Remote control of α- or β-stereoselectivity in (1→3)-glucosylations in the presence of a C-2 ester capable of neighboring-group participation

Article abstract of DOI:10.1016/S0008-6215(02)00455-X

In (1→3)-glucosylation the glycosyl bond originally present in either donor or acceptor is shown to control the stereoselectivity of the forthcoming bond, i.e., the newly formed glycosidic linkage has the opposite anomeric configuration of that of either the donor or acceptor. Therefore, with α-(1→3)-linked disaccharides with nonreducing ends that have the 3-OH free as the acceptor and an acetylated glucosyl trichloroacetimidate as the donor, or with an α-(1→3)-linked acetylated disaccharide trichloroacetimidate as the donor and a glucoside with 3-OH free as the acceptor, β-linked trisaccharides were obtained. Meanwhile, with β-(1→3)-linked disaccharides that have nonreducing ends with the 3-OH free as the acceptor and an acetylated glucosyl trichloroacetimidate as the donor, or with a β-(1→3)-linked acetylated disaccharide trichloroacetimidate as the donor and a glucoside with the 3-OH free as the acceptor, α-linked trisaccharides were obtained in spite of the C-2 neighboring group participation.

Full text of DOI:10.1016/S0008-6215(02)00455-X

Carbohydrate Research 338 (2003) 307–311
www.elsevier.com/locate/carres
Remote control of a- or b-stereoselectivity in (1“3)-glucosylations
in the presence of a C-2 ester capable of neighboring-group
participation
Ying Zeng, Jun Ning, Fanzuo Kong*
Research Center for Eco-En6ironmental Sciences, Academia Sinica, PO Box 2871, Beijing 100085, China
Received 30 July 2002; accepted 31 October 2002
Abstract
In (1“3)-glucosylation the glycosyl bond originally present in either donor or acceptor is shown to control the stereoselectivity
of the forthcoming bond, i.e., the newly formed glycosidic linkage has the opposite anomeric configuration of that of either the
donor or acceptor. Therefore, with a-(1“3)-linked disaccharides with nonreducing ends that have the 3-OH free as the acceptor
and an acetylated glucosyl trichloroacetimidate as the donor, or with an a-(1“3)-linked acetylated disaccharide trichloroacetim-
idate as the donor and a glucoside with 3-OH free as the acceptor, b-linked trisaccharides were obtained. Meanwhile, with
b-(1“3)-linked disaccharides that have nonreducing ends with the 3-OH free as the acceptor and an acetylated glucosyl
trichloroacetimidate as the donor, or with a b-(1“3)-linked acetylated disaccharide trichloroacetimidate as the donor and a
glucoside with the 3-OH free as the acceptor, a-linked trisaccharides were obtained in spite of the C-2 neighboring group
participation. © 2002 Elsevier Science Ltd. All rights reserved.
Keywords: Remote control; Trichloroacetimidates; Neighboring-group participation
1. Introduction
benzyl or azido group) at C-2 of a glycosyl donor is a
prerequisite for the synthesis of virtually all 1,2-cis-
glycopyranosidic linkages. However, Flowers reported
that under forcing conditions, i.e., with HgCN2 (3
equiv) as the promoter in nitromethane–benzene at
The stereospecific formation of glycosidic bonds is the
central challenge in carbohydrate chemistry. The chem-
ical formation of a glycosidic linkage involves activa-
tion of
a
glycosyl donor to create
a
reactive
60 °C for 3 days, coupling of 2,3,4-tri-O-acetyl-a-
L-
electrophilic species that couples with a nucleophilic
acceptor hydroxyl. This coupling reaction can take two
possible pathways resulting in formation of either a or
b anomers. Current methods to control the stereochem-
istry of the anomeric center rely on the participation of
a neighboring-group functionality, such as an ester
protecting group on the C-2 hydroxyl. Formation of a
cyclic oxonium ion intermediate then shields one face of
the molecule, leading exclusively to the formation of
trans-glycosidic linkage, whereas cis-glycosidic bonds
are difficult to construct in the presence of neighboring
group participation. A non-participating group (e.g., a
fucopyranosyl bromide with benzyl 6-O-benzoyl-3,4-O-
isopropylidene-b- -galactopyranoside gave the a-linked
D
disaccharide.1
2. Results and discussion
As part of our research to develop an immune stimu-
lant, we have been dealing with the synthesis of the
b-(1“3)- and a-(1“3)-D-glucooligosaccharides. These
oligosaccharides are fragments of medically important
natural b-(1“3)-linked glucans such as the antitumor-
active schizophyllan, scleroglucan and lentinan,2 and
a-(1“3)-linked glucans such as those from Cryphonec-
trini parasitica and Ganoderma lucidum.3 For investiga-
tion of structure, function relationships, a series of
* Corresponding author. Tel.: +86-10-62936613; fax:
+86-10-62923563
E-mail address: fzkong@mail.rcees.ac.cn (F. Kong).
