A simple access to 3,6-branched oligosaccharides: Synthesis of a glycopeptide derivative that relates to Lycium barbarum L.

Article abstract of DOI:10.1039/b108399f

An efficient method is described for the synthesis of galactopyranosyl-containing 3,6-branched oligosaccharides using isopropyl thiogalactopyranoside as starting material. This method is successfully applied to the preparation of a glycopeptide derivative that relates to Lycium barbarum L. The potential application of isopropyl thioglycoside in glycosylation is also investigated.

Full text of DOI:10.1039/b108399f

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A simple access to 3,6-branched oligosaccharides: Synthesis of a
glycopeptide derivative that relates to Lycium barbarum L.
Yuguo Du,* Meimei Zhang, Feng Yang and Guofeng Gu
1
Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, PO Box 2871,
Beijing 100085, Beijing, China
Received (in Cambridge, UK) 17th September 2001, Accepted 17th October 2001
First published as an Advance Article on the web 8th November 2001
An efficient method is described for the synthesis of galactopyranosyl-containing 3,6-branched oligosaccharides
using isopropyl thiogalactopyranoside as starting material. This method is successfully applied to the preparation of
a glycopeptide derivative that relates to Lycium barbarum L. The potential application of isopropyl thioglycoside in
glycosylation is also investigated.
tetra-O-benzoyl-α--galactopyranosyl trichloroacetimidate 7
Introduction
in anhydrous CH2Cl2 using TMSOTf as catalyst gave tri-
The availability of oligosaccharides and their analogues as sub-
saccharide 8 in 90% yield. No intermolecular aglycone transfer5
strates can provide insight into their biological roles and might
was observed in this case. Convergently, fully acetylated iso-
lead to the discovery of novel carbohydrate-based therapeutics.1
propyl β--galactopyranoside (IPTG) 9 was condensed with
Despite many advances in the chemical synthesis of oligo-
saccharides, it is still time-consuming and often difficult to syn-
thesize these highly asymmetric and densely functionalized
molecules. Among the glycosylation methodologies currently
-serine derivative 106 in methylene dichloride in the presence
of N-iodosuccinimide (NIS) and TMSOTf to afford glyco-
peptide derivative 11, which was subjected to a sequence of
protecting-group manipulations to give desired acceptor 14 in
a total yield of 45% from 10. Coupling reaction of 8 and 14
used in carbohydrate chemistry, those using glycosyl trichloro-
acetimidate and thioglycosides are the most attractive choices
likewise gave glycopeptide 15 in excellent yield.
for oligosaccharide assembly.2 We have recently disclosed a new
Encouraged by the above result, we also tried the coupling
method for one-pot synthesis of 3,6-differentially protected
reaction of glucosamine derivative 16 with 3,6-diol 3, and the
carbohydrate building blocks and have successfully applied
trisaccharide derivative 17, corresponding to human blood-
group substrates, was obtained in 53.6% yield (Scheme 2).
The fair yield of this reaction may be ascribed to the quick
consumption of imidate 16 and about 20% of isopropyl
this method to natural oligosaccharides’ preparation.3 Lycium
barbarum L., a famous traditional Chinese herbal medicine,
has been widely used in China as a health-protection agent
for 2300 years.4 We here report the first example of a simple
2,3,4,6-tetra-O-benzoyl-β--galactopyranosyl-(1 6)-2,4-di-O-
synthesis of a glycopeptide derivative that relates to Lycium
benzoyl-1-thio-β--galactopyranoside was also isolated after
barbarum L. using isopropyl thiogalactopyranosides as prac-
tical glycosylation building blocks.
separation on a column.
Condensation of fully benzylated isopropyl thioglycoside 18
and acceptor 197 in the presence of NIS and TMSOTf in
anhydrous methylene dichloride at 0 ЊC achieved α-linked
Results and discussion
disaccharide 20 in 80% yield. A singlet at δ 4.91 in the 1H NMR
spectrum, that was further determined as the signal for H-1Ј by
2D spectroscopy, confirmed the presence of an α glycosidic
linkage in 20. Similar reaction using MeOTf as promoter
gave an inseparable mixture of 1,2-cis- and 1,2-trans-linked
disaccharides in 56–70% yield. The yields seem dependent
on the amount of MeOTf used in the reactions (we used
2–5 equiv.) and part of the acceptor 19 could be recovered.
The armed–disarmed strategy8 was next investigated
using isopropyl thioglactopyranoside glycosyl donor 18 and
NIS–TMSOTf as catalyst. When armed donor 18 was regio-
selectively glycosylated with disarmed acceptor thioglycoside
219 in anhydrous methylene dichloride–diethyl ether (1 : 1, v/v)
co-solvent, α-linked disaccharide 22 was obtained in an isolated
yield of 62% after recovery of 60 mg of 21 (see Experimental
section). Glycosylation of 18 and acceptor 23 in diethyl ether,
on the other hand, furnished disaccharide 24 in 96% yield as a
mixture of the α- and β-anomer in the ratio of 2 : 1. Reaction of
18 and 25 was not straightforward. This may be caused by the
lower activity of 4-OH in 25.
In our previous communication,3 we have described a pro-
cedure for one-pot synthesis of 3,6-differentially protected
carbohydrate building blocks. Thus, commercially available
isopropyl 1-thio-β--galactopyranoside 1 was selectively tri-
tylated on the primary hydroxy group with triphenylmethyl
chloride (TrCl) in pyridine, silylated with tert-butylchlorodi-
methylsilane (TBDMSCl) in DMF on C-3 and then benzoylated
with benzoyl chloride in one pot to afford isopropyl 2,4-di-
O-benzoyl-3-O-tert-butyldimethylsilyl-6-O-trityl-1-thio-β--
galactopyranoside 2 in 76% isolated overall yield (Scheme 1).
