Synthesis of tetrasaccharide repeating unit of the O-antigen from enterohemorrhagic Escherichia coli O157 in the form of its 2-(trimethylsilyl) ethyl glycoside

Article abstract of DOI:10.1080/07328300500495878

Two α-linked disaccharide derivatives, ethyl 3,4,6-tri-O-acetyl-2- azido-2-deoxy-α-D-galactopyranosyl-(1 → 2)-4-azido-3-O-benzyl-4,6- dideoxy-1-thio-α-D-mannopyranoside (10) and 2-(trimethylsilyl)ethyl 3-O-acetyl-4-O-benzoyl-2-O-benzyl-α-L-fucopyranosyl-(

Full text of DOI:10.1080/07328300500495878

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Synthesis of Tetrasaccharide Repeating Unit
of the O‐Antigen from Enterohemorrhagic
Escherichia coli O157 in the form of its
2‐(trimethylsilyl)ethyl Glycoside
Kakali Sarkar a & Nirmolendu Roy a
a Department of Biological Chemistry , Indian Association for the Cultivation
of Science , Kolkata, India
Published online: 21 Aug 2006.
To cite this article: Kakali Sarkar & Nirmolendu Roy (2006) Synthesis of Tetrasaccharide Repeating Unit of the
O‐Antigen from Enterohemorrhagic Escherichia coli O157 in the form of its 2‐(trimethylsilyl)ethyl Glycoside,
Journal of Carbohydrate Chemistry, 25:1, 53-68, DOI: 10.1080/07328300500495878
To link to this article: http://dx.doi.org/10.1080/07328300500495878
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Journal of Carbohydrate Chemistry, 25:53–68, 2006
Copyright # Taylor & Francis Group, LLC
ISSN: 0732-8303 print 1532-2327 online
DOI: 10.1080/07328300500495878
Synthesis of
Tetrasaccharide Repeating
Unit of the O-Antigen from
Enterohemorrhagic
Escherichia coli O157 in the
form of its
2-(trimethylsilyl)ethyl
Glycoside
Kakali Sarkar and Nirmolendu Roy
Department of Biological Chemistry, Indian Association for the Cultivation of Science,
Kolkata, India
Two a-linked disaccharide derivatives, ethyl 3,4,6-tri-O-acetyl-2-azido-2-deoxy-a-D-
galactopyranosyl-(1 ! 2)-4-azido-3-O-benzyl-4,6-dideoxy-1-thio-a-D-mannopyranoside
(10) and 2-(trimethylsilyl)ethyl 3-O-acetyl-4-O-benzoyl-2-O-benzyl-a-L-fucopyrano-
syl-(1 ! 4)-2,3-di-O-benzyl-6-O-tert-butyldiphenylsilyl-b-D-glucopyranoside (16), were
prepared from appropriate monosaccharide synthons. The disaccharide 16 was deacety-
lated and debenzoylated to afford the acceptor 17, which was allowed to react with the
donor 10 to afford a tetrasaccharide derivative 18. This tetrasaccharide was trans-
formed in three steps into 21, the desired repeating unit of the antigen from enterohe-
morrhagic E. coli type O157.
Keywords Synthesis, Tetrasaccharide, Enterohemorrhagic Escherichia coli type O157
Received May 20, 2005; accepted August 12, 2005.
Address correspondence to Nirmolendu Roy, Department of Biological Chemistry,
Indian Association for the Cultivation of Science, Jadavpur, Kolkata 700 032, India.
E-mail: nirmolendu@yahoo.com
53

