Synthesis of a hexasaccharide that relates to the arabinogalactan epitope

Article abstract of DOI:10.1016/S0008-6215(01)00259-2

A hexasaccharide derivative of the arabinogalactan epitope, methyl β-D-galactopyranosyl-(1 → 6)-[α-L-arabinofuranosyl-(1 → 3)]-β-D-galactopyranosyl-(1 → 6)-β-D-galactopyranosyl-(1 → 6)-[α-L-arabinofuranosyl-(1 → 3)]-α-D-galactopyranoside, was synthesized efficiently using a 3 + 3 strategy. The key step is the preparation of the trisaccharide donor, isopropyl 2,3,4,6-tetra-O-benzoyl-β-D-galactopyranosyl-(1 → 6)-[2,3,5-tri-O-benzoyl-α-L-arabinofuranosyl-(1 → 3)]-2,4-di-O-benzoyl-1-thio-β-D-galactopyranoside, from isopropyl 1-thio-β-D-galactopyranoside using a one-pot synthesis of a 3,6-differentially protected building block.

Full text of DOI:10.1016/S0008-6215(01)00259-2

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Carbohydrate Research 336 (2001) 99–106
Synthesis of a hexasaccharide that relates to the
arabinogalactan epitope
Guofeng Gu, Feng Yang, Yuguo Du,* Fanzuo Kong
Research Center for Eco-En6ironmental Sciences, Academia Sinica, PO Box 2871, Beijing 100085, PR China
Received 19 August 2001; accepted 18 September 2001
Abstract
A hexasaccharide derivative of the arabinogalactan epitope, methyl b-
osyl-(1“3)]-b- -galactopyranosyl-(1“6)-b- -galactopyranosyl-(1“6)-[a-
pyranoside, was synthesized efficiently using a 3+3 strategy. The key step is the preparation of the trisaccharide
donor, isopropyl 2,3,4,6-tetra-O-benzoyl-b- -galactopyranosyl-(1“6)-[2,3,5-tri-O-benzoyl-a- -arabinofuranosyl-
(1“3)]-2,4-di-O-benzoyl-1-thio-b- -galactopyranoside using a one-pot
D
-galactopyranosyl-(1“6)-[a-
L
-arabinofuran-
D
D
L
-arabinofuranosyl-(1“3)]-a-
D
-galacto-
D
L
D
-galactopyranoside, from isopropyl 1-thio-b-
D
synthesis of a 3,6-differentially protected building block. © 2001 Elsevier Science Ltd. All rights reserved.
Keywords: Carbohydrate; Arabinogalactan; Regioselective reaction; Antigen; Epitope
1. Introduction
There has been no unambiguous structural
definition on CCRC-M7-recognized arabino-
galactan epitopes so far reported.3–5 The re-
sults of a series of immunoassays indicated
that arabinosyl residues constitute an impor-
tant part of the epitope. However, the number
of arabinosyl residues in this epitope and the
site of their attachment to the galactan back-
bone remain to be established.5 Besides, it is
very difficult to gain arabinose-containing
oligosaccharides with clear structural informa-
tion for biological studies from natural re-
sources. We present here the first synthesis of
a well-defined arabinogalactan hexasaccharide
derivative using our newly developed metho-
dology6 for the synthesis of 3,6-branched
oligosaccharides.
Antibodies generated against specific plant
cell-wall carbohydrates may serve as probes in
identifying cognate structural elements in the
outer membrane saccharides of other plant
species. The usefulness of this concept relies
on characterization and preparation of the
epitopes recognized by the corresponding anti-
bodies.1 As part of our ongoing research pro-
ject on the synthesis of epitopes related to
arabinogalactan proteins (AGPs),2 we have
synthesized dodecyl b-
(1“6)-b- -galactopyranosyl-(1“6)-[a-
binofuranosyl-(1“2)]-b- -galactopyranoside.
The synthesis of a 2-O-arabinofuranosylated
-(1“6)-linked galactan based on 1,2-an-
D
-galactopyranosyl-
D
L
-ara-
D
b-
D
hydrosugars had been reported earlier by van
Boom’s group.3
2. Results and discussion
* Corresponding author. Tel.: +86-10-62914475; fax: +
86-10-62923563.
E-mail address: ygdu@mail.rcees.ac.cn (Y. Du).
Isopropyl 2,4-di-O-benzoyl-3-O-tert-butyl-
dimethylsilyl-6-O-triphenylmethyl-1-thio-b- -
D
0008-6215/01/$ - see front matter © 2001 Elsevier Science Ltd. All rights reserved.
PII: S0008-6215(01)00259-2

100
G. Gu et al. / Carbohydrate Research 336 (2001) 99–106
dichloromethane in the presence of NIS (2.5
equiv) and TMSOTf (13% equiv) to give fully
protected hexasaccharide 19 (83.1%). Peaks at
l 97.9, 100.8, 100.9, 101.6, 107.5, 107.7 in the
13C NMR spectrum show all the C-1s in this
structure. Finally, deacylation of 19 in ammo-
nia-saturated methanol completed the synthe-
galactopyranoside (1) was prepared from com-
mercially available isopropyl 1-thio-b-
D
-
galactopyranoside (IPTG) according to our
previous method.6 FeCl3 hexahydrate cata-
lyzed detritylation7 was carried out smoothly
on compound 1 providing the 6-OH acceptor
2 in 85.5% yield. Standard glycosylation of 2
with fully benzoylated galactopyranosyl imi-
date 3 in anhydrous CH2Cl2 gave (1“6)-
linked di-galactopyranoside 4, followed by
desilylation with 90% trifluroacetic acid
(TFA), afforded the 3-OH derivative 5 in a
total yield of 64.7%. Coupling of disaccharide
sis of the target compound, methyl b-
galactopyranosyl-(1“6)-[a- -arabinofuran-
osyl - (1“3)] - b - - galactopyranosyl - (1“6)-
(b- -galactopyranosyl-(1“6)-[a- -arabino-
furanosyl-(1“3)]-a- -galactopyranoside (20),
D
-
L
D
D
L
D
in 97.6% isolated yield. The potential bioactiv-
ity of compound 20 is currently under investi-
gation (Scheme 1).