Treatment of compound 2 with 90% trifluoroacetic acid (TFA)
gave 3,6-diol 3 in 80% yield. Interestingly, treatment of 2 with
50% aq. TFA furnished 3-O-silylated product 4 as a major
component. It is noteworthy that attempted preparation of the
3,6-diol via acidic hydrolysis of acetylated analogue isopropyl
2,4-di-O-acetyl-3-O-tert-butyldimethylsilyl-6-O-trityl-1-thio-β-
-galactopyranoside3 5 gave exclusively acetyl-migrated prod-
uct isopropyl 2,6-di-O-acetyl-1-thio-β--galactopyranoside
6 (85%). Compared with 3, chemical shifts of H-6a and
H-6b in 6 moved downfield to δ 4.26 and 4.37 from δ 3.58 and
3.77, respectively, confirming the occurrence of this migration.
Coupling reaction of 3,6-diol 3 and 2.1 equiv. of 2,3,4,6-
In summary, we present here a highly efficient and practical
method for the preparation of 3,6-branched galactopyranosyl
oligosaccharides. This method is successfully applied to the
3122
J. Chem. Soc., Perkin Trans. 1, 2001, 3122–3127
This journal is © The Royal Society of Chemistry 2001
DOI: 10.1039/b108399f

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synthesis of a glycopeptide derivative that relates to Lycium
barbarum L. This is the first report of using isopropyl thio-
glycosides as glycosyl donors. Its applications in α-glycosidic
bond formation and the potential usage in the armed–disarmed
glycosylation strategy were also investigated.
Experimental
Optical rotations were determined at 25 ЊC with a Perkin-Elmer
Model 241-Mc automatic polarimeter and [α]D-values are in
units of 10Ϫ1 deg cm2 gϪ1. Melting points were determined with
Scheme 1 Reagents and conditions (yields): a) TrCl, pyridine; TBDMSCl, imidazole; BzCl (76%); b) 90% TFA (80%); c) Method A: FeCl3ؒ6H2O
(50%); Method B: 50% TFA (86.3%); d) 90% TFA (85%); e) TMSOTf (90%); f ) Ac2O, pyridine (100%); g) NIS, TMSOTf (87% for 11, 91% for 15).
Scheme 2 Reagents and conditions (yields): a) TMSOTf, CH2Cl2 (54%); b) NIS, TMSOTf, Et2O (80% for 20, 62% for 22, 96% for 24); c) MeOTf,
CH2Cl2 (56–70%).
J. Chem. Soc., Perkin Trans. 1, 2001, 3122–3127
3123

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1
a ‘Mel-Temp’ apparatus and are uncorrected. H NMR, 13C
The mixture was stirred at room temperature for 30 min, then
neutralized with sodium bicarbonate and extracted with
CH2Cl2 (2 × 20 mL). The organic phases were combined and
concentrated to dryness, and the residue was purified on a silica
gel column (petroleum ether–EtOAc, 2 : 1) to give 4 (253 mg,
NMR and 1H–1H, 1H–13C COSY spectra were recorded with a
Bruker ARX 400 spectrometer for solution in CDCl3. Chemical
shifts are given in ppm downfield from internal Me4Si. Mass
spectra were measured using MALDI-TOF-MS with α-cyano-
4-hydroxycinnamic acid as matrix. 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 UV detector. Column chromatography was conducted on
columns (16 × 240 mm, 18 × 300 mm, 35 × 400 mm) of silica
gel (100–200 mesh) using EtOAc–petroleum ether (60–90 ЊC) as
eluent. Solutions were concentrated at <60 ЊC under diminished
pressure.
86.3%) as crystals: mp 110–112 ЊC; [α]2D5 ϩ76 (c 1, CHCl3); H
1
NMR δ 0.01, 0.16 [2 s, 6 H, Si(CH3)2], 0.74 (s, 9 H, t-Bu), 1.41,
1.44 [2 d, 6 H, J 6.6 Hz, SCH(CH3)2], 3.35–3.41 (m, 1 H, SCH),
3.72 (dd, 1 H, J5,6a 6.3 Hz, J6a,6b 11.4 Hz, H-6a), 3.93 (dd, 1 H,
J5,6b 5.7 Hz, H-6b), 3.98–4.06 (m, 1 H, H-5), 4.28 (dd, 1 H,
J2,3 9.6 Hz, J3,4 < 1.0 Hz, H-3), 4.90 (d, 1 H, J1,2 9.9 Hz, H-1),
5.63 (d, 1 H, H-4), 5.73 (t, 1 H, H-2), 7.55–8.29 (m, 10 H, Ph)
(Calc. for C29H40O7SSi: C, 62.11; H, 7.19. Found: C, 62.39; H,
7.05%).
Isopropyl 2,4-di-O-benzoyl-3-O-tert-butyldimethylsilyl-6-O-
trityl-1-thio-ꢀ-D-galactopyranoside 2
Isopropyl 2,6-di-O-acetyl-1-thio-ꢀ-D-galactopyranoside 6
To a solution of 1 (710 mg, 2.98 mmol) in pyridine (2 mL)
were added TrCl (1.05 g, 3.7 mmol) and DMAP (20 mg). The
mixture was stirred at 80 ЊC for 16 h then cooled to 0 ЊC.
To the above reaction mixture was added imidazole (408 mg,
6.0 mmol) in one portion. A solution of TBDMSCl (450 mg,
3.0 mmol) in DMF (3 mL) was added portionwise during 1.5 h.
