An efficient and concise synthesis of a β-(1→6)-linked d-galactofuranosyl hexasaccharide

Article abstract of DOI:10.1016/j.carres.2004.11.001

A β-(1→6)-linked d-galactofuranosyl hexasaccharide was synthesized efficiently in a block construction manner by the well-known Schmidt glycosylation method using 6-O-acetyl-2,3,5-tri-O-benzoyl-β-d- galactofuranosyl trichloroacetimidate (1) and allyl 2,3,

Full text of DOI:10.1016/j.carres.2004.11.001

Carbohydrate
RESEARCH
Carbohydrate Research 340 (2005) 155–159
Note
An efficient and concise synthesis of a b-(1!6)-linked
D-galactofuranosyl hexasaccharide
Guohua Zhang, Mingkun Fu and Jun Ning*
Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, PO Box 2871, Beijing 100085, China
Received 16 September 2004; received in revised form 20 October 2004; accepted 1 November 2004
Available online 21 November 2004
Abstract—A b-(1!6)-linked D-galactofuranosyl hexasaccharide was synthesized efficiently in a block construction manner by the
well-known Schmidt glycosylation method using 6-O-acetyl-2,3,5-tri-O-benzoyl-b-D-galactofuranosyl trichloroacetimidate (1) and
allyl 2,3,5-tri-O-benzoyl-b-D-galactofuranoside (3) as the key synthons. Coupling of 3 with 1 gave b-(1!6)-linked disaccharide 4.
Subsequent selective deacetylation of 4 afforded the disaccharide acceptor 5, while deallylation of 4 followed by trichloroacetimidate
formation produced the disaccharide donor 6. Condensation of 5 with 6 gave the tetrasaccharide 7, and subsequent deacetylation
afforded the tetrasaccharide acceptor 8. Finally, coupling of 8 with 6 followed by deacylation yielded the target b-(1!6)-linked
galactofuranose hexasaccharide 10. All of the reactions in the synthesis were carried out smoothly and in high yield.
ꢀ 2004 Elsevier Ltd. All rights reserved.
Keywords: Galactofuranosyl hexasaccharide; Trichloroacetimidate; Synthesis
Increased appreciation of the roles of carbohydrates in
the biological and pharmaceutical sciences has led to in-
creased interest in carbohydrate chemistry. However,
compared with other biopolymers such as peptides and
nucleic acids, the roles of oligosaccharides have been rel-
atively neglected. This can be attributed, in part, to dif-
ficulties in oligosaccharide synthesis. The specific
structural constraints in glycosidic bond-formation of-
ten lead to laborious synthetic transformations, complex
protecting group manipulations, and tedious intermedi-
ate isolations, which complicate the overall synthetic
process and decrease efficiency. In spite of the consider-
able progression oligosaccharide synthesis over the past
few decades,1,2 a general method for glycosylation has
not yet appeared.3 In our efforts dedicated to the synthe-
sis of oligosaccharides, we have developed, in the last
few years, highly efficient strategies for the construc-
tion of 3,6-branched gluco-oligosaccharides,4,5 2,6-
branched manno-oligosaccharides,6,7 2,6-branched,8
3,6-branched, and 5,6-branched galacto-oligosaccha-
rides,9,10 respectively.