acceptor
5
with the arabinofuranosyl
trichloroacetimidate 6 gave thioglycoside 7 as
a latent trisaccharide donor in 78% yield. To
synthesize the acceptor part for the target
molecule assembly, building blocks 9 and 13
were each synthesized. Thus, compound 8 was
selectively silylated on the primary hydroxyl
group with tert-butylchlorodiphenylsilane,
then benzoylated in situ with benzoyl chloride
in pyridine, to afford 9 in a total yield of
74.4%. Synthon 13 was obtained by selective
benzoylation of 10,8 followed by removal of
the acetonide group in 90% TFA (“12) and
regioselective protection of the primary hy-
droxyl group with tert-butylchlorodiphenylsi-
lane in pyridine. A doublet of doublets at l
5.16 ppm clearly indicates the benzoylation of
3. Experimental
General methods.—Optical rotations were
determined at 20 °C with a Perkin–Elmer
model 241-Mc automatic polarimeter. Melting
points were determined with a ‘Mel-Temp’
1
13
1
1
apparatus. H, C NMR and H–1H, H–13C
COSY spectra were recorded with ARX 400
spectrometers for solutions in CDCl3, MeOD
and D2O. Chemical shifts are given in ppm
downfield from internal Me4Si, or DSS in the
case of D2O. Mass spectra were measured
using MALDI-TOF MS with a-cyano-4-hy-
droxycinnamic acid (CCA) as matrix or
recorded with a VG PLATFORM mass spec-
trometer using the ESI technique to introduce
the sample. Thin-layer chromatography (TLC)
was performed on Silica Gel HF254 with detec-
tion by charring with 30% (v/v) H2SO4 in
MeOH or in some cases by a UV detector.
Column chromatography was conducted by
elution of a column (16×240 mm, 18×300
mm, 35×400 mm) of silica gel (100–200
mesh) with EtOAc–petroleum ether (bp 60–
90 °C) as the eluent. Solutions were concen-
trated at B60 °C under diminished pressure.
Isopropyl 2,4-di-O-benzoyl-3-O-tert-butyl-
1
the 2-OH in 12 based on decoupled H NMR
analysis. It is noteworthy that direct conden-
sation of 11 with 6 in the presence of TM-
SOTf was troublesome providing significant
byproducts due to the lack of stability of the
4,6-acetonide of 11. Glycosylation of diol 13
with trichloroacetimidate 6 in anhydrous
CH2Cl2 using TMSOTf (10% equiv) as cata-
lyst gave the (1“3)-linked disaccharide 14 in
71.8% yield. The correct regioselectivity of 14
1
was confirmed by 2D H–1H COSY spec-
troscopy. Desilylation of 14 in 90% TFA (“
15), followed by NIS–TMSOTf catalyzed gly-
cosylation with 9 in anhydrous CH2Cl2 below
−15 °C furnished trisaccharide 16 in good
yield. Acetylation of the remaining 4-OH of
16 with acetic anhydride in pyridine gave 17,
which was then treated with 90% TFA to
complete trisaccharide acceptor 18. Coupling
reaction of trisaccharide donor 7 and trisac-
charide acceptor 18 proceeded in anhydrous
dimethylsilyl-1-thio-i- -galactopyranoside (2).
D
—Ferric trichloride hexahydrate (2.0 equiv)
was added to a mixture of 1 (4.24 g, 5.29
mmol) in dry CH2Cl2 (30 mL). The mixture
was stirred at rt for 3 h, then diluted with
more CH2Cl2 (50 mL), and washed twice with
ice-cold water. The washings were re-extracted
with CH2Cl2 (20 mL). The combined organic

G. Gu et al. / Carbohydrate Research 336 (2001) 99–106
101
Scheme 1.

102
G. Gu et al. / Carbohydrate Research 336 (2001) 99–106
under diminished pressure to give a residue.
Purification of the product by column chro-
matography (3:1 petroleum ether–EtOAc)
gave 5 (1.72 g, 76.4%) as a syrup: [h]2D0+45° (c
phase was dried and concentrated, then sub-
jected to a silica gel column using 3:1
petroleum ether–EtOAc as eluent to give crys-
talline 2 (2.53 g, 85.5%): mp 110–111 °C; [h]D20
1
1
1, CHCl3); H NMR (CDCl3): l 1.01 (d, 3 H,
+76° (c 1, CHCl3); H NMR (CDCl3): l 0.01
CH3), 1.06 (d, 3 H, CH3), 2.98 (m, 1 H, CH),
3.75–3.94 (m, 3 H, J6a,6b10.8, J6a,5 2.6, J6b,5 6.7
Hz, H-6a, H-6b, H-5), 4.04 (q, 1 H, J3,4 2.4
Hz, H-3), 4.10–4.25 (m, 2 H, J5%,6a% 6.3, J6b%,5%
6.0, J6a%,6b% 11.0 Hz, H-6a%, H-5%), 4.32 (q, 1 H,
H-6b%), 4.11 (d, 1 H, J1,2 9.8 Hz, H-1), 4.78 (d,
1 H, J1%,2%7.8 Hz, H-1%), 5.22 (br t, 1 H, J2,3 8.2
Hz, H-2), 5.45 (dd, 1 H, J3%,4%2.9 Hz, H-3%),
5.59 (d, 1 H, H-4), 5.68 (t, 1 H, J2%,3%9.9 Hz,
H-2%), 5.84 (d, 1 H, H-4%), 7.11–8.01 (m, 30 H,
PhCO). Anal. Calcd for C57H52O16S: C, 66.80;
H, 5.09. Found: C, 66.87; H, 5.20.
