Active-latent glycosylation strategy toward Lewis X pentasaccharide in a form suitable for neoglycoconjugate syntheses

Article abstract of DOI:10.1016/S0008-6215(99)00080-4

Glycosylation of 4-nitrophenyl 2-acetamido-6-O-tert-butyldiphenylsilyl-2-deoxy-1-thio-β-D-glucopyranoside with phenyl 2,3,4,6-tetra-O-benzoyl-1-thio-β-D-galactopyranoside in the presence of NIS and TfOH as catalyst gave the lactosamine derivative regiospe

Full text of DOI:10.1016/S0008-6215(99)00080-4

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Carbohydrate Research 318 (1999) 75–81
Active–latent glycosylation strategy toward Lewis X
pentasaccharide in a form suitable for neoglycoconjugate
synthesesꢀ
Suoding Cao, Zhonghong Gan, Rene´ Roy *
Department of Chemistry, Uni6ersity of Ottawa, Ottawa, ON K1N 6N5, Canada
Received 17 February 1999; accepted 29 March 1999
Abstract
Glycosylation of 4-nitrophenyl 2-acetamido-6-O-tert-butyldiphenylsilyl-2-deoxy-1-thio-b-
phenyl 2,3,4,6-tetra-O-benzoyl-1-thio-b- -galactopyranoside in the presence of NIS and TfOH as catalyst gave the
lactosamine derivative regiospecifically in high yield. Further 3-O-fucosylation with phenyl 2,3,4-tri-O-benzyl-1-thio-
b-
-fucopyranoside using DMTST as promoter afforded the Lex trisaccharide intermediate. The latent glycosyl
D-glucopyranoside with
D
L
donor was transformed into its active form (p-acetamidothiophenyl) by reduction with zinc in acetic acid and
N-acetylation. Glycosidation with p-nitrothiophenyl lactoside acceptor in the presence of NIS/TfOH as catalyst gave
the Lex pentasaccharide in 71% yield. © 1999 Elsevier Science Ltd. All rights reserved.
Keywords: Active–latent; Glycosylation; 4-Nitrophenyl thioglycoside; Lewis X; Pentasaccharide
be possible under suitable conditions. The ‘ac-
1. Introduction
tive–latent’ glycosylation strategy was also ex-
ploited with aryl sulfoxides [5], allyl versus
vinyl glycosides [6], and bulky alkyl thiogly-
cosides [7] by other groups. In order to further
study the usefulness of ‘active–latent’ glycosy-
lation strategy, we choose the synthesis of
Lewis X pentasaccharide [8], which is widely
distributed in many different human and ani-
mal tissues, and also in human milk oligo-
saccharides.
Earlier studies from our laboratory demon-
strated that ‘active–latent’ para-substituted
phenyl 1-thioglycosides could be used effi-
ciently as glycosyl donors or acceptors de-
pending on the electron density of the aryl
substituents [1–4]. Thus, p-nitrophenyl thio-
glycosides are inert (latent) towards thiophilic
promoters, but the electron-withdrawing p-ni-
tro substituent can be ‘turned on’ into an
electron-donating N-acetyl group which is ac-
tive with suitable thiophilic promoters. The
glycosylation of this ‘active’ thioglycoside with
a ‘latent’ p-nitrophenyl thioglycoside should
2. Results and discussion
Zemple´n deacetylation of 4-nitrophenyl 3,4,
6-tri-O-acetyl-2-deoxy-2-phthalimido-1-thio-b-
ꢀ Active–latent glycosylation strategy, Part 5. For Part 4,
see Ref [4].
* Corresponding author. Tel.: +1-613-562-5800, ext. 6055;
fax: +1-613-562-5170.
D-glucopyranoside (1) [4] and selective silyla-
tion of OH-6 with tert-butylchlorodiphenylsi-
lane in pyridine gave 3,4-O-unprotected p-ni-
trophenyl acceptor 2 in 82% yield. Condensa-
E-mail address: rroy@science.uottawa.ca (R. Roy)
0008-6215/99/$ - see front matter © 1999 Elsevier Science Ltd. All rights reserved.