0008-6215/03/$ - see front matter © 2002 Elsevier Science Ltd. All rights reserved.
PII: S0008-6215(02)00455-X

308
Y. Zeng et al. / Carbohydrate Research 338 (2003) 307–311
Table 1 (Continued)
b-(1“3)- and -a-(1“3)-linked gluco-oligosaccharides
were needed as probes. Our preceding communication4
reported that pure a-linked products can be obtained in
high yields in glycosylation with glucosyl trichloroace-
timidate donors with a C-2 ester capable of neighboring
group participation. Also, it was found that sugar
orthoesters were the intermediates that were trans-
formed to a-linked oligosaccharides in the presence of
TMSOTf through C-1 and O-1 bond breaking. How-
ever, the rationale concerning the stereoselectivity con-
trol factor in (1“3)-glucosyl linkage formation is still
obscure. To explore the puzzle encountered in the
Table 1
(1“3)-Glycosylation results with different pairs of donors
and acceptors
synthesis of (1“3)-linked gluco-oligosaccharides, a se-
ries of experiments was carried out as described in the
following sections.
As indicated in the Table 1, glucosylation of
methoxyphenyl 2,4,6-tri-O-acetyl-b-
D
-glucopyranoside
-glucopyranosyl
(2) with 2,3,4,6-tetra-O-acetyl-a-
D
trichloroacetimidate (1) in the presence of TMSOTf
(3% equiv) gave an inseparable mixture consisting of
the a- and b-linked disaccharides in a ratio of 3:7.
However,
with
2,4,6-tri-O-acetyl-3-O-allyl-a-D-
glucopyranosyl trichloroacetimidate (3) as the donor
instead of 1, a separable mixture consisting of predom-
inantly the a (70%) together with the b anomer (30%)
was obtained, indicating the effect of 3-O-alkylation of
the donor. The a- and b-linked disaccharides obtained
from entry 2 were defined as 4a and 4b that were used
to prepare the required disaccharide acceptors 5 and 7
and donors 9 and 10, respectively. With these disaccha-
rides in hand, a series of reactions was carried out for
investigating the effect of the 3-O-glucosyl group of the
donor, and the effect of 1-O-glucosylation of the accep-
tor, on the stereoselectivity of the forthcoming glycosyl
bond. The newly constructed bond is drawn with a bold
line in the Table 1 for reading convenience.

Y. Zeng et al. / Carbohydrate Research 338 (2003) 307–311
309
Coupling of 3 with an a-linked disaccharide 5 (entry
3) gave a completely b-linked trisaccharide 6. Com-
pared to entry 2, entry 3 indicated the influence of the
a-linked glucosyl residue in the acceptor. Furthermore,
coupling of 3 with a b-linked disaccharide 7 (entry 4)
afforded a sole a-linked trisaccharide 8. The results of
these two entries revealed that the 1-O-glycosyl bond of
the acceptor controlled the stereoselectivity, i.e., the
a-bond of the acceptor led to a forthcoming b-linkage,
while the b-bond of the acceptor led to a forthcoming
a-linkage. Next, a question is to estimate the effect of
3-O-glucosylation of the donor. Entries 5 and 6 an-
swered this. In entry 5, with 3-O-a-glucosylated disac-
charide 9 as the donor and 2 as the acceptor, a sole
b-linked trisaccharide 8, the same as the coupling
product of 3 with 7, was obtained. In contrast, with
3-O-b-glucosylated disaccharide 10 as the donor (entry
6) and 2 as the acceptor, coupling gave a-linked trisac-
charide 6, the same as the coupling product of 3 with 5.