(s, 3 H, SiCH3), 0.16 (s, 3 H, SiCH3), 0.74 (s,
9 H, C(CH3)3), 1.41 (d, 3 H, CH3), 1.44 (d, 3
H, CH3), 3.39 (m, 1 H, CH), 3.72 (q, 1 H,
J6a,6b11.1, J6a,5 6.3 Hz, H-6a), 3.93 (q, 1 H,
J6b,5 5.7 Hz, H-6b), 4.02 (t, 1 H, H-5), 4.28 (d,
1 H, J3,4 B1.0 Hz, H-3), 4.88 (d, 1 H, J1,2 9.9
Hz, H-1), 5.62 (d, 1 H, H-4), 5.73 (t, 1 H, J2,3
9.6 Hz, H-2), 7.58–8.28 (m, 10 H, PhCO).
Anal. Calcd for C29H40O7SSi: C, 62.14; H,
7.14. Found: C, 62.05; H, 7.29.
Isopropyl
galactopyranosyl-(1“6)-2,4-di-O benzoyl-3-
O-tert-butyldimethylsilyl-1-thio-i- -galactopyr
2,3,4,6-tetra-O-benzoyl-i-
D
-
Isopropyl
galactopyranosyl-(1“6)-[2,3,5-tri-O-benzoyl-
h- -arabinofuranosyl-(1“3)]-2,4-di-O-ben-
zoyl-1-thio-i- -galactopyranoside (7).—To a
2,3,4,6-tetra-O-benzoyl-i-
D
-
D
anoside (4).—Compounds 2 (2.00 g, 3.57
mmol) and 3 (2.27 g, 3.75 mmol) were pre-
dried in one flask under vacuum at 60 °C for
4 h. The mixture was then dissolved in CH2Cl2
(20 mL). To the solution was added Me3SiOTf
(40 mL, 0.22 mmol) under an N2 atmosphere
at 0 °C. The mixture was stirred at this tem-
perature for 1 h, then neutralized with triethyl-
amine, concentrated under reduced pressure,
and purified on a silica gel column with 3:1
petroleum ether–EtOAc as the eluent to give
4 (3.44 g, 84.7%) as a syrup: [h]2D0 +74° (c 5.4,
L
D
mixture of compound 5 (1.50 g, 1.46 mmol)
and 6 (0.933 g, 1.54 mmol) in anhyd CH2Cl2
(15 mL) was added Me3SiOTf (26 mL, 0.15
mmol) under an N2 atmosphere at 0 °C. The
mixture was stirred under these conditions for
1 h, at which time TLC (2:1 petroleum ether–
EtOAc) indicated that all starting materials
were consumed. The reaction mixture was
neutralized with Et3N, then concentrated.
Column chromatography (2:1 petroleum
ether–EtOAc) of the residue gave 7 (1.68 g,
78%) as a syrup: [h]2D0 +69° (c 5.0, CHCl3);
1H NMR (CDCl3): l 1.08 (d, 3 H, CH3), 1.17
(d, 3 H, CH3), 3.06 (m, 1 H, CH), 3.78 (q, 1
H, J6a,6b11.8 Hz, H-6aI), 4.08–4.15 (m, 2 H,
J6a,5 2.7, J6b,5 5.8 Hz, H-6bI, H-5I), 4.18–4.23
(m, 3 H, J3,4 3.4, J5,6a 6.3, J5,6b 6.0 Hz, H-3I,
H-6aII, H-5II), 4.36 (q, 1 H, J6a,6b10.8 Hz,
H-6bII), 4.66 (d, 1 H, J1,2 10.0 Hz, H-1I), 4.70
(dd, 1 H, J4,5a 3.7, J5a,5b 12.2 Hz, H-5aIII), 4.84
(m, 1 H, J4,3 5.7 Hz, H-4III), 4.87 (d, 1 H, J1,2
7.9 Hz, H-1II), 4.93 (dd, 1 H, J4,5b 2.8 Hz,
H-5bIII), 5.25 (br s, 1 H, H-2III), 5.31 (s, 1 H,
H-1III), 5.48 (br d, 1 H, J3,4 5.5 Hz, H-3III),
5.52 (dd, 1 H, J3,4 3.4 Hz, H-3II), 5.66 (t, 1 H,
J2,3 9.8 Hz, H-2II), 5.77 (dd, 1 H, J2,3 7.9 Hz,
H-2I), 5.88 (d, 1 H, J3,4 3.4 Hz, H-4I), 5.92 (d,
1 H, J3,4 3.4 Hz, H-4II), 7.21–8.09 (m, 45 H,
PhCO); 13C NMR (100 MHz, CDCl3): l 23.39
(CH3), 23.78 (CH3), 35.00 (CH), 61.68 (C-6II),
63.27 (C-5III), 67.93 (C-4II), 68.19 (C-6I), 69.68
1
CHCl3); H NMR (CDCl3): l 0.01 (s, 3 H,
SiCH3), 0.16 (s, 3 H, SiCH3), 0.74 (s, 9 H,
C(CH3)3), 1.31 (d, 3 H, CH3), 1.41 (d, 3 H,
CH3), 3.12 (m, 1 H, CH), 3.99 (q, 1 H, J3,4 2.4
Hz, H-3), 4.15–4.38 (m, 3 H, J6a,6b10.8, J6a,5
2.6, J6b,5 6.7 Hz, H-6a, H-6b, H-5), 4.44 (br t,
1 H, J5%,6b%=J5%,6a%=6.3 Hz, H-5%), 4.52 (q, 1
H, J6a%,6b%11.0 Hz, H-6a%), 4.65 (q, 1 H, H-6b%),
4.80 (d, 1 H, J1,2 9.8 Hz, H-1), 5.08 (d, 1 H,
J1%,2%7.8 Hz, H-1%), 5.64 (br t, 1 H, J2,37.6 Hz,
H-2), 5.72 (dd, 1 H, J3%,4%3.0 Hz, H-3%), 5.78 (d,
1 H, H-4), 5.96 (t, 1 H, J2%,3%10.0 Hz, H-2%),
6.13 (d, 1 H, H-4%), 7.37–8.29 (m, 30 H,
PhCO). Anal. Calcd for C63H66O16SSi: C,
66.43; H, 5.80. Found: C, 66.32; H, 6.08.