PII: S0008-6215(99)00080-4

76
S. Cao et al. / Carbohydrate Research 318 (1999) 75–81
tion of thiophenyl donor 3 with 6-O-tert-
butyldiphenylsilyl acceptor 2 was performed
using N-iodosuccinimide and trifluoro-
methanesulfonic acid as promoter at
−30 °C. The reaction afforded exclusively
the desired b-(1“4)-linked disaccharide 4 in
74% yield (Scheme 1). No (1“3)-linked re-
gioisomer was detected during the coupling
reaction. The b-configuration of the disac-
1
charide 4 was deduced from the H NMR
spectrum, which showed H-1% as a doublet at
l 5.09 ppm (J1%,2% 8.1 Hz). The regiochem-
istry of the newly introduced glycosidic link-
age of 4 was proved by converting 4 into its
corresponding 4-acetate 4a, which showed
H-3 at l 5.87 ppm (Dl= +1.2 ppm) as a
Scheme 1. Reagents and conditions: (a) [i] NaOMe–MeOH, [ii] TBDPSCl, pyridine, 82%; (b) NIS–TfOH, CH2Cl2, −30 °C, 74%;
(c) Ac2O–pyridine; (d) DMTST, C6H6–CH2Cl2, 0 °C; 72%; (e) [i] Zn–AcOH, [ii] Ac2O–pyridine, 84%; (f) [i] BzCl–pyridine, [ii]
p-TsOH, 40 °C, 92%; (g) NIS–TfOH, CH2Cl2, −45 °C, 71%.

S. Cao et al. / Carbohydrate Research 318 (1999) 75–81
77
1
In conclusion, the ‘active–latent’ glycosyla-
tion strategy made it possible to manipulate
the reactivity of both glycosyl donors and
acceptors by means of changing the electron
density of the aryl substituents at the anomeric
center. This strategy provides a facile ap-
proach toward the synthesis of complex
oligosaccharides in a highly convergent man-
ner. Therefore, pentasaccharide 10 with its
p-nitrothiophenyl aglycone can be reiteratively
introduced into a new glycosylation cycle or
simply transformed into various neoglycocon-
jugates using well-established strategy [12].
downfield shift signal in its H NMR spec-
trum.
It seemed that the bulky 6-O-tert-
butyldiphenylsilyl protecting group in accep-
tor 2 played a key role for the regiospecificity.
Under such reaction conditions, the very
bulky protecting group could cover the top
side (3,5-cis) of the OH-3 of the acceptor 2 and
block the glycosyl donor from approaching
the OH-3 [9]. This strategy, coupled with the
steric hindrance imparted by the neighboring
2-phthalimido group on OH-3, concurred to
the total regiospecificity of the glycosylation.
Previous studies [10] have shown that the 2-
phthalimido group alone could not be entirely
responsible for the selectivity/specificity ob-
served.
3. Experimental
General methods.—Melting points were de-
Further 3-O-fucosylation of disaccharide 4
with phenyl 2,3,4-tri-O-benzyl-1-thio-b- -fu-
termined on a Gallenkamp apparatus and are
L
1
uncorrected. H and 13C NMR spectra were
copyranoside (5) [11] using DMTST as pro-
moter at 0 °C afforded Lex trisaccharide 6 in
good yield (72%). The a configuration of the
newly introduced anomeric center in 6 was
recorded on a Bruker AMX 500 instrument or
a Varian Gemini 200 MHz. Proton chemical
shifts (l) were given relative to internal CHCl3
(7.24 ppm) for CDCl3 solutions and to inter-
nal HOD (4.76 ppm) for D2O solutions. Car-
bon chemical shifts were given relative to
CDCl3 (77.0 ppm). Mass spectra were ob-
tained using a Kratos II H instrument (FAB-
glycerol) or VG 7070-E spectrometer (CI).
Optical rotations were measured at 23 °C on a
Perkin–Elmer 241 polarimeter. Thin-layer
chromatography (TLC) was performed on Sil-
ica Gel 60 F-254, and column chromatogra-
phy was carried out on Silica Gel 60 (E.
Merck).
1
assigned from its H NMR spectrum (J1¦,2¦ 3.6
Hz). The p-nitrothiophenyl group of 6 was
then reduced with zinc in acetic acid, and the
resulting amine was N-acetylated to give the
active p-acetamidothiophenyl donor 7 in 84%
yield.