K. Sarkar and N. Roy
54
INTRODUCTION
The enterohemorrhagic Escherichia coli O157:H7 is probably the most import-
ant pathogen in the species E. coli that can cause hemorrhagic colitis and
hemolytic uremic syndrome.[1] The structure of the O-antigen of enterohemor-
rhagic E. coli O157:H7 (I) has been reported by Perry and his coworkers.[2]
As a continuation of our program to synthesize oligosaccharides[3,4] related
to the O-antigens of enterohemorrhagic E. coli with the broader objective of
developing glycoconjugate vaccines against these pathogens, we report here
the synthesis of the tetrasaccharide repeating unit of the O-antigen from
enterohemorrhagic E. coli type O157 in the form of its 2-(trimethylsilyl)ethyl
glycoside. The strategy is to synthesize the blocks BA and DC and couple
them together to prepare a blocked tetrasaccharide, which can then be
transformed in three steps into the desired tetrasaccharide repeating unit.
RESULTS AND DISCUSSION
The known ethyl 2,3-O-isopropylidene-1-thio-a-D-mannopyranoside[5] (1) was
converted to the corresponding 6-iodo compound (2) with triphenylphosphine,
imidazole, and iodine.[6] Reduction of 2 with H2[7] in the presence of 10% Pd-C
gave the 6-deoxy compound (3). Oxidation of 3 with methyl sulfoxide[8] gave a
ketohexose, which on reduction with sodium borohydride[8–10] gave ethyl
1
6-deoxy-2,3-O-isopropylidene-1-thio-a-D-talopyranoside (4). H NMR signal of
H-4 in compound 4 appeared at a downfield position compared to that for
compound 3. Treatment of 4 with methanesulfonyl chloride and triethyl-
amine[10,11] gave the mesyl derivative 5. Removal of isopropylidene
group[12,13] from 5 followed by treatment of the resulting 6 with sodium
azide[14] afforded the azido compound 7 (56% overall), which is a precurser
for the D-perosamine moiety. Selective benzylation of 7 via stanylidene
complex[15] gave ethyl 4-azido-3-O-benzyl-4,6-dideoxy-1-thio-a-D-mannopyra-
noside (8). The acceptor 8 was allowed to react with the known 3,4,6-tri-O-
acetyl-2-azido-2-deoxy-a-D-galactopyranosyl trichloroacetimidate[16,17] 9 in
the presence of triethylsilyltrifluoromethanesulfonate (TESOTf)[17,18] at
–258C to give the disaccharide ethyl 3,4,6-tri-O-acetyl-2-azido-2-deoxy-a-D-
galactopyranosyl-(1 ! 2)-4-azido-3-O-benzyl-4,6-dideoxy-1-thio-a-D-mannopy
ranoside (10) (Sch. 1) in 57.3% yield. The structure of 10 was confirmed by its
signals at d 5.18 (H-1I), 5.16 (H-1II), 3.51 (H-2II), and 1.55 (H-6I) in its 1H NMR

Tetrasaccharide Repeating Unit
55
Scheme 1: (a) I2, imidazole, PPh3, toluene; (b) H2,10% Pd-C, EtOH-NEt3 (19:1); (c) i. DMSO,
(COCl)2, CH2Cl2; ii. NaBH4, EtOH; (d) MsCl, NEt3, CH2Cl2; (e) 2N HCl in MeOH, MeOH, 08C; (f) NaN3,
DMSO, 1008C; (g) i. Bu2SnO, benzene; ii. BnBr, Bu4NBr, 638C, 62.9%; (h) TESOTf, CH2Cl2, 57.3%.
spectrum and at d 99.86 (C-1I), 83.70 (C-1II), 64.84 (C-4I), 57.76 (C-2II), and
I
15.36 (C-6 ) in its 13C NMR spectrum.
In another experiment, the known 2-(trimethylsilyl)ethyl 2,3-di-O-benzyl-
b-D-glucopyranoside[19] 11, prepared from D-glucose, on treatment with tert--
butyldiphenylsilyl (TBDPS) chloride[20,21] and pyridine, afforded the acceptor
12 in 70% yield (Sch. 2).
In a separate experiment, ethyl 2-O-benzyl-1-thio-b-D-fucopyranoside[22,23]
(13) was prepared by known technique starting from L-fucose. Treatment of 13
with trimethylorthobenzoate in the presence of p-TsOH[24] followed by mild
hydrolysis of the product gave 14, which on acetylation afforded the donor 15.
The acceptor 12 was then allowed to react with the thioglycoside donor 15 in the
presence of N-iodosuccinimide (NIS) and trifluoromethanesulfonic acid[25,26]
(TfOH) to give the disaccharide 16 in 72% yield. Removal of acetyl and benzoyl
groups in 16 afforded the acceptor 17 having two hydroxyl groups (Sch. 3). The dis-
accharide 17 gave signals at d 5.16 (H-1II), 4.4 (H-1I) and 0.8 (H-6II) in its 1H NMR
spectrum and at d 103.00 (C-1I), and 95.86 (C-1II) in its 13C NMR spectrum.
The disaccharide acceptor 17, having two hydroxyl groups, was allowed
to react with the disaccharide donor 10 in the presence of NIS and
Scheme 2: (a) t-Butyldiphenylsilylchloride (TBDPSCl), Pyr, 12 h.