Isopropyl
galactopyranosyl-(1“6)-2,4-di-O-benzoyl-1-
thio-i- -galactopyranoside (5).—A solution
2,3,4,6-tetra-O-benzoyl-i- -
D
D
of compound 4 (2.50 g, 2.20 mmol) in 90% aq
trifluroacetic acid (10 mL) was stirred at rt for
about 1 h, then co-evaporated with toluene

G. Gu et al. / Carbohydrate Research 336 (2001) 99–106
103
(C-2I), 70.18 (C-2II), 70.58 (C-4I), 71.15 (C-3I),
71.73 (C-3II), 77.10 (C-5I), 77.54 (C-3III), 77.66
(C-5II), 81.57 (C-4III), 82.52 (C-2III), 83.56 (C-
1I), 100.99 (C-1II), 107.67 (C-1III), 164.61–
166.11 (9 C, PhCO); MALDI-TOF MS Calcd
for C83H72O23S: 1468 [M]; Found 1491.6
[M+Na]+, 1507.6 [M+K]+. Anal. Calcd for
C83H72O23S: C, 67.85; H, 4.90. Found: C,
67.91; H, 5.01.
J6a,6bB 1, J6a,5=J6b,5=6.4 Hz, H-6a, H-6b),
4.18 (br t, 1 H, J4,51.7 Hz, H-5), 4.33 (dd, 1 H,
H-4), 4.55 (dd, 1 H, J3,4 6.8 Hz, H-3), 5.00 (d,
1 H, J1,2 3.4 Hz, H-1), 5.14 (dd, 1 H, J2,3 8.1
Hz, H-2), 7.27–8.11 (m, 5 H, PhCO). Anal.
Calcd for C17H22O7: C, 60.36; H, 6.51. Found:
C, 60.40; H, 7.01.
Preparation of methyl 2-O-benzoyl-h- -
D
galactopyranoside (12).—Compound 11 (2.90
g, 8.85 mmol) was dissolved in 90% aq tri-
fluroacetic acid (8 mL). The solution was
stirred at rt for 30 min and co-evaporated
with toluene to dryness under diminished
pressure. The residue was purified on a silica
gel column using EtOAc as eluent to give 12
(2.50 g, 97.6%) as crystals: mp 158–159 °C;
[h]2D0 +143° (c 2.1, water), lit.9 mp 171–
Phenyl 2,3,4-tri-O-benzoyl-6-O-tert-butyl-
diphenylsilyl-1-thio-i-
—To the solution of phenyl 1-thio-b-
D
-galactopyranoside (9).
D
-
galactopyranoside (2.20 g, 8.09 mmol) in pyri-
dine (8 mL) was added tert-butylchloro-
diphenylsilane (2.7 mL, 9.72 mmol). The mix-
ture was stirred at rt for 16 h, at which time
TLC (2:1 petroleum ether–EtOAc) indicated
that all starting materials were consumed.
Then benzoyl chloride (3.30 mL, 28.4 mmol)
was added dropwise. The mixture was stirred
at rt for 10 h, then co-evaporated with toluene
to remove pyridine under diminished pressure.
The residue was purified on a silica gel column
using 3:1 petroleum ether–EtOAc as eluent to
give 9 (4.95 g, 74.4%) as a syrup: [h]2D0 +97°
1
173 °C; [h]2D0 +170° (c 1, MeOH); H NMR
(300 MHz, CDCl3): l 3.30 (s, 3 H, OCH3),
3.78–4.10 (br m, 5 H, J6a,6b10.2, J2,3 6.6 Hz,
H-6a, H-6b, H-5, H-4, H-3), 4.96 (d, 1 H, J1,2
3.3 Hz, H-1), 5.22 (dd, 1 H, J
7.24–8.01 (m, 5 H, PhCO).