The latent diol lactoside acceptor 9 was
obtained through benzoylation and hydrolysis
from the known 4-nitrophenyl 3%,4%-O-iso-
propylidene-1-thio-b-
D
-lactopyranoside (8) [3].
p-acetamidothiophenyl
Condensation of
donor 7 with the p-nitrothiophenyl acceptor 9
was performed using NIS and TfOH as pro-
moter at −45 °C. The reaction afforded b-
(1“3)-linked pentasaccharide 10 in 71% yield.
The stereochemistry of the newly introduced
b-anomeric center in 10 was assigned from the
1H NMR spectrum which showed a doublet
4-Nitrophenyl 2-acetamido-6-O-tert-butyl-
diphenylsilyl-2-deoxy-1-thio-i- -glucopyran-
D
oside (2).—To a suspension of 4-nitrophenyl
3,4,6-tri-O-acetyl-2-deoxy-2-phthalimido-1-
thio-b- -glucopyranoside 1 [4] (4.0 g, 6.99
D
mmol) in MeOH (100 mL), NaOMe in
MeOH (0.3 mL, 1.0 M) was added. After
stirring for 2 h at room temperature, the
reaction was quenched with H+ resin (Dowex
50W-X8) and then filtered. The filtrate was
evaporated under reduced pressure. Toluene
was added to and distilled from the residue.
The crude product was then dissolved in dry
pyridine (20 mL), and tert-butylchloro-
diphenylsilane (2.1 mL, 8.20 mmol) was
added in one portion. The mixture was
stirred for 3 h at room temperature (rt)
1
for H-1¦ at l 5.15 ppm (J1¦,2¦ 8.5 Hz). The H
NMR spectrum of 10 was less informative to
confirm the regiochemistry of the newly intro-
duced glycosidic linkage of 10. However, the
regioselectivity could be confirmed from the
13C NMR spectrum, which showed
a
downfield shift signal for C-3% at l 80.1 ppm
(Dl= +7.5 ppm) for pentasaccharide 10
compared to l 72.6 ppm for C-3% of the lactose
acceptor 9.

78
S. Cao et al. / Carbohydrate Research 318 (1999) 75–81
H, J1,2 10.6 Hz, H-1), 5.57 (dd, 1 H, J3%,4% 3.4
Hz, H-3%), 5.09 (d, 1 H, J1%,2% 8.1 Hz, H-1%),
4.69 (dd, 1 H, J5%,6a% 4.2, J6a%,6b% 12.5 Hz, H-6a%),
4.67 (dd, 1 H, J3,4 8.9 Hz, H-3), 4.36 (dd, 1 H,
J2,3 10.3 Hz, H-2), 4.34 (dd, 1 H, J5%,6b% 4.7 Hz,
H-6b%), 4.30 (dd, 1 H, H-5%), 4.15 (dd,1 H, J4,5
9.2 Hz, H-4), 3.85 (dd, 1 H, J5,6a 1.4, J6a%,6b%
11.8 Hz, H-6a), 3.79 (dd, 1 H, J5,6b 2.5 Hz,
H-6b), 3.57 (ddd, 1 H, H-5), 0.95 (s, 9 H,
SiCMe3); 13C NMR (CDCl3) l 168.2, 167.2,
166.1, 165.4, 165.3, 165.0 (6×CꢀO), 146.5–
123.4 (48 C, aromatic), 101.0 (C-1%), 81.9 (C-
1), 79.0 (C-4), 78.7 (C-5), 72.5 (C-5%), 71.4
(C-3%), 70.2 (C-3), 69.6 (C-2%), 68.1 (C-4%), 62.6
(C-6%), 61.5 (C-6), 55.0 (C-2), 26.8 (SiCMe3),
19.4 (SiCMe3). Anal. Calcd for C70H62-
N2O17SSi: C, 66.55; H, 4.95; N, 2.22. Found:
C, 66.61; H, 4.81; N, 2.19.
and poured into ice water, extracted with
CH2Cl2, and washed with satd aq NaHCO3.