The mixture was stirred at room temperature for 4 h, then
premixed benzoyl chloride (1.05 g, 7.46 mmol) and pyridine
(1 mL) was added. The reaction mixture was stirred at 50 ЊC for
24 h, then poured into ice-cold water, and extracted with
EtOAc. The organic phase was concentrated to dryness by co-
evaporation with toluene. The residue was subjected to column
chromatography on silica gel using petroleum ether–EtOAc (3 :
2) as eluent to give 2 (1.65 g, 76%) as a white foam; [α]2D5 ϩ17
Compound 53 (200 mg, 0.29 mmol) was dissolved in 90% aq.
trifluoroacetic acid (5 mL). The solution was stirred at room
temperature for 2 h and then co-evaporated with toluene to
dryness under diminished pressure. Column chromatography
using 1 : 1, petroleum ether–EtOAc as eluent gave syrupy 6
(80 mg, 85%); [α]2D5 ϩ4 (c 1, CHCl3); 1H NMR δ 1.30, 1.31 [2 d,
6 H, J 5.4 Hz, SCH(CH3)2], 2.08, 2.13 (2 s, 6 H, 2 × COCH3),
3.16–3.20 (m, 1 H, SCH), 3.65–3.68 (m, 2 H, H-5, H-3), 3.93
(s, 1 H, H-4), 4.26 (dd, 1 H, J5,6a 6.0 Hz, J6a,6b 11.2 Hz, H-6a),
4.37 (dd, 1 H, J5,6b 5.6 Hz, H-6b), 4.48 (d, 1 H, J1,2 9.6 Hz, H-1),
4.98 (t, 1 H, J2,3 11.6 Hz, H-2) (Calc. for C13H22O7S: C, 48.43;
H, 6.88. Found: C, 48.30; H, 6.99%).
1
2,3,4,6-Tetra-O-benzoyl-ꢁ-D-galactopyranosyl trichloro-
acetimidate 7
(c 1, CHCl3); H NMR δ Ϫ0.12, 0.11 [2 s, 6 H, Si(CH3)2], 0.61
(s, 9 H, t-Bu), 1.26, 1.32 [2 d, 6 H, J 6.8 Hz, CH(CH3)2], 3.18
(dd, 1 H, J5,6a 6.6 Hz, J6a,6b 9.6 Hz, H-6a), 3.22–3.31 (m, 1 H,
SCH), 3.44 (dd, 1 H, J5,6b 6.6 Hz, H-6b), 3.80 (t, 1 H, H-5), 4.06
(dd, 1 H, J2,3 9.2 Hz, J3,4 3.2 Hz, H-3), 4.68 (d, 1 H, J1,2 9.2 Hz,
H-1), 5.46 (t, 1 H, H-2), 5.71 (d, 1 H, H-4), 7.14–8.17 (m, 25 H,
Ph) (Calc. for C48H54O7SSi: C, 71.79; H, 6.78. Found: C, 71.96;
H, 6.65%).
1,2,3,4,6-Penta-O-benzoyl--galactopyranose (6 g, 8.57 mmol)
was dissolved in ammonia-saturated THF–MeOH (6 : 4, 100
mL). The mixture was stirred at room temperature for 15 h,
then concentrated to dryness, and purified on a silica gel
column with 3 : 1, petroleum ether–EtOAc as eluent to yield
2,3,4,6-tetra-O-benzoyl--galactose (4.08 g, 80%). To a solution
of 2,3,4,6-tetra-O-benzoyl--galactose (4 g, 6.71 mmol) in
anhydrous CH2Cl2 (25 mL) were added trichloroacetonitrile
(2 mL, 20 mmol) and 1,8-diazabicyclo[5.4.0]undec-7-ene
(DBU), (0.45 mL, 3.0 mmol), and the mixture was stirred at
room temperature for 4 h. TLC (3 : 1, petroleum ether–EtOAc)
indicated that the reaction was complete. The mixture was con-
centrated and purified on a silica gel column using 2 : 1, petrol-
eum ether–EtOAc as eluent to give foamy 7 (4.47 g, 90%);
[α]2D5 ϩ122 (c 1, CHCl3); 1H NMR δ 4.49 (dd, 1 H, J5,6a 6.0 Hz,
J6a,6b 11.2 Hz, H-6a), 4.66 (dd, 1 H, J5,6b 6.9 Hz, J6a,6b 11.2 Hz,
H-6b), 4.92 (dd, 1 H, H-5), 6.03 (dd, 1 H, J1,2 3.6 Hz, J2,3 10.5
Hz, H-2), 6.14 (dd, 1 H, J3,4 2.6 Hz, H-3), 6.22 (d, 1 H, H-4),
6.98 (d, 1 H, H-1), 7.22–8.13 (m, 20 H, Ph), 8.69 (s, 1 H, NH)
[MALDI-TOF-MS Calc. for C36H28Cl3NNaO10 (M ϩ Na)ϩ:
762. Found: m/z, 762 (M ϩ Na)ϩ].
Isopropyl 2,4-di-O-benzoyl-1-thio-ꢀ-D-galactopyranoside 3
Compound 2 (1.65 g, 2.07 mmol) was dissolved in 90% aq. TFA
(15 mL) and the solution was stirred at room temperature for 2
h. Toluene (50 mL) was added and the solvents were evaporated
in vacuo to give a residue, which was purified by silica gel
column chromatography (petroleum ether–EtOAc, 2 : 1) to give
3 (765 mg, 80%) as a syrup; [α]2D5 ϩ15 (c 1, CHCl3); H NMR
1
δ 1.34, 1.28 [2 d, 6 H, J 6.8 Hz, CH(CH3)2], 3.23–3.30 (m, 1 H,
SCH), 3.58 (dd, 1 H, J5,6a 7.2 Hz, J6a,6b 12 Hz, H-6a), 3.77 (dd,
1 H, J5,6b 6.4 Hz, H-6b), 3.86–3.90 (m, 1 H, H-5), 4.14 (dd, 1 H,
J2,3 10.0 Hz, J3,4 3.4 Hz, H-3), 4.80 (d, 1 H, J1,2 10.0 Hz, H-1),
5.43 (t, 1 H, H-2), 5.62 (d, 1 H, H-4), 7.26–8.14 (m, 10 H, Ph)
(Calc. for C23H26O7S: C, 61.87; H, 5.87. Found: C, 61.53; H,
5.91%).