6.6Hz, H-2),
2,3
Methyl 2-O-benzoyl-6-O-tert-butyldiphenyl-
silyl-h- -galactopyranoside (13).—To a solu-
D
tion of compound 12 (2.50 g, 8.39 mmol) in
pyridine (10 mL) was added TBDPSCl (2.80
mL, 10.08 mmol) with a catalytic amount of
4-dimethylaminopyridine (DMAP). The mix-
ture was stirred at rt overnight, and then
poured into cold water, extracted with CH2Cl2
(2×50 mL), and the organic layer was dried
over Na2SO4 and concentrated. Purification of
the product by column chromatography (2:1
petroleum ether–EtOAc) gave 13 (4.05 g,
90%) as a syrup: [h]2D0 +36° (c 2.9, CHCl3);
1H NMR (300 MHz, CDCl3): l 0.99 (s, 9 H,
C(CH3)3), 3.23 (s, 3 H, OCH3), 3.77 (q, 1 H,
J6b,5 5.2, J6a,5 4.8 Hz, H-5), 3.82–3.93 (br m, 2
H, J6b,6a10.8 Hz, H-6b, H-6a), 4.03 (dd, 1 H,
J3,2 9.9 Hz, H-3), 4.12 (d, 1 H, J3,4 3.3 Hz,
H-4), 4.93 (d, 1 H, J1,2 3.6 Hz, H-1), 5.16 (dd,
1 H, H-2), 7.16–8.00 (m, 15 H, PhCO). Anal.
Calcd for C30H36O7Si: C, 67.16; H, 6.72.
Found: C, 67.10; H, 6.81.
1
(c 11.1, CHCl3); H NMR (CDCl3): l 1.01 (s,
9 H, C(CH3)3), 3.79 (q, 1 H, J6a,6b10.1, J6a,5 7.7
Hz, H-6a), 3.90 (q, 1 H, J6b,5 6.1 Hz, H-6b),
4.14 (br t, 1 H, H-5), 4.98 (d, 1 H, J1,2 9.5 Hz,
H-1), 5.61 (dd, 1 H, J3,4 2.9 Hz, H-3), 5.68 (t,
1 H, J2,3 9.8 Hz, H-2), 6.0.6 (d, 1 H, H-4),
7.21–7.97 (m, 30 H, PhCO). Anal. Calcd for
C49H46O8SSi: C, 71.53; H, 5.60. Found: C,
71.45; H, 5.71.
Preparation of methyl 2-O-benzoyl-4,6-O-
isopropylidene-h-
To a solution of methyl 4,6-O-isopropylidene-
a-
-galactopyranoside8 (7.00 g, 29.9 mmol) in
D
-galactopyranoside (11).—
D
pyridine (25 mL) was added benzoyl chloride
(3.8 mL, 32.7 mmol) and a catalytic amount
of 4-dimethylaminopyridine (DMAP). The
mixture was stirred at 50–60 °C for 5 h, then
poured into cold water, and extracted with
CH2Cl2 (2×50 mL). The organic layer was
dried over Na2SO4 and concentrated. Column
chromatography (3:1 petroleum ether–
EtOAc) of the residue gave syrupy 11 (4.20 g,
Methyl 2,3,5-tri-O-benzoyl-h-
nosyl - (1“3) - 2 - O - benzoyl - 6 - O - tert - butyl-
diphenylsilyl-h- -galactopyranoside (14).—To
L
-arabinofura-
D
a mixture of compound 13 (2.50 g, 4.46 mmol)
and 6 (2.97 g, 4.90 mmol) in anhyd CH2Cl2
(20 mL) was added Me3SiOTf (42 mL, 0.23
mmol) under an N2 atmosphere at 0 °C. The
1
41.6%): [h]2D0 +135° (c 1.5, CHCl3); H NMR
(CDCl3): l 1.53 (s, 3 H, CH3), 1.64 (s, 3 H,
CH3), 3.48 (s, 3 H, OCH3), 3.79 (d, 2 H,

104
G. Gu et al. / Carbohydrate Research 336 (2001) 99–106
mixture was stirred under these conditions for
1 h, neutralized with Et3N, and then concen-
tions for 1 h, at which time TLC (5:2
petroleum ether–EtOAc) indicated that start-
ing material 15 was completely consumed. The
reaction mixture was neutralized with Et3N,
then concentrated. Column chromatography
(5:2 petroleum ether–EtOAc) of the residue
gave 16 (2.31 g, 70.2%) as a syrup: [h]2D0 +97°
trated.
Column
chromatography
(4:1
petroleum ether–EtOAc) of the residue gave
syrupy 14 (3.28 g, 71.8%): [h]2D0 +19° (c 0.3,
1
CHCl3); H NMR (300 MHz, CDCl3): l 0.96
(s, 9 H, C(CH3)3), 3.23 (s, 3 H, OCH3), 3.75–
3.94 (br d, 3 H, J6b,5=J6a,5=5.1, J6b,6a B1
Hz, H-5, H-6b, H-6a), 4.17 (d, 1 H, J3,4 3.0
Hz, H-4), 4.29 (dd, 1 H, J2,3 10.2 Hz, H-3),
4.48–4.64 (m, 2 H, J5a%,5b% 10.0, J4%,5a% 4.8, J4%,5b%
5.4 Hz, H-4%, H-5a%), 4.70 (dd, 1 H, H-5b%),
5.09 (d, 1 H, J1,2 3.6 Hz, H-1), 5.34 (dd, 1 H,
J2,3 10.2 Hz, H-2), 5.41 (br s, 1 H, H-2%), 5.49
(d, 1 H, J3%,4% 3.9 Hz, H-3%), 5.52 (s, 1 H, H-1%),
7.06–8.10 (m, 30 H, PhCO). Anal. Calcd for
C56H56O14Si: C, 68.57; H, 5.71. Found: C,
68.49; H, 5.90.
