A highly efficient and convergent synthesis of a hexasaccharide, a dimer of the repeating unit of the antigen O2 polysaccharide of Stenotrophomonas maltophilia

Article abstract of DOI:10.1016/S0008-6215(99)00004-X

A highly efficient and convergent synthesis of a hexasaccharide, which is a dimer of the repeating unit of the antigen O2 polysaccharide of Stenotrophomonas maltophilia, was achieved via coupling of 2,3,4-tri-O-acetyl-α-L-xylopyranosyl bromide with the tetrasaccharide, allyl 4-O-{3-O-[4-O-(3,4-di-O-benzoyl-α-L-rhamnopyranosyl)-2,3,6-tri-O-benzoyl-α-D-mannopyranosyl]-4-benzoyl-α-L-rhamnopyranosyl}-2,3,6-tri-O-benzoyl-α-D-mannopyranoside (18) by the Koenigs-Knorr method followed by deacylation. Compound 18 was readily prepared from the coupling of the disaccharide trichloroacetimidate, 4-O-(2-O-acetyl-3,4-di-O-benzoyl-α-L-rhamnopyranosyl)-2,3,6-tri-O-benzoyl-α-D-mannopyranosyl trichloroacetimidate (8) with the disaccharide acceptor, allyl 4-O-(2-O-acetyl-4-O-benzoyl-α-L-rhamnopyranosyl)-2,3,6-tri-O-benzoyl-α-D-mannopyranoside (16), and both 8 and 16 were prepared via the trichloroacetimidate method from simple starting materials. The sole use of acyl protecting groups substantially simplified protection and deprotection, and the allyl group at the reducing end of allyl 4-O-{2-O-[2,3,4-tri-O-acetyl-β-L-xylopyranosyl]-3-O-[4-O-(2-O-(2,3,4-tri-O-acetyl-β-L-xylopyranosyl)-3,4-di-O-benzoyl-α-L-rhamnopyranosyl)-2,3,6-tri-O-benzoyl-α-D-mannopyranosyl]-4-O-benzoyl-α-L-rhamnopyranosyl}-2,3,6-tri-O-benzoyl-α-D-mannopyranoside 19 allowed further chemical transformation. Copyright (C) 1999 Elsevier Science Ltd.

Full text of DOI:10.1016/S0008-6215(99)00004-X

Carbohydrate Research 315 (1999) 128–136
A highly efficient and convergent synthesis of a
hexasaccharide, a dimer of the repeating unit of the
antigen O2 polysaccharide of Stenotrophomonas
maltophilia
Wei Wang, Fanzuo Kong *
Research Center for Eco-En6ironmental Sciences, Academia Sinica, PO Box 2871,
Beijing 100085, People’s Republic of China
Received 15 August 1998; revised 25 November 1998; accepted 1 December 1998
Abstract
A highly efficient and convergent synthesis of a hexasaccharide, which is a dimer of the repeating unit of the
antigen O2 polysaccharide of Stenotrophomonas maltophilia, was achieved via coupling of 2,3,4-tri-O-acetyl-a- -xyl-
opyranosyl bromide with the tetrasaccharide, allyl 4-O-{3-O-[4-O-(3,4-di-O-benzoyl-a- -rhamnopyranosyl)-2,3,6-
tri-O-benzoyl-a- -mannopyranosyl]-4-benzoyl-a- -rhamnopyranosyl}-2,3,6-tri-O-benzoyl-a- -mannopyranoside (18)
by the Koenigs–Knorr method followed by deacylation. Compound 18 was readily prepared from the coupling of
the disaccharide trichloroacetimidate, 4-O-(2-O-acetyl-3,4-di-O-benzoyl-a- -rhamnopyranosyl)-2,3,6-tri-O-benzoyl-
a- -mannopyranosyl trichloroacetimidate (8) with the disaccharide acceptor, allyl 4-O-(2-O-acetyl-4-O-benzoyl-a-
rhamnopyranosyl)-2,3,6-tri-O-benzoyl-a- -mannopyranoside (16), and both 8 and 16 were prepared via the
L
L
D
L
D
L
D
L-
D
trichloroacetimidate method from simple starting materials. The sole use of acyl protecting groups substantially
simplified protection and deprotection, and the allyl group at the reducing end of allyl 4-O-{2-O-[2,3,4-tri-O-acetyl-
b-
L
-xylopyranosyl]-3-O-[4-O-(2-O-(2,3,4-tri-O-acetyl-b-
L
-xylopyranosyl)-3,4-di-O-benzoyl-a-
L
-rhamnopyranosyl)-
-mannopy-
2,3,6-tri-O-benzoyl-a-
D
-mannopyranosyl]-4-O-benzoyl-a-
L
-rhamnopyranosyl}-2,3,6-tri-O-benzoyl-a-
D
ranoside 19 allowed further chemical transformation. © 1999 Elsevier Science Ltd. All rights reserved.
Keywords: Synthesis of hexasaccharide; O2 antigen of Stenotrophomonas maltophilia; Glycosylation
1. Introduction
cystic fibrosis population, which is partly
based on the multidrug resistance of many
strains [2]. A polysaccharide consisting of
The organism known as Stenotrophomonas
(Xanthomonas or Pseudomonas) maltophilia [1]
is a free-living organism which is commonly
present in clinical specimens. The organism
has a growing reputation as an opportunistic
pathogen, particularly as an agent of nosoco-
mial infection, and a potential threat to the
[(-3)L
-Xylp(b1-2)
L
-Rhap(a1-4) -Manp(a1-)]n
D
was isolated from the lipopolysaccharide
(LPS) present in the reference strain for
Stenotrophomonas maltophilia serogroup O2
by Winn and Wilkinson in 1997 [2]. We report
here a facile synthesis of a hexasaccharide 20,
which is a dimer of the repeating unit of the
antigen O2 polymer.
* Corresponding author. Fax: +86-10-62923563.
E-mail address: fzkong@mail.rcees.ac.cn (F. Kong)
0008-6215/99/$ - see front matter © 1999 Elsevier Science Ltd. All rights reserved.