These two entries also revealed that the a-bond of the
3-O-glucosylated donor led to a forthcoming b-linkage,
while the b-bond of the donor led to a forthcoming
a-linkage. Coupling results in entries 7 and 8 further
confirmed the above observations. Condensation of the
a-linked disaccharide donor 9 with the a-linked disac-
charide acceptor 5 readily afforded a b-linked tetra-
saccharide 11, since the two disaccharides had a
synergistic effect leading to the b-linkage formation.
Meanwhile, coupling of the b-linked disaccharide 10
with the b-linked disaccharide 7, in spite of C-2 neigh-
boring group participation, gave an a-linked tetra-
saccharide, as expected. Logically, people would ask
what happened when the disaccharide donor and the
disaccharide acceptor had contradictory effects, i.e.,
when an a-(1“3)-linked disaccharide was used as the
donor and a b-(1“3)-linked disaccharide as the accep-
tor, or when a b-(1“3)-linked disaccharide was used as
the donor and an a-(1“3)-linked disaccharide as the
acceptor. In fact, the two couplings were carried out,
giving a complex product. The main problem in these
couplings was that the reaction rate was very slow, and
decomposed byproduct was obtained in substantial
amount.
The new findings could be used in the synthesis of
(1“3)-linked high oligosaccharides with alternative a-
and b-linkages. For example, hexasaccharide 14 was
synthesized readily by coupling of the disaccharide
donor 9 with the tetrasaccharide acceptor 13.
The coupling reactions described above were carried
out under normal conditions with catalytic TMSOTf as
the promoter at −20 °C to rt for several hours. A long
reaction time (overnight) for entries 7 and 8 did not
change the outcome, indicating that anomerization un-
der reaction conditions was excluded. The oligosaccha-
rides obtained were characterized with 1H and 13C
NMR spectroscopy, and mass spectroscopy, and ele-
mental analysis. For the di- and trisaccharides, 1H
NMR spectra usually gave clear identification since the
signals in the 4–6 ppm region were well resolved, and
H-1a and H-1b showed coupling constants of ꢀ3 Hz
and ꢀ8 Hz, respectively. For higher oligosaccharides,
13C NMR spectra were also recorded giving the C-1 a
in the l 94.8–96.05 ppm with JC1ꢀH1 at 174–177 Hz,
and the C-1 b in the l 99.7–100.8 ppm with JC1ꢀH1 at
161–166 Hz.
Control of the glycosyl linkage by means of a remote
substituent has been discussed in several reports,5 and
in these reports, no C-2 neighboring group participa-
tion was involved. However, Spijker and van Boeckel
reported that double stereodifferentioation affected a/b
ratio in carbohydrate coupling reactions in the presence
of neighboring-group participation.6
In summary, this Note has revealed the exitence of
remote control of the stereoselectivity in construction of
the (1“3)-glucosyl bond by the glycosyl bond in either
donor or acceptor. The newly built glycosyl bond has a
configuration opposite to that of the established bond
in either donor or acceptor in spite of C-2 neighboring
group participation. Stereospecific synthesis of a (1“
3)-glucan with alternative a- and b-linkages was
achieved by this method.
3. Experimental
3.1. General methods
It was found from the above experiments that the
stereoselectivity outcome in the construction of the
(1“3)-glucosyl bond was defined by the 3-O-glucosyl
linkage in the donor or the glucosyl bond at the nonre-
ducing end of the acceptor. Either the donor or the
acceptor tended to give a product with a glycosyl bond
with configuration opposite to that of the established
bond in the donor or the acceptor. Clearly, this effect
overruled the C-2 ester neighboring group participa-
tion. To illustrate the mechanism in detail for the
remote interaction, complex calculations on the transi-
tion state of the coupling reactions are needed, and that
is our future project.
