Enzymatic resolution of methyl (2E, 4R*,5S*)-4-(N-benzyl-N- methyl)amino-5-hydroxyhex-2-enoate

Article abstract of DOI:10.1016/j.molcatb.2010.12.005

For the purpose of preparation of optically active aminoalcohol congeners possessing both hydroxyl- and dialkylamino-substituted vicinal chiral carbons, lipase-assisted acylation of methyl (2E,4R*,5S*)-4-(N-benzyl-N- methyl)amino-5-hydroxyhex-2-enoate (4)

Full text of DOI:10.1016/j.molcatb.2010.12.005

Journal of Molecular Catalysis B: Enzymatic 69 (2011) 21–26
Contents lists available at ScienceDirect
Journal of Molecular Catalysis B: Enzymatic
journal homepage: www.elsevier.com/locate/molcatb
Enzymatic resolution of methyl (2E,
4R*,5S*)-4-(N-benzyl-N-methyl)amino-5-hydroxyhex-2-enoate
Mikio Fujiia, Machiko Onob, Miyuki Satoa, Hiroyuki Akitaa,c,∗
a School of Pharmaceutical Sciences, Toho University, 2-2-1, Miyama, Funabashi, Chiba 274-8510, Japan
b School of Pharmaceutical Sciences, International University of Health and Welfare, 2600-1 Kitakanemaru Ohtawara, Tochigi 324-8501, Japan
c Nihon Pharmaceutical University, 10281, Komuro, Inamachi, Kitaadachigun, Saitama 362-0806, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
For the purpose of preparation of optically active aminoalcohol congeners possessing both hydroxyl- and
dialkylamino-substituted vicinal chiral carbons, lipase-assisted acylation of methyl (2E,4R*,5S*)-4-(N-
benzyl-N-methyl)amino-5-hydroxyhex-2-enoate (4) using CAL-B with vinyl hexanoate as an acyl donor
was carried out to give (4S,5R)-hexenoate (7) (44%, 99.2% ee) as the reaction product and (4R,5S)-alcohol
(4) (46%, 98.2% ee) as the unreacted starting material. The E-value of the present lipase-assisted resolution
was estimated to be more than 1000. Thus obtained acylated product was successfully converted into
methyl ␤-d-vicenisaminide (12).
Received 27 October 2010
Received in revised form
13 December 2010
Accepted 13 December 2010
Available online 21 December 2010
Keywords:
Lipase
© 2011 Elsevier B.V. All rights reserved.
CAL-B
Enzymatic resolution
Enantioselective acylation
Methyl ␤-d-vicenisaminide
1. Introduction
the reaction of ( ) trans-4,5-epoxy-2(E)-hexenoate (3) with
N-methylbenzylamine or dimethylamine gave ( )-4 or ( )-5
respectively, in highly regioselective manner[5]. d-Vicenisamine
(1) and l-forosamine (2) could be synthesized from optically
active (4S,5R)-4 and (4S,5R)-5, respectively. Although lipase-
catalysed resolution of ( )-N,N-dimethylaminopropan-2-ol was
reported,[6] none of the methods describe examples whose both
of hydroxyl- and dialkylamino-substituted vicinal carbons are
chiral. Herein, we report enzymatic resolution of ( )-4 and
show an application toward the synthesis of d-vicenisamine
(1).
Racemic acylamino- or dialkylaminoalcohols have been the
substrates for enzymatic resolution and the resulting optically
pure products are important building blocks for the synthe-
sis of biologically and pharmacologically active compounds[1].
Meanwhile aminosugars are isolated from many antibiotics or
natural products as constituents of those compounds, and the
role of the whole structure has a close connections with their
biological activities [2]. For the synthesis of deoxy-aminosugars
such as d-vicenisamine (1) [3] and l-forosamine (2) pos-
sessing methylamino and dimethylamino group, respectively,
effective methods for the construction of chiral form of moi-
ety A as shown in Scheme 1 are desirable. d-Vicenisamine
(1) is the constituted aminosugar of vicenistatin which is
2. Methods and materials
2.1. General
isolated from Streptomyces sp. HC34 as
a novel antitumour
antibiotics[4]. The chiral structural unit A possessing hydroxyl
and N,N-disubstituted amino groups with vicinal relationship
All melting points were measured on a Mettler FP-62 melt-
ing point apparatus and are uncorrected. 1H and 13C NMR spectra
were recorded on JEOL AL 400 spectrometer or Bruker AV400M
digital spectrometer in CDCl3, MeOH-d4, and DMSO-d6 with or
without Me4Si as an internal reference. High-resolution mass
spectra (HRMS) and the fast atom bombardment mass spectra
(FAB MS) were obtained with a JEOL JMS-600H (matrix; glyc-
erol, m-nitrobenzyl alcohol) spectrometer. High-resolution FAB
MS were obtained with a JEOL JMS-SX-102A or JMS-T100LP.