PII: S0008-6215(99)00004-X

W. Wang, F. Kong / Carbohydrate Research 315 (1999) 128–136
129
route, especially since the ABCD block can be
readily constructed from two disaccharide
blocks AB and CD. Thus, the glycoside accep-
tor 1, allyl 2,3,6-tri-O-benzoyl-a-
D
-mannopy-
ranoside, was obtained from allyl a-
D-
mannopyranoside [3] through selective triben-
zoylation with benzoyl chloride in pyridine
under the conditions designated for selective
benzoylation of trehalose [4] (Scheme 1). The
1H NMR of 1 gave H-4 as an upfield triplet (l
4.3 ppm), a clear indication of a free OH
hydroxyl. For the synthesis of disaccharide 6,
2. Results and discussion
Retrosynthetic analysis indicated that build-
ing a tetrasaccharide ABCD block first and
then coupling the
L
-xylose unit at the B-2 and
D-2 positions would be an effective and simple
Scheme 1.

130
W. Wang, F. Kong / Carbohydrate Research 315 (1999) 128–136
an orthoester intermediate was used. Treat-
ment of ‘acetobromorhamnose’ with MeOH
in the presence of 2,4-lutidine/tBu4NBr instead
of sym-collidine/tBu4NBr [5] gave orthoester 2
in high yield. Deacetylation of 2, followed by
benzoylation, gave orthoester 3 in quantitative
yield. Hydrolysis of 3 in 70% AcOH solution
under the conditions for the transformation of
an orthoester to an acetate of an axial hy-
droxyl group [6] selectively afforded 2-O-
forded
15,
and
subsequent
selective
3%-deprotection with DDQ [14] furnished a
product identical to that obtained from direct
selective 3%-deacetylation of 13, as indicated
from TLC (Rf 0.65, 2:1 petroleum ether–
1
EtOAc) and H NMR.
Glycosylation of the disaccharide donor 8
with the disaccharide acceptor 16 in the pres-
ence of Me3SiOTf afforded the tetrasaccharide
17 in 75% yield . The 1H NMR spectrum of 17
showed two singlets at l 2.26 and 2.02 (2
CH3CO), and two doublets at l 0.85 and 0.72
(–CH3 of rhamnose), which came from the
rhamnose moieties, and four broad singlets at
l 5.14, 5.08, 5.04 and 4.99 for H-1 of A, B, C,
and D units. Selective B-2 and D-2 deacetyla-
tion of 17 with CH3COCl–MeOH gave te-
trasaccharide acceptor 18 in high yield.
acetyl-3,4-di-O-benzoyl-a,b- -rhamnopyranose
L
4 with O-1 free, which was converted to the
trichloroacetimidate glycosyl donor 5 on treat-
ment with CNCCl3/DBU [7]. Glycosylation [8]
of the acceptor 1 with the trichloroacetimidate
donor 5 was promoted with Me3SiOTf, af-
fording the disaccharide 6 in a high yield
(\90%). Deallylation [9] of 6 with palladium
chloride in MeOH followed by treatment with
trichloroacetonitrile in the presence of DBU
afforded the disaccharide donor 8, which was
directly used in the next coupling reaction.
The disaccharide acceptor 16 was prepared
Glycosylation of the acceptor 18 with 2,3,4-
tri-O-acetyl-a- -xylopyranosyl bromide [15]
L
promoted by silver triflate gave the final hex-
asaccharide 19 in good yield. All of the triben-
zoylated mannose-containing oligosaccha-
rides, i.e., the disaccharides 6, 7, 8, 14, 15, and
16, the tetrasaccharides 17 and 18, and the
hexasaccharide 19, showed the H-6 of rham-
starting from allyl a- -rhamnopyranoside [10].
L
Isopropylidenation of allyl rhamnopyranoside
(giving 9) followed by benzoylation afforded
1
allyl 4-O-benzoyl-2,3-O-isopropylidene-a-
L-
nose residues at l 0.61–0.87 in their H NMR
rhamnopyranoside (10) [11]. Hydrolysis of 10
followed by acetylation, then deallylation, and
subsequent treatment with trichloroacetoni-
trile in the presence of DBU afforded the
required donor 12. Me3SiOTf-promoted gly-
cosylation of the acceptor 1 with the
trichloroacetimidate 12 gave the disaccharide
13 in 86% yield. Selective deacetylation [12] of
13 with CH3COCl–MeOH gave the disaccha-
ride 16 as the major product (Rf 0.65, 2:1
petroleum ether–EtOAc) in 65% yield, which
was easily separated from a minor product (Rf
0.29, 2:1 petroleum ether–EtOAc) and from
the starting material 13 (Rf 0.82, 2:1
petroleum ether–EtOAc). To confirm the se-
lective 3%-deacetylation, an unambiguous, al-
ternative synthesis of 16 from 13 was carried
out. Thus complete deacetylation of 13 with
CH3COCl–MeOH after extended reaction
spectra. These values differed from the normal
region of around l 1.3(e.g., l 1.31 for 4) and
we rationalized that the unusual upfield shift-
ing was the result of shielding by the benzene
ring in the tribenzoylated mannose moieties.
Deprotection [16] of 19 in MeOH–MeONa
readily afforded the title hexasaccharide 20 in
quantitative yield.
The allyl hexasaccharide glycoside consist-
ing of the two trisaccharide units can be used
not only for bioactivity study, but also for the
preparation of glycoconjugates via conjuga-
tion to protein carriers. In addition, the desig-
nated strategy for the preparation of the
hexasaccharide can be extended to the synthe-
sis of higher oligosaccharides corresponding
to the antigen O2 polymer.
time gave allyl 4-O-(4-O-benzoyl-a-
L
-rhamno-
-manno-
3. Experimental
pyranosyl)-2,3,6-tri-O-benzoyl-a-
D
pyranoside 14 (Rf 0.29, 2:1 petroleum ether–
EtOAc). Selective 3%-O-4-methoxybenzylation
via the corresponding dibutyltin complex in-
termediate [13] followed by acetylation af-
General methods.—Melting points were de-
termined with a ‘Mel-Temp’ apparatus and
optical rotations were determined with a
Perkin–Elmer model 241-MC automatic po-

W. Wang, F. Kong / Carbohydrate Research 315 (1999) 128–136
131
J2,3 2.6 Hz, H-2), 5.41–5.20 (m, 2 H,
CH2ꢀCH–CH2–), 5.07 (d, 1 H, J1,2 1.0 Hz,
H-1), 4.89 (dd, 1 H, J5,6 4.0 Hz, J6,6% 12.6 Hz,
H-6), 4.66 (dd, 1 H, J5,6% 2.1 Hz, J6,6% 12.6 Hz,
H-6%), 4.30 (t, 1 H, J 9.3 Hz, H-4), 4.38–4.15
(m, 3 H, H-5, CH2ꢀCH–CH2–). Anal. Calcd
for C30H28O9: C, 67.66; H, 5.30. Found: C,
67.80; H, 5.36.
larimeter for solutions in a 1-dm, jacketed cell.