b-(1!6)-Linked galactofuranosyl oligosaccharides
are present as constituents of the cell-wall polysaccha-
rides from bacteria and fungi, including some clinically
significant pathogens.11–13 McNeil et al.11 have demon-
strated that the highly immunogenic arabinogalactans
from Mycobacterium leprae and Mycobacterium tubercu-
losis contain, exclusively, arabinofuranosyl and galacto-
furanosyl moieties, and some b-(1!6)-linked
galactofuranose residues. b-(1!6)-Linked galactofura-
nose oligomers are also found in the cell-wall polysac-
charide of Fusarium.13 The fungus Fusarium causes
many physiological or genetic disorders, nutrient defi-
ciencies, and environmental stress both in plants and
in animals, including humans. Plants react to penetra-
tion by Fusarium by accumulation of callose or plant
cell-wall components, by an increase of the steady-state
mRNA level of phenylpropanoid pathway enzymes or
pathogenesis-related like proteins.10 Plants infested by
the fungus also elicit chitinases and accumulate phyto-
alexins.10 Research revealed that the b-(1!6)-linked gal-
actofuranoside fraction of Fusarium origin exhibited
elicitor activity, although its mechanism is still unclear.12
The synthesis of b-(1!6)-linked galactofuranose olig-
omers is therefore of interest. These oligosaccharides are
*
Corresponding author. Tel.: +86 10 62849157; fax: +86 10 62923563;
e-mail: jning@mail.rcees.ac.cn
0008-6215/$ - see front matter ꢀ 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.carres.2004.11.001

156
G. Zhang et al. / Carbohydrate Research 340 (2005) 155–159
expected to be can be valuable in immunological stud-
ies14 and in fundamental biochemical studies that may
lead to the isolation and purification of the appropriate
biosynthetic enzymes. Previously, acquisition of these
oligosaccharides has involved hydrolysis of polysaccha-
rides and separation of the resulting oligomers.11,13
Among the synthetic work done on the preparation of
b-(1!6)-linked oligosaccharides is the work by de Led-
erkremer and co-workers, who prepared methyl b-galac-
tofuranosyl-(1!6)-b-galactofuranoside with a benzo-
ylated galactofuranosyl benzoate as the donor and
SnCl4 as the catalyst.15 We describe here a strategy for
the synthesis of b-(1!6)-linked galactofuranose oligo-
mers using 6-O-acetyl-2,3,5-tri-O-benzoyl-b-D-galacto-
furanosyl trichloroacetimidate16 as the starting
material. To demonstrate the use of the methodology,
a b-(1!6)-linked galactofuranosyl hexasaccharide allyl
glycoside was synthesized.
In our synthesis, the key starting material, 6-O-acetyl-
2,3,5-tri-O-benzoyl-b-D-galactofuranosyl trichloroace-
timidate (1),16 was obtained from methyl b-D-galacto-
furanoside.17 As shown in Scheme 1, coupling of
imidate 1 with allyl alcohol afforded allyl 6-O-acetyl-
2,3,5-tri-O-benzoyl-b-D-galactofuranoside (2). Selective
6-O-deacetylation of 2 by methanolysis in acetyl chlo-
ride and methanol (0.5%, v/v) afforded the monosaccha-
ride acceptor 3 in high yield (95%). The disaccharide 4
was obtained in 87% yield from condensation of 1 and
3 with TMSOTf as the catalyst in dichloromethane at
room temperature. The 1H NMR spectrum of 4 showed
two singlets at d 5.36 and 5.35, respectively, for the ano-
meric protons, indicating the b-configuration of the two
galactofuranose units.18 Under the same conditions as
described for the preparation of 3, selective removal of
acetyl group of 4 afforded disaccharide acceptor 5.
Meanwhile, deallylation of 4 with PdCl2 in methanol–
O
OR1
OBz
OBz
OCNHCCl3
O
O
OAll
OBz
OBz
OBz
a
OBz
1
O
O
OBz
5
4
6
R = H, R1 = All
R = Ac, R1 = All
OBz
OBz
OR
a
OBz
b
c
OAc
OBz
OBz
OR
R=Ac
R=H
2
3
R=Ac R1 = CNHCCl3
1
b
O
OAll
OBz
OBz
OBz
a
O
O
5
+
6
OBz
OBz
OBz
O
O
OBz
OBz
OBz
O
O
OBz
OBz
OBz
OR
R = Ac
7
8
b
R = H
O
OAll
OH
O
OAll
OH
OBz
OBz
OBz
OH
O
O
O
OH
O
a
d
6
+
8
OBz
OBz
OH
OH
OBz
O
O
O
O
4
OBz
OH
4
OBz
OH
OBz
OH
OH
OAc
10
9
˚
Scheme 1. Reagent and conditions: (a) allyl alcohol, TMSOTf (cat), CH2Cl2 (dry), 4A MS, rt, 2h; (b) CH2Cl2–CH3OH/0.6% acetyl chloride, rt, 12h;
(c) i. PdCl2, CH3OH, 40ꢁC, 4h; ii. CCl3CN, K2CO3, CH2Cl2 (dry), rt, overnight; (d) CH3OH saturated with dry NH3, rt, 24h.