could be derived from
a chiral moiety B possessing azido
alcohol functionality. On the other hand, we reported that
∗
Corresponding author at: School of Pharmaceutical Sciences, Toho University,
2-2-1, Miyama, Funabashi, Chiba 274-8510, Japan. Tel.: +81 048 721 1155x3305.
E-mail address: hiroakita@nichiyaku.ac.jp (H. Akita).
1381-1177/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.molcatb.2010.12.005

22
M. Fujii et al. / Journal of Molecular Catalysis B: Enzymatic 69 (2011) 21–26
NHMe
NMe2
Me
Me
OH
P
P'
N3
N
R1
R1
O
O
R2 (or H)
R2 (or H)
OH
OH
OH
moiety A
OH
moiety B
2
D-Vicenisamine 1
L-Forosamine
NMe2
Me
NMeBn
Me
Me
BnMeNH
or Me2NH
COOMe
COOMe
COOMe or
O
( )-5
3
OH
( )-
OH ( )-4
Scheme 1.
IR spectra were recorded on
a
JASCO FT/IR-300 spectrome-
2.3. General procedure for enzymatic resolution of methyl
(2E,4R*,5S*)-4-(N-benzyl-N-methyl)amino-5-hydroxyhex-2-
enoate (4)
ter. Optical rotations were measured with a JASCO DIP-370 or
P-1020 digital polarimeter. HPLC analysis was performed on
SSC-3210 pump equipped with chiral column, SSC-5200 UV
detector and SIR Chromatocorder 21. Chemicals were purchased
from Tokyo Kasei Industry Co. Ltd., and Wako Chemicals or
Aldrich Inc. otherwise indicated. Lipase PS and CAL-B were
purchased from Amano Enzymes Co. and Sigma–Aldrich Inc.,
respectively. For column chromatography, silica gel (Kieselgel 60,
Merck) or Chromatorex® NH (Fuji Silysia Chermical Ltd.) were
employed.
To a solution of ( )-4 (50 mg, 0.19 mmol) and acyl donor
(500 mg) in various amount of i-Pr2O (0, 1, 3, 10 mL) was added
CAL-B (50 mg), then the mixture was stirred at room temper-
ature. The reaction mixture was filtrated through Celite 545
and the filtrate was evaporated under reduced pressure. The ee
and absolute configuration of recovered 4 was determined by
HPLC analysis. The ee of acylated compound (6 or 7) was esti-
mated based on the conversion yield by NMR analyses of reaction
mixture and the ee of recovered 4. The results are shown in
Table 1.
2.2. Enzymatic resolution of methyl (2E,4R*,5S*)-4-(N-benzyl-N-
methyl)amino-5-acetoxyhex-2-enoate (6)
2.4. Methyl (2E,4S,5R)-4-(N-benzyl-N-methyl)amino-5-
hexanoyloxyhex-2-enoate ((4S,5R)-7) and methyl
(2E,4R,5S)-4-(N-benzyl-N-methyl)amino-5-hydoxyhex-2-enoate
((4R,5S)-4)
A suspension of the reported ( )-6 [4] (230 mg, 0.75 mmol)
and lipase “Amano PS” (0.1 g) in phosphate buffer (0.1 M, pH 7.25,
20 mL) was stirred at 35 ◦C for 6d. The reaction mixture was diluted
with Et2O (50 mL) and solid materials were removed by filtration
through celite pad. The reaction mixture was extracted with Et2O
and organic extracts were dried over MgSO4 and filtered. Evapora-
tion of the organic solvent gave a crude product, which was purified
by silica gel column chromatography (20 g) to afford (4R,5S)-6
(108 mg, 47%, 36% ee by HPLC analysis) from n-hexane/EtOAc = 10/1
elution and (4S,5R)-4 (53 mg, 27%, 53% ee by HPLC analysis)
from n-hexane/EtOAc = 5/1 elution. HPLC equipped Chiralcel AD-
H (4.6 mm × 250 mm), eluents: n-hexane/i-PrOH = 20/1, Flow rate;
0.4 mL/min, Detection; 254 nm. ( )-4; tR = 42.1 and 45.2 min. The ee
of (4R,5S)-6 was calculated based on HPLC analysis after conversion
of (4R,5S)-6 into (4R,5S)-4 with K2CO3 in MeOH.