K. Sarkar and N. Roy
56
Scheme 3: (a) i. Triethylorthobenzoate, DMF, p-TsOH; ii. 80% AcOH, rt, 73.6%; (b) Ac2O, Pyr,
85.8%; (c) 12, NIS, TfOH, CH2Cl2, 1 h, 72%; (d) NaOMe, MeOH, rt.
TfOH[25,26] to afford the tetrasaccharide derivative 2-(trimethylsilyl)ethyl
3,4,6-tri-O-acetyl-2-azido-2-deoxy-a-D-galactopyranosyl-(1 ! 2)-4-azido-3-O-
benzyl-4,6-dideoxy-a-D-mannopyranosyl-(1 ! 3)-2-O-benzyl-a-L-fucopyranosyl-
(1 ! 4)-2,3-di-O-benzyl-6-O-tert-butyldiphenylsilyl-a-D-glucopyranoside (18)
in 57% yield together with the corresponding (1 ! 4) linked tetrasaccharide
derivative 2-(trimethylsilyl)ethyl 3,4,6-tri-O-acetyl-2-azido-2-deoxy-a-D-galac-
topyranosyl-(1 ! 2)-4-azido-3-O-benzyl-4,6-dideoxy-a-D-mannopyranosyl-
(1 ! 4)-2-O-benzyl-a-L-fucopyranosyl-(1 ! 4)-2,3-di-O-benzyl-6-O-tert-butyl-
diphenylsilyl-b-D-glucopyranoside (19) (Sch. 4) in 7.8% yield. The acceptor 17
had one equatorial and one axial hydroxyl groups, and it was expected that gly-
cosidation would take place mostly at the equatorial 3-OH position. However,
some reaction had also taken place at the axial 4-OH, probably because of
the proximity of 6-deoxy status of the accepter 17. The tetrasaccharide 18
1
was characterized by its H NMR signals at d 5.12 (H-1II), 4.87 (H-1III), 4.79
(H-1IV), 4.23 (H-1I), 4.50 (m, 1 H, H-3II), and 3.87 (bs, 1 H, H-4II); 13C NMR
signals at d 102.90 (C-1I), 97.90 (C-1IV), 97.20 (C-1III), and 96.20 (C-1II); and
DEPT 135 spectrum of the compound. The 13C NMR and DEPT 135 spectra
showed, apart from the characteristic peaks, all the carbon peaks clearly
separated except those in the aromatic region. The tetrasaccharide 19 was
1
also characterized by its H NMR signals at d 5.02 (H-1II), 4.93 (H-1III), 4.88
(H-1IV), 4.83 (H-4II), 4.20 (H-1I), and 3.83 (H-3II); 13C NMR signals at
d 103.00 (C-1I), 99.85 (C-1IV), 99.00 (C-1III), and 95.50 (C-1II); and the DEPT
135 spectrum. That the linkage between the a-D-perosamine precurser and
the a-L-fucose unit were 1 ! 3 in compound 18 and 1 ! 4 in compound 19
1
was confirmed by comparing the H NMR signals of their acetyl derivatives.
Acetylation of 18 gave 4II-O-acetyl derivative 18A, which manifested the
1
shift of its H NMR signal for H-4II from d 3.87 in 18 to d 5.14 in the acetate
18A, while the position of the signals for H-3II remained practically unchanged.
Similarly, the tetrasaccharide 19 manifested similar shift in 19A where the