G. Zhang et al. / Carbohydrate Research 340 (2005) 155–159
157
dichloromethane and subsequent trichloroacetimidate
formation produced the disaccharide donor 6.
reaction was complete. The reaction mixture was neu-
tralized with Et3N, filtered, and the filtrate was concen-
trated. Purification of the residue by chromatography
(4:1, petroleum ether–EtOAc) afforded 2 (4.0g, 92%).
[a]D ꢀ12.0 (c 1.0, CHCl3); 1H NMR (400MHz, CDCl3):
d 8.09–7.30 (m, 15H, 3PhH), 5.98–5.95 (m, 1H,
CH@CH2), 5.92–5.88 (m, 1H, H-5), 5.57 (d, 1H,
J = 9.2Hz, H-3), 5.49 (s, 1H, H-2), 5.39 (dd, 1H,
Glycosylation of 5 with 6 under the promotion of
TMSOTf at room temperature provided tetrasaccharide
7 in 90% yield. Serious overlap in the 1H NMR spectrum
of 7 made assignment difficult, however, the 13C NMR
spectrum of 7 showed four clear anomeric carbon sig-
nals (d 106.8, 106.4, 106.3, 104.9) corresponding to four
b-galactofuranosyl residues.
We were gratified to find that there was no difficulty in
repeating the selective removal of acetyl group from 7,
and the tetrasaccharide acceptor 8 was obtained readily.
Finally, the condensation of 8 with 6 yielded 90% of the
protected hexasaccharide 9, which was deprotected
affording the target hexasaccharide 10 in 90% yield.
The stereoselectivity of the glycosylation was confirmed
in the 13C NMR spectrum of 9, which showed six b-Galf
anomeric carbons at d 106.8, 106.7, 106.5, 106.3, 105.6,
and 104.9, respectively.
3
2J = 1.6Hz, Jtrans = 17.2Hz, CH@CH2), 5.35 (s, 1H,
3
H-1), 5.25 (dd, 1H, 2J = 1.3Hz, Jcis = 10.4Hz,
CH@CH2), 4.61–4.58 (m, 1H, H-4), 4.57–4.54 (dd, 1H,
J = 4.5, 11.7Hz, H-6a), 4.50–4.46 (dd, 1H, J = 6.0,
11.7Hz, H-6b), 4.27–4.11 (m, 2H, CH2CH@CH2), 2.00
(s, 3H, CH3CO). Anal. Calcd for C32H30O10: C, 66.89;
H, 5.26. Found: C, 66.75; H, 5.20.
1.3. Allyl 2,3,5-tri-O-benzoyl-b-D-galactofuranoside (3)
To a solution of 2 (3.0g, 5.2mmol) in CH2Cl2 (5mL)
and CH3OH (200mL) was added acetyl chloride
(1.2mL). The mixture was stirred at rt for 12h when
TLC (4:1, petroleum ether–EtOAc) indicated that the
reaction was complete. The reaction mixture was neu-
tralized with Et3N, concentrated under reduced pressure
and purified by chromatography (4:1, petroleum ether–
EtOAc) to give monosaccharide acceptor 3 (2.6g,
In summary, an efficient synthesis of a b-(1!6) linked
galactofuranosyl hexasaccharide was achieved in a block
construction manner with TMSOTf as catalyst using the
well-known Schmidt glycosylation method.19
1. Experimental
1
95%). [a]D ꢀ87.0 (c 1.0, CHCl3); H NMR (400MHz,
1.1. General methods
CDCl3): d 8.06–7.24 (m, 15H, 3PhH), 5.98–5.95 (m,
1H, CH@CH2), 5.63–5.59 (m, 2H, H-5, H-3), 5.49 (s,
1H, H-2), 5.38–5.33 (m, 3H, H-1, CH@CH2), 4.67–
4.65 (m, 1H, H-4), 4.30–4.10 (m, 2H, CH2CH@CH2),
4.05–4.04 (m, 2H, H-6a, H-6b). Anal. Calcd for
C30H28O9: C, 67.66; H, 5.30. Found: C, 68.37; H, 5.32.