To a solution of ( )-4 (623 mg, 2.40 mmol) and vinyl hex-
anoate (1.15 g, 8.04 mmol) in i-Pr2O (50 mL) was added CAL-B
(200 mg), then the mixture was stirred at room temperature for
3 days. The reaction mixture was filtrated through Celite 545 and
the filtrate was evaporated under reduced pressure. The residue
was purified by column chromatography [silica gel: Chromatorex®
NH (10 g)] to afford (4S,5R)-7 (376 mg, 44%) from hexane/AcOEt
(5/1) fractions and (4R,5S)-4 (287 mg, 46%, 98.2% ee by HPLC)
19
from hexane/AcOEt (1/2) fractions. (4R,5S)-4: [␣]D
−55.6 (c
0.76, CHCl3). NMR data of (4R,5S)-4 were identical with those
of the reported ( )-4 [5]. (4S,5R)-7: [␣]D19 + 48.4 (c 1.16, CHCl3),
Table 1
Enzymatic resolution of ( )-4 using CAL-B in the presence of acyl donor.
NMeBn
CAL-B
NMeBn
COOMe
Acyl donar
Me
Me
( )-4
COOMe
(4R,5S)-4
+
in iPr2O
6
OH
OR R=Ac : (4S,5R)-
R=COC5H11 : (4S,5R)-7
Entry
Acyl donor
iPr2O (mL)
Time (h)
Conv. (%)a
Ee of 4 (%)b
Ee of 6 or 7 (%)c
E value
d
1
2
3
4
5
Vinyl acetate
Vinyl acetate
Vinyl acetate
Vinyl acetate
Vinyl hexanoate
0
1
3
10
10
–
5
6
26
26
–
–
–
–
39
160
>1000
>1000
27.7
26.1
48.5
49.5
35.6
34.7
94.1
98.1
92.2
98.2
99.9
>99.9
a
Estimated by 1H NMR.
Measured by HPLC analysis.
Calculated value from conv. and ee of 4.
Polymerized with vinyl acetate.
b
c
d

M. Fujii et al. / Journal of Molecular Catalysis B: Enzymatic 69 (2011) 21–26
23
1H NMR(400 MHz, CDCl3): ı 0.87 (3H, t, J = 7.0 Hz), 1.20–1.33
(4H, m), 1.32 (3H, d, J = 6.0 Hz), 1.51–1.59 (2H, m), 2.20 (2H, t,
J = 7.6 Hz), 2.24 (3H, s), 3.07 (1H, dd, J = 6.0, 8.8 Hz), 3.47 (1H,
d, J = 13.2 Hz), 3.66 (1H, d, J = 13.2 Hz), 3.77 (1H, s), 4.82 (1H, s),
5.18–5.25 (1H, m), 5.90 (1H, d, J = 12.0 Hz), 6.94 (1H, dd, J = 9.0,
12.0 Hz), 7.21–7.34 (5H, m); 13C NMR (CDCl3): 13.8, 18.1, 22.2,
24.6, 31.2, 34.6, 37.8, 51.6, 58.9, 67.6, 69.7, 125.3, 127.1, 128.3
(2C), 128.6 (2C), 138.8, 143.6, 166.0, 173.1. IR:(neat) 1727, 1654,
1495, 1172 cm−1. HR-EI-MS calcd. for C21H31NO4: 361.2255, found:
361.2253.
C14H19NO3:C, 67.45; H, 7.78; N, 5.62. Found: C, 67.10; H, 7.85; N,
5.33.
