Synthesis of 3,6-Branched β-D-Glucose Oligosaccharides

Article abstract of DOI:10.1081/CAR-120026599

A glucohexasaccharide, β-D-Glcp-(1→3)-[β-D-Glcp-(1→3)- β-D-Glcp-(1→6)]-β-D-Glcp-(1→3)-β-D-Glcp-(1→3) -β-D-Glcp was synthesized as its 4-methoxyphenyl glycosidevia 2 + 2 + 2 strategy with benzylidenated glucose mono- and disaccharides as the key intermedia

Full text of DOI:10.1081/CAR-120026599

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Synthesis of 3,6‐Branched β‐d‐Glucose Oligosaccharides
Youlin Zeng a & Fanzuo Kong a
a Research Center for Eco‐Environmental Sciences , Academia Sinica , P.O. Box 2871, Beijing,
100085, China
Published online: 02 Feb 2007.
To cite this article: Youlin Zeng & Fanzuo Kong (2003) Synthesis of 3,6‐Branched β‐d‐Glucose Oligosaccharides, Journal of
Carbohydrate Chemistry, 22:9, 881-890, DOI: 10.1081/CAR-120026599
To link to this article: http://dx.doi.org/10.1081/CAR-120026599
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JOURNAL OF CARBOHYDRATE CHEMISTRY
Vol. 22, No. 9, pp. 881–890, 2003
Synthesis of 3,6-Branched b-D-Glucose Oligosaccharides
*
Youlin Zeng and Fanzuo Kong
Research Center for Eco-Environmental Sciences, Academia Sinica, Beijing, China
ABSTRACT
A
glucohexasaccharide, b-D-Glcp-(1!3)-[b-D-Glcp-(1!3)-b-D-Glcp-(1!6)]-b-D-
Glcp-(1!3)-b-D-Glcp-(1!3)-b-D-Glcp was synthesized as its 4-methoxyphenyl gly-
cosidevia 2 + 2 + 2 strategy with benzylidenated glucose mono- and disaccharides
as the key intermediates.
Key Words: b-D-Glucans; Trichloroacetimidates; Regio- and stereoselective
synthesis.
INTRODUCTION
Glucans consisting of a b-(1!3)-linked backbone with various b-(1!6)-linked
mono-, di-, and trisaccharide branches having 0, 1, or 2 (1!3) linked b-D-glucose
residues (Figure 1), were found in fruiting bodies and culture broths of Phytophthora
parasitica.[1] Similarly, the glucans from spores of Ganoderma lucidum (Fr.) Karst
were shown to have a b-(1!3)-linked glucose backbone with branches of mono-, di-,
and oligosaccharide side chains substituted at the C-6 of the glucosyl residues.[2] As
these glucans show antitumor activity, chemists are interested in synthesizing the
*
Correspondence: Fanzuo Kong, Research Center for Eco-Environmental Sciences, Academia Si-
nica, P.O. Box 2871, Beijing 100085, China; Fax: 86-10-62923563; E-mail: fzkong@vip.sina.com.
881
DOI: 10.1081/CAR-120026599
0732-8303 (Print); 1532-2327 (Online)
www.dekker.com
Copyright D 2003 by Marcel Dekker, Inc.

882
Zeng and Kong
minimum active fragments of the polysaccharides, so that they can investigate their
structure-activity relationship and develop new antitumor medicines.[3–7] There have
been several reports dealing with the syntheses of linear and branched glucans.[3–8] We
present herein the stereoselective synthesis of the 4-methoxyphenyl glycoside of b-D-
Glcp-(1!3)-[b-D-Glcp-(1!3)-b-D-Glcp-(1!6)-]b-D-Glcp-(1!3)-b-D-Glcp-(1!3)-b-D-
Glcp. with 4,6-benzylidenated glucose derivatives as the key intermediates.
RESULTS AND DISCUSSION
Retrosynthetic analysis suggests that the best way to assemble the target hexaose is
to first construct a b-(1!3)-linked tetrasaccharide backbone and a b-(1!3)-linked
disaccharide side chain, then couple them at the C-6@-position of the tetrasaccharide
backbone. It is well known that the presence of a C-2 ester group capable of neigh-
boring group participation is necessary for the formation of the b-glucosyl linkage.
However, our previous work[9] revealed that in (1!3)-glucosylation, the glycosyl bond
originally present in either donor or acceptor controlled the stereoselectivity of the
forthcoming bond, i.e., the newly formed glycosidic linkage had the opposite anomeric
configuration of that of either the donor or acceptor. With acylated b-(1!3)-linked
disaccharides as the acceptors and acylated b-(1!3)-linked disaccharide trichlo-
roacetimidates as the donors, a-linked tetrasaccharides are always obtained in spite
of the presence of a C-2 ester group. This was troublesome for the synthesis of b-
(1!3)- linked tetrasaccharides. However, some reports[4,7] revealed that with 4,6-
benzylidenated glucose derivatives as either donor or acceptor, b-linked oligosac-
charides are readily obtained.