The organic extract was dried (Na2SO4) and
concentrated. The crude product was sub-
jected to column chromatography (1:10
MeOH–CH2Cl2) to give pure 2 as a foamy
solid (3.93 g, 82%): [h]D +37.8° (c 1.0,
CHCl3); FABMS (glycerol) gave m/z (ion,
relative intensity): 530.3 ([M–SPhNO2]+,
1
0.9%); H NMR (CDCl3) l 7.87–7.18 (m, 18
H, aromatic H), 5.75 (d, 1 H, J1,2 10.3 Hz,
H-1), 4.40 (dd, 1 H, J3,4 8.3 Hz, H-3), 4.23
(dd, 1 H, J2,3 10.3 Hz, H-2), 4.05 (dd, 1 H,
J5,6a 2.7, J6a,6b 10.3 Hz, H-6a), 3.94 (dd, 1 H,
J5,6a 3.0 Hz, H-6b), 3.80–3.68 (m, 2 H, H-4,
H-5), 3.45–3.25 (br, 2 H, OH) 1.06 (s, 9 H,
SiCMe3); 13C NMR (CDCl3) l 168.2, 167.7
(2×CꢀO), 148.8–123.3 (24 C, aromatic), 81.9
(C-1), 80.2 (C-5), 72.5 (C-3), 71.9 (C-4), 63.9
(C-6), 55.1 (C-2), 26.7 (SiCMe3), 19.2
(SiCMe3). Anal. Calcd for C36H36N2O8SSi: C,
63.14; H, 5.30; N, 4.09. Found: C, 63.09; H,
5.32; N, 4.13.
4-Nitrophenyl 2,3,4,6-tetra-O-benzoyl-i- -
D
galactopyranosyl - (1“4) - 2 - acetamido - 3 - O-
acetyl-6-O-tert-butyldiphenylsilyl-2-deoxy-1-
thio-i- -glucopyranoside (4a).—Acetic anhy-
D
dride (150 mL) was added to a solution of
compound 4 (20 mg, 0.016 mmol) in dry
pyridine (1 mL) and the mixture was stirred at
rt for 2 h. The solution was directly evapo-
rated under reduced pressure to give com-
pound 4a (21 mg) in quantitative yield: [h]D
4-Nitrophenyl 2,3,4,6-tetra-O-benzoyl-i-
galactopyranosyl - (1“4) - 2 - acetamido - 6 - O-
tert-butyldiphenylsilyl-2-deoxy-1-thio-i- -glu-
D-
D
copyranoside (4).—To compound 2 (500 mg,
0.73 mmol) and phenyl 2,3,4,6-tetra-O-ben-
zoyl-1-thio-b-
D
-galactopyranoside 3 [9] (720
1
+90.8° (c 1.0, CHCl3); H NMR (500 Hz,
mg, 1.05
mmol) dissolved in dry
CDCl3) l 8.11–7.14 (m, 38 H, aromatic H),
5.93 (d, 1 H, H-4%), 5.87 (dd, 1 H, J3,4 9.1 Hz,
H-3), 5.82 (d, 1 H, J1,2 10.5 Hz, H-1), 5.75 (dd,
1 H, J2%,3% 10.4 Hz, H-2%), 5.50 (dd, 1 H, J3%,4%
3.4 Hz, H-3%), 5.20 (d, 1 H, J1%,2% 8.1 Hz, H-1%),
4.60 (dd, 1 H, J5%,6a% 5.3, J6a%,6b% 11.5 Hz, H-6a%),
4.43 (dd, 1 H, J4,5 9.9 Hz, H-4), 4.40 (dd, 1 H,
J2,3 10.4 Hz, H-2), 4.39 (dd, 1 H, J5%,6b% 7.8 Hz,
H-6b%), 4.30 (m, 1 H, H-5%), 3.92 (s, 2 H, H-6a,
H-6b), 3.53 (d, 1 H, H-5), 1.93 (s, 3 H, OAc),
1.03 (s, 9 H, SiCMe3); 13C NMR (CDCl3) l
170.1, 167.8, 167.0, 166.0, 165.4, 165.3, 164.6
(7×CꢀO), 146.7–123.7 (48 C, aromatic),
101.2 (C-1%), 81.6 (C-1), 79.3 (C-5), 73.9 (C-4),
71.9 (C-3%), 71.5 (C-5%), 71.4 (C-3), 69.8 (C-2%),
68.1 (C-4%), 62.0 (C-6%), 60.9 (C-6), 53.6 (C-2),
26.8 (SiCMe3), 20.6 (OAc), 19.4 (SiCMe3).
dichloromethane (10 mL) under nitrogen,
powdered 4 A molecular sieves (1.2 g) were
,
added. The mixture was stirred at rt for 2 h,
and then cooled to −30 °C. N-Iodosuccin-
imide (330 mg, 1.46 mmol) and trifl-
uoromethanesulfonic acid (40 mL, 0.44 mmol)
were added. After stirring at −30 °C for 55
min, the mixture was diluted with
dichloromethane (20 mL) and filtered through
Celite. The filtrate was washed with 10% aq
sodium thiosulfate (30 mL), sat aq NaHCO3
(2×30 mL), and brine (30 mL). The solution
was dried (Na2SO4) and concentrated.