Optical rotations were determined at 25 °C with a
Perkin–Elmer Model 241-Mc automatic polarimeter.
1
1H NMR 13C NMR and H-13C COSY spectra were
recorded with Bruker ARX 400 spectrometers (400
MHz for 1H, 100 MHz for 13C) at 25 °C for solutions in
CDCl3 as indicated. Mass spectra were recorded with a
VG PLATFORM mass spectrometer using the ESI
mode. Thin-layer chromatography (TLC) was per-
formed 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 (16×240 mm, 18×300 mm, 35×

310
Y. Zeng et al. / Carbohydrate Research 338 (2003) 307–311
400 mm) of silica gel (100–200 mesh) with EtOAc–
petroleum ether (60–90 °C) as the eluent. Solutions
were concentrated at B60 °C under reduced pressure.
H), 4.17–4.06 (m, 3 H), 3.95 (m, 1 H), 3.81–3.77 (m, 4
H), 3.59–3.53 (m, 2 H), 2.16 (s, 3 H, CH3CO), 2.10 (s,
3 H, CH3CO), 2.08 (s, 6 H, 2 CH3CO), 2.06 (s, 3 H,
CH3CO), 2.04 (s, 3 H, CH3CO). Anal. Calcd for
C34H44O18: C, 55.14; H, 5.95. Found: C, 55.01; H, 5.80.
3.2. General procedure for deallylation to prepare
acceptors
3.6. 4-Methoxyphenyl 2,4,6-tri-O-acetyl-3-O-allyl-a-D-
To a solution of 4a (1.2 g, 1.7 mmol) or 4b (1.85 g, 2.6
mmol) in MeOH was added PdCl2 (60 mg). After
stirring for several h at rt, TLC indicated that the
reaction was complete. The mixture was filtered, and
the combined filtrate and washings were concentrated
to dryness. The resultant residue was purified by flash
chromatography to give acceptor 5 (931 mg, 82%) or 7
(1.48 g, 85%).
glucopyranosyl-(1“3)-2,4,6-tri-O-acetyl-b-
D-gluco-
pyranoside (4a)
Donor 3 (2.50 g, 5 mmol) was coupled with acceptor 2
(2.08 g, 5 mmol) to give 4a (2.05 g, 55%): [h]D +44.2°
1
(c 0.6, CHCl3); H NMR (CDCl3): l 6.93–6.79 (m, 4
H, C6H4), 5.78 (m, 1 H, ꢀCHꢁ), 5.27 (d, 1 H, J 4.0 Hz,
a-H-1), 5.27–5.11 (m, 4 H), 5.05 (t, 1 H, J 9.6 Hz), 4.80
(d, 1 H, J 8.0 Hz, b-H-1), 4.70 (dd, 1 H, J 3.4, 10.4 Hz,
H-2%), 4.24–3.95 (m, 8 H), 3.73 (s, 3 H, CH3O), 3.74 (m,
1H), 3.72 (m, 1 H), 2.11 (s, 3 H, CH3CO), 2.10 (s, 3 H,
CH3CO), 2.08 (s, 3 H, CH3CO), 2.07 (s, 3 H, CH3CO),
2.06 (s, 3 H, CH3CO), 2.04 (s, 3 H, CH3CO). 13C NMR
(CDCl3): l 170.65, 170.65, 170.65, 169.97, 169.94,
169.62, 156.00, 152.10, 134.43, 118.69, 116.69, 114.68,
100.65 (b-C-1, JC1ꢀH1 161 Hz), 96.05 (a-C-1, JC1ꢀH1 176
Hz), 76.25, 73.96, 73.17, 72.18, 71.88, 70.30, 69.47,
68.42, 62.12, 61.70, 55.71, 20.93. Anal. Calcd for
C34H44O18: C, 55.14; H, 5.95. Found: C, 54.95; H, 5.80.