Therefore, in the present research, benzylidenated glucose mono- or disaccharide
derivatives were used as the key intermediates as outlined in Scheme 1. First, condensation
of the acceptor 2,[10] obtained by coupling of 2,4,6-tri-O-acetyl-3-O-allyl-a-D-glucopy-
ranosyl trichloroacetimidate[11] with 4-methoxyphenol and followed by deallylation, with
3-O-allyl-2-O-benzoyl-4,6-O-benzylidene-a-D-glucopyranosyl trichloroacetimidate (1)[4]
afforded a b-(1!3)-linked disaccharide 3. Debenzylidenation, benzoylation, and deal-
lylation furnished the disaccharide acceptor 6. The disaccharide donor 12 was similarly
prepared, i.e., condensation of fully benzoylated glucosyl trichloroacetimidate 7[12]
with isopropyl 4,6-O-benzylidene-1-thio-b-D-glucopyranoside (8)[3] selectively offered
b-(1!3)-linked disaccharide 9. The use of isopropyl thioglycoside 8 as the donor rather
than methyl or ethyl thioglycosides ensured good reactivity of the donor, but avoided
the operation difficulty caused by low boiling points of methanethiol or ethanethiol.
Figure 1. Polysaccharide structure of Phytophthora parasitica.

3,6-Branched -D-Glucose Oligosaccharides
883
Scheme 1. Conditions and reagents: a: TMSOTf, CH2Cl2, ꢀ20°C to rt; b: 90% HOAc-H2O, 80°C,
3 h; c: BzCl, pyridine, rt; d: PdCl2, CH2Cl2, MeOH, rt; e: NIS, TMSOTf, CH2Cl2, 3 h; f: CCl3CN,
CH2Cl2, DBU, rt; g: Ac2O, pyridine, rt,12 h; h: MeOH, NH3, rt, two weeks.

884
Zeng and Kong
1
The regioselectivity was confirmed by benzoylation to give 10, whose 2D H NMR
spectrum showed H-2 at d 5.31 ppm with J1,2 = 8.9 Hz and J2,3 = 9.7 Hz. It was
reported[13] that transformation of thioglycosides to the corresponding hemiacetals was
achieved by treating the thioglycosides with water, N-iodosuccinimide (NIS) and
catalytic TMSOTf in acetone. It was found in our research, that treatment of 10 with
NIS and catalytic TMSOTf in reagent grade dichloromethane without addition of
water gave better results, affording the hemiacetal 11 smoothly (85%). Subsequent
trichloroacetimidation of 11 furnished the disaccharide donor 12 (93%). Coupling of
12 with 6 gave b-(1!3)-linked tetrasaccharide 13 in acceptable yield (51%). This is
different from the coupling that gives completely a-linked tetrasaccharide[10] with
acylated b-(1!3)-linked disaccharides as the donors and acylated b-(1!3)-linked
disaccharides as the acceptors, indicating the important role of the 4,6-O-benzylidene
group in controlling stereoselectivity of glycosylation. Debenzylidenation afforded the
tetrasaccharide acceptor 14 (92%). The branch disaccharide donor 18 was prepared
from 10 by debenzylidenation, acetylation, dethiopropylation, and trichloroacetimida-
tion (69% for four steps). Glycosylation of the tetrasaccharide acceptor 14 with the
disaccharide donor 18 selectively gave b-(1!6)-linked hexasaccharide 19 (80%), and
subsequent deacylation in saturated ammonia-methanol solution yielded the target
1
hexaoside 20 (95%). The H and 13C NMR spectra of 20 showed some characteris-
tic signals such as at d 4.88 (1 H, J1,2 7.6, H-1), 4.70 (1 H, J1,2 8.2, H-1), 4.66
(1 H, J1,2 8.0, H-1), 4.65 (1 H, J1,2 8.0, H-1), 4.60 (1 H, J1,2 7.6, H-1), 4.43 (1 H,
J1,2 8.0, H-1), 103.0, 102.8, 102.6, 102.6, 102.6, 101.0 (6 C-1, JC-1,H-1 = 164.2, 165.5,
165.0, 164.7, 164.9, 165.3 Hz ), 84.8, 84.6, 84.2, 84.2 (4 C, glycosylated C-3), 68.0
(1 C, glycosylated C-6). The C-3 data also confirmed the C-6@-selective glycosylation
of 14 with 18, otherwise, if C-4@ was glycosylated, one more signal at ꢁ80 ppm
would appear.
In summary, a convergent synthesis of glucans consisting of a (1!3)-b-D-linked
tetrasaccharide backbone with a (1!6)-b-D-linked disaccharide branch having one
(1!3)-linked b-D-glucose residue was achieved. The method is simple and practical,
and should be possible for large-scale synthesis.