Isopropyl 2,4-di-O-benzoyl-3-O-tert-butyldimethylsilyl-1-thio-ꢀ-
D-galactopyranoside 4
Isopropyl O-[2,3,4,6-tetra-O-benzoyl-ꢀ-D-galactopyranosyl-
(1
(1
6)]-O-[2,3,4,6-tetra-O-benzoyl-ꢀ-D-galactopyranosyl-
3)]-2,4-di-O-benzoyl-1-thio-ꢀ-D-galactopyranoside 8
Method A. To a solution of 2 (1 g, 1.47 mmol) in methylene
dichloride (10 mL) was added FeCl3 hexahydrate (947 mg,
3.50 mmol) and the mixture was stirred at room temperature for
3 h. It was then diluted with CH2Cl2 (50 mL) and washed with
cold water (× 3). The water phase was re-extracted with CH2Cl2
(20 mL) and the organic phases were combined and con-
centrated to dryness, and the residue was subjected to silica gel
column chromatography (petroleum ether–EtOAc, 2 : 1) to give
crystalline compound 4 (322 mg, 50%).
To a cooled solution (Ϫ15 ЊC) of 3 (300 mg, 0.67 mmol) and 7
(1.06 g, 1.43 mmol) in dry CH2Cl2 (5 mL) was added TMSOTf
(12 µL, 0.06 mmol) under N2, and the mixture was stirred at this
temperature for 2 h, then neutralized with triethylamine. The
reaction mixture was concentrated to a residue, which was
purified by silica gel column chromatography (petroleum ether–
EtOAc, 2 : 1) to give 8 (966 mg, 90%) as a white foam; [α]2D5 ϩ14
(c 1, CHCl3); 1H NMR δ 1.01, 1.13 [2 d, 6 H, J 6.5 Hz,
SCH(CH3)2], 2.97–3.01 (m, 1 H, SCH), 3.88 (dd, 1 H, J 8.4 Hz,
10.8 Hz, H-6a), 4.04–4.06 (m, 1 H, H-6), 4.19–4.49 (m, 5 H),
4.50 (dd, 1 H, J 6.0 Hz, 11.4 Hz, H-6), 4.64 (d, 1 H, J1,2 10.2 Hz,
Method B. To a solution of 2 (420 mg, 0.52 mmol) in
methylene dichloride (0.5 mL) was added 50% aq. TFA (3 mL).
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J. Chem. Soc., Perkin Trans. 1, 2001, 3122–3127

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H-1A), 4.69–4.63 (m, 1 H, H-6), 4.75 (dd, 1 H, J 5.7 Hz, 10.8 Hz,
H-6), 5.00 (dd, 1 H, J 7.8, 9.6 Hz, H-2A), 5.00 (d, 1 H, J 7.8 Hz,
H-1C), 5.43 (dd, 1 H, J 10.5, 3.3 Hz, H-3C), 5.61 (distorted t,
1 H, J 8.7, 9.9 Hz, H-2B), 5.58–5.64 (m, 2 H, H-3, H-1B), 5.91
(distorted t, 1 H, J 9.0, 9.6 Hz, H-2C), 5.92 (d, 1 H, J 3.0 Hz,
H-4B), 5.98 (d, 1 H, J 3.0 Hz, H-4C), 6.06 (d, 1 H, J 3.3 Hz,
H-4A), 7.05–8.23 (m, 50 H, Ph) (Calc. for C91H78O25S: C, 68.16;
H, 4.90. Found: C, 68.01; H, 5.02%).
H-4), 7.05–8.05 (m, 35 H, Ph) (Calc. for C58H51NO13: C, 71.81;
H, 5.30. Found: C, 71.57; H, 5.38%).
O-(2,3,4-Tri-O-benzoyl-ꢀ-D-galactopyranosyl)-N-benzyloxy-
carbonyl-L-serine methyl ester 14
To a solution of 13 (600 mg, 0.62 mmol) in methylene dichlor-
ide (10 mL) was added FeCl3 hexahydrate (406 mg, 1.5 mmol).
The mixture was stirred at room temperature for 3 h and then
diluted with more CH2Cl2 (50 mL). The above mixture was
washed with cold water three times and the combined water
phase was re-extracted with CH2Cl2 (30 mL). The organic phase
were combined and concentrated to dryness, and the residue
was subjected to silica gel column chromatography (petroleum
ether–EtOAc, 3 : 2) to give 14 (400 mg, 89%) as an amorphous
Isopropyl 2,3,4,6-tetra-O-acetyl-1-thio-ꢀ-D-galactopyranoside 9
Standard acetylation of IPTG (2.0 g, 8.4 mmol) with acetic
anhydride (8 mL) in pyridine (10 mL) gave a quantitative yield
1
of crystalline 9, mp 70–72 ЊC; H NMR δ 1.31, 1.32 [2 d, 6 H,
CH(CH3)2], 1.99, 2.04, 2.06, 2.15 (4 s, 12 H, 4 × Ac), 3.19 [m,
1 H, CH(CH3)2], 3.93 (br t, 1 H, J5,6a 6.4, J5,6b 6.9 Hz, H-5), 4.10
(dd, 1 H, J6a,6b 11.3 Hz, H-6a), 4.18 (dd, 1 H, H-6b), 4.58 (d,
1 H, J1,2 10.0 Hz, H-1), 5.06 (dd, 1 H, J3,4 3.6 Hz, H-3), 5.22 (t,
1 H, J2,3 10.0 Hz, H-2), 5.43 (d, 1 H, H-4) (Calc. for C17H26O9S:
C, 50.24; H, 6.45. Found: C, 50.37; H, 6.55%).
solid; [α]2D5 ϩ1 (c 1, CHCl3); H NMR δ 3.35 (s, 3 H, OCH3),
1
3.56–3.62 (m, 1 H, H-5), 3.77 (dd, 1 H, J5,6a 7.2 Hz, J6a,6b 11.7
Hz, H-6a), 3.99 (dd, 1 H, J5,6b 5.7 Hz, H-6b), 4.09–4.12 (m, 2 H,
OCH2), 4.50–4.53 (m, 1 H, OCH), 4.74 (d, 1 H, J1,2 7.8 Hz,
H-1), 5.02 (d, 1 H, J 8.4 Hz, NH), 5.09 (s, 2 H, OCH2), 5.51–
5.55 (m, 2 H, H-2, H-3), 5.73 (br s, 1 H, H-4), 7.20–8.09 (m, 20
H, Ph) (Calc. for C39H37NO13: C, 64.37; H, 5.12. Found: C,
64.25; H, 5.20%).