Tetrasaccharide Repeating Unit
57
Scheme 4: (a) NIS, TfOH, CH2Cl2, 45 min; (b) Bu4NF, THF, 51.5%; (c) i. H2, 10% Pd-C, MeOH-Ac2O
(20:1), 3 d, rt; ii. MeOH, 0.05 M NaOMe, 3 h, rt, 56% overall.
1H NMR signal for H-3II had shifted from d 3.83 in 19 to d 4.86 in 19A as
expected, while the signals for H-4II remained unchanged.
Compound 18 was treated with tetrabutylammoniumfluoride[27,28] in THF
at 08C to remove the t-butyldiphenylsilyl protecting group. The product 20 was
hydrogenolyzed with hydrogen and 10% Pd-C[29] in the presence of acetic anhy-
dride, a condition under which the azido groups were converted into acetamido
groups, with simultaneous removal of the benzyl substituents. The product was
then deacetylated with 0.05 M NaOMe to afford the desired tetrasaccharide
repeating unit 21 of the antigen from E. coli O157. The final compound 21
1
was characterized from its H NMR signals at d 5.08 (H-1III), 4.81 (H-1IV),
4.69 (H-1II), and 4.30 (H-1I); and 13C NMR signals at d 102.5 (C-1I), 100.5
(C-1IV), 99.2 (C-1III), and 97.2 (C-1II); and DEPT spectrum.
EXPERIMENTAL
General
All the reactions were monitored by TLC on silica gel G (E. Merck). Column
chromatography was performed on 100–200 mesh silica gel (SRL, India).

K. Sarkar and N. Roy
58
All solvents were distilled and/or dried before use and all evaporations were
conducted below 508C under reduced pressure unless stated otherwise.
Petroleum ether used in this work has a boiling range of 608C to 808C.
Optical rotations were measured with a Perkin Elmer model 241 MC
1
polarimeter. The H and 13C NMR spectra were recorded on a Bruker DPX
300 Spectrometer using CDCl3 as solvent. Tetramethylsilane was used as
1
internal standard in H NMR spectra unless otherwise mentioned. Melting
points were determined on a paraffin oil bath and are uncorrected.
Ethyl 6-deoxy-6-iodo-2,3-O-isopropylidene-1-thio-a-D-mannopyrano-
side (2). To a solution of ethyl 2,3-O-isopropylidene-1-thio-a-D-mannopyrano-
side 1 (5.32 g, 20.1 mmol) in toluene (160 mL), triphenylphosphine (6.80 g,
25.9 mmol), imidazole (4.72 g, 69.3 mmol), and iodine (6.14 g, 24.2 mmol) were
added and the mixture was boiled under reflux with vigorous stirring until
the color disappeared (30 min). A solution of sodium hydrogen carbonate
(6.7 g) and water (80 mL) were then introduced and after stirring for 5 min,
iodine was added until the color of the mixture remained purple. Aqueous
10% sodium thiosulphate solution was added dropwise with stirring until the
purple color of iodine disappeared. The mixture was then diluted with ethyl
acetate, washed twice with water, and concentrated. A solution of the residue
in ether (100 mL) was cooled to –108C and after 1 h, the solution was filtered
and concentrated to a syrup, which on column chromatography with 3:1
toluene-EtOAc gave compound 2 (6.80 g, 90.3%); [a]2D5 þ106.28 (c 3.7, CHCl3).
1H NMR: d 5.58 (s, 1 H, H-1), 4.19 (d, 1 H, J2,3 ¼ 5.5 Hz, H-2), 4.10 (dd, 1 H,
J3,4 ¼ 5.6 Hz, J4,5 ¼ 7.2 Hz, H-4), 3.79 (ddd, 1 H, J4,5 ¼ 9.0 Hz, J5,6a ¼ 2.5 Hz,
J5,6b ¼ 6.9 Hz, H-5), 3.58 (m, 1 H, H-3), 3.56 (dd, 1 H, J5,6a ¼ 2.5 Hz,
J6a,6b ¼ 10.5 Hz, H-6a), 3.35 (dd, 1 H, J5,6b ¼ 7.0 Hz, J6a,6b ¼ 10.8, H-6b), 2.75
(m, 2 H, SCH2CH3), 1.54, 1.35 [2 s, 6 H, C(CH3)2], 1.31 (t, 3 H, J ¼ 7.4 Hz,
SCH2CH3).
Anal. Calcd for C11H19O4SI: C, 35.3; H, 5.12. Found C, 35.05; H, 5.14.
Ethyl 6-deoxy-2,3-O-isopropylidene-1-thio-a-D-mannopyranoside (3). A
solution of 2 (6.80 g, 18.2 mmol) in ethanol (75 mL) containing 5% triethylamine
was stirred under hydrogen in the presence of 10% Pd-C (0.71 g) at rt. The
reaction was completed in 4 d as ascertained by TLC with 5:1 toluene-EtOAc.
The reaction mixture was filtered and the filtrate was concentrated to a
syrup, which on column chromatography with 5:1 toluene-EtOAc gave 3
1
(2.5 g, 55.4%) as a syrup; [a]2D5 þ145.18 (c 1.93, CHCl3). H NMR: d 5.52 (s, 1
H, H-1), 4.18 (d, 1 H, J2,3 ¼ 5.5 Hz, H-2), 4.04 (dd, 1 H, J3,4 ¼ 5.8 Hz,
J4,5 ¼ 7.5 Hz, H-4), 3.97 (m, 1 H, H-5), 3.44 (dd, 1 H, J2,3 ¼ 5.6 Hz,
J3,4 ¼ 5.8 Hz, H-3), 2.62 (m, 2 H, SCH2CH3), 1.54, 1.35 [2 s, 6 H, C(CH3)2],
1.30 (t, 3 H, J ¼ 7.7 Hz, SCH2CH3), 1.29 (d, 3 H, J ¼ 6.7 Hz, H-6).
Anal. Calcd for C11H20O4S: C, 53.20; H, 8.12. Found: C, 52.98; H, 8.05.