3.3. General procedure for preparation of donors
Oxidative cleavage of 1-OMP of 4a (3.08 g, 4.16 mmol)
or 4b (2.20 g, 2.97 mmol) was carried out with CAN
(4.5 equiv) in 4:1 CH3CN–H2O at rt for 30 min. The
reaction mixture was diluted with water, and extracted
with CH2Cl2. The extracts were washed with water,
satd aq Na2CO3 and satd aq NaCl. The organic phase
was dried over anhyd Na2SO4, then concentrated to
dryness. Purification of the residue on a silica gel
column gave disaccharide with the 1-OH free. A mix-
ture of the product, trichloroacetonitrile, and DBU in
dry CH2Cl2 was stirred for 3 h and then concentrated.
The residue was purified by flash chromatography read-
ily afforded 9 (2.46 g, 76% for two steps) or 10 (1.73 g,
75% for two steps).
3.7. 4-Methoxyphenyl 2,4,6-tri-O-acetyl-3-O-allyl-b-
glucopyranosyl-(1“3)-2,4,6-tri-O-acetyl-a- -gluco-
-glucopyranoside
D-
D
pyranosyl-(1“3)-2,4,6-tri-O-acetyl-b-
D
(6)
3.4. General procedure for the glycosidations
Compound 6 was obtained (185 mg, 84%) by coupling
of donor 3 (100 mg, 0.21 mmol) with acceptor 5 (150
mg, 0.21 mmol), or obtained (130 mg, 62%) from donor
10 (160 mg, 0.20 mmol) and acceptor 2 (85 mg, 0.20
The mixture of donor and acceptor was dried together
under high vacuum for 2 h, then dissolved in anhyd
CH2Cl2. TMSOTf (0.05 equiv) was added dropwise at
−20 °C with N2 protection. The reaction mixture was
stirred for 3 h, during which time the temperature was
gradually raised to ambient temperature. Then the mix-
ture was neutralized with Et3N. Concentration of the
reaction mixture, followed by purification on a silica gel
column, gave the desired products.
1
mmol): [h]D +6.7° (c 0.86, CHCl3); H NMR (CDCl3):
l 6.93–6.80 (m, 4 H, C6H4), 5.74 (m, 1 H, ꢀCHꢁ), 5.27
(t, 1 H, J 9.6 Hz), 5.25 (t, 1 H, J 9.6 Hz), 5.21 (d, 1 H,
J 4.0 Hz, a-H-1), 5.20–5.10 (m, 2 H, CH2ꢁ), 5.02 (t, 1
H, J 9.6 Hz), 5.00 (t, 1 H, J 9.2 Hz), 4.88 (t, 1 H, J 9.0
Hz), 4.81 (d, 1 H, J 8.0 Hz, b-H-1), 4.75 (dd, 1 H, J 3.8,
10.4 Hz, H-2%), 4.54 (d, 1 H, J 8.0 Hz, b-H-1), 4.28–
4.21 (m, 2 H), 4.17–4.16 (m, 2 H), 4.12–3.92 (m, 7 H),
3.77 (s, 3 H, CH3O), 3.67–3.59 (m, 2 H), 3.52 (t, 1 H,
J 9.2 Hz), 2.19, 2.11, 2.10, 2.09, 2.07, 2.06, 2.02, 2.00.