Optical rotations were determined at 20ꢁC with a Per-
kin–Elmer Model 241-Mc automatic polarimeter. 1H
NMR and 13C NMR spectra were recorded on a Bruker
1
ARX 400 spectrometer (400MHz for H, 100MHz for
13C) for solutions in CDCl3 or D2O as indicated. Chem-
ical shifts are given in ppm downfield from internal
(CH3)4Si for spectra recorded in CDCl3, or internal
DSS (sodium 4,4-dimethyl-4-silapentane-sulfonate) for
spectra recorded in D2O. 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 detector. Column chromatography was
conducted by elution of a column (16 · 240mm,
18 · 300mm, 35 · 400mm) of silica gel (100–200mesh)
with mixtures of EtOAc and petroleum ether (60–
90ꢁC) as the eluent. Solutions were concentrated at
<60ꢁC under reduced pressure.
1.4. Allyl 6-O-acetyl-2,3,5-tri-O-benzoyl-b-D-galactofu-
ranosyl-(1!6)-3,4,5-tri-O-benzoyl-b-D-galactofuranoside
(4)
A solution of 3 (1.8g, 3.4mmol) and 1 (2.5g, 3.7mmol)
˚
in dry CH2Cl2 (100mL) was stirred with activated 4A
molecular sieves (2g) at rt for 20min and then TMSOTf
(50lL) was added. The reaction mixture was stirred for
2h, at which time TLC (4:1, petroleum ether–EtOAc)
indicated that the reaction was complete. The reaction
mixture was neutralized with Et3N, filtered, and the fil-
trate was concentrated. Purification of the residue by
chromatography (4:1, petroleum ether–EtOAc) afforded
disaccharide 4 (3.1g, 87%). [a]D ꢀ16.5 (c 1.0, CHCl3);
1H NMR (400MHz, CDCl3): d 8.10–7.24 (m, 30H,
6PhH), 5.98–5.95 (m, 1H, CH@CH2), 5.91–5.81 (m,
2H, H-5, H-50), 5.62 (d, 1H, J = 4.8Hz, H-3), 5.54 (d,
1H, J = 4.8Hz, H-30), 5.49 (s, 1H, H-2), 5.38 (s, 1H,
H-20), 5.36 (s, 1H, H-1), 5.35 (s, 1H, H-10), 5.31–5.27
1.2. Allyl 6-O-acetyl-3,4,5-tri-O-benzoyl-b-D-galactofur-
anoside (2)
A solution of 1 (5.1g, 7.5mmol) and allyl alcohol
(1.1mL, 16mmol) in dry CH2Cl2 (150mL) was stirred
˚
with activated 4A molecular sieves (2g) at rt for
20min. To the solution was added TMSOTf (45lL).
The reaction mixture was stirred for 2h, at which time
TLC (4:1, petroleum ether–EtOAc) indicated that the
3
(dd, 1H, 2J = 1.4Hz, Jtrans = 18.5Hz, CH@CH2),
5.26–5.23 (dd, 1H, 2J = 1.3Hz, 3Jcis = 10.4Hz,
CH@CH2), 4.73–4.70 (m, 1H, J = 4.3Hz, H-4),

158
G. Zhang et al. / Carbohydrate Research 340 (2005) 155–159
4.62–4.67 (m, 1H, J = 4.3Hz, H-40), 4.57–4.46 (m, 2H, H-
6a, 6b), 4.20–4.01 (m, 2H, H-6a0, 6b0), 4.29–4.10 (m, 2H,
CH2CH@CH2), 2.0 (s, 3H, CH3CO). Anal. Calcd for
C59H52O18: C, 67.55; H, 5.00. Found: C, 67.40; H, 5.10.
6b0), 2.00 (s, 3H, CH3CO). Anal. Calcd for
C58H48O18NCl3: C, 60.40; H, 4.19. Found: C, 60.31;
H, 4.22.
1.7. Allyl 6-O-acetyl-3,4,5-tri-O-benzoyl-b-D-galactofu-
ranosyl-(1!6)-2,3,5-tri-O-benzoyl-b-D-galactofuranosyl-
(1!6)-2,3,5-tri-O-benzoyl-b-D-galactofuranosyl-(1!6)-
2,3,5-tri-O-benzoyl-b-D-galactofuranoside (7)
1.5. Allyl 2,3,5-tri-O-benzoyl-b-D-galactofuranosyl-
(1!6)-2,3,5-tri-O-benzoyl-b-D-galactofuranoside (5)
To a solution of 4 (1.5g, 1.4mmol) in CH2Cl2 (3mL)
and CH3OH (100mL) was added acetyl chloride
(0.6mL). The mixture was stirred at rt for 12h, when
TLC (3:1, petroleum ether–EtOAc) indicated that the
reaction was complete. The reaction mixture was neu-
tralized with Et3N, concentrated under reduced pres-
sure, and purified by chromatography (3:1, petroleum
ether–EtOAc) to provide disaccharide 5 (1.3g, 90%).