Tetrasaccharide Repeating Unit
59
Ethyl 6-deoxy-2,3-O-isopropylidene-1-thio-a-D-talopyranoside (4). A
solution of oxalyl chloride (0.84 mL, 9.6 mmol) in dichloromethane (2.6 mL)
under nitrogen was cooled to –788C and a solution of methyl sulfoxide
(1.3 mL, 18.0 mmol) in dichloromethane (2.4 mL) was added dropwise with
stirring. After 30 min at –788C, a solution of compound 3 (1.01 g, 4.1 mmol)
in CH2Cl2 (28 mL) was slowly added to it. After another 40 min, N,N-diisopro-
pylethylamine (4.80 mL, 27.6 mmol) was added and the mixture was kept at
–708C for 2.5 h and then allowed to attain rt. TLC with 5:1 toluene-EtOAc
showed complete conversion of compound 3 into the corresponding ketohexose
compound. The mixture was diluted with dichloromethane (50 mL), washed
with water (50 mL ꢀ 3), dried (Na2SO4), and concentrated in vacuo. The
syrupy residue was dissolved in ethanol (3 mL), sodium borohydride (450 mg,
11.8 mmol) was added to it and the mixture was stirred for 3 h at rt. The
reaction was monitored by TLC with 5:1 toluene- EtOAc. Excess NaBH4 was
destroyed by adding a few drops of acetone and the solution was concentrated
to dryness. The residue was diluted with dichloromethane (50 mL) and washed
with water (2 ꢀ 50 mL), NaHCO3 (2 ꢀ 50 mL), and water (2 ꢀ 50 mL), and the
organic layer was concentrated. Column chromatography of the resulting
syrupy residue with 7:1 toluene-EtOAc gave compound 4 (850 mg, 84.0%);
[a]2D5 þ152.88 (c 0.99, CHCl3). H NMR: d 5.54 (d, 1 H, J1,2 ¼ 1.4 Hz, H-1),
1
4.19 (dd, 1 H, J3,4 ¼ 5.5 Hz, J4,5 ¼ 0.7 Hz, H-4), 4.13 (dq, 1 H, J4,5 ¼ 0.7 Hz,
J5,6 ¼ 6.5 Hz, H-5), 4.05 (dd, 1 H, J1,2 ¼ 1.5 Hz, J2,3 ¼ 6.1 Hz, H-2), 3.61 (t, 1
H, J ¼ 5.6 Hz, H-3), 2.63 (m, 2 H, SCH2CH3), 1.60, 1.38 [2 s, 6 H, C(CH3)2],
1.33 (d, 3 H, J ¼ 6.4 Hz, H-6), 1.32 (t, 3 H, J ¼ 7.2 Hz, SCH2CH3).
Anal. Calcd for: C11H20O4S: C, 53.20; H, 8.12. Found: C, 53.29; H, 8.15.
Ethyl 6-deoxy-2,3-O-isopropylidene-4-O-(methylsulfonyl)-1-thio-a-D-
talopyranoside (5). A solution of 4 (1.33 g, 5.35 mmol) in CH2Cl2 (16 mL)
was cooled to 08C under nitrogen atmosphere and triethylamine (1.4 mL) and
methanesulfonyl chloride (0.83 mL) were added to it. The reaction mixture
was stirred for 10 min at 08C and then allowed to attain rt. After 1.5 h the
reaction was completed as revealed by TLC using 5:1 toluene-EtOAc. The
reaction was quenched with saturated NaHCO3 (2 mL) with stirring for
30 min. Dichloromethane (50 mL) was added and the organic phase was
washed successively with saturated NaHCO3, water, saturated CuSO4
solution, and water; dried (Na2SO4); and concentrated to a syrup, which crys-
tallized from ethanol to give 5 (1.6 g, 91.6%); m.p 1058C, [a]2D5 þ67.78 (c 0.5,
1
CHCl3). H NMR: d 5.46 (d, 1 H, J1,2 ¼ 2.0 Hz, H-1), 4.66 (dd, 1 H, J4,5
¼
1.9 Hz, J3,4 ¼ 5.6 Hz, H-4), 4.36 (t, 1 H, J ¼ 6.0 Hz, H-3), 4.28 (dq, 1 H,
J4,5 ¼ 1.8 Hz, J5,6 ¼ 6.5 Hz, H-5), 4.08 (dd, 1 H, J1,2 ¼ 2.1 Hz, J2,3 ¼ 6.2 Hz,
H-2), 3.10 (s, 3 H, SO2CH3), 2.65 (m, 2 H, SCH2CH3), 1.60, 1.37 [2 s, 6 H, 2
C(CH3)2], 1.38 (d, 3 H, J ¼ 6.1 Hz, H-6), 1.32 (t, 3 H, J ¼ 7.5 Hz, CH2CH3).
Anal. Calcd for C12H22O6S2: C, 44.15; H, 6.79. Found: C, 44.17; H, 6.91.