EXPERIMENTAL
Optical rotations were determined at 25 °C with a Perkin–Elmer Model 241-Mc
1
1
1
automatic polarimeter. H NMR, 13C NMR and H–1H, H–13C COSY spectra were
recorded with Bruker ARX 400 spectrometers (400 MHz for H, 100 MHz for 13C) at
1
25°C for solutions in CDCl3 or D2O as indicated. Mass spectra were recorded with a
VG PLATFORM mass spectrometer using the ESI mode. Thin-layer chromatography
(TLC) was performed on silica gel HF254 with detection by charring with 30% (v/v)
H2SO4 in MeOH or in some cases by a UV lamp. Column chromatography was
conducted by elution of a column (16 ꢂ 240 mm, 18 ꢂ 300 mm, 35 ꢂ 400 mm) of
silica gel (100–200 mesh) with EtOAc-petroleum ether (60–90°C) as the eluent.
Solutions were concentrated at <60 °C under reduced pressure.
General procedure for glycosylations. A mixture of donor and acceptor was
dried together under high vacuum for 2 h, then dissolved in anhyd CH2Cl2. TMSOTf

3,6-Branched -D-Glucose Oligosaccharides
885
(0.05 equiv) was added dropwise at ꢀ20 °C under nitrogen. The reaction mixture
was stirred for 3 h, during which time the temperature was gradually raised to
ambient temperature. Then the mixture was neutralized with Et3N. Concentration of
the reaction mixture, followed by purification on a silica gel column, gave the de-
sired products.
4-Methoxyphenyl 3-O-allyl-2-O-benzoyl-4,6-O-benzylidene- -D-glucopyranosyl-
(1!3)-2,4,6-tri-O-acetyl- -D-glucopyranoside (3). Donor 1 (3.67 g, 6.59 mmol)
ꢀꢀ
and acceptor 2 (2.42 g, 6.09 mmol) were coupled as described in the general pro-
cedure. Purification by chromatography with 3:1 petroleum ether-EtOAc as the eluent
1
gave disaccharide 3 (3.63 g, 74%): [a]D + 21.1 (c 1.0, CHCl3). H NMR (CDCl3): d
8.10–6.75 (m, 14H, Bz-H, Ph-H, Mp-H), 5.55 (m, 1H, CH2–CH CH2), 5.48 (s, 1H,
PhCH), 5.12 (dd, 1H, J 1.3 Hz, J 17.2 Hz, CH2–CH CH2), 5.10 (dd, 1H, J1,2 7.7
Hz, J2,3 9.5 Hz, H-2’), 5.01 (dd, 1H, J3,4 = J4,5 = 9.6 Hz, H-4), 4.99 (dd, 1H, J 1.3 Hz,
J 10.2 Hz, CH2–CH CH2), 4.97 (dd, 1H, J1,2 8.0 Hz, J2,3 9.6 Hz, H-2), 4.83 (d, 1H,
J1,2 7.7 Hz, H-1’), 4.69 (d, 1H, J1,2 7.6 Hz, H-1), 4.40 (dd, 1H, J5,6’e 5.7 Hz, J6’a,6’e
11.2 Hz, H-6’e), 4.19–4.09 (m, 5H, H-6’a, H-6e, H-6a, CH2–CH CH2), 3.81 (dd,
1H, J3,4 = J4,5 = 9.5 Hz, H-4’), 3.78 (dd, 1H, J2,3 = J3,4 = 9.5 Hz, H-3’), 3.74 (dd, 1H,
J2,3 = J3,4 = 9.6 Hz, H-3), 3.62 (s, 3H, OCH3), 3.62 (ddd, 1H, J4,5 9.5 Hz, J5,6’e 5.7
Hz, J5,6’a 4.2 Hz, H-5’), 3.54 (ddd, 1H, J4,5 9.5 Hz, J5,6e 5.8 Hz, J5,6a 4.6 Hz, H-5),
2.08, 2.05, 1.90 (3s, 9H, 3 MeCO).
Anal. Calcd for C42H46O16: C 62.52; H 5.75. Found: C 62.37; H 5.67.
4-Methoxyphenyl 2,4,6-tri-O-benzoyl- -D-glucopyranosyl-(1!3)-2,4,6-tri-O-
ꢀꢀ
acetyl- -D-glucopyranoside (6). A mixture of 3 (3.39 g, 4.21 mmol) and 90%
HOAc-H2O (100 mL) was refluxed for 2 h. The reaction mixture was concentrated to a
syrup, and then co-evaporated with toluene (10 mL) three times. The residue was
purified by chromatography with 1:1 petroleum ether-EtOAc as the eluent to give
compound 4 (2.90 g, 93%). Benzoyl chloride (1.50 mL, 12.8 mmol) was added to the
solution of 4 in pyridine (10 mL). The reaction mixture was stirred at rt for 4 h, the
excess benzoyl chloride was destroyed by MeOH, then the mixture was concentrated.
The residue was dissolved in CH2Cl2 (50 mL) and washed with 0.2 M HCl, saturated
aqueous sodium bicarbonate, water and then concentrated. The residue was purified by
chromatography with 2:1 petroleum ether-EtOAc as the eluent to give 5 (3.34 g, 90%).