Column chromatography (1:49 MeOH–
CH2Cl2) of the residue on silica gel afforded
disaccharide 4 (681 mg, 74%): [h]D +114.5° (c
1.0, CHCl3); FABMS (glycerol) gave m/z (ion,
relative intensity): 1108.4 ([M–SPhNO2]+,
4-Nitrophenyl 2,3,4,6-tetra-O-benzoyl-i-
galactopyranosyl-(1“4)-[2,3,4-tri-O-benzyl-h-
- fucopyranosyl - (1“3)] - 2 - phthalimido-6-O-
tert-butyldiphenylsilyl-2-deoxy-1-thio-i- -glu-
D
-
1
0.5%); H NMR (500 Hz, CDCl3) l 8.09–7.13
L
(m, 38 H, aromatic H), 5.95 (d, 1 H, H-4%),
5.84 (dd, 1 H, J2%,3% 10.5 Hz, H-2%), 5.71 (d, 1
D

S. Cao et al. / Carbohydrate Research 318 (1999) 75–81
79
4-Acetamidophenyl2,3,4,6-tetra-O-benzyl-i-
-galactopyranosyl-(1“4)-[2,3,4-tri-O-benz-
copyranoside (6).— To a solution of phenyl
2,3,4-tri-O-benzyl-1-thio-b-
L
-fucopyranoside 5
D
(200 mg, 0.38 mmol) and compound 4 (328
yl-h-
6 -O-tert-butyldiphenylsilyl-2-deoxy-1-thio-i-
-glucopyranoside (7).—To a solution of 6
L
-fucopyranosyl-(1“3)]-2-phthalimido-
mg, 0.26 mmol) in 10 mL of 5:1 benzene–
,
CH2Cl2 were added powdered 4 A molecular
D
sieves (500 mg). The mixture was stirred for 2
h at rt under nitrogen. DMTST (156 mg, 0.76
mmol) was added to the stirred mixture at
0 °C. After 1 h, TLC (1:49 MeOH–CH2Cl2)
showed complete conversion of the donor.
Then triethylamine (200 mL) and MeOH (200
mL) were added to the reaction mixture, which
was stirred for an additional 25 min. The
mixture was then diluted with dichloro-
methane (15 mL) and filtered through Celite.
The filtrate was washed with 10% aq sodium
thiosulfate (10 mL), satd aq NaHCO3 (2×10
mL), and brine (10 mL). The solution was
dried (Na2SO4) and concentrated. Column
chromatography (1:49 MeOH–CH2Cl2) of the
residue on silica gel afforded 6 (314 mg, 72%):
[h]D +24.5° (c 1.0, CHCl3); FABMS (glyc-
erol) gave m/z (ion, relative intensity): 1678.7
(150 mg, 0.089 mmol) in CH2Cl2 (5 mL) was
added acetic acid (1 mL) and zinc dust (75
mg). The mixture was stirred for 1 h at rt.