O-(2,3,4,6-Tetra-O-acetyl-ꢀ-D-galactopyranosyl)-N-benzyloxy-
carbonyl-L-serine methyl ester 11
To a pre-cooled solution (0 ЊC) of compound 106 (708 mg,
2.8 mmol) and 9 (1.2 g, 2.95 mmol) in CH2Cl2 (20 mL) were
added NIS (900 mg, 4 mmol) and TMSOTf (90 µL, 0.5 mmol)
under a nitrogen atmosphere. The mixture was stirred at this
temperature for 2 h, TLC (2 : 1, petroleum ether–EtOAc)
showed the starting material had disappeared. The reaction
mixture was quenched with Et3N, then concentrated, and the
residue was subjected to flash chromatography with 2 : 1,
petroleum ether–EtOAc as eluent to give 11 (1.42 g, 87%) as
a syrup; [α]2D5 ϩ6 (c 1, CHCl3); 1H NMR δ 1.95, 2.00, 2.01, 2.11
(4 s, 4 × 3 H, 4 × Ac), 3.74 (s, 3 H, OCH3), 3.76–3.82 (m, 3 H,
H-5, H-6a, H-6b), 3.84–3.88 (m, 1 H, one proton of OCH2),
4.20–4.24 (m, 1 H, other proton of OCH2), 4.41 (d, 1 H, J1,2 7.8
Hz, H-1), 4.44–4.46 (m, 1 H, OCH), 4.94 (dd, 1 H, J2,3 10.2 Hz,
J3,4 3.3 Hz, H-3), 5.11–5.14 (m, 3 H, OCH2, H-2), 5.33 (d, 1 H,
J3,4 3.3 Hz, H-4), 5.55 (d, 1 H, J 8.1 Hz, NH), 7.23–7.33 (m, 5 H,
Ph) (Calc. for C26H33NO14: C, 53.51; H, 5.70. Found: C, 53.69;
H, 5.61%).
O-{2,3,4,6-Tetra-O-benzoyl-ꢀ-D-galactopyranosyl-(1
[2,3,4,6-tetra-O-benzoyl-ꢀ-D-galactopyranosyl-(1
6)-
3)]-2,4-di-
O-benzoyl-ꢀ-D-galactopyranosyl-(1
6)-2,3,4-tri-O-benzoyl-ꢀ-
D-galactopyranosyl)}-N-benzyloxycarbonyl-L-serine methyl
ester 15
A solution of compound 8 (368 mg, 0.23 mmol) and 14
(153 mg, 0.21 mmol) in anhydrous CH2Cl2 (3 mL) was treated
with NIS (140 mg, 0.62 mmol) and TMSOTf (37 µL, 0.2 mmol)
under N2 at 0 ЊC. The mixture was stirred under these con-
ditions for 2 h, then neutralized with Et3N and concentrated.
Column chromatography (2 : 1, petroleum ether–EtOAc) of
the residue gave glycopeptide 15 (430 mg, 91%) as a syrup;
[α]2D5 ϩ87 (c 1, CHCl3); H NMR δ 3.50 (s, 3 H, OCH3), 3.50–
1
3.65 (m, 3 H, H-5, H2-6), 3.89–3.95 (m, 4 H, H2-6, H-5, one
proton of OCH2), 4.08–4.11 (m, 2 H, H-3B, other proton of
OCH2), 4.24–4.40 (m, 5 H, 3 × H-6, 2 × H-5), 4.53 (d, 1 H, J 8.0
Hz, H-1A), 4.52–4.55 (m, 2 H, H-1B, OCH), 4.70 (dd, 1 H, J 6.4,
11.4 Hz, H-6b), 4.80 (d, 1 H, J 7.6 Hz, H-1D), 4.93 (d, 1 H, J1,2
8.8 Hz, H-1C), 4.94, 5.01 (2 d, 2 H, J 12.4 Hz, OCH2), 5.37
(d, 1 H, J 7.8 Hz, NH), 5.37 (dd, 1 H, J 9.2, 3.2 Hz, H-3D), 5.42
(dd, 1 H, J 9.6, 3.2 Hz, H-3A), 5.51–5.55 (m, 3 H, H-2A, H-2B,
H-2D), 5.64 (dd, 1 H, J 9.6, 3.2 Hz, H-3C), 5.70 (d, 1 H, J 3.2 Hz,
H-4A), (5.75 (dd, 1 H, J 8.0, 9.2 Hz, H-2C), 5.84 (d, 1 H, J 3.2
Hz, H-4D), 5.89 (d, 1 H, J 2.8 Hz, H-4B), 5.99 (d, 1 H, J 3.2 Hz,
H-4C), 7.03–8.15 (m, 70 H, Ph); 13C NMR (100 MHz; CDCl3)
δ 170.00, 165.95, 165.92, 165.86, 165.54, 165.44 (2 C), 165.36,
165.19 (2 C), 165.15 (2 C), 164.39 (2 C), 154 (BnOCO), 100.55,
101.40, 101.40, 101.65 (4 C-1), 73.95, 72.89, 71.62, 71.48,
71.29, 71.04, 70.92, 70.61, 69.87, 69.49, 69.35, 68.63, 68.31,
68.12, 67.55, 66.88, 66.69, 61.93, 61.46, 54.12, 53.74, 52.46.
