6.74 (dd, 1H, H2); 13C NMR:
ı 20.5, 20.6, 20.6, 20.7, 52.4, 68.9, 69.9, 70.2, 71.7, 130.1, 137.8,
163.9, 169.5, 169.6, 169.8, 169.9; IR: 1734, 1367, 1273, 1223, 1026,
970 cm−1. Its 13C NMR spectra was identical with that reported
previously [7].
2.18. (3R,4S,5S,6R)-3,4,5,6-Tetraacetoxy-1-cyclohexenylmethyl
acetate (7b)
To a solution of 6 (14.3 mg, 0.04 mmol) in anhydrous THF
(140 ␮L) was added DIBAL (300 ␮L, 0.30 mmol, 7.8 equiv.) at 0 ◦C.
The mixture was stirred for 10 h at room temperature, then the
reaction was quenched with water (600 ␮L) and NaOH aqueous
solution (10%, 300 ␮L). After removal of insoluble materials by
filtration with a pad of Celite, the filtrate was concentrated in
vacuo. The residue was treated with pyridine (100 ␮L) and Ac2O
(10 ␮L, 0.33 mmol, 8.3 equiv.) for 12 h at room temperature. Con-
ventional workup and purification afforded 7b (5.4 mg, 34%) as
colorless oil. [␣]D26–61.3 (c 0.24, CHCl3); 1H NMR: ı 1.95 (s, 3H,
Ac), 1.96 (s, 3H, Ac), 1.98 (s, 3H, Ac), 1.99 (s, 3H, Ac), 2.00 (s, 3H,
Ac), 4.32 (d, J = 10.8 Hz, 1H), 4.61 (dd, J = 1.2 Hz, J = 10.4 Hz, 1H),
5.25 (d, J = 14.8 Hz, 1H), 5.30 (d, J = 14.8 Hz, 1H), 5.52 (dd, J = 1.2 Hz,
J = 5.6 Hz, 1H), 5.69 (br s, 1H), 5.72 (d, J = 5.6 Hz, 1H); 13C NMR:
ı 20.5, 20.6. 20.7, 20.8, 62.4, 70.2, 70.7, 71.9, 72.0, 126.2, 133.6,
169.8, 170.0, 170.2, 170.3; IR: 1745, 1433, 1371, 1209, 1024, 958,
920 cm−1. Its 13C NMR spectra was identical with that reported
previously [8].
Scheme 3. Reagents and conditions: (a) TBSCl, imidazole, CH2Cl2 (96%); (b) p-
methoxybenzyl alcohol, Yb(OTf)3 (81%); (c) DDQ, CH2Cl2/H2O (93%); (d) Novozym
435, vinyl acetate [48% for 2f (73.4% ee) and 34% for 2e (77.6% ee)].

M. Hamada et al. / Journal of Molecular Catalysis B: Enzymatic 67 (2010) 78–84
83
Scheme 4. Reagents and conditions: (a) Proton Sponge®, Me3OBF4, CH2Cl2 (69%);
(b) DDQ, CH2Cl2/H2O (quant.); (c) Novozym 435, vinyl acetate [20% for 2i (44.6% ee)
and 32% for 2h (16.4% ee)].
the assistance with Yb(OTf)3 [10], and the subsequent treatment
with DDQ provided trans-diols ( )-2e.
The result of lipase-catalyzed acetylation is shown in Scheme 3.
By virtue of bulky TBS ether in an adjacent position, the hydroxy
group at C-4 did not react at all. The reaction proceeded on C-3
exclusively and its enantioselective ratio (E value) was 15.7. We
assumed the reason why the reaction proceeded in an enantiose-
lective manner, to be the difference of steric hindrance of connected
to the secondary alcohol at C-3. Then we increased one of hydroxy
to methoxy group at C-4 as shown is Scheme 4. From the regioselec-
tively protected synthetic intermediate 2d, C-4 methoxy derivative
Scheme 5. Reagents and conditions: (a) Ac2O, DMAP, Py (93%); (b) Novozym 435,
cyclopentanol [38% for 2k (>99.9% ee) and 48% for 2j (90.4% ee)]; (c) Novozym 435,
cyclopentanol [45% for 2m, 37% for 2b (56.8% ee) and 18% for 2n].
(
)-2h was prepared by the action of Me3OBF4 and Proton Sponge®
[11].