1
(c 1.6, CHCl3); H NMR (CDCl3): l 0.97 (s, 9
H,C(CH3)3), 2.87 (s, 3 H, OCH3), 3.80–3.90
(m, 3 H, H-6aI, H-6bI, H-6aII), 3.97 (br d, 1 H,
J5,6a 8.3 Hz, H-5I), 4.07–4.13 (m, 3 H, H-4I,
H-5II, H-6bII), 4.28 (dd, 1 H, J3,4 3.4 Hz,
H-3I), 4.59–4.64 (m, 2 H, J4,5a 3.9, J5a,5b 12.1
Hz, H-5aIII, H-4III), 4.73 (q, 1 H, J4,5b 2.7 Hz,
H-5bIII), 4.80 (d, 1 H, J1,2 3.6 Hz, H-1I), 4.85
(d, 1 H, J1,2 7.8 Hz, H-1II), 5.32 (dd, 1 H, J2,3
10.4 Hz, H-2I), 5.45 (br s, 1 H, H-2III), 5.51 (s,
1 H, H-1III), 5.53 (br d, 1 H, J3,4 3.0 Hz,
H-3III), 5.63 (dd, 1 H, J3,4 3.3 Hz, H-3II), 5.72
(dd, 1 H, J2,3 10.4 Hz, H-2II), 6.07 (d, 1 H,
H-4II), 7.07–8.03 (m, 45 H, PhCO). Anal.
Calcd for C83H78O22Si: C, 68.50; H, 5.36.
Found: C, 68.33; H, 5.62.
Methyl 2,3,5-tri-O-benzoyl-h-
L
-arabinofura-
nosyl-(1“3)-2-O-benzoyl-h- -galactopyran-
D
oside (15).—A solution of compound 14
(3.00 g, 3.06 mmol) in 90% aq trifluroacetic
acid (15 mL) was stirred at rt for 1 h, then
neutralized with NaHCO3 and extracted with
CH2Cl2 (3×50 mL). The organic phases were
combined and concentrated. The residue was
purified on a silica gel column using 3:2
petroleum ether–EtOAc as eluent to give
syrupy 15 (1.94 g, 85.5%): [h]2D0 +81° (c 1.8,
Methyl 2,3,4-tri-O-benzoyl-6-O-tert-butyl-
diphenylsilyl - i -
[2,3,5 - tri - O - benzoyl - h -
(1“3)]-4-O-acetyl-2-O-benzoyl-h-
D
- galactopyranosyl - (1“6)-
- arabinofuranosyl-
-galacto-
L
D
pyranoside (17).—To a solution of compound
16 (1.42 g, 0.979 mmol) in pyridine (4 mL)
was added Ac2O (2 mL). The mixture was
stirred at rt for about 20 h, then co-evapo-
rated with toluene under diminished pressure
to remove pyridine. Column chromatography
(5:2 petroleum ether–EtOAc) of the residue
1
CHCl3); H NMR (300 MHz, CDCl3): l 3.31
(s, 3 H, OCH3), 3.70–4.00 (br m, 3 H, J6b,5
=
J
6a,5=5.1, J6b,6a 9.9 Hz, H-5, H-6b, H-6a),
4.22 (d, 1 H, J3,4 3.0 Hz, H-4), 4.35 (dd, 1 H,
J3,2 9.9 Hz, H-3), 4.52–4.68 (br m, 2 H,
J5a%,5b%10.0, J4%,5a% 4.8, J4%,5b% 5.4 Hz, H-4%, H-5a%),
4.74 (dd, 1 H, H-5b%), 5.10 (d, 1 H, J1,2 3.3 Hz,
H-1), 5.40 (dd, 1 H, J2,3 9.9 Hz, H-2), 5.44 (br
s, 1 H, H-2%), 5.51 (br d, 1 H, J3%,4% 3.9 Hz,
H-3%), 5.54 (s, 1 H, H-1%), 7.16–8.00 (m, 30 H,
PhCO). Anal. Calcd for C40H38O14: C, 64.69;
H, 5.12. Found: C, 64.60; H, 5.22.
gave 17 (1.22 g, 83.6%) as a syrup: [h]D20
+
1
115° (c 3.0, CHCl3); H NMR (CDCl3): l 1.00
(s, 9 H, C(CH3)3), 1.87 (s, 3 H, CH3CO), 2.92
(s, 3 H, OCH3), 3.61 (q, 1 H, J6a,6b 10.6 Hz,
H-6aI), 3.78–3.85 (m, 2 H, J6a,6b 13.1 Hz,
H-6aII, H-6bII), 3.94 (q, 1 H, J5,6b 2.5 Hz,
H-6bI), 4.07 (t, 1 H, J6b,5=J6a,5=7.4 Hz,
H-5II), 4.14 (br d, 1 H, J5,6a 8.0 Hz, H-5I), 4.44
(dd, 1 H, J3,4 3.4 Hz, H-3I), 4.67 (dd, 1 H, J4,5a
3.9, J5a,5b 12.1 Hz, H-5aIII), 4.78 (m, 1 H,
H-4III), 4.83 (d, 1 H, J1,2 7.8 Hz, H-1II), 4.85
(d, 1 H, J1,2 3.6 Hz, H-1I), 4.90 (dd, 1 H, J4,5b
2.7 Hz, H-5bIII), 5.28 (dd, 1 H, J2,3 10.6 Hz,
H-2I), 5.36 (br s, 1 H, H-2III), 5.45 (s, 1 H,
H-1III), 5.48–5.54 (br d, 2 H, J3,4 5.0 Hz, H-4I,
H-3III), 5.62 (dd, 1 H, J3,43.3 Hz, H-3II), 5.69
(dd, 1 H, J2,310.4 Hz, H-2II), 6.06 (d, 1 H,
Methyl 2,3,4-tri-O-benzoyl-6-O-tert-butyl-
diphenylsilyl - i -
[2,3,5 - tri - O - benzoyl - h -
(1“3)]-2-O-benzoyl-h-
D
- galactopyranosyl - (1“6)-
L
- arabinofuranosyl-
-galactopyranoside
D
(16).—To a solution of compound 15 (1.68 g,
2.26 mmol) and 9 (1.96 g, 2.38 mmol) in
anhyd CH2Cl2 (15 mL) was added NIS
(1.34 g, 5.96 mmol) and Me3SiOTf (120 mL,
0.66 mmol) under an N2 atmosphere at 0 °C.