To a solution of 5 (3.12 g, 3.28 mmol) in CH2Cl2 (60 mL) and CH3OH (30 mL) was
added PdCl2 (75 mg, 0.42 mmol), the reaction mixture was stirred at rt until TLC (2:1
petroleum ether-EtOAc) suggested that the reaction was complete. Then the mixture
was filtered, the solution was concentrated to dryness, and the residue was purified by
flash chromatography with 2:1 petroleum ether-EtOAc as the eluent to give 6 (2.75 g,
1
92%): [a]D + 6.1 (c 1.0, CHCl3). H NMR (CDCl3): d 8.10–6.75 (m, 19H, 3 Bz-H,
Mp-H), 5.41 (dd, 1H, J3,4 = J4,5 = 9.5 Hz, H-4’), 5.19 (dd, 1H, J1,2 7.8 Hz, J2,3 9.5 Hz,
H-2’), 5.09 (dd, 1H, J3,4 = J4,5 = 9.6 Hz, H-4), 5.06 (dd, 1H, J1,2 7.7 Hz, J2,3 9.6 Hz, H-
2), 4.90 (s, 1H, J1,2 7.8 Hz, H-1’), 4.76 (s, 1H, J1,2 7.7 Hz, H-1), 4.61 (dd, 1H, J5’,6’e
12.2 Hz, J6’e, 6’a 4.2 Hz, H-6’e), 4.48 (dd, 1H, J5’,6’a 12.1 Hz, J6’e, 6’a 4.2 Hz, H-6’a),
4.18–4.39 (m, 5H, H-3’, H-3, H-5’, H-6e, H-6a), 3.74 (s, 3H, OCH3), 3.61 (ddd, 1H,
J4,5 9.6 Hz, J5,6e 12.3 Hz, J5,6a 12.1 Hz, H-5), 2.04, 2.02, 1.94 (3s, 9H, 3 MeCO).
Anal. Calcd for C46H46O18: C 62.30; H 5.23. Found: C 62.37; H 5.20.

886
Zeng and Kong
Isopropyl 2,3,4,6-tetra-O-benzoyl- -D-glucopyranosyl-(1!3)-2-O-benzoyl-4,6–
ꢀꢀ
O-benzylidene-1-thio- -D-glucopyranoside (10). Fully benzoylated glucosyl tri-
chloroacetimidate 7 (7.41 g, 10.0 mmol) and isopropyl 4,6-O-benzylidene-1-thio-b-D-
glucopyranoside 8 (2.84 g, 8.86 mmol) were coupled as described in the general
procedure. The product was purified by chromatography with 3:1 petroleum ether-
EtOAc as the eluent to yield disaccharide 9 (7.68 g, 95%). Benzoyl chloride (1.30 mL,
11.1 mmol) was added to the solution of 9 (7.50 g, 8.24 mmol) in pyridine (30 mL).
The reaction mixture was stirred at rt for 4 h, excess benzoyl chloride was destroyed by
MeOH. The mixture was concentrated. The residue was dissolved in CH2Cl2 (100 mL)
and washed with 0.2 M HCl, saturated aqueous sodium bicarbonate, water, and then
concentrated. The residue was purified by chromatography with 2:1 petroleum ether-
EtOAc as the eluent to give 10 (7.64 g, 92%), which is a mixture of R,S isomers. The
mixture was directly used for further reaction without separation, but one isomer was
isolated in pure form for spectral analysis: [a]D + 17.2 (c 1.0, CHCl3). 1H NMR
(CDCl3): d 8.03–7.18 (m, 30H, 5 Bz-H, Ph-H), 5.70 (dd, 1H, J3,4 = J4,5 = 9.5 Hz, H-
4’), 5.63 (s, 1H, PhCH), 5.59 (dd, 1H, J2,3 = J3,4 = 9.5 Hz, H-3’), 5.46 (dd, 1H, J1,2 7.9
Hz, J2,3 9.5 Hz, H-2’), 5.31 (dd, 1H, J1,2 8.9 Hz, J2,3 9.7 Hz, H-2), 5.01 (d, 1H, J1,2 7.9
Hz, H-1’), 4.66 (d, 1H, J1,2 8.9 Hz, H-1), 4.47 (dd, 1H, J5,6’e 12.1 Hz, J6’e, 6’a 4.1 Hz, H-
6’e), 4.36 (dd, 1H, J5,6e 12.1 Hz, J6e, 6a 4.8 Hz, H-6e), 4.27 (dd, 1H, J5,6’a 12.1 Hz,
J6’e,6’a 4.1 Hz, H-6’a), 4.21 (dd, 1H, J2,3 = J3,4 = 9.7 Hz, H-3), 3.91 (dd, 1H,
J3,4 = J4,5 = 9.7 Hz, H-4), 3.87–3.82 (m, 2H, H-5’, H-6a), 3.55 (ddd, 1H, J4,5 9.7 Hz,
J5,6e 12.1 Hz, J5,6a 12.1 Hz, H-5), 3.10 (m, 1H, CH(CH3)2), 1.20 (s, 3H, CH(CH3)2),
1.18 (s, 3H, CH(CH3)2).
Anal. Calcd for C57H52O15S: C 67.84; H 5.19. Found: C 67.71; H 5.09.