13C NMR (CDCl3): l 170.34, 170.25, 170.10, 170.07,
169.09, 169.27, 168.83, 168.64, 168.64, 168.37, 156.10,
151.2, 133.69, 118.06, 116.46, 114.14, 100.45 (b-C-1,
JC1ꢀH1 165 Hz), 100.19 (b-C-1, JC1ꢀH1 166 Hz), 94.93
(a-C-1, JC1ꢀH1 175 Hz), 79.52, 74.70, 74.57, 72.08, 71.92,
71.70, 71.56, 70.93, 70.13, 68.73, 67.54, 67.17, 61.59,
61.45, 61.08, 55.21, 20.95, 20.87, 20.76, 20.69, 20.66,
20.57, 20.42. Anal. Calcd for C46H60O26: C, 53.70; H,
5.84. Found: C, 53.57; H, 5.77.
3.5. 4-Methoxyphenyl 2,4,6-tri-O-acetyl-3-O-allyl-b-D-
glucopyranosyl-(1“3)-2,4,6-tri-O-acetyl-b-
D-gluco-
pyranoside (4b)
Donor 3 (2.50 g, 5 mmol) was coupled with acceptor 2
(2.10 g, 5 mmol) to give 4b (900 mg, 23%): [h]D −72.5°
1
(c 0.2, CHCl3); H NMR (CDCl3): l 6.92–6.79 (m, 4
H, C6H4), 5.74 (m, 1 H, ꢀCHꢁ), 5.29–5.11 (m, 3 H),
5.05 (t, 1 H, J 9.6 Hz), 5.02 (t, 1 H, J 9.2 Hz), 4.90 (t,
1 H, J 9.0 Hz), 4.81 (d, 1 H, J 8.0 Hz, b-H-1), 4.53 (d,
1 H, J 8.4 Hz, b-H-1), 4.30 (m, 1 H), 4.28–4.26 (m, 2

Y. Zeng et al. / Carbohydrate Research 338 (2003) 307–311
311
3.8. 4-Methoxyphenyl 2,4,6-tri-O-acetyl-3-O-allyl-a-
glucopyranosyl-(1“3)-2,4,6-tri-O-acetyl-b- -glucopy-
-glycopyranoside
D-
(a-C-1). Anal. Calcd for C58H76O34: C, 52.89; H, 5.78.
Found: C, 52.78; H, 5.90.
D
ranosyl-(1“3)-2,4,6-tri-O-acetyl-b-
D
(8)
3.11. 4-Methoxyphenyl 2,4,6-tri-O-acetyl-3-O-allyl-a-
glucopyranosyl-(1“3)-2,4,6-tri-O-acetyl-b- -glucopy-
ranosyl-(1“3)-2,4,6-tri-O-acetyl-a- -glucopyranosyl-
(1“3)-2,4,6-tri-O-acetyl-b- -glucopyranosyl-(1“3)-
2,4,6-tri-O-acetyl-a- -glucopyranosyl-(1“3)-2,4,6-tri-
O-acetyl-b- -glucopyranoside (14)
D-
D
Compound 8 was obtained (160 mg, 73%) by coupling
of donor 3 (100 mg, 0.21 mmol) with acceptor 7 (150
mg, 0.21 mmol), or obtained (155 mg, 74%) from donor
9 (160 mg, 0.20 mmol) and acceptor 2: [h]D −19° (c
D
D
D
D
1
1.2, CHCl3); H NMR (CDCl3): l 6.98–6.79 (m, 4 H,
C6H4), 5.77 (m, 1 H, ꢀCHꢁ), 5.23 (d, 1 H, J 3.6 Hz,
a-H-1), 5.22–5.11 (m, 4 H), 5.06–4.97 (m, 3 H), 4.81
(d, 1 H, J 8.0 Hz, b-H-1), 4.66 (dd, 1 H, J 3.6, 12.0 Hz,
H-2¦), 4.49 (d, 1 H, J 8.0 Hz, b-H-1), 3.77 (s, 3 H,
CH3O), 3.69 (t, 1 H, J 9.6 Hz), 3.55 (m, 1 H), 2.14,
2.10, 2.09, 2.08, 2.07, 2.06, 2.05; 13C NMR (CDCl3): l
170.21, 170.21, 168.90, 168.70, 168.65, 168.56, 168.22,
133.87, 116.25, 100.41 (b-C-1), 99.74 (b-C-1), 95.28
(a-C-1), 77.80, 75.61, 75.46, 73.50, 72.61, 72.45, 71.63,
71.39, 71.00, 68.90, 67.99, 67.89, 61.85, 61.32, 61.13,
55.21, 20.45, 20.41, 20.35, 20.24, 20.19, 20.05. Anal.