The mixture was stirred under these condi-

G. Gu et al. / Carbohydrate Research 336 (2001) 99–106
105
H-4II), 7.09–8.06 (m, 45 H, PhCO). Anal.
Calcd for C85H80O23Si: C, 68.18; H, 5.35.
Found: C, 68.31; H, 5.23.
acetyl - 2 - O - benzoyl - h -
D
- galactopyranoside
(19).—To a mixture of compound 18 (600
mg, 0.477 mmol) and 7 (735 mg, 0.501 mmol)
in anhyd CH2Cl2 (10 mL) was added NIS (282
mg, 1.25 mmol) and Me3SiOTf (47 mL, 0.26
mmol) under an N2 atmosphere at −15 °C.
The mixture was stirred under these condi-
tions for 1 h, at which time TLC (5:2
petroleum ether–EtOAc) indicated the com-
pletion of the reaction. The reaction mixture
was neutralized with Et3N, and concentrated.
Column chromatography (5:2 petroleum
ether–EtOAc) of the residue gave 19 (1.05 g,
83.1%) as a syrup: [h]2D0 +61° (c 3.4, CHCl3);
1H NMR (CDCl3): l 1.86 (s, 3 H, CH3CO),
2.93 (s, 3 H, OCH3), 3.33 (dd, 1 H, J5,6b 2.71,
J6a,6b 11.8 Hz, H-6aIII), 3.58 (dd, 1 H, J6a,6b
9.3, J5,6a 8.0 Hz, H-6aI), 3.75–3.92 (m, 5 H,
H-6aII, H-6bII, H-5II, H-6aIV, H-6bI), 3.95 (dd,
1 H, J5,6b 5.8 Hz, H-6bIII), 4.02–4.15 (m, 5 H,
H-3III, H-5III, H-5IV, H-6bIV, H-5I), 4.44 (dd, 1
H, J2,3 10.5, J3,4 3.4 Hz, H-3I), 4.51 (d, 1 H,
J1,2 8.0 Hz, H-1III), 4.54 (d, 1 H, J1,2 7.8 Hz,
H-1IV), 4.66 (dd, 1 H, J4,5a 3.9, J5a,5b 12.1 Hz,
H-5aV), 4.72–4.85 (br, 4 H, H-1I, H-1II, H-
5aVI, H-4V), 4.91 (dd, 1 H, J4,5b 2.8 Hz, H-
5bV), 4.98–5.05 (br, 2 H, H-5bVI, H-4VI),
5.24–5.29 (m, 3 H, H-1VI, H-2VI, H-2I), 5.36
(s, 1 H, H-2V), 5.44 (s, 1 H, H-1V), 5.46–5.62
(m, 6 H, H-2III, H-3IV, H-3VI, H-4I, H-3II,
H-3V), 5.64–5.68 (m, 2 H, H-2IV, H-2II), 5.81–
5.84 (m, 2 H, H-4III, H-4IV), 5.96 (d, 1 H,
Methyl 2,3,4-tri-O-benzoyl-i-
ranosyl-(1“6)-[2,3,5-tri-O-benzoyl-h-
binofuranosyl-(1“3)]-4-O-acetyl-2-O-ben-
zoyl-h- -galactopyranoside (18).—A solution
D
-galactopy-
L
-ara-
D
of compound 17 (1.00 g, 0.668 mmol) in 90%
aq trifluroacetic acid (10 mL) was stirred at rt
for 3 h, at which time TLC (3:2 petroleum
ether–EtOAc) indicated the completion of the
reaction. The mixture was co-evaporated with
toluene under diminished pressure to dryness
and purified on a silica gel column with 3:2
petroleum ether–EtOAc as the eluent to fur-
nish 18 (651 mg, 77.4%) as a syrup: [h]D20
1
+178° (c 1.2, CHCl3); H NMR (CDCl3): l
1.94 (s, 3 H, CH3CO), 2.99 (s, 3 H, OCH3),
3.64–3.68 (m, 2 H, H-6aI, H-6aII), 3.85 (dd, 1
H, J6a,6b11.9 Hz, H-6bII), 3.96 (dd, 1 H,
J6a,6b9.3 Hz, H-6bI), 4.07 (t, 1 H, J6b,5=J6a,5
=
7.0 Hz, H-5II), 4.18 (dd, 1 H, J5,6a=J5,6b =4.6
Hz, H-5I), 4.46 (dd, 1 H, J3,43.4 Hz, H-3I),
4.68 (dd, 1 H, J4,5a 3.9, J5a,5b 12.1 Hz, H-5aIII),
4.78 (m, 1 H, H-4III), 4.85–4.87 (q, 2 H, J1A,2A
3.6, J1B,2B 7.8 Hz, H-1I, H-1II), 4.93 (dd, 1 H,
J4,5b 2.8 Hz, H-5bIII), 5.31 (dd, 1 H, J2,3 10.5
Hz, H-2I), 5.36 (s, 1 H, H-2III), 5.46 (s, 1 H,
H-1III), 5.51 (br d, 1 H, J3,4 3.7 Hz, H-3III),
5.57 (d, 1 H, J3,4 3.4 Hz, H-4I), 5.58 (dd, 1 H,
J3,4 3.3, J2,310.6 Hz, H-3II), 5.82–5.87 (m, 2 H,
13
H-2II, H-4II), 7.22–8.10 (m, 35 H, PhCO); C
H-4II), 7.21–8.21 (m, 80 H, PhCO); C NMR
13
NMR (100 MHz, CDCl3): l 20.70 (CH3CO),
55.02 (OCH3), 60.54 (C-6II), 63.30 (C-5III),
68.38 (C-5I), 68.94 (C-4II), 69.28 (C-6I), 69.95
(C-2II), 70.98 (C-4I), 71.24 (C-2I), 71.71 (C-3II),
71.95 (C-3I), 74.04 (C-5II), 77.86 (C-3III), 81.29
(C-4III), 82.26 (C-2III), 97.07 (C-1I), 101.92
(C-1II), 107.54 (C-1III), 164.78–166.83 (7 C,
PhCO), 170.24 (CH3CO); MALDI-TOF MS
Calcd for C69H62O23: 1258 [M]; Found 1281.4
[M+Na], 1297.3 [M+K]. Anal. Calcd for
C69H62O23: C, 65.82; H, 4.93. Found: C, 65.70;
H, 5.17.