2,3,4,6-Tetra-O-benzoyl- -D-glucopyranosyl-(1!3)-2-O-benzoyl-4,6-O-benzyli-
ꢀꢀ
dene- -D-glucopyranosyl trichloroacetimidate (12). A solution of 10 (3.00 g, 2.97
mmol) and NIS (0.82 g, 3.56 mmol) in CH2Cl2 was cooled to ꢀ20 °C, then TMSOTf (55.0
mL, 0.30 mmol) was added dropwise under nitrogen. The solution was stirred for 3 h, during
which time the temperature was gradually raised to ambient temperature. The reaction
mixture was neutralized with Et3N, then concentrated, and the residue was purified by
chromatography with 2:1 petroleum ether-EtOAc as the eluent to give 11 (2.44 g, 85%). A
mixture of 11, trichloroacetonitrile (1.2 mL, 5.63 mmol), and DBU (0.2 mL, 1.62 mmol) in
dry CH2Cl2 (20 mL) was stirred for 3 h and then concentrated. The residue was purified by
flash chromatography with 2:1 petroleum ether-EtOAc to give donor 12 (2.59 g, 93%) as
a foamy solid: [a]D + 39.8 (c 1.0, CHCl3). 1H NMR (CDCl3): d 8.45 (s, 1H, CNHCCl3),
7.95–7.08 (m, 30H, 5 Bz-H, Ph-H), 6.50 (d, 1H, J1,2 3.8 Hz, H-1), 5.76 (dd, 1H,
J3,4 = J4,5 = 9.5,H-4’),5.65(s,1H,PhCH),5.60(dd,1H,J2,3 = J3,4 = 9.5Hz,H-3’),5.50(dd,
1H,J1,27.9Hz,J2,39.5Hz,H-2’),5.30(dd,1H,J1,23.8Hz,J2,39.7Hz,H-2),5.11(d,1H,J1,27.9
Hz,H-1’),4.55(dd,1H,J5,6’e 12.0Hz,J6’e, 6’a 3.4Hz,H-6’e),4.48(dd,1H,J5,6’a 12.0 Hz, J6’e, 6’a
3.4 Hz, H-6’a), 4.38–4.31 (m, 2H, H-6e, H-6a), 4.11–4.03 (m, 2H, H-5, H-5’), 3.93 (dd, 1H,
J2,3 = J3,4 = 9.7 Hz, H-3), 3.81 (dd, 1H, J3,4 = J4,5 = 9.7 Hz, H-4), 1.67 (s, 3H, MeCO).
Anal. Calcd for C56H46Cl3NO16: C 61.41; H 4.23. Found: C 61.23; H 4.19.
4-Methoxyphenyl 2,3,4,6-tetra-O-benzoyl- -D-glucopyranosyl-(1!3)-2-O-ben-
ꢀꢀ
zoyl-4, 6-O-benzylidene- -D-glucopyranosyl-(1!3)-2,4,6-tri-O-benzoyl- -D-glucopy-
ꢀꢀ
ranosyl-(1!3)-2,4,6-tri-O-acetyl- -D-glucopyranoside (13). Donor 12 (1.34 g, 1.22
ꢀꢀ

3,6-Branched -D-Glucose Oligosaccharides
887
mmol) and acceptor 6 (965 mg, 1.06 mmol) were coupled as described in the general
procedure. The product was purified by chromatography with 2:1 petroleum ether-
EtOAc as the eluent to give tetrasaccharide 13 (1.02 g, 51%): [a]D ꢀ 11.2 (c 1.0,
1
CHCl3). H NMR (CDCl3): d 8.05–6.70 (m, 49H, 8 Bz-H, Mp-H, Ph-H), 5.54 (dd, 1H,
J3,4 = J4,5 = 9.5 Hz, H-4), 5.51 (dd, 1H, J3,4 = J4,5 = 9.4 Hz, H-4), 5.32 (dd, 1H,
J2,3 = J3,4 = 9.5 Hz, H-3), 5.27 (dd, 1H, J1,2 8.2 Hz, J2,3 9.5 Hz, H-2), 5.22 (s, 1H,
PhCH), 5.11 (dd, 1H, J1,2 8.2 Hz, J2,3 9.5 Hz, H-2), 4.95–4.87 (m, 3H, 2 H-1, H-4),
4.79 (dd, 1H, J1,2 7.8 Hz, J2,3 9.4 Hz, H-2), 4.78 (dd, 1H, J1,2 7.8 Hz, J2,3 9.4 Hz, H-2),
4.66 (s, 1H, J1,2 7.8 Hz, H-1), 4.65 (s, 1H, J1,2 7.8 Hz, H-1), 4.54 (dd, 1H, J5,6e 2.7,
J6e,6a 12.2, H-6e), 4.44–4.31(m, 3H, 3 H-6), 4.25 (dd, 1H, J5,6a 3.6, J6e,6a 12.0, H-6a),
4.15–4.07 (m, 3H, H-3, 2 H-6), 3.97–3.80 (m, 3H, 2 H-3, H-6), 3.73 (m, 2H, H-5,
OCH3), 3.68–3.24 (m, 3H, 3 H-5), 2.74 (dd, 1H, J3,4 = J4,5 = 9.5 Hz, H-4), 1.99, 1.88,
1.86 (3s, 9H, 3 MeCO). 13C NMR (100 MHz, DCCl3): d 170.6, 169.3, 168.3 (3C, 3