[a]D ꢀ19.5 (c 1.0, CHCl3); 1H NMR (400MHz, CDCl3):
d 8.07–7.26 (m, 30H, 6PhH), 6.03–6.01 (m, 1H, H-5),
5.98–5.95 (m, 1H, CH@CH2), 5.61–5.58 (m, 1H, H-50),
5.57 (d, 1H, J = 4.8Hz, H-3), 5.53 (d, 1H, J = 4.8Hz,
H-30), 5.49 (s, 1H, H-2), 5.41 (s, 1H, H-20), 5.40 (s,
1H, H-1), 5.37 (s, 1H, H-10), 5.36–5.35 (dd, 1H,
A solution of 5 (1.0g, 0.99mmol) and 6 (1.4g, 1.2mmol)
˚
in dry CH2Cl2 (100mL) was stirred with activated 4A
molecular sieves (1.5g) at rt for 20min and then
TMSOTf (20lL) was added. The reaction mixture was
stirred for 2h, at which time TLC (3:1, petroleum
ether–EtOAc) indicated that the reaction was complete.
The reaction mixture was neutralized with Et3N, fil-
tered, and the filtrate was concentrated. Chromatogra-
phy (3:1, petroleum ether–EtOAc) of the residue gave
tetrasaccharide 7 (1.8g, 90%). [a]D ꢀ11.6 (c 1.0, CHCl3);
1H NMR (400MHz, CDCl3): d 8.09–7.26 (m, 60H,
12PhH), 5.93–5.86 (m, 5H, 4H-5, CH@CH2), 5.59–
5.52 (m, 3H, 3H-3), 5.47–5.45 (d, 2H, H-3, H-2), 5.36–
5.28 (m, 8H, 4H-1, 3H-2, CH@CH2), 5.15–5.13 (dd,
3
2J = 1.4Hz, Jtrans = 18.5Hz, CH@CH2), 5.19–5.17
2
3
3
(dd, 1H, J = 1.3Hz, Jcis = 10.4Hz, CH@CH2), 4.84–
4.82 (m, 1H, J = 4.3Hz, H-4), 4.69–4.67 (m, 1H,
J = 4.3Hz, H-40), 4.16–4.03 (m, 4H, H-6a, 6b, 6a0, 6b0,
CH2CH@CH2), 2.86–2.81 (m, 1H, OH). Anal. Calcd
for C57H50O17: C, 67.99; H, 5.00. Found: C, 67.74; H,
4.95.
1H, 2J = 1.3Hz, Jcis = 10.4Hz, CH@CH2), 4.74–4.65
(m, 4H, 4H-4), 4.48–4.45 (m, 2H, 2H-6), 4.25–4.04 (m,
8H, 6H-6, CH2CH@CH2), 2.00 (s, 3H, CH3CO); 13C
NMR (100MHz, CDCl3): d 170.2, 166.0, 165.9, 165.8,
165.8, 165.7, 165.7, 165.6, 165.3, 165.2, 165.1, 133.7,
133.4, 133.3, 133.2, 133.1, 130.0–128.4, 117.6, 106.8,
106.4, 106.3, 104.9, 82.4, 82.3, 82.1, 82.0, 81.8, 81.4,
71.9, 71.7, 71.3, 70.4, 68.1, 67.4, 67.2, 62.9, 20.4. Anal.
Calcd for C113H96O34: C, 67.93; H, 4.84. Found: C,
67.84; H, 4.75.