TLC (1:99 EtOH–dichloromethane) indicated
the transformation was completed. Triethy-
lamine was then added (1.25 mL), and the
mixture was concentrated under reduced pres-
sure. The resulting crude p-aminophenyl thio-
glycoside was immediately treated overnight
with pyridine (2 mL) and acetic anhydride (1
mL) at rt. The solution was thoroughly evapo-
rated under reduced pressure. The crude
residue was purified by silica gel chromatogra-
phy using 0.5:99.5 MeOH–CH2Cl2 as eluent
to give 7 (127 mg, 84%): [h]D +28.6° (c 1.0,
CHCl3); FABMS (glycerol) gave m/z (ion,
relative intensity): 1691.8 (M+, 0.4%). 1H
NMR (500 MHz, CDCl3) l 8.13–7.01 (m, 53
H, aromatic), 5.87 (d, 1 H, J3%,4% 3.6 Hz, H-4%),
5.78 (dd, 1 H, J2%,3% 10.3 Hz, H-2%), 5.49 (dd, 1
H, H-3%), 5.37 (d, 1 H, J1,2 10.6 Hz, H-1), 5.35
(d, 1 H, J1%,2% 8.3 Hz, H-1%), 5.04 (d, 1 H, J1%,2%
3.6 Hz, H-1%), 4.81 (dd, 1 H, J3,4 9.8 Hz, H-3),
4.80 (m, 1 H, H-5%), 4.62–4.11 (3×AB pat-
tern, 6 H, 3×PhCH2), 4.56 (dd, 1 H, J5%,6a%
6.6, J6a%,6b% 11.2 Hz, H-6a%), 4.48 (dd, 1 H, J2,3
10.7 Hz, H-2), 4.42 (dd, 1 H, J4,5 9.8 Hz, H-4),
4.32 (dd, 1 H, J5%,6b% 7.4 Hz, H-6b%), 4.10 (m, 1
H, H-5%), 3.98–3.95(m, 2 H, H-3%, H-6a), 3.88
(d, 1 H, J6a,6b 10.1 Hz, H-6b), 3.79 (dd, 1 H,
J2%,3% 10.2 Hz, H-2%), 3.55 (d, 1 H, J3¦,4¦ 1.7 Hz,
H-4¦), 3.24 (m, 1 H, H-5), 2.10 (s, 3 H,
NHAc), 1.42 (d, J5%,6% 6.5 Hz, H-6%), 1.05 (s, 9
H, SiCMe3); 13C NMR (CDCl3) l 139.0–119.3
(66 C, aromatic), 100.1 (C-1%), 97.0 (C-1¦),
84.6 (C-1), 79.6 (2 C, C-5, C-4¦), 79.3 (C-3¦),
75.2 (2 C, C-2¦, CH2), 75.0 (C-4), 73.2 (C-3),
72.9 (CH2), 72.0 (C-3%), 71.7 (CH2), 71.6 (C-
5%), 69.7 (C-2%), 68.5 (C-4%), 66.7 (C-5¦), 61.4 (2
C, C-6%, C-6), 55.5 (C-2), 26.9 (SiCMe3), 24.6
(OAc), 19.4 (SiCMe3), 16.9 (C-6%). Anal Calcd
for C99H94N2O20SSi: C, 70.28; H, 5.60; N,
1.66. Found: C, 70.10; H, 5.63; N, 1.70.
1
(M+, 0.1%); H NMR (500 MHz, CDCl3) l
8.16–7.00 (m, 53 H, aromatic H), 5.89 (d, 1
H, J4%,5% 3.6 Hz, H-4%), 5.83 (dd, 1 H, J2%,3% 10.2
Hz, H-2%), 5.61 (d, 1 H, J1,2 10.6 Hz, H-1),
5.54 (dd, 1 H, J3%,4% 3.6 Hz, H-3%), 5.39 (d, 1 H,
J1%,2%’ 8.3 Hz, H-1%), 5.02 (d, 1 H, J1¦,2¦ 3.6 Hz,
H-1¦), 4.89 (dd 1 H, J3,4 9.3 Hz, H-3), 4.81
(m, 1 H, H-5%), 4.63 (dd, 1 H, J5%,6a% 7.7, J6a%,6b%
11.2 Hz, H-6a%), 4.62–4.11 (3×AB pattern, 6
H, 3×PhCH2), 4.58 (dd, 1 H, J2,3 9.9 Hz,
H-2), 4.43 (dd, 1 H, J4,5 9.4 Hz, H-4), 4.29
(dd, 1 H, J5%,6b% 3.6 Hz, H-6b%), 4.18 (m, 1 H,
H-5%), 4.02 (dd, 1 H, J5,6a 1.5, J6a,6b 12.0 Hz,
H-6a), 3.97 (dd, 1 H, J3¦,4¦ 2.7 Hz, H-3¦), 3.88
(dd, 1 H, J5,6b 1.4 Hz, H-6b), 3.79 (dd, 1 H,
J2¦,3¦ 10.2 Hz, H-2¦), 3.53 (d, 1 H, H-4%), 3.38
(m, 1 H, H-5), 1.43 (d, 3 H, J5¦,6¦ 6.4 Hz,
H-6¦), 1.02 (s, 9 H, SiCMe3); 13C NMR
(CDCl3) l 146.3–123.8 (66 C, aromatic),
100.2 (C-1%), 97.2 (C-1¦), 82.2 (C-1), 79.6 (C-
5), 79.4 (C-4¦), 79.3 (C-3%), 75.3 (C-2%), 75.2
(CH2), 74.9 (C-4), 73.0 (2 C, C-3, CH2), 71.9
(C-3%), 71.8 (C-5%), 71.7 (CH2), 69.7 (C-2%),
68.5 (C-4%), 66.9 (C-5¦), 61.4 (C-6%), 61.0 (C-
6), 55.0 (C-2), 26.8 (SiCMe3), 19.3 (SiCMe3),
16.8 (C-6%). Anal Calcd for C97H90N2O21SSi:
C, 69.35; H, 5.40; N, 1.67. Found: C, 69.29;
H, 5.47; N, 1.66.