CH3CO), 166.2, 166.1, 165.7, 165.1, 164.9, 164.8, 164.4, 164.2 (8C, 8 PhCO), 155.6,
151.2 (2C, Mp-1, Mp-4), 136.9, 134.6, 133.7, 133.6, 133.5, 133.4, 133.3, 133.2, 133.1,
132.8, 130.0, 129.9, 129.8, 129.7, 129.6, 129.5, 129.2, 128.9, 128.7, 128.5, 128.4,
128.3, 128.2, 128.1, 128.0, 126.0 (Ph-C, some signals overlapped), 118.3, 114.6 (4C,
Mp-2, Mp-3, Mp-5, Mp-6), 101.4 (PhCH), 101.2, 100.6, 100.6, 100.2 (4 C-1), 78.8,
78.3, 77.8, 74.4, 73.2, 73.0, 72.6, 72.4, 72.3, 72.0, 71.8, 71.7, 71.4, 71.0, 69.9, 69.7,
69.3, 68.2, 68.0, 66.3, 63.5, 63.2, 62.4, 62.3, 55.8 (C-2 ꢁ 6, OCH3, some signals
overlapped), 21.1, 20.8, 20.7 (3C, CH3CO).
Anal. Calcd for C100H90O33: C 66.00; H 4.98. Found: C 65.89; H 4.90.
4-Methoxyphenyl 2,3,4,6-tetra-O-benzoyl- -D-glucopyranosyl-(1!3)-2-O-ben-
ꢀꢀ
zoyl- -D-glucopyranosyl-(1!3)-2,4,6-tri-O-benzoyl- -D-glucopyranosyl-(1!3)-
ꢀꢀ
ꢀꢀ
2,4,6-tri-O-acetyl- -D-glucopyranoside (14). A mixture of 13 (1.02 g, 0.56 mmol)
and 90% HOAc-H2O (40 mL) were refluxed for 2 h, and then concentrated to dryness
and co-evaporated with toluene (10 mL) three times. The residue was purified by
chromatography with 1:1 petroleum ether-EtOAc as the eluent to give 14 (860 mg,
1
92%): [a]D + 19.8 (c 1.0, CHCl3). H NMR (CDCl3): d 8.25–6.75 (m, 44H, 8 Bz-H,
Mp-H), 5.69 (dd, 1H, J3,4 = J4,5 = 9.8 Hz, H-4), 5.51 (dd, 1H, J3,4 = J4,5 = 9.7 Hz, H-
4), 5.40 (dd, 1H, J1,2 8.0 Hz, J2,3 9.8 Hz, H-2), 5.13–4.87 (m, 5H, 3 H-2, H-3, H-4),
4.75–4.53 (m, 8H, 4 H-1, 4 H-6), 4.45–4.27 (m, 3H, 3 H-6), 4.15–3.87 (m, 5H, 3 H-3,
H-4, H-6), 3.74 (s, 3H, OCH3), 3.61–3.25 (m, 4H, 4 H-5), 2.01, 1.93, 1.87 (3s, 9H, 3
MeCO).
Anal. Calcd for C93H86O33: C 64.50; H 5.01. Found: C 64.37; H 4.98.
Isopropyl 2,3,4,6-tetra-O-benzoyl- -D-glucopyranosyl-(1!3)-2-O-benzoyl-1-
ꢀꢀ
thio- -D-glucopyranoside (15). A mixture of 10 (5.52 g, 5.43 mmol) and 90%
HOAc-H2O (100 mL) were refluxed for 2 h, and then concentrated to dryness and
co-evaporated with toluene (10 mL) three times. The residue was purified by chro-
matography with 1:1 petroleum ether-EtOAc as the eluent to afford 15 (4.49 g, 90%):
1
[a]D + 24.5 (c 1.0, CHCl3). H NMR (CDCl3): d 8.13–7.09 (m, 20H, 4 Bz-H), 5.82
(dd, 1H, J3,4 = J4,5 = 9.8 Hz, H-4’), 5.58 (dd, 1H, J2,3 = J3,4 = 9.8 Hz, H-3’), 5.24 (dd,
1H, J1,2 7.9 Hz, J2,3 9.8 Hz, H-2’), 5.17 (dd, 1H, J1,2 10.9 Hz, J2,3 9.7 Hz, H-2), 5.01
(d, 1H, J1,2 7.9 Hz, H-1’), 4.79 (dd, 1H, J5,6’e 12.2 Hz, J6’e, 6’a 3.2 Hz, H-6’e), 4.56 (d,
1H, J1,2 10.9 Hz, H-1), 4.40 (dd, 1H, J5,6e 12.0 Hz, J6e, 6a 3.2 Hz, H-6e), 4.26–4.20 (m,

888
Zeng and Kong
2H, H-3, H-6’a), 3.96 (ddd, 1H, J4,5 9.8 Hz, J5,6e 12.2 Hz, J5,6a 12.0 Hz, H-5’), 3.91 (dd,
1H, J3,4 = J4,5 = 9.7 Hz, H-4), 3.75 (dd, 1H, J5,6a 12.0 Hz, J6e, 6a 3.2 Hz, H-6a), 3.43
(ddd, 1H, J4,5 9.7 Hz, J5,6e 12.1 Hz, J5,6a 12.0 Hz, H-5), 3.07 (m, 1H, CH(CH3)2), 1.16
(s, 3H, CH(CH3)2), 1.15 (s, 3H, CH(CH3)2).