Calcd for C46H60O26: C, 53.70; H, 5.84. Found: C,
53.89; H, 5.95.
Donor 9 (60 mg, 0.078 mmol) was coupled with accep-
tor 13 (100 mg, 0.078 mmol) to give 14 (106 mg, 72%):
[h]D +98.7° (c 0.4, CHCl3); H NMR (CDCl3): l 5.75
(m, 1 H, ꢀCHꢁ), 5.26–5.17 (m, 5 H, 3 a-H-1), 4.81 (d,
1 H, J 8.0 Hz, b-H-1), 4.51 (d, 1 H, J 8.4 Hz, b-H-1),
4.44 (d, 1 H, J 8.4 Hz, b-H-1). 13C NMR: l 100.54
(b-C-1), 100.44 (2 b-C-1), 95.81 (a-C-1), 95.2 (a-C-1),
95.00 (a-C-1). Anal. Calcd for C82H108O50: C, 52.01; H,
5.71. Found: C, 52.34; H, 5.63.
1
Acknowledgements
This work was supported by The Chinese Academy
of Sciences (KZCX3-J-08), The National Natural Sci-
ence Foundation of China (59973026 and 29905004),
and The Beijing Natural Science Foundation (6021004),
and Science and Technology Ministry.
3.9. 4-Methoxyphenyl 2,4,6-tri-O-acetyl-3-O-allyl-a-
glucopyranosyl-(1“3)-2,4,6-tri-O-acetyl-b- -glucopy-
ranosyl-(1“3)-2,4,6-tri-O-acetyl-a- -glucopyranosyl-
(1“3)-2,4,6-tri-O-acetyl-b- -glucopyranoside (11)
D-
D
D
D
Donor 9 (390 mg, 0.5 mmol) was coupled with acceptor
5 (350 mg, 0.5 mmol) to give 11 (500 mg, 76%): [h]D
1
+42° (c 1.1, CHCl3); H NMR (CDCl3): l 5.75 (m, 1
References
H, ꢀCHꢁ), 5.28–5.17 (m, 5 H, 2 a-H-1), 4.80 (d, 1 H,
J 7.8 Hz, b-H-1), 4.73 (dd, 1 H, J 3.6, 10.2 Hz, H-2%),
4.66 (dd, 1 H, J 4.0, 10.2 Hz, H-2§), 4.49 (d, 1 H, 8.4
Hz, b-H-1), 13C NMR (CDCl3): l 100.21 (b-C-1, JC1ꢀH1
161 Hz), 100.14 (b-C-1, JC1ꢀH1 161 Hz), 95.50 (a-C-1,
JC1ꢀH1 177 Hz), 94.89 (a-C-1, JC1ꢀH1 174 Hz). Anal.
Calcd for C58H76O34: C, 52.89; H, 5.78. Found: C,
53.05; H, 5.90.
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3.10. 4-Methoxyphenyl 2,4,6-tri-O-acetyl-3-O-allyl-b-
glucopyranosyl-(1“3)-2,4,6-tri-O-acetyl-a- -glucopy-
ranosyl-(1“3)-2,4,6-tri-O-acetyl-b- -glucopyranosyl-
(1“3)-2,4,6-tri-O-acetyl-b- -glucopyranoside (12)
D-
D
D
D
Donor 10 (340 mg, 0.43 mmol) was coupled with
acceptor 7 (300 mg, 0.43 mmol) to give 11 (405 mg,
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1
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72%): [h]D +9.9° (c 0.8, CHCl3); H NMR (CDCl3): l
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(m, 1 H, J 8.0 Hz, b-H-1), 4.71 (dd, 1H, J 3.6, 10.2 Hz,
H-2¦), 4.50 (d, 2 H, J 8.4 Hz, 2 b-H-1). 13C NMR: l
100.76 (b-C-1), 100.69 (b-C-1), 100.01 (b-C-1), 94.96
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