4-Nitrophenyl
2,6-di-O-benzoyl-i- -gal-
D
actopyranosyl (1“4) - 2,3,6 - tri - O-benzoyl-1-

80
S. Cao et al. / Carbohydrate Research 318 (1999) 75–81
0.048 mmol) in dry CH2Cl2 (3 mL) were
added powdered 4 A molecular sieves (120
thio-i- -glucopyranoside (9).—4-Nitrophenyl
D
,
3%,4%-O-isopropylidene-b-lactoside derivative 8
[3] (250 mg, 0.481 mmol) was dissolved in dry
pyridine (10 mL), the solution was cooled to
0 °C, and benzoyl chloride (0.5 mL) was
added. The mixture was then allowed to reach
rt and stir overnight. The reaction mixture
was poured onto ice water and extracted with
CH2Cl2 (3×20 mL). The combined extracts
were washed successively with 5% HCl solu-
tion, satd aq NaHCO3, and water. The solu-
tion was dried (Na2SO4) and concentrated to a
foam, which was dissolved in 15 mL of a 1:1
mixture of CH2Cl2 and CH3OH, to which
p-toluenesulfonic acid (100 mg) was added.
The mixture was stirred at 40 °C for 2 h. The
reaction mixture was neutralized with triethyl-
amine and concentrated under reduced pres-
sure. The residue was purified by silica gel
chromatography using 1:2 hexane–EtOAc as
eluent to afford 9 (440 mg, 92%): mp 178–
180 °C; [h]D +11.8° (c 1.0, CHCl3); FABMS
(glycerol) gave m/z (ion, relative intensity):
mg) under nitrogen. The mixture was stirred
at rt for 3 h and then cooled to −30 °C.
N-Iodosuccinimide (22 mg, 0.096 mmol) and
trifluoromethanesulfonic acid (4.2 mL, 0.048
mmol) were added. After stirring at −45 °C
for 45 min, the mixture was diluted with
CH2Cl2 (12 mL) and filtered through Celite.
The filtrate was washed with 10% aq sodium
thiosulfate (15 mL), satd aq NaHCO3 (2×15
mL), and brine (15 mL). The solution was
dried (Na2SO4) and concentrated to a foam
that was chromatographed on silica gel (1:99
ethanol–dichloromethane) to afford pentasac-
charide 10 (86.2 mg, 71%): [h]D +12.8° (c 1.0,
CHCl3); FABMS (glycerol) gave m/z (ion,
1
relative intensity): 2524.9 ([M]+, 0.1%); H
NMR (500 Hz, CDCl3) l 8.08–6.97 (m, 78 H,
aromatic H), 5.78 (d, 1 H, H-4d), 5.67 (dd,
1H, J2,3 10.4 Hz, H-2d), 5.61 (dd, 1 H, J3,4 9.3
Hz, H-3a), 5.32 (dd, 1 H, J2,3 9.5 Hz, H-2a),
5.31 (dd, 1 H, J3,4 3.5 Hz, H-3d), 5.18 (dd, 1
H, J2,3 9.6 Hz, H-2b), 5.15 (d, 1 H, J1,2 8.5 Hz,
H-1c), 5.12 (d, 1 H, J1,2 8.2 Hz, H-1d), 4.96 (d,