Anal. Calcd for C50H48O15S: C 65.21; H 5.25. Found: C 65.12; H 5.18.
2,3,4,6-Tetra-O-benzoyl- -D-glucopyranosyl-(1!3)-4,6-di-O-acetyl-2-O-ben-
ꢀꢀ
zoyl- -D-glucopyranosyl trichloroacetimidate (18). Acetic anhydride (2 mL, 21.2
mmol) was added to a solution of 15 (4.49 g, 4.89 mmol) in pyridine (10 mL), the
mixture was stirred at rt for 3 h, at which time TLC (2:1 petroleum ether-EtOAc)
suggested the reaction was finished. The mixture was concentrated and purified by
chromatography with 2:1 petroleum ether-EtOAc as the eluent to afford 16 (4.67 g,
95%). To a mixture of 16 (4.51g, 4.42 mmol) and NIS (1.22 g, 5.30 mmol) in CH2Cl2
(100 mL) was added TMSOTf (80 mL, 0.44 mmol) dropwise at ꢀ 20°C under nitrogen.
The reaction mixture was stirred for 3 h, during which time the temperature was
gradually raised to ambient temperature. The mixture was neutralized with Et3N, then
concentrated, and the residue was purified by chromatography with 2:1 petroleum
ether-EtOAc as the eluent to afford 17. A mixture of 17, trichloroacetonitrile (2.0 mL,
9.38 mmol), and DBU (0.25 mL, 2.03 mmol) in dry CH2Cl2 (40 mL) was stirred for 3
h and then concentrated. The residue was purified by flash chromatography with 2:1
petroleum ether-EtOAc to give donor 18 (3.90 g, 81% for two steps) as a foamy solid:
1
[a]D + 43.9 (c 1.0, CHCl3). H NMR (CDCl3): d 8.51 (s, 1H, CNHCCl3), 8.07–7.05
(m, 25H, 5 Bz-H), 6.56 (d, 1H, J1,2 3.6 Hz, H-1), 5.80 (dd, 1H, J2,3 = J3,4 = 9.6 Hz, H-
3’), 5.84 (dd, 1H, J3,4 = J4,5 = 9.6, H-4’), 5.48 (dd, 1H, J1,2 8.0 Hz, J2,3 9.6 Hz, H-2’),
5.28 (dd, 1H, J3,4 = J4,5 = 9.8 Hz, H-4), 5.19 (dd, 1H, J1,2 3.6 Hz, J2,3 10.0 Hz, H-2),
5.05 (d, 1H, J1,2 8.0 Hz, H-1’), 4.71 (dd, 1H, J5,6’e 12.2 Hz, J6’e, 6’a 3.2 Hz, H-6’e), 4.47
(dd, 1H, J5,6’a 12.2 Hz, J6’e, 6’a 3.2 Hz, H-6’a), 4.41 (dd, 1H, J2,3 = J3,4 = 10.0 Hz, H-3),
4.23 (ddd, 1H, J4,5 9.6 Hz, J5,6e = J5,6a = 12.2 Hz, H-5’), 4.20–4.11 (m, 3H, H-5, H-6e,
H-6a) , 2.09 (s, 3H, MeCO), 2.04 (s, 3 H, MeCO).
Anal. Calcd for C53H46Cl3NO18: C 58.33; H 4.25. Found: C 58.11; H 4.21.