1.6. 6-O-Acetyl-2,3,5-tri-O-benzoyl-b-D-galactofuranos-
yl-(1!6)-2,3,5-tri-O-benzoyl-b-D-galactofuranosyl tri-
chloroacetimidate (6)
To a solution of 4 (2.0g, 1.9mmol) in anhydrous
CH3OH (150mL) was added PdCl2 (20mg, 0.11mmol),
and the mixture was stirred at 40ꢁC for 4h, at which
time TLC (3:1, petroleum ether–EtOAc) indicated that
the reaction was complete. The reaction mixture was fil-
tered through Celite, and the filtrate was concentrated to
dryness. The resulting residue was dissolved in dry
CH2Cl2 (100mL), and then CCl3CN (2.0mL) and
K2CO3 (10.0g) were added. The reaction mixture was
stirred at rt overnight, when TLC (3:1 petroleum
ether–EtOAc) indicated that the reaction was complete.
The mixture was filtered, and the filtrate was concen-
trated. Purification of the residue by chromatography
(3:1, petroleum ether–EtOAc) gave disaccharide 6
(1.4g, 63%). [a]D ꢀ12.3 (c 1.0, CHCl3); 1H NMR
(400MHz, CDCl3): d 8.79 (s, 1H, OC(NH)CCl3), 8.05–
6.68 (m, 30H, 6PhH), 6.68 (s, 1H, H-1), 5.99–5.98 (m,
1H, H-5), 5.90–5.85 (m, 1H, H-50), 5.74 (d, 1H,
J = 4.8Hz, H-3), 5.73 (s, 1H, H-2), 5.48 (d, 1H,
J = 4.8Hz, H-30), 5.34 (s, 1H, H-10), 5.33 (s, 1H, H-20),
4.89–4.88 (m, 1H, H-4), 4.62–4.60 (m, 1H, H-40), 4.58–
4.43 (m, 2H, H-6a, H-6b), 4.23–4.01 (m, 2H, H-6a0,
1.8. Allyl 2,3,5-tri-O-benzoyl-b-D-galactofuranosyl-
(1!6)-2,3,5-tri-O-benzoyl-b-D-galactofuranosyl-(1!6)-
2,3,5-tri-O-benzoyl-b-D-galactofuranosyl-(1!6)-2,3,5-
tri-O-benzoyl-b-D-galactofuranoside (8)
To a solution of 7 (1.0g, 0.50mmol) in CH2Cl2 (3mL)
and CH3OH (100mL) was added acetyl chloride
(0.6mL). The mixture was stirred at rt for 12h, at which
point TLC (2:1 petroleum ether–EtOAc) indicated the
reaction was complete. The reaction mixture was neu-
tralized with Et3N, and then concentrated to dryness.
Purification of the residue by chromatography (2:1,
petroleum ether–EtOAc) afforded tetrasaccharide 8
(0.88g, 90%). [a]D ꢀ17.5 (c 1.0, CHCl3); 1H NMR
(400MHz, CDCl3): d 8.04–7.16 (m, 60H, 12PhH),
6.25–5.88 (m, 4H, CH@CH2, 3H-5), 5.59–5.52 (m, 3H,
3H-3), 5.47–5.45 (m, 2H, H-3, H-2), 5.36–5.28 (m, 8H,
4H-1, 3H-2, CH@CH2), 5.15–5.13 (dd, 1H,
3
2J = 1.3Hz, Jcis = 10.4Hz, CH@CH2), 4.80–4.69 (m,
4H, 4H-4), 4.25–4.00 (m, 10H, 8H-6, CH2CH@CH2),
3.16 (t, 1H, OH). Anal. Calcd for C111H94O33: C,
68.16; H, 4.84. Found: C, 68.31; H, 4.79.

G. Zhang et al. / Carbohydrate Research 340 (2005) 155–159
159
1.9. Allyl 6-O-acetyl-3,4,5-tri-O-benzoyl-b-D-galactofu-
ranosyl-(1!6)-2,3,5-tri-O-benzoyl-b-D-galactofuranosyl-
(1!6)-2,3,5-tri-O-benzoyl-b-D-galactofuranosyl-(1!6)-
2,3,5-tri-O-benzoyl-b-D-galactofuranosyl-(1!6)-2,3,5-
tri-O-benzoyl-b-D-(1!6)-2,3,5-tri-O-benzoyl-b-D-gal-
actofuranoside (9)
4.22–3.63 (m, 52H); 13C NMR (100MHz, D2O): d
136.4, 121.1, 110.5 (5C-1), 109.2, 85.9, 83.6, 79.6, 73.6,
72.3, 71.8, 71.4, 65.5. Anal. Calcd for C39H66O31: C,
45.44; H, 6.45. Found: C, 45.34; H, 6.58.