2.8. Methyl ˇ-d-vicenisaminide (12) and methyl
˛-d-vicenisaminide (13)
(i) To a solution of (2R,3R,4S)-9 (610 mg, 2.4 mmol) in toluene
(10 mL) at −40 ◦C was added 1 M solution of diisobutylaluminum
hydride (Dibal-H) in toluene (4.9 mL, 4.9 mmol), then the mixture
was stirred at 40 ◦C for 1 h. To the reaction mixture was added
Et2O (30 mL) and 1 M NaOH solution (20 mL) at 0 ◦C and the organic
layer was separated. The organic layer was dried over MgSO4 and
evaporated to give a residue which was used for the next reac-
tion without further purification. To a solution of acetyl chloride
(AcCl; 10 mL) in MeOH (5 mL) was added a solution of the above
residue in MeOH (2 mL) and the whole was stood for 3 d. The reac-
tion mixture was evaporated and diluted with sat. Na2CO3 (10 mL),
extracted with Et2O. The organic layer was dried over MgSO4 and
evaporated to give a residue which was subjected to silica gel
column chromatography (20 g, n-hexane/AcOEt = 5/1) to afford 11
(86 mg, 13%) and 10 (140 mg, 22%) in elution order. 10: 1H NMR
(400 MHz, CDCl3): ı 1.40 (3H, d, J = 8.0 Hz), 1.70 (1H, d, J = 4.0 Hz),
1.99 (1H, dd, J = 2.0, 4.0 Hz), 2.01 (1H, dd, J = 2.0, 4.0 Hz), 2.39 (3H,
s), 2.46 (1H, d, J = 3.4 Hz), 3.48 (3H, s), 3.78 (1H, s), 3.81 (1H, s),
4.11 (1H, s), 4.36 (1H, q, J = 4.2 Hz), 4.67 (1H, d, J = 6.4 Hz). 13C NMR
(100 MHz, CDCl3): ı 20.2, 39.0, 39.4, 56.2, 59.2, 66.5, 66.8, 67.9,
98.6, 126.7, 128.0 (4C), 138.6. 11: 1H NMR (400 MHz, CDCl3): ı
1.40 (3H, d, J = 6.0 Hz), 1.83 (1H, dd, J = 3.8, 6.2 Hz), 1.87 (1H, dd,
J = 3.8, 6.2 Hz), 2.37 (1H, d, J = 3.6 Hz), 2.40 (3H, s), 3.40 (3H, s),
3.58 (1H, br. s), 3.81 (1H, s), 3.87 (1H, s), 4.32 (1H, q, J = 5.6 Hz),
4.37 (1H, s), 4.77 (1H, d, J = 4.0 Hz). 13C NMR (100 MHz, CDCl3): ı
18.0, 37.0, 38.5, 54.9, 58.0, 62.3, 65.9, 66.5, 98.8 126.4, 127.9 (4C),
140.1. (ii) A solution of 10 (150 mg, 0.6 mmol) in AcOEt (10 mL)
was hydrogenated over 10% Pd(OH)2/C (100 mg) at room tem-
perature under atmospheric pressure of hydrogen for 12 h. After
removal of the catalyst by filtration through Celite pad, evaporation
of the organic solvent gave a crude product, which was purified
by NH-silica gel column chromatography (3 g, gradient, CH2Cl2
to CH2Cl2/MeOH = 19/1) to afford methyl ␤-d-vicenisaminide 12
2.5. Methyl (2E,4S,5R)-4-(N-benzyl-N-methyl)amino-5-
hydoxyhex-2-enoate ((4S,5R)-4)
To a solution of (4S,5R)-7 (350 mg, 0.970 mmol) in MeOH
(10 mL) and i-Pr2O (30 mL) was added CAL-B (200 mg), then
the mixture was stirred at room temperature for 3 days. After
the spot of (4S,5R)-7 was disappeared on TLC analysis of the
reaction mixture, the reaction mixture was filtrated through
Celite 545 and the filtrate was evaporated under reduced pres-
sure. The residue was purified by column chromatography [silica
gel: Chromatorex® NH (10 g), hexane/AcOEt (1/2)] to afford
(4S,5R)-4 (230 mg, 90%, 99.2% ee by HPLC). [␣]D17 + 54.0 (c 1.16,
CHCl3).