1H NMR spectra were recorded with Varian
XL-400 and Varian XL-200 spectrometers, for
solutions in CDCl3 with Me4Si as the internal
standard. Chemical shifts are expressed in
ppm downfield from the internal Me4Si ab-
sorption. Mass spectrometry was conducted
on a JDS-D 3005 mass spectrometer using a
direct-insertion technique to introduce the
sample. Thin-layer chromatography (TLC)
was performed on silica gel HF, detection
being effected by charring with 30% (v/v) sul-
furic acid in methanol or sometimes by UV
detection. Column chromatography was con-
ducted by elution of a column of silica gel
(100–200 mesh) using EtOAc–petroleum
ether (bp 60–90 °C) as the solvent. Solutions
were concentrated at a temperatureB60 °C
under diminished pressure. Analytical LC was
performed with a Gilson HPLC consisting of
a pump (model 306), a stainless steel column
packed with silica gel (Spherisorb SiO2, 10×
300 mm or 4.6×250 mm), a differential re-
fractometer (132-RI Detector), and a UV–Vis
detector (model 118), and EtOAc–petroleum
ether (bp 60–90 °C) was used as the solvent at
a flow rate of 1–4 mL/min.
3,4-Di-O-acetyl-1,2-O-methoxyethylidene-i-
L
-rhamnopyranose (2).—A mixture of 2,3,4-
tri-O-acetyl-a-
L
-rhamnopyranosyl
bromide
(2.0 g, 5.7 mmol), 2,4-lutidine (0.8 mL, 7.2
mmol), and tetrabutylammonium bromide
(0.8 g, 2.4 mmol) in CH2Cl2 (15 mL) was
stirred at rt for 3–5 min, then MeOH (anhyd,
0.5 mL, 12 mmol) was added. TLC (1:1
petroleum ether–EtOAc) indicated that the
reaction was complete. The reaction mixture
was concentrated and subjected to column
chromatography to give the title compound 2
(1.7 g, 97%). Compound 2 gave 1H NMR data
identical to those reported in the literature
[5b]; mp 80–84 °C; [h]2D0+31° (c 1.0, CHCl3);
Ref. [5c] mp 84–86 °C; [h]2D0+34.7°.
3,4-Di-O-benzoyl-2-O-acetyl-h,i- -rham-
L
nopyranose (4).—Compound 2 (1.5 g, 4.9
mmol) was deacetylated with MeOH–Me-
ONa, and then benzoylated with BzCl–
pyridine to furnish 3 in quantitative yield.
Hydrolysis of 3 with 70% aq HOAc [6] at rt
furnished 4 (1.6 g, 3.9 mmol) as a colorless
syrup in 80% yield. Flash chromatography
(2:1 petroleum ether–EtOAc) of the residue
gave an anomeric mixture (a/b, 10/1); for a
anomer: [h]2D0+63.9° (c 0.5, CHCl3); 1H NMR
(CDCl3): l(a) 7.96, 7.85 (2 d, 4 H, J 7.6 Hz,
Bz–H), 7.56–7.25 (m, 6 H, Bz–H), 5.81 (dd, 1
H, J2,3 3.4 Hz, J3,4 9.8 Hz, H-3), 5.57 (t, 1 H,
J 9.8 Hz, H-4), 5.52 (dd, 1 H, J1,2 1.5 Hz, J2,3
3.4 Hz, H-2), 5.31 (d, 1 H, J1,2 1.5 Hz, H-1),
4.49–4.31 (m, 1 H, H-5), 2.17 (s, 3 H,
CH3CO), 1.31 (d, 3 H, J5,6 6.7 Hz, CH3).
Anal. Calcd for C22H22O8: C, 63.76; H, 5.35.
Found: C, 63.90; H, 5.35.
Allyl 2,3,6-tri-O-benzoyl-h- -mannopyran-
D
oside (1).—Freshly distilled benzoyl chloride
(11 mL, 92 mmol) was added dropwise to a
solution of allyl a- -mannopyranoside (5.0 g,
D
23 mmol) in dry pyridine (200 mL) at 0 °C.
The mixture was allowed to warm to room
temperature (rt) and was stirred overnight.
The reaction was quenched with MeOH (10
mL), the mixture was concentrated, and the
residual solution was poured into ice-water,
extracted with CH2Cl2 (80 mL) and washed
sequentially with N HCl (50 mL), satd aq
NaHCO3 (50 mL), and aq NaCl (50 mL). The
aq phases were re-extracted with CH2Cl2 (40
mL), and the combined organic solutions were
dried, concentrated, and purified by column
chromatography with 1:1 petroleum ether–
EtOAc as the eluent to give the title com-
pound 1 as a colorless syrup (9.2 g, 76%);
[h]2D0+1.85° (c 1.6, CHCl3); 1H NMR
(CDCl3): l 8.20–7.90 (m, 6 H, Bz–H), 7.70–
7.23 (m, 9 H, Bz–H), 6.08–5.84 (m, 1 H,
CH2ꢀCH–CH2 –), 5.65 (dd, 1 H, J2,3 2.6 Hz,
J3,4 9.3 Hz, H-3), 5.63 (dd, 1 H, J1,2 1.0 Hz,
Allyl 4-O-(2-O-acetyl-3,4-di-O-benzoyl-h-
L
-
rhamnopyranosyl) - 2,3,6 - tri - O - benzoyl - h -
D
-
mannopyranoside (6).—Treatment [7] of 4
(330 mg, 0.80 mmol) with trichloroacetonitrile
(Cl3CCN,
3
equiv) and 1,8-diazabicy-
clo[5,4,0]undec-7-ene (DBU, 0.25 equiv) at
0 °C in anhyd CH2Cl2 gave the glycoside
donor, trichloroacetimidate 5 (370 mg, 72%)

132
W. Wang, F. Kong / Carbohydrate Research 315 (1999) 128–136
5.60 (dd, 1 H, J2%,3% 3.2 Hz, J3%,4% 9.8 Hz, H-3%),
5.45 (d, 1 H, J1,2 1.9 Hz, H-1), 5.43 (dd, 1 H,
J1%,2% 1.7 Hz, J2%,3% 3.2 Hz, H-2%), 5.40 (t, 1 H, J
9.8 Hz, H-4%), 5.14 (d, 1 H, J1%2% 1.7 Hz, H-1%),
5.06 (dd, 1 H, J5,6a 0.7 Hz, J6a,6b 12.4 Hz,
H-6a), 4.65 (dd, 1 H, J5,6b 2.0 Hz, J6a,6b 12.4
Hz, H-6b), 4.60 (t, 1 H, J 9.2 Hz, H-4),
4.62–4.51 (m, 1 H, H-5), 4.12–3.96 (m, 1 H,
H-5%), 2.07 (s, 3 H, CH3CO), 0.78 (d, 3 H, J
6.2 Hz, CH3). Anal. Calcd for C49H44O16: C,
66.21; H, 4.99. Found: C, 66.14, H, 5.05.
after flash chromatography, which was used
directly in the glycosylation reaction. A mix-
ture of the donor 5 (370 mg, 0.66 mmol) and
the acceptor 1 (266 mg, 0.50 mmol) in anhyd
˚
CH2Cl2 (20 mL) containing 4 A activated
molecular sieves (0.5 g) was stirred under N2
for 1 h at rt and then cooled to −40 °C.