Acknowledgements
A solution of 8 (0.25g, 0.13mmol) and 6 (0.16g,
0.14mmol) in dry CH2Cl2 (50mL) was stirred with acti-
˚
vated 4A molecular sieves (1.0g) at rt for 20min and
This work was supported by the National Key Project
for Basic Research (2003CB114400), the Beijing Natural
Science Foundation (6021004), and The Ministry of Sci-
ence and Technology (2001AA246014).
then TMSOTf (15lL) was added. The reaction mixture
was stirred for 2h, at which time TLC (1:1, petroleum
ether–EtOAc) indicated that the reaction was complete.
The reaction mixture was neutralized with Et3N, fil-
tered, and the filtrate was concentrated. Chromatogra-
phy (1:1, petroleum ether–EtOAc) of the residue
afforded hexasaccharide 9 (90%, 0.34g). [a]D ꢀ27.5 (c
References
1. Plante, O. J.; Palmacci, E. R.; Seeberger, P. H. Science
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1
1.0, CHCl3); H NMR (400MHz, CDCl3): d 8.01–7.13
(m, 90H, 18PhH), 5.96–5.85 (m, 8H, CH@CH2, 6H-5,
H-3), 5.58–5.43 (m, 7H, 5H-3, 2H-2), 5.35–5.27 (m,
11H, 6H-1, 4H-2, CH@CH2), 5.15–5.13 (dd, 1H,
2. Sears, P.; Wong, C. H. Science 2001, 291, 2344.
3. Davis, B. G. J. Chem. Soc., Perkin Trans. 1 2000, 2137.
4. Ning, J.; Yi, Y.; Kong, F. Tetrahedron Lett. 2002, 43,
5545.
5. Ning, J.; Zhang, W.; Yi, Y.; Yang, G.; Wu, Z.; Yi, Z.;
Kong, F. Bioorg. Med. Chem. 2003, 11, 2193.
6. Xing, Y.; Ning, J. Tetrahedron: Asymmetry 2003, 14, 1275.
7. Ning, J.; Heng, L.; Kong, F. Tetrahedron Lett. 2002, 43,
673.
3
2J = 1.3Hz, Jcis = 10.4Hz, CH@CH2), 4.73–4.69 (m,
6H, 6H-4), 4.46–4.00 (m, 4H, 12H-6, CH2CH@CH2),
2.00 (s, 3H, CH3CO); 13C NMR (100MHz, CDCl3): d
170.6, 166.0–165.1, 133.7, 133.3, 133.0, 130.0, 117.6,
106.8, 106.7, 106.5, 106.3, 105.6, 104.9, 82.6, 82.4,
82.3, 82.1, 82.0, 81.8, 81.3, 72.0, 71.7, 71.3, 70.2, 68.1,
67.8, 67.4, 67.2, 66.2, 62.9, 20.4. Anal. Calcd for
8. Ning, J.; Yi, Y.; Yao, Z. Synlett 2003, 14, 2208.
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7349.
C167H140O50: C, 68.07; H, 4.79. Found: C, 67.95; H,
4.83.
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1.10. Allyl b-D-galactofuranosyl-(1!6)-b-D-galactofu-
ranosyl-(1!6)-b-D-galactofuranosyl-(1!6)-b-D-galacto-
furanosyl-(1!6)-b-D-galactofuranosyl-(1!6)-b-D-gal-
actofuranoside (10)
14. Suzuki, E.; Mortara, R. A.; Takahashi, H. K.; Straus, A.
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1994, 50, 21.
Compound 9 (0.34g, 0.12mmol) was dissolved in
CH3OH saturated with ammonia (50mL). After 24h
at rt, the reaction mixture was concentrated to about
10mL, then CH2Cl2 (100mL) was added. The resultant
precipitate was filtered and washed four times with
CH2Cl2 to afford 10 (0.11g, 90%). [a]D ꢀ11.6 (c 1.0,
1
H2O); H NMR (400MHz, D2O): d 5.96 (m, 1H), 5.33
(s, 1H), 5.28 (d, 1H), 5.25 (d, 1H), 5.03–4.78 (m, 5H),