[MALDI-TOF-MS Calc. for C127H107NNaO38 (M ϩ Na)ϩ:
O-(2,3,4-Tri-O-benzoyl-6-O-trityl-ꢀ-D-galactopyranosyl)-N-
benzyloxycarbonyl-L-serine methyl ester 13
A solution of 11 (3.2 g, 5.5 mmol) in MeOH (50 mL) was
treated with NaOMe (2.5 mL; 0.5 M in MeOH) at room tem-
perature for 4 h. The mixture was neutralized with Amberlite
120 (Hϩ) resin, then filtered, and the filtrate was evaporated to
give O-(β--galactopyranosyl)-N-benzyloxycarbonyl--serine
methyl ester 12 (2.2 g) as a syrup. Compound 12 (2.2 g,
5.3 mmol) was dissolved in pyridine (10 mL), and trityl chloride
(2.57 g, 9.54 mmol) and DMAP (20 mg) were added. The
mixture was stirred at room temperature for 48 h, then cooled
to 0 ЊC. To the above reaction mixture was added premixed
benzoyl chloride (2.2 mL, 18.5 mmol) and pyridine (3 mL), and
the mixture was stirred vigorously at room temperature for
48 h, and then poured into ice-cold water, and extracted with
CH2Cl2 (2 × 50 mL). The organic phase was concentrated to
dryness by repeated co-evaporation with toluene. The residue
was subjected to column chromatography on silica gel with
toluene–petroleum ether–EtOAc as eluent (0.2 : 1.5 : 1) to give
13 (3.1 g, 58%); [α]2D5 ϩ8 (c 1, CHCl3); 1H NMR δ 3.24 (dd, 1 H,
J5,6a 8.7, J6a,6b 12 Hz, H-6a), 3.42 (dd, 1 H, J5,6b 5.7 Hz, H-6b),
3.57 (s, 3 H, OCH3), 3.87–3.91 (m, 1 H, one proton of OCH2),
3.96 (dd, 1 H, J5,6a 7.5, J5,6b 6.0 Hz, H-5), 4.28–4.30 (m, 1 H,
other proton of OCH2), 4.40–4.43 (m, 1 H, OCH), 4.67 (d, 1 H,
J1,2 7.2 Hz, H-1), 4.96, 5.04 (2 d, 2 H, J 12.3 Hz, OCH2), 5.44 (d,
1 H, J 7.5 Hz, NH), 5.56–5.62 (m, 2 H, H-2, H-3), 6.02 (s, 1 H,
2276.6. Found: m/z, 2276.9 (M ϩ Na)ϩ] (Calc. for C127H107
NO38: C, 67.64; H, 4.78. Found: C, 67.85; H, 4.70%).
-
Isopropyl O-[3,4,6-tri-O-acetyl-2-deoxy-2-phthalimido-ꢀ-D-
glucopyranosyl-(1
phthalimido-ꢀ-D-glucopyranosyl-(1
thio-ꢀ-D-galactopyranoside 17
6)]-O-[3,4,6-tri-O-acetyl-2-deoxy-2-
3)]-2,4-di-O-benzoyl-1-
To a mixture of 3 (200 mg, 0.45 mmol), 16 (577 mg, 1.00 mmol)
and 4 Å molecular sieves in anhydrous CH2Cl2 (8 mL) was
added TMSOTf (12 µL, 0.06 mmol) under N2 at Ϫ15 ЊC.
The mixture was stirred these conditions for 2 h, at the end of
which time TLC (1 : 1, petroleum ether–EtOAc) indicated that
starting material 16 had disappeared. The reaction mixture
was neutralized with Et3N, then filtered, and the filtrate was
J. Chem. Soc., Perkin Trans. 1, 2001, 3122–3127
3125

View Article Online
concentrated. The residue was purified by silica gel column
chromatography (petroleum ether–EtOAc, 1 : 1) to give 17 (308
mg, 53.6%) as a syrup; [α]2D5 ϩ58 (c 1, CHCl3); 1H NMR δ 0.91,
0.99 [2 d, 6 H, CH(CH3)2], 1.69, 1.83 (2 s, 6 H, 2 × Ac), 1.96
(s, 6 H, 2 × Ac), 2.03, 2.15 (2 s, 6 H, 2 × Ac), 2.79–2.87 (m, 1 H,
SCH), 3.56 (dd, 1 H, J 8.6, 10.8 Hz, H-6aA), 3.75 (m, 1 H,
H-5A), 3.85–3.91 (m, 2 H, H-3A, H-6bA), 4.00–4.09 (m, 2 H,
H-5B, H-6aB), 4.12 (dd, 1 H, J 8.4 Hz, H-2C), 4.13–4.25 (m, 3 H,
H-6bB, H-5C, H-6aC), 4.29 (dd, 1 H, J 8.5 Hz, H-2B), 4.35 (dd,
1 H, J 9.6, 12.6 Hz, H-6bC), 4.52 (d, 1 H, J 10.1 Hz, H-1A), 5.02
(t, 1 H, J 10.5 Hz, H-4C), 5.16 (t, 1 H, J 10.5 Hz, H-4B), 5.35
(t, 1 H, J 10.1 Hz, H-2A), 5.40 (d, 1 H, J 8.5 Hz, H-1B), 5.51
(d, 1 H, J 8.4 Hz, H-1C), 5.55 (dd, 1 H, H-3C), 5.63 (d, 1 H, J 3.4
Hz, H-4A), 5.72 (dd, 1 H, H-3B), 7.22–8.02 (m, 18 H, Ph)
(Calc. for C63H64N2O25S: C, 59.06; H, 5.03. Found: C, 59.27; H,
5.11%).
0.07 mmol) under N2 at Ϫ42 ЊC. The mixture was stirred under
these conditions for 1 h, at which time TLC (2 : 1, petroleum
ether–EtOAc) indicated that starting material 18 was consumed
completely. The reaction mixture was neutralized with Et3N,
then concentrated. Column chromatography (4 : 1, petroleum
ether–EtOAc) of the residue gave the pure product 22 (48 mg,
62% based on 60 mg of recovered acceptor 21) as a syrup;
[α]2D5 ϩ 5 (c 1, CHCl3); H NMR δ 2.85 (dd, 1 H, J5,6a 8.4 Hz,
1
J6b,6a 5.6 Hz, H-6aЈ), 3.28 (t, 1 H, J5,6b 8.4 Hz, H-5Ј), 3.76
(dd, 1 H, H-6bЈ), 3.74–3.99 (m, 9 H), 4.01 (dd, 1 H, J 10, 2.8 Hz,
H-2Ј), 4.39–4.89 (m, 8 H, 4 × PhCH2), 4.77 (d, 1 H, J 2.8 Hz,
H-1Ј), 4.80 (d, 1 H, J 10 Hz, H-1), 5.52 (t, 1 H, J 10 Hz,
H-2), 7.04–7.63 (m, 30 H, Ph), 8.06–8.92 (m, 5 H, Ph) (Calc.
for C60H58O12S: C, 71.84; H, 5.83. Found: C, 72.03; H, 5.92%).