Trimethylsilyl triflate (Me3SiOTf, 20 mL, 0.2
equiv) was added and the mixture was stirred
under N2 below −30 °C for 40 min. TLC
showed the starting material had disappeared.
Triethylamine (15 mL) was added to the reac-
tion solution and the solid was filtered off and
washed with CH2Cl2 (30 mL). The combined
filtrate and washings were washed sequentially
with H2O (30 mL), N HCl (30 mL), satd aq
NaHCO3 (30 mL), and satd aq NaCl (30 mL).
The aq washings were re-extracted with
CH2Cl2 (30 mL) and the combined organic
solutions were dried and concentrated, and
the residue was subjected to flash chromatog-
raphy with 3:1 petroleum ether–EtOAc as the
eluent to give 6 (420 mg, 0.45 mmol) in high
4-O-(2-O-Acetyl-3,4-di-O-benzoyl-h-
nopyranosyl)-2,3,6-tri-O-benzoyl-h-
L
-rham-
-man-
D
nopyranosyl trichloroacetimidate (8).—Tri-
chloroacetonitrile (Cl3CCN, 0.11 mL, 3 equiv)
and 1,8-diazabicyclo[5,4,0]undec-7-ene (DBU,
14 mL, 0.25 equiv) were added to a solution of
7 (310 mg, 0.35 mmol) in anhyd CH2Cl2 (10
mL) and the mixture was stirred at 0 °C for 1
h, at the end of which time TLC showed the
starting material had disappeared. The sol-
vents were evaporated and flash chromatogra-
phy (1:1 EtOAc–petroleum ether) of the
residue gave the disaccharide donor 8 (300
mg, 0.29 mmol, 83%), which was used directly
in the glycosylation reaction; 1H NMR
(CDCl3): l 8.68 (s, 1 H, NH), 8.12–7.16 (m,
25 H, Bz–H), 6.42 (d, J1,2 1.8 Hz, H-1), 6.02
(dd, 1 H, J2,3 3.5 Hz, J3,4 9.2 Hz, H-3), 5.87
(dd, 1 H, J1,2 1.8 Hz, J2,3 3.5 Hz, H-2), 5.67
(dd, 1 H, J2%,3% 3.2 Hz, J3%,4% 9.8 Hz, H-3%), 5.56
(dd, 1 H, J1%,2% 1.7 Hz, J2%,3% 3.2 Hz, H-2%), 5.45
(t, 1 H, J 9.8 Hz, H-4%), 5.20 (d, 1 H, J1%2% 1.7
Hz, H-1%), 5.02 (dd, 1 H, J5,6a 0.9 Hz, J6a,6b
12.4 Hz, H-6a), 4.66 (dd, 1 H, J5,6b 2.0 Hz,
J6a,6b 12.4 Hz, H-6b), 4.60 (t, 1 H, J 9.2 Hz,
H-4), 4.59–4.47 (m, 1 H, H-5), 4.12–3.96 (m,
1 H, H-5%), 2.10 (s, 3 H, CH3CO), 0.87 (d, 3
H, J 6.2 Hz, CH3).
1
yield (90%); [h]D20−40.4° (c 0.6, CHCl3); H
NMR (CDCl3): l 8.20–7.80 (m, 10 H, Bz–H),
7.67–7.24 (m, 15 H, Bz–H), 6.10–5.90 (m, 1
H, CH2ꢀCH–CH2–), 5.91 (dd, 1 H, J2,3 3.4
Hz, J3,4 9.5 Hz, H-3), 5.65(dd, 1 H, J1,2 1.5 Hz,
J2,3 3.4 Hz, H-2), 5.60 (dd, 1 H, J2%,3% 3.2 Hz,
J3%,4% 9.8 Hz, H-3%), 5.41 (dd, 1 H, J1%,2% 1.7 Hz,
J2%,3% 3.2 Hz, H-2%), 5.45–5.25 (m, 3 H, H-4%,
CH2ꢀCH–CH2 –), 5.11 (d, 1 H, J1,2 1.5 Hz,
H-1), 5.05 (d, 1 H, J1%,2% 1.7 Hz, H-1%), 5.00 (dd,
1 H, J5,6a 1.7 Hz, J6a,6b 12.7 Hz, H-6a), 4.67
(dd, 1 H, J5,6b 3.4 Hz, J6a,6b 12.7 Hz, H-6b),
4.57 (t, 1 H, J3,4 9.5 Hz, J4,5 9.5 Hz, H-4),
4.40–3.94 (m, 4 H, H-5, 5%, CH2ꢀCH–CH2–),
2.03 (s, 3 H, CH3CO), 0.74 (d, 3 H, J5%,6% 6.5
Hz, CH3). Anal. Calcd for C52H48O16: C,
67.23; H, 5.21. Found: C, 67.12; H, 5.32.
Allyl 4-O-benzoyl-h- -rhamnopyranoside (11).
L
4-O-(2-O-Acetyl-3,4-di-O-benzoyl-h-
rhamnopyranosyl)-2,3,6-tri-O-benzoyl-h,i-
L
-
-
—Compound 11 was obtained as crystals
from hydrolysis of 10, which was prepared
from benzoylation of 9, according to the liter-
ature [11].