2.6. Methyl [(4S,5R,6R)-5-(N-benzyl-N-methyl)amino-6-methyl-
2-phenyl-[1,3]dioxan-4-yl]-acetate (8)
To a solution of (4S,5R)-4 (530 mg, 2.0 mmol) in THF (4 mL)
at 0 ◦C was added benzaldehyde (430 mg, 4.0 mmol), followed by
KOtBu (340 mg, 3.0 mmol), then the orange solution was stirred
at same temperature for 15 min. The reaction mixture was poured
into saturated aqueous NH4Cl and extracted with Et2O. The organic
layer was washed with brine, dried over MgSO4. Evaporation of the
organic solvent gave a crude product, which was purified by silica
gel column chromatography (20 g, hexane/EtOAc = 15/1) to afford
(4S,5R,6R)-8 (349 mg, 47%) as a homogeneous oil. (4S,5R,6R)-8:
[␣]D −27.3 (c 0.54, CHCl3). IR (neat): 1739 cm−1
.
1H NMR (CDCl3):
22
ı 1.47 (3H, d, J = 6 Hz), 2.32 (3H, s), 2.42 (1H, t, J = 10 Hz), 2.57 (1H,
dd, J = 8, 16 Hz), 3.09 (1H, dd, J = 4, 16 Hz), 3.69 (3H, s), 3.79, 3.85
(each 1H, d, J = 14 Hz), 4.10 (1H, dq, J = 6, 10 Hz), 4.37 (1H, ddd,
J = 4, 8, 10 Hz), 5.54 (1H, s), 7.23–7.48 (10H, m). Anal. Calcd for
22
(64 mg, 64%) as pale yellow oil. 12: [␣]D −3.7 (c 0.40, MeOH).
HRMS (FAB+) Calcd for C8H18NO3: 176.1287. Found: 176.1286.
The free form was dissolved in Et2O (1 mL) and 4 M HCl in diox-
ane was added to the solution. The resulted white needle was
collected by filtration to afford 12 hydrochloride (48 mg, 62%)
as a colorless needles. 12 hydrochloride: mp 182◦C, 1H NMR
(hydrochloride, MeOH-d4): ı 1.35 (3H, d, J = 6.3 Hz), 1.67 (1H,
ddd, J = 2.8, 9.1, 14 Hz), 2.03 (1H, ddd, J = 2.3, 4.3, 14 Hz), 2.74
(3H, s), 2.92 (1H, dd, J = 3.2, 9.3 Hz), 3.44 (3H, s), 4.01 (1H, dq,
J = 6.3, 9.3 Hz), 4.35 (1H), 4.75 (1H, dd, J = 2.3, 9.1 Hz). 13C NMR
(hydrochloride, MeOH-d4): ı 18.6, 31.2, 38.8, 56.7, 62.4, 63.3, 67.9,
100.4.
C22H27NO4: C, 71.52; H, 7.37; N, 3.79. Found: C, 71.56; H, 7.77;
N, 3.69.
2.7. (2R,3R,4S)-3-(N-Benzyl-N-methyl)amino-4-hydroxy-2-
methyl-6-oxotetrahydropyran (9)
To a solution of (4S,5R,6R)-8 (640 mg, 1.7 mmol) in THF (5 mL)
was added conc. HCl (3 mL) and the mixture was stirred at
70 ◦C for 2 h. The reaction mixture was evaporated to give a
residue which was diluted with 2 M HCl (5 mL). The HCl layer
was extracted with ether and HCl layer was evaporated to afford
a residue. To this residue was added sat. Na2CO3 (3 mL) and the
whole was evaporated to give a residue which was extracted
with AcOEt. The organic layer was dried over MgSO4 and evapo-
rated to give a residue which was subjected to silica gel column
chromatography (20 g, n-hexane/AcOEt = 5/1) to afford (2R,3R,4S)-
9 (230 mg, 53%) as an oil. (2R,3R,4S)-9: [␣]D22+ 68.1 (c 0.63,
(iii) A solution of 11 (92 mg, 0.35 mmol) in AcOEt (10 mL) was
hydrogenated over 10% Pd(OH)2/C (100 mg) at room temperature
under atmospheric pressure of hydrogen for 12 hr. After removal
of the catalyst by filtration through Celite pad, evaporation of
the organic solvent gave a crude product, which was purified
by NH-silica gel column chromatography (3 g, gradient, CH2Cl2
to CH2Cl2/MeOH = 19/1) to afford methyl ␣-d-vicenisaminide 13
(44 mg, 72%) as pale yellow oil. 13: [␣]D22+198.0 (c 0.6, CHCl3),
HRMS (FAB+) Calcd for C8H18NO3: 176.1287. Found: 176.1300. 1
H
CHCl3). IR (KBr): 3398, 1697 cm−1 1H NMR (400 MHz, CDCl3):
.