Phenyl O-[2,3,4,6-tetra-O-benzyl-D-galactopyranosyl-(1
2,3,4-tri-O-benzoyl-1-thio-ꢀ-D-galactopyranoside 24
6)]-
Isopropyl 2,3,4,6-tetra-O-benzyl-1-thio-ꢀ-D-galactopyranoside
18
To a mixture of compound 18 (470 mg, 0.786 mmol) and 23
(330 mg, 0.56 mmol) in anhydrous Et2O (5 mL) were added NIS
(174 mg, 0.78 mmol) and Me3SiOTf (7 µL, 0.04 mmol) under
N2 at Ϫ42 ЊC. The mixture was stirred under these conditions
for 1 h, at which time TLC (2 : 1, petroleum ether–EtOAc)
indicated that starting material was consumed completely. The
reaction mixture was neutralized with Et3N, then concentrated.
Column chromatography (2 : 1, petroleum ether–EtOAc) of the
residue gave 24 (600 mg, 96%; β : α = 1 : 2) as a syrup; 1H NMR
δ 3.47–3.52 (m, 3 H), 3.55 (dd, 0.33 H), 3.68 (dd, 0.33 H), 3.81–
4.05 (m, 4.33 H), 4.07 (t, 0.33 H, J 9.8 Hz, H-2Ј of β isomer),
4.31–5.00 (m, 10.67 H), 5.51 (dd, 0.67 H, J 9.8, 3.2 Hz, H-3 of
α isomer), 5.55 (dd, 0.33 H, J 9.8, 3.2 Hz, H-3 of β isomer), 5.69
(t, 0.33 H, J 9.8 Hz, H-2 of β isomer), 5.70 (t, 0.67 H, J 9.8 Hz,
H-2 of α isomer), 5.88 (d, 0.67 H, J 3.1 Hz, H-4 of α isomer),
5.91 (d, 0.33 H, J 3.1 Hz, H-4 of β isomer), 7.22–7.97 (m, 40 H,
Ph) (Calc. for C67H62O13S: C, 72.68; H, 5.64. Found: C, 72.91;
H, 5.57%).
To a cold (0 ЊC) solution of IPTG (1.0 g, 4.20 mmol) in DMF
(10 mL) were added NaH (50%; 1.66 g, 34.6 mmol) and BnBr
(2.3 mL, 18.9 mmol) cautiously. The reaction mixture was
stirred at room temperature for 6 h, then poured into cold
water, extracted with CH2Cl2 (2 × 30 mL), and the organic layer
was dried over Na2SO4, and concentrated. Column chroma-
tography (5 : 1, petroleum ether–ethyl acetate) of the residue
gave 18 (2.1 g, 85%) as a syrup; [α]2D5 Ϫ5 (c 1, CHCl3); 1H NMR
δ 1.28, 1.30 [2 d, 6 H, SCH(CH3)2], 3.14–3.23 (m, 1 H, SCH),
3.51–3.57 (m, 4 H, H-3, H-5, H-6a, H-6b), 3.77 (t, 1 H, J = 9.6
Hz, H-2), 3.91 (d, 1 H, J3,4 2.7 Hz, H-4), 4.35 (d, 1 H, J 11.4 Hz,
CH2), 4.42 (d, 1 H, J 11.4 Hz, CH2), 4.46 (d, 1 H, J1,2 9.6 Hz,
H-1), 4.58 (d, 1 H, J 11.7 Hz, CH2), 4.69 (s, 2 H, CH2), 4.73 (d,
1 H, J 9.9 Hz, CH2), 4.85 (d, 1 H, J 10.2 Hz, CH2), 4.91 (d, 1 H,
J 11.7 Hz, CH2), 7.18–7.36 (m, 20 H, Ph) (Calc. for C37H42O5S:
C, 74.22; H, 7.07. Found: C, 74.54; H, 6.96%).
Phenyl 2,3-di-O-benzoyl-6-O-benzyl-1-thio-ꢀ-D-galacto-
pyranoside 25
Methyl O-[2,3,4,6-tetra-O-benzyl-ꢁ-D-galactopyranosyl-
(1
4)]-3-O-benzoyl-2,6-di-O-benzyl-ꢀ-D-galacto-
pyranoside 20
1.04 g of phenyl 4,6-O-benzylidene-1-thio-β--galactopyrano-
side9 (2.86 mmol) was dissolved in 10 mL of pyridine, then
premixed benzoyl chloride (2.2 mL, 18.5 mmol) and pyridine
(3 mL) was added; the mixture was stirred vigorously at 50 ЊC
overnight, and then poured into ice-cold water, and extracted
with CH2Cl2 (2 × 30 mL). The organic phase was concentrated
to dryness by repeated co-evaporation with toluene. The residue
was subjected to column chromatography on silica gel with
petroleum ether–EtOAc as eluent (2 : 1) to give phenyl 2,3-
di-O-benzoyl-4,6-O-benzylidene-1-thio-β--galactopyranoside
(1.5 g, 92%); [α]2D5 ϩ6 (c 1, CHCl3); 1H NMR δ 3.76 (br s, 1 H,
H-5), 4.10 (dd, 1 H, J5,6a 1.2 Hz, J6a,6b 12.4 Hz, H-6a), 4,45 (dd,
1 H, J5,6b 1 Hz, J6a,6b 12.4 Hz, H-6b), 4.60 (d, 1 H, J3,4 3.2 Hz,
H-4), 4.97 (d, 1 H, J1,2 9.8 Hz, H-1), 5.36 (dd, 1 H, J 9.8, 3.2 Hz,
H-3), 5.51 (s, 1 H, PhCH), 5.81 (t, 1 H, J 9.8 Hz, H-2), 7.24–
7.98 (m, 20 H, Ph).