D
mannopyranose (7).—Deallylation [9] of 6
(400 mg, 0.43 mmol) with PdCl2 (1:20 g/g) in
MeOH (10 mL) at rt furnished an amorphous
solid 7 (320 mg, 0.36 mmol, 84%), presented
mostly as a anomer; [h]2D0−40.4° (c 0.7
Allyl 4-O-(2,3-di-O-acetyl-4-O-benzoyl-h-
rhamnopyranosyl) - 2,3,6 - tri - O - benzoyl - h -
L
-
-
D
1
mannopyranoside (13).—Acetylation of com-
pound 11 (6.5 g, 21 mmol) with Ac2O (5 mL)
in pyridine (10 mL) furnished allyl 2,3-di-O-
CHCl3); H NMR (CDCl3): l 8.20–7.80 (m,
10 H, Bz–H), 7.68–7.20 (m, 15 H, Bz–H),
5.97 (dd, 1 H, J2,3 3.4 Hz, J3,4 9.2 Hz, H-3),
5.67 (dd, 1 H, J1,2 1.9 Hz, J2,3 3.4 Hz, H-2),
acetyl - 4 - O - benzoyl - a - - rhamnopyranoside
L

W. Wang, F. Kong / Carbohydrate Research 315 (1999) 128–136
133
freshly distilled MeOH (6 mL) and the solu-
tion was stirred at 48–54 °C. The reaction was
quenched when TLC (2:1 petroleum ether–
EtOAc) showed 14 (Rf 0.29) was the sole
product. The solution was cooled to 0 °C and
pyridine (1.5 mL) was added dropwise to neu-
tralize the acid. The solution was concentrated
to a semi-solid residue that was dissolved in
CH2Cl2 (50 mL) and washed sequentially with
M HCl (20 mL), satd aq NaHCO3 (20 mL),
and H2O (20 mL). The aq washings were
re-extracted with CH2Cl2 (30 mL) and the
combined organic solutions were dried and
concentrated. Gradient flash chromatography
(1:1–1.5:1 EtOAc–petroleum ether) of the
residue gave the diol 14 (540 mg, 0.69 mmol,
84%) as a colorless syrup; [h]2D0−34.2° (c 1.2,
quantitatively. Deallylation with PdCl2 (1/20
g/g) in MeOH furnished a mixture of 2,3-di-
O-acetyl-4-O-benzoyl-a,b- -rhamnopyranose.
L
Subsequent treatment with trichloroacetoni-
trile (Cl3CCN, 3 equiv) and 1,8-diazabicy-
clo[5,4,0]undec-7-ene (DBU, 0.25 equiv) at
0 °C in anhyd CH2Cl2 gave, after flash chro-
matography, the trichloroacetimidate donor
12 (595 mg, overall yield 72% for two steps),
which was used directly in the glycosylation
reaction [8]. A mixture of the donor 12 (595
mg, 1.19 mmol) and the acceptor 1 (535 mg,
1.0 mmol) in anhyd CH2Cl2 (20 mL) contain-
˚
ing 4 A activated molecular sieves (1 g) was
stirred under N2 for 1 h at rt and then cooled
to −40 °C. Trimethylsilyl triflate (Me3SiOTf,
20 mL, 0.1 equiv) was added and the mixture
was stirred under N2 below −30 °C for 40
min. TLC showed the starting material had
disappeared. Triethylamine (25 mL) was added
and the reaction mixture was handled as de-
scribed for the preparation of 6. Flash chro-
matography (1:2 EtOAc–petroleum ether) of
the residue gave the disaccharide 13 (745 mg,
0.86 mmol, 86%) as a colorless syrup; [h]2D0−
24° (c 1.5, CHCl3); 1H NMR (CDCl3): l 8.16–
7.04 (m, 8 H, Bz–H), 7.69 (m, 12 H, Bz–H),
6.09–5.86 (m, 1 H, CH2ꢀCH–CH2–), 5.85
(dd, 1 H, J2,3 3.7 Hz, J3,4 9.3 Hz, H-3), 5.62
(dd, 1 H, J2,3 3.7 Hz, J1,2 1.8 Hz, H-2), 5.42
(dd, 1 H, J2%,3% 3.8 Hz, J1%,2% 1.0 Hz, H-2%), 5.41
(dd, 1 H, J2%,3% 3.5 Hz, J3%,4% 9.8 Hz, H-3%),
5.35–5.22 (m, 2 H, CH2ꢀCH–CH2–), 5.18 (t,
1 H, J 9.8 Hz, H-4%), 5.03 (d, 1 H, J1,2 1.8 Hz,
H-1), 5.00 (d, 1 H, J1%,2% 1.0 Hz, H-1%), 4.91 (dd,
1 H, J5,6a 2.0 Hz, J6a,6b 12.0 Hz, H-6a), 4.64
(dd, 1 H, J5,6b 3.6 Hz, J6a,6b 12.0 Hz, H-6b),
4.50 (t, 1 H, J3,4 9.3 Hz, J4,5 9.3 Hz, H-4),
4.39–4.06 (m, 3 H, H-5, CH2ꢀCH–CH2–),
4.00–3.84 (m, 1 H, H-5%), 2.09, 1.88, (2 s, 6 H,
2 CH3CO), 0.73 (d, 3 H, J 6.7 Hz, CH3). Anal.
Calcd for C47H46O16: C, 65.12; H, 5.35.
Found: C, 65.41; H, 5.27.
1
CHCl3); H NMR (CDCl3): l 8.16–7.79 (m, 8
H, J 8.4 Hz, Bz–H), 7.66–7.23 (m, 12 H,
Bz–H), 6.07–5.86 (m, 1 H, CH2ꢀCH–CH2–),
5.84 (dd, 1 H, J2,3 3.6 Hz, J3,4 9.7 Hz, H-3),
5.60 (dd, 1 H, J1,2 1.7 Hz, J2,3 3.6 Hz, H-2),
5.42–5.22 (m, 2 H, CH2ꢀCH–CH2–), 5.06 (d,
1 H, J1,2 1.7 Hz, H-1), 5.01 (d, 1 H, J1%,2% 0.8
Hz, H-1%), 4.93 (t, 1 H, J 9.7 Hz, H-4%), 4.77
(dd, 1 H, J5,6a 1.8 Hz, J6a,6b 12.3 Hz, H-6a),
4.16 (dd, 1 H, J5,6b 3.2 Hz, J6a,6b 12.3 Hz,
H-6b), 4.50 (t, 1 H, J 9.7 Hz, H-4), 4.36–4.08
(m, 3 H, H-5, CH2ꢀCH–CH2–), 4.04 (dd, 1
H, J1%2% 0.8 Hz, J2%,3% 3.4 Hz, H-2%), 3.94 (dd, 1
H, J2%,3% 3.4 Hz, J3%,4% 9.7 Hz, H-4%), 3.93–3.78
(m, 1 H, H-5%), 0.74 (d, 3 H, J 6.7 Hz, CH3).