NMR (CDCl3): ı 1.32 (3H, d, J = 6.3 Hz), 1.85 (1H, dt, J = 3.5, 14.4 Hz),
2.08 (1H, dd, J = 3.0, 9.9 Hz), 2.15 (1H, ddd, J = 1.3, 3.5, 14.4 Hz), 2.44
(3H, s), 3.37 (3H, s), 3.69 (1H, dq, J = 6.3, 9.9 Hz), 4.07 (1H, dq, J = 6.3,
9.3 Hz), 4.77 (1H, d, J = 3.5 Hz). 13C NMR (CDCl3): ı 18.7, 33.9, 35.3,
55.1, 62.9, 63.9, 64.1, 98.5.
ı 1.51 (3H, d, J = 6.0 Hz), 2.41 (3H, s), 2.69 (2H, d, J = 4.4 Hz),
2.72 (1H, dd, J = 4.0, 9.6 Hz), 3.74 (1H, d, J = 13.0 Hz), 3.87 (1H, d,
J = 13.0 Hz), 4.38 (1H, q, J = 4.0 Hz), 4.94 (1H, dd, J = 8.4, 9.8 Hz).
13C NMR (100 MHz, CDCl3): ı 20.5, 39.1, 39.8, 59.7, 62.5, 64.0,
73.6, 127.1, 128.2 (2C), 128.3 (2C), 138.6, 169.6. Anal. Calcd for

24
M. Fujii et al. / Journal of Molecular Catalysis B: Enzymatic 69 (2011) 21–26
NMeBn
NMeBn
Me
Me
Lipase PS
COOMe
COOMe
OH (4S,5R)-4
( )-6
in phosphate buffer
(pH 7.2)
6
OAc (4R,5S)-
47%, 36% ee
E = 5
27%, 53% ee
Scheme 2.
Scheme 2.
NMeBn
NMeBn
CAL-B
CH2=CHOCOC5H11
Me
Me
( )-4
COOMe
+
COOMe
in iPr2O
OH
OCOC5H11
(4S,5R)-7 44%
(4R,5S)-4 46% (98.2% ee)
CAL-B / MeOH
in iPr2O
90%
NMeBn
Me
COOMe
OH
(4S,5R)- 99.2% ee)
4 (
Scheme 3.
NMeBn
OH
NHMe
(4S,5R)-4
Me
Me
OH
d
a
O
O
NMeBn
NMeBn
OH
OMe
(22%)
+
OMe
Me
Me
b
c
10
12 (64%)
COOMe
O
O
O
NMeBn
NHMe
Me
OH
Me
OH
O
Ph
d
9
8
(2R,3R,4S)- (53%)
(4S,5R,6R)- (47%)
O
O
(a) PhCHO / KOtBu (b) HCl
(c) 1) Dibal-H 2) AcCl / MeOH (d) H2 / Pd-C
OMe
OMe
11
13 (72%)
(13%)
Scheme 4.
3. Results and discussion
should be much improved. In the next section, lipase-catalysed
acylation of methyl (2E,4R*,5S*)-4-(N-benzyl-N-methyl)amino-5-
hydroxyhex-2-enoate (4) in the presence of acyl donor was carried
out (Scheme 2).
3.1. The lipase-catalysed resolution of methyl (2E,4R*,5S*)-4-(N-
benzyl-N-methyl)amino-5-acetoxyhex-2-enoate (6)
Firstly, the enantioselective hydrolysis of ( )-6 using the lipase
“Amano PS” from Burkholderia cepacia (EC 3.1.1.34) in phosphate
buffer solution at pH 7.25 gave (4S,5R)-4 (27%, 53% ee) and (4R,5S)-
6 (47%, 36% ee). The enantiomeric excess (ee) of the hydrolyzed
product 4 was calculated by the reported equation [7]. The absolute
structure and enantiomeric excess (ee) of the hydrolyzed product
4 (tR = 45.2 min: tR = 42.1 min = 76.5: 23.5) were determined by a
comparison of retention times of authentic (4S,5R)-4 ([␣]D25 + 52.2
(c 1.01, CHCl3), >99% ee, tR = 45.2 min),[5] thence absolute structure
of the present 4 was confirmed to possess 4S, 5R configurations.