To our disappointment, the enantioselectivity (E value) was
steps). During the removal of TBS group in 1e by treatment with
TBAF under weakly acidic conditions, a migration of acetyl group
for C-4 hydroxy to C-5 hydroxy group was detected. The liberated
C-4 hydroxy group was acetylated to give triacetate (3S,4R,5S)-1f.
This was an antipodal form of naturally occurring shikimic acid, by
comparison of its sign of optical rotation with a literary known data
[6].
In this way, the enantiomerically pure 3-epi-shikimic acid
derivatives 2j and 2k became in hand. Towards the bioactive
substances with the identical carbon skeleton, such as voglibose
4, a very potent ␣-glucosidase inhibitor [12], the stereoselective
introduction of additional two hydroxy groups is the indispens-
able task. Epi-shikimate 2j was found to be a very good precursor
as low as 3.3 for ( )-2h, compared with 15.7 for 2e. Due to an
enhanced steric hindrance caused by neighboring methoxy group,
it was supposed that the reaction rate of the “fast” (3R,4S,5S)-isomer
lowered.
In contrast, we were really surprised that very high enan-
tioselectivity (E > 500) was observed when 3,4-diacetate ( )-2j
was treated with the same enzyme under transesterification con-
ditions (Scheme 5). Even at as high conversion as 47%, the ee
of the reaction product [(3R,4S,5S)-2k] was >99.9%. We suppose
that the higher enantioselectivity is due to an introduction of
electron-withdrawing group acetate at C-4, which enhanced the
electrophilicity of the acetate at C-3 in (3R,4S,5S)-2j, the “fast enan-
tiomer”. The repetition of the lipase-catalyzed reaction on the
unreacted recovery provided enantiomerically pure (3S,4R,5R)-2j.
The blocking of C-5 hydroxy group with bulky TBS group
had crucial role on the above successful transformation. When
TBS group was replaced with acetate in ( )-2, a side reaction,
the transesterificaiton on C-5 acetate took place in the “slow”
(3S,4S,5R)-isomer to give 2n. The enantioselectivity (E = 3.4) was
also lower compared to that in ( )-2j.
The absolute configuration of the lipase-catalyzed transesteri-
fication product, (+)-2k, was determined as shown in Scheme 6.
First, the stereochemistry of allylic position was invented by the
introduction of mesyl group and the subsequent treatment with
CsOAc in the presence of 18-crown-6, to give 1e (65%, over two
Scheme 6. Reagents and conditions: (a) MsCl, Et3N, CH2Cl2; (b) CsOAc, 18-crown-6,
toluene (65% over two steps); (c) TBAF, AcOH, THF; (d) Ac2O, DMAP, Py (36% over
two steps).

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M. Hamada et al. / Journal of Molecular Catalysis B: Enzymatic 67 (2010) 78–84
ondary alcohol (66%, over two steps), the resulted tertiary alcohol
5b was dehydrated by the action of Martin’s sulfurane to give
(2R,3S,4S,5R)-6 with minus sign of optical rotation. For the antipo-
dal (2S,3R,4R,5S)-isomer, plus sign had so far been reported [7].
DIBAL reduction of ␣,␤-unsaturated ester also worked well, 1-epi-
valienol was obtained as its pentaacetylated form 7b [8].
4. Conclusion
The effect of substituents on regio- and enantioselectivity for
the transformation of polyoxygenated carbacycles under the catal-
ysis by C. antarctica lipase B was examined. This achievement is
promising to provide new routes to highly oxygenated bioactive
cyclohexanoids.
Acknowledgements
The authors thank Dr. Yoichi Suzuki of Novozymes Japan for
generous gift of Novozym 435. This work was supported both by
a Grant-in-Aid for Scientific Research (No.18580106) and “’High-
Tech Research Center” Project for Private Universities: matching
fund subsidy 2006-2011 from the Ministry of Education, Culture,
Sports, Science and Technology, Japan, and acknowledged with
thanks.
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Scheme 7. Reagents and conditions: (a) cat. K2OsO2(OH)4, NMO, tert-BuOH/H2O
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taking advantage of its stereochemistry and protective groups.
Dihydroxylation with in situ-formed OsO4 [13] proceeded in
an exclusively diastereofacially selective manner to give 5a in
89% yield (Scheme 7). The orientation of the newly introduced
hydroxy groups were unambiguously confirmed to be ␣, as shown
below. After removal of TBS group followed by acetylation of sec-