129 mg of phenyl 2,3-di-O-benzoyl-4,6-O-benzylidene-β--
galactopyranoside (0.225 mmol) and 311 mg of sodium
cyanoborohydride (4.5 mmol) were dissolved in 3 mL of dry
THF (distilled from sodium), then 5 mL of hydrogen chloride
saturated diethyl ether was added with vigorous stirring at
room temperature. A second portion of hydrogen chloride
in diethyl ether (2 mL) was added dropwise during 1.5 h
until evolution of the gas ceased. The reaction mixture was
diluted with CH2Cl2 (50 mL), then washed with saturated
aq. NaHCO3. The organic phase was dried over Na2SO4 and
concentrated to dryness. The residue was subjected to column
chromatography on silica gel with petroleum ether–EtOAc as
eluent (4 : 1) to give 25 (106 mg, 82%) as a syrup; [α]2D5 ϩ85 (c 1,
CHCl3); 1H NMR δ 2.72 (br s, 1 H, 4-OH), 3.84–3.92 (m, 3 H,
H-5, H2-6), 4.42 (d, 1 H, J3,4 2.7 Hz, H-4), 4.60 (2 d, 2 H, J 12.0
To a solution of compound 18 (300 mg, 0.5 mmol) and 197
(240 mg, 0.50 mmol) in anhydrous CH2Cl2 (6 mL) were added
NIS (282 mg, 1.25 mmol) and Me3SiOTf (27 µL, 0.18 mmol)
under N2 at 0 ЊC. The mixture was stirred under these con-
ditions for 2 h, at which time TLC (2 : 1, petroleum ether–
EtOAc) indicated that starting material 18 was consumed
completely. The reaction mixture was neutralized with Et3N,
then concentrated. Column chromatography (5 : 2, petroleum
ether–EtOAc) of the residue gave 20 (400 mg, 80%) as a syrup;
[α]2D5 ϩ44 (c 1, CHCl3); 1H NMR δ 3.08 (dd, 1 H, J5,6a 8.4, J6a,6b
5.4 Hz, H-6a), 3.40 (dd, 1 H, J 9.6, 8.4 Hz, H-5), 3.63 (s, 3 H,
OCH3), 3.67–3.83 (m, 4 H, H-2Ј, H-5, H-6a, H-6b), 3.89 (dd,
1 H, J5,6b 9.6 Hz, H-6b), 3.99–4.03 (m, 2 H, H-2, H-3Ј), 4.04 (s,
1 H, H-4), 4.11 (s, 1 H, H-4Ј), 4.26 (s, 2 H, CH2), 4.31 (s, 2 H,
CH2), 4.42 (d, 1 H, J1,2 7.2 Hz, H-1), 4.50 (d, 1 H, J 11.7 Hz,
CH2), 4.60 (d, 1 H, J 11.7 Hz, CH2), 4.61 (d, 1 H, J 11.7 Hz,
CH2), 4.75 (s, 2 H, CH2), 4.80 (d, 1 H, J 11.7 Hz, CH2), 4.82 (d,
1 H, J 11.7 Hz, CH2), 4.89 (d, 1 H, J 11.4 Hz, CH2), 4.91 (s, 1 H,
H-1Ј), 5.11 (dd, 1 H, J2,3 10.2 Hz, J3,4 3.0 Hz, H-3), 7.06–8.09
(m, 35 H, Ph) [Calc. for C62H64NaO12 (M ϩ Na)ϩ: 1023.4.
Found: m/z, 1023.1 (M ϩ Na)ϩ] (Calc. for C62H64O12: C, 74.38;
H, 6.44. Found: C, 74.70; H, 6.32%).
Phenyl O-[2,3,4,6-tetra-O-benzyl-ꢁ-D-galactopyranosyl-
(1
3)]-2,6-di-O-benzoyl-1-thio-ꢀ-D-galacto-
pyranoside 22
To a solution of compound 18 (145 mg, 0.24 mmol) and 21
(97 mg, 0.2 mmol) in anhydrous Et2O–CH2Cl2 (1: 1; 3 mL)
were added NIS (63 mg, 0.28 mmol) and Me3SiOTf (13 µL,
3126
J. Chem. Soc., Perkin Trans. 1, 2001, 3122–3127

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C.-H. Wong, Chem. Rev., 1998, 98, 833; (b) R. A. Dwek, Chem. Rev.,
Hz, PhCH2), 4.94 (d, 1 H, J1,2 9.8 Hz, H-1), 5.32 (dd, 1 H, J 9.8,
3.0 Hz, H-3), 5.79 (t, 1 H, J 9.8 Hz, H-2), 7.25–7.98 (m, 20 H,
Ph) (Calc. for C33H30O7S: C, 69.46; H, 5.30. Found: C, 69.71; H,
5.39%).
1996, 96, 683.
2 G.-J. Boons and K. J. Hale, Organic Synthesis with Carbohydrates,
Sheffield Academic Press, England, 2000.
3 Y. Du, M. Zhang and F. Kong, Org. Lett., 2000, 2, 3797.
4 (a) L. J. Huang, Y. Lin and G. Y. Tian, Acta Pharma. Sin., 1998, 33,
512; (b) L. J. Huang, G. Y. Tian and G. Z. Ji, J. Asian Nat. Prod. Res.,
1999, 1, 259.
Acknowledgements
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7 M. Zhang, MSc dissertation, Chinese Academy of Sciences, 2001.
8 K. Toshima and K. Tatsuta, Chem. Rev., 1993, 93, 1503.
9 A. Fernandez-Mayoralas, A. Marra, M. Trumtel, A. Veyrières and
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This work was supported by National Nature Science Founda-
tion of China (Projects 29972053 and 39970179).
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J. Chem. Soc., Perkin Trans. 1, 2001, 3122–3127
3127