Methanolysis of acetate 6 with K2CO3 provided the hydrolyzed
product 4 (tR = 45.2 min: tR = 42.1 min = 32: 68), thence absolute
structure of the present 6 was confirmed to possess 4R, 5S con-
figurations. The E value of the present enzymatic hydrolysis of
3.2. Screening experiment
Previously we reported enantioselective lipase-catalysed acy-
lation of methyl (2E,4R*,5R*)-4-aryl-5-hydroxyhex-2-enoate pos-
sessing the similar structure of ( )-4 by CAL-B from Candida
antarctica (lipase B, supported by polyacrylic ester)[8]. We consid-
ered CAL-B could catalyze the enantioselective acylation of ( )-4.
By a screening experiment in the presence of vinyl acetate as an
acyl donor, CAL-B was found to be suitable lipase. Firstly, in the
reaction of ( )-4 using CAL-B with vinyl acetate, the products were
not obtained because the polymerization of vinyl acetate occurred.
(Table 1, entry 1). This polymerization was considered to be caused
by basicty of substrate ( )-4. Meanwhile, the reaction of ( )-4 using
CAL-B with vinyl acetate and diisopropyl ether as a reaction sol-
vent to avoid the polymerization gave (4R,5S)-4 (35.6% ee) and an
(
)-6 was found to be 5 (E = 5) by the reported equation [7] and

M. Fujii et al. / Journal of Molecular Catalysis B: Enzymatic 69 (2011) 21–26
25
BnMeN
PhCHO / KOtBu
COOMe
Me
8
(4S,5R,6R)-
4
(4S,5R)-
-
O
O
Ph
Fig. 1. Plausible mechanism for the formation of (4S,5R,6R)-8 from (4S,5R)-4.
L
M
R=COR'
enzymatic hydrolysis
HO
H
H
L
M
L
M
R=H
RO
H
enzymatic acylation
R'OCO
M: a medium substituent
L: a large substituent
H
NMeBn
COOMe
Me
RO
Scheme 5.
moiety C
moiety D
H
acetate (4S,5R)-6 (92.9% ee) at 5 h (Table 1, entry 2). However the
prolonged reaction time in order to reach 50% conversion caused
the polymerization reaction. Dilution of vinyl acetate concentration
with diisopropyl ether (10 mL) allowed prolonged reaction time to
reach 48.5% conversion and gave the ee of (4R,5S)-4 (94.1% ee) and
acetate (4S,5R)-6 (99.9% ee). E-value (E > 1000) was also improved
dramatically by the dilution (Table 1, entry 4). This improvement
of E value was depended on the ratio of vinyl acetate and diiso-
propyl ether, since the use of large volume (5 mL) of vinyl acetate
in diisopropyl ether (ca. 33%, v/v corresponding to entry 2) gave
about the same E value as entry 2 and caused polymerization by
long reaction time. Above results indicated diisopropyl ether was
considered as good solvent for the stereoselective enzymatic reac-
tion. The influence of acyl donor on ee in lipase-catalysed acylation
of alcoholic substrate was reported[9–11]. For the purpose of both
enrichment of the ee of reaction products and being speeded up
reaction rate, the reaction of ( )-4 with vinyl hexanoate as an
acyl donor under the same reaction condition as entry 4 was car-
ried out to afford of (4R,5S)-4 (98.1% ee) and hexanoate 7 (more
than 99.9% ee), and E-value was estimated to be more than 1000
(Table 1, entry 5). To confirm the absolute structure of hexanoate 7,
preparative scale experiment of entry 5 was carried out in the next
section.
3.4. Synthesis of methyl ˇ-d-vicenisaminide12 from (4S,5R)-4
Conversion of (4S,5R)-4 into methyl ␤-d-vicenisaminide (12)
was performed as shown in Scheme 4. To introduce the oxygen
functionality at the 3-position of (4S,5R)-4, treatment of (4S,5R)-
4 with benzaldehyde in the presence of KOtBu afforded acetal
(4S,5R,6R)-8 ([␣]D−27.3 (c 0.54, CHCl3)) in 47% yield with high
diastereoselectivity from the 1H NMR measurement. This high
diastereoselectivity could be explained via a chair-like interme-
diate as shown in Fig. 1. Acid treatment of (4S,5R,6R)-8 gave
ı-lactone (2R,3R,4S)-9: ([␣]D+68.1 (c 0.63, CHCl3)) in 53% yield,
which was subjected to consecutive treatment of Dibal-H and anhy-
drous hydrogen chloride in MeOH to afford ␤-methyl glycoside (10)
(22%) and ␣-methyl glycoside (11) (13%). Catalytic debenzylation
of both ␤-anomer 10 and ␣-anomer 11 gave ␤-d-vicenisaminide
(12) (64%, [␣]D−3.7 (c 0.40, MeOH)) and ␣-d-vicenisaminide (13)
(72%, [␣]D +198.0 (c 0.6, CHCl3)), respectively. Treatment of 12 in
Et2O with 4 M HCl in dioxane gave the corresponding hydrochloride
salt, whose spectroscopic data were identical with those previously
reported[12].