1 H, J1,2 3.5 Hz, H-1e), 4.85 (d, 1 H, J1,2 9.8
Hz, H-1a), 3.46 (m, 1 H, H-5c), 1.32 (d, 3 H,
J5,6 6.5 Hz, H-6e), 1.02 (s, 9 H, SiCMe3); 13C
NMR (CDCl3) l 166.0, 165.9, 165.8, 165.6,
165.2, 165.1, 164.6, 164.1 (9×CꢀO) 146.7–
123.2 (96 C, aromatic), 100.5 (C-1b), 99.6
(C-1d), 99.0 (C-1c), 96.6 (C-1e), 84.0 (C-1a),
80.1 (C-3b), 79.3 (C-4e), 79.1 (C-3e), 77.3
(C-2e), 75.5 (2 C, C-5a, C-5c), 75.2 (CH2),
75.0 (2 C, C-4C, C-5d), 74.7 (C-3a), 73.2
(CH2), 72.8 (C-5b), 72.2 (C-3c), 71.9 (CH2),
71.8 (C-3d), 71.7(C-4a), 71.4 (C-2b), 70.8 (C-
2a), 70.0 (C-2d), 69.7 (C-4d), 68.2 (C-4b), 67.8
(C-5e), 66.7 (C-6b), 62.8 (C-6a), 61.5 (C-6c),
61.2 (C-6d), 55.9 (C-2c), 26.9 (SiCMe3), 19.5
(SiCMe3), 16.8 (C-6e). Anal. Calcd for
C144H130N2O36SSi: C, 68.51; H, 5.19; N, 1.11.
Found: C, 68.39; H, 5.23; N, 1.19.
1
1000.3 ([M+1]+, 3%); H NMR (500 MHz,
CDCl3) l 8.01–7.27 (m, 29 H, aromatic H),
5.72 (dd, 1 H, J3,4 9.2 Hz, H-3), 5.41 (dd, 1 H,
J2,3 9.7 Hz, H-2), 5.31 (dd, 1 H, J2%,3% 7.7 Hz,
H-2%), 4.97 (d, 1 H, J1,2 9.9 Hz, H-1), 4.65 (dd,
1 H, J5,6a 1.8, J6a,6b 12.1 Hz, H-6a), 4.62 (d, 1
H, J1%,2% 7.8 Hz, H-1%), 4.51 (dd, 1 H, J5,6b 5.9
Hz, H-6b), 4.05 (dd, 1 H, J4,5 9.8 Hz, H-4),
4.02 (dd, 1 H, J6a%,6b% 11.3 Hz, H-6a%), 3.96
(ddd, 1 H, H-5), 3.84 (d, 1 H, H-4%), 3.73 (dd,
1 H, J3%,4% 3.4 Hz, H-3%), 3.64 (dd, 1 H, J5%,6b% 6.5
Hz, H-6b%), 3.65 (dd, 1 H, J5%,6a% 6.4 Hz, H-5%);
13C NMR (CDCl3) l 166.4, 166.1, 165.7,
165.7, 165.2, (5×CꢀO), 146.8–123.7 (36 C,
aromatic), 100.9 (C-1%), 84.1 (C-1), 77.4 (C-5),
76.1 (C-4), 73.8 (C-3), 73.7 (C-2%), 72.7 (C-5%),
72.6 (C-3%), 70.1 (C-2), 68.5 (C-4), 62.7 (C-6),
61.9 (C-6%). Anal. Calcd for C53H45NO17S: C,
63.66; H, 4.54; N, 1.40. Found: C, 63.71; H,
4.68; N, 1.30.
4-Nitrophenyl 2,3,4,6-tetra-O-benzoyl-i-
galactopyranosyl-(1“4)-[2,3,4-tri-O-benzyl-h-
-fucopyranosyl-(1“3)]-(2-acetamido-6-O-
tert-butyldiphenylsilyl-2 -deoxy-i- -glucopyr-
anosyl)-(1“3)-2,6-di-O-benzoyl-i- -galacto-
pyranosyl-(1“4)-2,3,6-tri-O-benzoyl-1-thio-
i- -glucopyranoside (10).—To compound 7
(81 mg, 0.048 mmol) and compound 9 (48 mg,
D-
L
Acknowledgements
D
D
The authors thank the Natural Sciences and
Engineering Research Council of Canada
(NSERC) for financial support.
D

S. Cao et al. / Carbohydrate Research 318 (1999) 75–81
81
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