Anal. Calcd for C43H42O14: C, 65.98; H, 5.41.
Found: C, 65.70; H, 5.54.
Allyl 4-O-[2-O-acetyl-3-O-(p-methoxybenz-
yl)-4-O-benzoyl-h-
L
-rhamnopyranosyl]-2,3,
6-tri-O-benzoyl-h-
D
-mannopyranoside (15).—
To a solution of 14 (500 mg, 0.64 mmol) in
MeOH (5 mL) was added dibutyltin oxide
(160 mg, 1 equiv) and the mixture was
refluxed. After the mixture became clear, heat-
ing was continued for 1 h, and the stannylene
complex was obtained as a white foamy
residue after evaporation of the methanol un-
der diminished pressure. To the residue were
added toluene (6 mL), tetrabutylammonium
iodide (238 mg, 1 equiv), and p-methoxyben-
zyl chloride (120 mL, 1.5 equiv), and the mix-
ture was stirred for 20 h at 60–70 °C. The
reaction was monitored by TLC using 1:2
EtOAc–petroleum ether as the developing sol-
Allyl 4-O-(4-O-benzoyl-h-
osyl)-2,3,6-tri-O-benzoyl-h-
L
-rhamnopyran-
-mannopyran-
D
oside (14).—A methanolic solution [12] of
HCl (1.04 N, 9 mL), prepared by adding
acetyl chloride (0.8 mL) to freshly distilled
MeOH (10 mL), was added to a solution of
the disaccharide 13 (710 mg, 0.82 mmol) in

134
W. Wang, F. Kong / Carbohydrate Research 315 (1999) 128–136
was quenched when TLC showed that the
maximum amount of major product (Rf 0.65)
[minor product (Rf 0.29), starting material (Rf
0.82)] had been reached. The solution was
cooled to 0 °C and pyridine (1 mL) was added
dropwise to neutralize the acid. The solution
was concentrated to a semi-solid residue that
was dissolved in CH2Cl2 (10 mL) and washed
sequentially with M HCl (10 mL), satd aq
NaHCO3 (10 mL), and H2O (10 mL). The aq
washings were re-extracted with CH2Cl2 (10
mL) and the combined organic solutions were
dried and concentrated. Gradient flash chro-
matography (1:2–1:1–1.5:1 EtOAc–petro-
leum ether) of the residue gave 16 (206 mg,
0.25 mmol, 65%) as a colorless syrup; [h]2D0−
80° (c 1.2, CHCl3); 1H NMR (CDCl3): l 8.20–
7.80 (m, 8 H, Bz–H), 7.68–7.26 (m, 12 H,
Bz–H), 6.07–5.87 (m, 1 H, CH2ꢀCH–CH2–),
5.85 (dd, 1 H, J3,4 9.7 Hz, J2,3 3.6 Hz, H-3),
5.61 (dd, 1 H, J1,2 1.7 Hz, J2,3 3.2 Hz, H-2),
5.42–5.22 (m, 2 H, CH2ꢀCH–CH2–), 5.09 (d,
1 H, J1,2 1.7 Hz, H-1), 5.05 (dd, 1 H, J1%,2% 1.2
Hz, J2%,3% 3.3 Hz, H-2%), 5.03 (d, 1 H, J1%,2% 1.2
Hz, H-1%), 4.99 (dd, 1 H, J5,6a 1.2 Hz, J6a,6b
12.2 Hz, H-6a), 4.94 (t, 1 H, J 9.7 Hz, H-4%),
4.59 (dd, 1 H, J5,6b 3.1 Hz, J6a,6b 12.2 Hz,
H-6b), 4.53 (t, 1 H, J 9.7 Hz, H-4), 4.36–4.05
(m, 4 H, H-3%,5, CH2ꢀCH–CH2–), 3.95–3.78
(m, 1 H, H-5%), 2.08 (s, 3 H, CH3CO), 0.73 (s,
3 H, J 6.8 Hz, CH3). Anal. Calcd for
C45H44O15: C, 65.53; H, 5.38. Found: C, 65.40;
H, 5.27.
vent. After completion of the alkylation [13],
the solvent was evaporated under diminished
pressure, and the residue was subjected to
column chromatography on silica gel with 1:2
EtOAc–petroleum ether as the eluent. Acetyl-
ation of the resulting compound was carried
out quantitatively with Ac2O–pyridine, and
the reaction mixture was poured into ice water
(10 mL) and extracted with CH2Cl2 (10 mL).
The aq washings were re-extracted with
CH2Cl2 (5 mL) and the combined organic
solutions were washed sequentially with 5% aq
HOAc (10 mL), satd aq NaHCO3 (10 mL),
and aq NaCl (10 mL). The organic phase was
dried and concentrated under reduced pres-
sure, and the pure, colorless syrupy product
15 (450 mg, 75%) was obtained after separa-
tion on a silica gel column with 1:3 EtOAc–
petroleum ether as eluent; [h]2D0−54.1° (c 3.7,
1
CHCl3); H NMR (CDCl3): l 8.10–7.73 (4 d,
8 H, J 8.6 Hz, Bz–H), 7.68–7.24 (m, 12 H,
Bz–H), 7.05, 6.64 (2 d, 4 H, J 9.1 Hz, pMB–
H), 6.09–5.86 (m, 1 H, CH2ꢀCH–CH2 –), 5.84
(dd, 1 H, J2,3 2.3 Hz, J3,4 9.3 Hz, H-3), 5.61
(dd, 1 H, J1,2 1.7 Hz, J2,3 2.3 Hz, H-2), 5.44–
5.24 (m, 2 H, CH2ꢀCH–CH2–), 5.25 (dd, 1 H,
J1%,2% 1.2 Hz, J2%,3% 3.6 Hz, H-2%), 5.13 (t, 1 H, J
9.8 Hz, H-4%), 5.05 (d, 1 H, J1,2 1.7 Hz, H-1),
5.03 (d, 1 H, J1%,2% 1.2 Hz, H-1%), 4.94 (dd, 1 H,
J5,6a 1.2 Hz, J6a.6b 12.3 Hz, H-6a), 4.52 (t, 1 H,
J 9.3 Hz, H-4), 4.51 (dd, 1 H, J5,6b 5.6 Hz,
2
J6a,6b 12.3 Hz, H-6b), 4.49, 4.37 (ABq, 2 H, J
11.6 Hz, pMBCH2), 4.38–4.07 (m, 4 H, H-5,
5%, CH2ꢀCH–CH2–), 3.84 (dd, 1 H, J2%,3% 3.6
Hz, J3%,4% 9.8 Hz, H-3%), 3.74 (s, 3 H, OCH3),
2.09 (s, 3H, CH3CO), 0.74 (d, 3 H, J 6.8 Hz,
CH3). Anal. Calcd for C53H52O16: C, 67.36; H,
5.55. Found: C, 67.50; H, 5.58.
Allyl
4-O-(2-O-acetyl-4-O-benzoyl-h-
L
-
-
rhamnopyranosyl) - 2,3,6 - tri - O - benzoyl - h -
D
mannopyranoside (16).—Solid 2,3-dichloro-
5,6-dicyano-1,4-benzoquinone (DDQ, 0.11 g,
0.48 mmol) [14] was added with stirring at rt
to a mixture of compound 15 (420 mg, 0.44
mmol), CH2Cl2 (5 mL), and water (0.25 mL).