4. Discussion
In case of lipase-catalysed hydrolysis of ( )-6, poor results (E = 5)
were obtained and could be explained as follows. Previously, we
reported optical resolution of the neutral methyl (2E,4R*,5R*)-4-
aryl-5-acetoxyhex-2-enoate possessing similar structure of ( )-6
by Amano PS to give low reactivity and unsatisfied stereoselectiv-
ity. While the transesterification of the above neutral compounds
by CAL-B afforded good results [8]. The low E value for the hydrol-
ysis of ( )-6 by Amano PS was not concerned with basicity of
3.3. Preparative scale experiment (preparation of (4R,5S)- and
(4S,5R)-4)
Lipase-catalysed optical resolution of 623 mg of ( )-4 using
1.15 g of vinyl hexanoate and 200 mg of CAL-B in 50 mL of
diisopropyl ether was carried out to give (4R,5S)-4 (46%, [␣]D
(
)-6 and ( )-6 could be not good substrate for Amano PS. The
−55.6 (c 0.76, CHCl3), 98.2% ee) and (+)-hexanoate
7 (44%,
results of the enantioselective hydrolysis of ( )-6 with the lipase PS
from Burkholderia cepacia (EC 3.1.1.34) and enantioselective acyla-
tion of ( )-4 with CAL-B from Candida antarctica were coincided
well with the theoretical transition state model [13,14] to indi-
cate which enantiomer possessing secondary hydroxyl or acyloxyl
groups reacts faster in lipase-catalysed reactions by comparing the
relative sizes of substituents at the stereocenter. The moiety C
[␣]D +48.4 (c 1.16, CHCl3) (Scheme 3). To confirm the abso-
lute structure of (+)-7, methanolysis of (+)-7 using CAL-B in
MeOH and diisopropyl ether was performed to afford (4S,5R)-
4
(90%, [␣]D +54.0 (c 1.16, CHCl3), 99.2% ee)). Thence the
absolute structure of (+)-7 was determined to possess 4S, 5R
configurations.

26
M. Fujii et al. / Journal of Molecular Catalysis B: Enzymatic 69 (2011) 21–26
seems to be a relatively small-sized substituent (M) and the moiety
D appears to be a relatively large-sized substituent (L) (Scheme 5).
References
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5. Conclusion
For the purpose of preparation of optically active aminoalcohol
congener possessing hydroxyl and N,N-disubstituted amino groups
with vicinal relationship, enzymatic hydrolysis of methyl (2E,4R*,
5S*)-4-(N-benzyl-N-methyl)amino-5-acetoxyhex-2-enoate
(6)
and lipase-assisted acylation of methyl (2E,4R*,5S*)-4-(N-benzyl-
N-methyl)amino-5-hydroxyhex-2-enoate (4) in the presence
of vinyl hexanoate were carried out. In case of hydrolysis of
(
)-6 using lipase PS, poor results were obtained from the
standpoint of isolation yield and enantiomeric excess (ee). Mean-
while, enantioselective acylation of ( )-4 using CAL-B with vinyl
hexanoate as an acyl donor afforded (4S,5R)-4-(N-benzyl-N-
methylamino)-5-hexanoyloxy-2(E)-hexenoate (7) (44%, 99.2% ee)
and (4R,5S)-alcohol 4 (46%, 98.2% ee) corresponding to starting
material. The E-value of the present lipase-assisted resolution was
estimated to be more than 1000. Thus obtained (4S,5R)-7 was
successfully converted into methyl ␤-d-vicenisaminide (12).
[13] M. Cygler, P. Grochulski, R.J. Kazlauska, J.D. Schrag, F. Bouthillier, B. Rubin, A.N.
Serreqi, A.K. Gupta, J. Am. Chem. Soc. 116 (1994) 3180–3186.
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