4-Methoxyphenyl 2,3,4,6-tetra-O-benzoyl- -D-glucopyranosyl-(1!3)-[2,3,4,6-
ꢀꢀ
tetra-O-benzoyl- -D-glucopyranosyl-(1!3)-4,6-di-O-acetyl-2-O-benzoyl- -D-
ꢀꢀ
glucopyranosyl-(1!6)]-2-O-benzoyl- -D-glucopyranosyl-(1!3)-2,4,6-tri-O-benzoyl-
ꢀꢀ
ꢀꢀ
-D-glucopyranosyl-(1!3)-2,4,6-tri-O-acetyl- -D-glucopyranoside (19). Donor 18
ꢀꢀ
(204 mg, 0.19 mmol) was coupled with acceptor 14 (300 mg, 0.17 mmol) as described
in the general procedure. The product was purified by chromatography with 1:1 pe-
troleum ether-EtOAc as the eluent to give hexsaccharide 19 (361 mg, 80%): [a]D
+
1
25.6 (c 1.0, CHCl3). H NMR (CDCl3): d 8.10–6.74 (m, 69 H, 13 Bz-H, Mp-H), 5.65–
5.40 (m, 5H, 2 H-3, 3 H-4), 5.40 (dd, 1H, J1,2 8.0 Hz, J2,3 9.0 Hz, H-2), 5.28 (dd, 1H,
J1,2 7.7 Hz, J2,3 9.8 Hz, H-2), 5.16–4.74 (m, 7H, H-1, 4 H-2, 2 H-4), 4.75–4.48 (m,
9H, 5 H-1, 4 H-6), 4.34–3.97 (m, 12H, 4 H-3, 8 H-6), 3.90 (dd, 1H, J3,4 = J4,5 = 9.3
Hz, H-4), 3.74 (s, 3H, OCH3), 3.73–3.01 (m, 6H, 6 H-5), 2.06, 2.01, 2.01, 1.93, 1.78
(5s, 15H, 5 MeCO). 13C NMR (100 MHz, DCCl3): d 170.5, 170.5, 169.3, 169.2, 168.2
(5C, 5 CH3CO), 166.1, 166.0, 165.9, 165.6, 165.5, 165.0, 164.9, 164.8, 164.6, 164.4,
164.1, 164.0, 163.8 (13C, 13 PhCO), 156.7, 150.9 (2C, Mp-1, Mp-4), 133.4, 133.2,
132.7, 130.0, 129.9, 129.8, 129.7, 129.6, 129.5, 129.4, 129.3, 129.2, 129.1, 128.7,

3,6-Branched -D-Glucose Oligosaccharides
889
128.5, 128.4, 128.3, 128.2, 128.0, 127.8 (72C, 12 Bz-C, some signals overlapped),
118.3, 114.4 (4C, Mp-2, Mp-3, Mp-5, Mp-6), 101.4, 101.2, 101.1, 100.7, 100.3, 99.9 (6
C-1), 85.9, 85.7, 78.6, 77.8, 77.4, 77.3, 77.1, 76.7, 76.3, 75.1, 73.6, 73.5, 73.4, 72.9,
72.4, 72.1, 71.9, 71.6, 71.1, 69.6, 68.9, 68.7, 68.5, 68.4, 68.3, 68.1, 63.3, 63.1, 62.4,
62.3, 60.3, 55.6 (C-2 ꢁ 6, OCH3, some signals overlapped).
Anal. Calcd for C144H130O50: C 65.01; H 4.93. Found: C 64.75; H 4.89.
4-Methoxyphenyl
-D-glucopyranosyl-(1!3)-[ -D-glucopyranosyl-(1!3)- -D-
ꢀꢀ ꢀꢀ
glucopyranosyl-(1!6)]- -D-glucopyranosyl-(1!3)- -D-glucopyranosyl-(1!3)- -D-
ꢀꢀ
ꢀꢀ
ꢀꢀ
glucopyranoside (20). Compound 19 (350 mg, 0.13 mmol) was dissolved in a sat-
urated solution of ammonia in MeOH (10 mL). After two weeks at rt, the reaction
solution was concentrated, and the residue was purified on a Biogel P2 column with
MeOH-water as the eluent to afford 20 (135 mg, 95%) as an amorphous solid: [a]D +
1
21.2 (c 1.0, H2O); H NMR (400 MHz , D2O): 7.00–6.80 (m, 4H, Mp-H), 4.88 (1H,
J1,2 7.6 Hz, H-1), 4.70 (1H, J1,2 8.2 Hz, H-1), 4.66 (1H, J1,2 8.0 Hz, H-1), 4.65 (1H, J1,2
8.0 Hz, H-1), 4.60 (1H, J1,2 7.6 Hz, H-1), 4.43 (1H, J1,2 8.0 Hz, H-1), 4.12–3.26 (m,
36H, H-2 ꢁ 6). 13C NMR (100 MHz, D2O): d 154.7, 150.9 (2C, Mp-1, Mp-4), 118.3,
115.0 (4C, Mp-2, Mp-3, Mp-5, Mp-6), 103.0, 102.8, 102.6, 102.6, 102.6, 101.0 (6C-1,
JC-1,H-1 = 164.2, 165.5, 165.0, 164.7, 164.9, 165.3 Hz ), 84.8, 84.6, 84.2, 84.2 (4C,
glycosylated C-3), 76.6, 75.7, 75.6, 75.5, 74.5, 73.5, 73.1, 73.0, 72.9, 72.8, 72.7, 69.6,
68.8, 68.2, 68.1, 68.0, 60.8, 60.6 (C-2 ꢁ 6, some signals overlapped).
Anal. Calcd for C43H68O32: C, 47.08; H, 6.25. Found: C, 47.11; H, 6.21.
ACKNOWLEDGMENTS
This work was supported by The Chinese Academy of Sciences (KZCX3-J-08) and by
The National Natural Science Foundation of China (Projects 30070185 and 39970864).
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Received June 17, 2003
Accepted August 18, 2003