Stirring was continued for 6 h, when TLC (1:2
EtOAc–petroleum ether) showed complete
conversion of the starting material to a slower
moving product. CH2Cl2 (5 mL) was added,
the resulting solution was washed with aq
Na2S2O3, dried, and concentrated, and the
residue was chromatographed to give 16 (318
Allyl
4-O-(2-O-acetyl-4-O-benzoyl-h-
L
-
-
rhamnopyranosyl) - 2,3,6 - tri - O - benzoyl - h -
D
mannopyranoside (16) by direct selecti6e 3%-
deacetylation of 13.—A methanolic solution
of HCl (1.04 N, 5 mL), prepared by adding
acetyl chloride (0.8 mL) to freshly distilled
MeOH (10 mL), was added to a solution of
the disaccharide 13 (340 mg, 0.39 mmol) in
freshly distilled MeOH (3.3 mL) and the solu-
tion was stirred at 45–50 °C for about 1 h.
The reaction was monitored by TLC (2:1
petroleum ether–EtOAc), and the reaction
1
mg, 88%). Its H NMR spectrum was the
same as that of the product obtained from the
direct selective 3%-deacetylation of 13.

W. Wang, F. Kong / Carbohydrate Research 315 (1999) 128–136
135
5.68–5.02 (m, 8 H, H-2A, 2C, 3C, 3D, 4D, 6A,
CH2ꢀCH–CH2–), 5.22, 5.12, 5.05, 5.04 (4 d, 4
H, H-1A, 1B, 1C, 1D), 4.89–3.80 (m, 14 H,
H-2B, 2D, 3B, 4A, 4C, 5A, 5B, 5C, 5D, 6A, 6C,
6C, CH2ꢀCH–CH2–), 0.81, 0.76 (2 d, 6 H, J
6.2 Hz, 2 CH3). Anal. Calcd for C90H82O28: C,
67.07; H, 5.13. Found: C, 67.01; H, 5.15.
Allyl 4-O-{3-O-[4-O-(2-O-acetyl-3,4-di-O-
benzoyl - h -
benzoyl-h-
O - benzoyl - h -
O-benzoyl-h-
L
- rhamnopyranosyl) - 2,3,6 - tri - O-
D
-mannopyranosyl]-2-O-acetyl-4-
L
- rhamnopyranosyl} - 2,3,6 - tri-
D
-mannopyranoside (17).—A
mixture of the disaccharide donor 8 (289 mg,
0.28 mmol) and the disaccharide acceptor 16
(230 mg, 0.28 mmol) in anhyd CH2Cl2 (15 mL)
Allyl 4-O-{2-O-[2,3,4-tri-O-acetyl-i-
opyranosyl] - 3 - O - [4 - O - (2 - O - (2,3,4 - tri - O-
acetyl-i- -xylopyranosyl)-3,4-di-O-benzoyl-
h- -rhamnopyranosyl)-2,3,6-tri-O-benzoyl-h-
-mannopyranosyl]-4-O-benzoyl-h- -rhamno-
pyranosyl}-2,3,6-tri-O-benzoyl-h- -manno-
pyranoside (19).—Coupling of 2,3,4-tri-O-
acetyl-a- -xylopyranosyl bromide (128 mg, 0.3
mmol), obtained from -xylose (purchased
L
-xyl-
˚
containing 4 A activated molecular sieves (1 g)
L
was stirred under N2 for 1 h at rt and then
cooled to −40 °C. Trimethylsilyl triflate
(Me3SiOTf, 5 mL, 0.1 equiv) was added and the
mixture was stirred under N2 below −30 °C
for another 40 min. TLC showed the starting
material had disappeared. Triethylamine (5
mL) was added and the mixture was treated as
described for the preparation of 6. Flash chro-
matography (2:1 EtOAc–petroleum ether) of
the residue gave the tetrasaccharide 17 (360
mg, 0.21 mmol, 75%) as a colorless syrup;
[h]2D0−42.6° (c 1.0, CHCl3); 1H NMR (CDCl3):
l 8.20–7.74 (m, 18 H, Bz–H), 7.70–7.16 (m, 27
H, Bz–H), 6.08–5.86 (m, 1 H, CH2ꢀCH–
CH2–), 5.87 (dd, 1 H, J2A,3A 3.7 Hz, J3A,4A 9.8
Hz, H-3A), 5.64 (dd, 1 H, J1A,2A 1.7 Hz, J2A,3A
3.7 Hz, H-2A), 5.58–5.21 (m, 8 H, H-2B, 2C,
2D, 3C, 3D, 4D, CH2ꢀCH–CH2–), 5.14, 5.08,
5.04, 4.99 (4 d, 4 H, H-1A, 1B, 1C, 1D), 4.83
(dd, 1 H, J5A,6A 0.7 Hz, J6A,6A 12.7 Hz, H-6A),
4.65–3.70 (m, 12 H, H-3B, 4A, 4C, 5A, 5B, 5C,
5D, 6A, 6C, 6C, CH2ꢀCH–CH2–), 2.26, 2.02
(2 s, 6 H, 2 CH3CO), 0.85, 0.72 (2 d, 6 H, J 6.2
Hz, 2 CH3). Anal. Calcd for C94H86O30: C,
66.58; H, 5.11. Found: C, 66.59; H, 5.20.