(100 MHz, CDCl3): l 20.61 (CH3CO), 54.89
(OCH3), 61.22 (C-6IV), 63.22 (C-5V), 63.37
(C-5VI), 66.36 (C-6III), 66.46 (C-6II), 67.75 (C-
4IV), 67.99 (C-4II), 68.28 (C-5I), 68.69 (C-6I),
69.44 (C-4III), 69.87 (C-2IV), 69.92 (C-2II),
70.76 (C-3IV), 70.90 (C-3III), 71.24 (C-2I),
71.61 (C-3II), 71.68 (2 C, C-2III, C-4I), 71.92
(C-3I), 72.40 (C-5III), 72.57 (C-5II), 76.40 (C-
5IV), 77.65 (C-3V), 77.81 (C-3VI), 81.18 (C-4V),
81.64 (C-4VI), 82.28 (C-2V), 82.61 (C-2VI),
97.93 (C-1I), 100.79 (C-1IV), 100.94 (C-1III),
101.60 (C-1II), 107.50 (C-1V), 107.68 (C-1VI),
164.62–166.18 (16 C, PhCO), 169.91
(CH3CO); MALDI-TOF MS Calcd for
C149H126O46: 2650 [M]; Found 2673.6 [M+
Na]+. Anal. Calcd for C149H126O46: C, 67.47;
H, 4.75. Found: C, 67.30; H, 5.19.
Methyl 2,3,4,6-tetra-O-benzoyl-i-
topyranosyl-(1“6)-[2,3,5-tri-O-benzoyl-h-
arabinofuranosyl-(1“3)]-2,4-di-O-benzoyl-i-
-galactopyranosyl-(1“6)-2,3,4-tri-O-ben-
zoyl-i- -galactopyranosyl-(1“6)-[2,3,5-tri-
O-benzoyl-h- -arabinofuranosyl-(1“3)]-4-O-
D
-galac-
L
-
D
D
L

106
G. Gu et al. / Carbohydrate Research 336 (2001) 99–106
Methyl i-
arabinofuranosyl - (1“3)] - i - D - galactopyran-
osyl - (1“6) - i - - galactopyranosyl - (1“6)-
[h- -arabinofuranosyl-(1“3)]-h- -galactopy-
D
-galactopyranosyl-(1“6)-[h-
L
-
Acknowledgements
D
This work was supported by CAS KIP-
RCEES9904 and NNSF of China (Projects
39970179 and 29972053).
L
D
ranoside (20).—Ammonia was bubbled into a
mixture of 19 (1.05 g, 0.369 mmol) in anhyd
MeOH (150 mL) at 4 °C until saturation. The
mixture was kept at rt for about 7 days and
then evaporated to dryness. Purification on a
Sephadex LH-20 column with MeOH as elu-
ent furnished 20 (365 mg, 97.6%) as an amor-
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1
phous solid: [h]D20 −11° (c 0.5, water); H
NMR (MeOD): l 3.35 (s, 3 H, OCH3), 3.50–
4.20 (m, 34 H), 4.31–4.34 (br t, 2 H, J 7.3, J
5.7 Hz, H-1III, H-1IV), 4.40 (d, 1 H, J 7.1 Hz,
H-1II), 4.72 (d, 1 H, J 3.6 Hz, H-1I), 5.19 (s, 1
13
H, H-1VI), 5.24 (s, 1 H, H-1V); C NMR (100
Hz, MeOD): l 55.93 (1 C, OCH3), 62.55 (1
C), 63.33 (2 C), 69.13 (1 C), 69.83–70.41 (8
C), 71.74 (1 C), 72.41 (1 C), 72.49 (1 C), 74.56
(1 C), 74.84 (1 C), 75.16 (2 C), 76.64 (1 C),
77.99 (1 C), 78.97 (1 C), 79.30 (1 C), 80.93 (1
C), 82.84 (1 C), 82.92 (1 C), 86.66 (1 C), 86.69
(1 C), 101.53 (C-1I), 105.04 (C-1IV), 105.43 (2
C, C-1II, C-1III), 111.11 (C-1VI), 111.17 (C-1V);
ESIMS Calcd for C35H60O29: 944 [M]; Found
ESIMS (negative-ion): 979 [M+NH4OH]−,
ESIMS (positive-ion): 967 [M+Na]+.
9. Kaifu, R.; Plantefaber, L. C.; Goldstein, I. J. Carbohydr.
Res. 1985, 140, 37–49.