L
D
L
D
L
L
from Fluka) according to the standard method
for the preparation of ‘acetobromoglucose’
[15], with the tetrasaccharide acceptor 18 (170
mg, 0.106 mmol), promoted by silver triflate
(77 mg, 0.3 mmol), in dry CH2Cl2 (10 mL)
˚
containing 4 A activated molecular sieves (0.5
g) under N2 was carried out at −5 °C for 2 h,
at the end of which time TLC showed the
starting material had disappeared. Pyridine
(150 mL) and 10% aq Na2S2O3 (1 mL) were
added to quench the reaction. The reaction
mixture was dissolved in CH2Cl2 (10 mL) and
washed sequentially with N HCl (10 mL), satd
aq NaHCO3 (10 mL), and H2O (10 mL). The
aq washings were re-extracted with CH2Cl2 (5
mL) and the combined organic solutions were
dried and concentrated. After flash chromatog-
raphy with 3:1 petroleum ether–EtOAc as the
eluent, hexasaccharide 19 (152 mg, 0.071
mmol, 67%) was obtained; [h]2D0+36.8° (c 1.8
CHCl3); 1H NMR (CDCl3): l 8.18–7.84 (m, 18
H, Bz–H), 7.72–7.22 (m, 27 H, Bz–H), 6.04–
5.93 (m, 1 H, CH2ꢀCH–CH2–), 5.85 (dd, 1 H,
J2A,3A 3.4 Hz, J3A,4A 9.6 Hz, H-3A), 5.74 (dd, 1
H, J1A,2A 1.7 Hz, J2A,3A 3.4 Hz, H-2A), 5.63–
5.59 (m, 2 H, H-2C, 3C), 5.39–5.20 (m, 2 H,
CH2ꢀCH–CH2–), 5.30–4.52 (m, 17 H, H-1A,
1B, 1C, 1D, 2E, 2F, 3D, 3E, 3F, 4B, 4D, 4E,
4F, 6A, 6C), 4.46–4.10 (m, 13 H, H-1E, 1F,
2B, 2D, 3B, 4A, 4C, 6E, 6F, CH2ꢀCH–CH2–),
4.05–3.11 (m, 8 H, H-5A, 5B, 5C, 5D, 5E, 5F),
2.12, 2.03, 2.03, 2.02, 1.74, 1.57 (6 s, 18 H, 6
CH3CO), 0.73 (d, 3 H, J 6.2 Hz, CH3), 0.61 (d,
3 H, J 6.2 Hz, CH3). Anal. Calcd for
C112H110O42: C, 63.21; H, 5.21. Found: C,
63.10; H, 5.25.
Allyl 4-O-{3-O-[4-O-(3,4-di-O-benzoyl-h-
L
-
-
rhamnopyranosyl) - 2,3,6 - tri - O - benzoyl - h -
D
mannopyranosyl]-4-benzoyl-h-
osyl}-2,3,6-tri-O-benzoyl-h-
L
-rhamnopyran-
-mannopyran-
D
oside (18).—A methanolic solution of HCl
(1.04 N, 2.2 mL) prepared by adding acetyl
chloride (0.8 mL) to freshly distilled MeOH (10
mL), was added to a solution of 17 (320 mg,
0.19 mmol) in freshly distilled MeOH (1.5 mL)
and the solution was stirred at 48–52 °C for 1.5
h to give 18 as a syrup (260 mg, 0.16 mmol,
84%) after flash chromatography; [h]2D0−49.4°
1
(c 0.7 CHCl3); H NMR (CDCl3): l 8.17–7.80
(m, 18 H, Bz–H), 7.68–7.20 (m, 27 H, Bz–H),
6.07–5.82 (m, 1 H, CH2ꢀCH–CH2–), 5.86 (dd,
1 H, J2A,3A 3.2 Hz, J3A,4A 9.8 Hz, H-3A),

136
W. Wang, F. Kong / Carbohydrate Research 315 (1999) 128–136
Allyl 4-O-{2-O-[i-
L
-xylopyranosyl]-3-O-[4-
- xylopyranosyl) - h - - rhamno-
-mannopyranosyl]-h- -rhamno-
-mannopyranoside (20).—The
References
O - (2 - O - (i -
pyranosyl)-h-
L
L
[1] (a) N.J. Palleroni, J.F. Bradbury, Int. J. Syst. Bacte-
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[4] R.W. Bassily, M.A. Nashed, A.S. Nematalla, Carbo-
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[5] (a) R.U. Lemieux, A.R. Morgan, Can. J. Chem., 43
(1965) 2199–2213. (b) D.R. Bundle, S. Josephson, Can.
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Forooghian, B.M. Pinto, Carbohydr. Res., 291 (1996)
21–41.
D
L
pyranosyl}-h-
D
protected hexasaccharide 19 (120 mg, 0.056
mmol) was suspended in freshly distilled
MeOH (10 mL), a solution of sodium methox-
ide (2 M, 0.5 mL) was added, and the mixture
was stirred overnight at rt. More sodium
methoxide (0.5 mL) was added, and the reac-
tion was heated at 40 °C for another 8 h. TLC
showed that the reaction was complete. The
resulting solution was de-ionized with Amber-
lite IR-120 (H+) anion-exchange resin,
filtered, and evaporated. The hexasaccharide
20 was obtained after chromatography on
Sephadex G-25 (H2O solvent) as an amor-
phous powder (51 mg, 97%) after freeze-dry-
ing; [h]2D0+33.5° (c 1.8, MeOH); ESMS for
C37H62O27 (938.88): 937.7 [M−1]+. H NMR
1
(D2O): l 6.00–5.85 (m, 1 H, CH2ꢀCH–CH2–
), 5.32–5.17 (m, 2 H, CH2ꢀCH–CH2–), 5.00,
4.94, 4.94, 4.87 (4 s, 4 H, H-1A, 1B, 1C, 1D),
4.32, 4.30 (2 d, 2 H, J1E,2F 7.6 Hz, H-1E, 1F),
4.24–4.15 (m,
2
H, CH2ꢀCH–CH2–),
1.23,1.23 (2 d, 6 H, J 4.3 Hz, CH3).
[13] G. Yang, F. Kong, Carbohydr. Res., 211 (1991) 179–
182.
[14] K. Horita, T. Yoshioka, T. Tanaka, Y. Oikawa, O.
Yonemitsu, Tetrahedron, 42 (1986) 3021–3028.
[15] R.U. Lemieux, Methods Carbohydr. Chem., 2 (1963)
221–222.
Acknowledgements
This work was supported by the Chinese
Academy of Sciences (Project KJ952J,510)
and by the National Natural Science Founda-
tion of China (Project 29802009).
[16] T. Ziegler, E. Eckhardt, D. Keller, J. Carbohydr.
Chem., 16 (1997) 719–738.
.