K. Sarkar and N. Roy
60
Ethyl 4-azido-4,6-dideoxy-1-thio-a-D-mannopyranoside (7). To a solution
of 5 (1.70 g, 5.3 mmol) in anhydrous methanol (59 mL), 2N HCl in MeOH
(1.2 mL) was added and the mixture was stirred at 08C for 2 h at rt. The
solution was concentrated under diminished pressure to afford ethyl 6-deoxy-
4-O-(methylsulfonyl)-a-D-talopyranoside 6. The product 6 (1.52 g, 5.2 mmol)
was quickly dissolved in DMSO (13.3 mL) and stirred with NaN3 (1.80 g,
27.7 mmol) for 5 h at 1008C. Solvents were removed, and the syrupy residue
was dissolved in ethanol (40 mL) and filtered through a Celite bed. The
filtrate was concentrated and column chromatographed with 3:1 toluene-
EtOAc to give 7 (700 mg, 56% overall), which crystallized from hexane;
m.p. 888C; [a]2D5 þ210.68 (c 0.67, CHCl3). H NMR: d 5.20 (s, 1 H, H-1), 3.96
1
(d, 1 H, J2,3 ¼ 3.5 Hz, H-2), 3.91 (dd, 1 H, J2,3 ¼ 3.5 Hz, J3,4 ¼ 10.0 Hz, H-3),
3.74 (m, 1 H, H-5), 3.25 (t, 1 H, J ¼ 9.8, H-4), 2.55 (m, 2 H, SCH2CH3), 1.28
(d, 3 H, J ¼ 6.2 Hz, H-6), 1.22 (t, 3 H, J ¼ 7.4 Hz, SCH2CH3); 13C NMR: d
84.31 (C-1), 72.12 (C-2), 71.36 (C-3), 67.60 (C-5), 66.49 (C-4), 25.57
(SCH2CH3), 18.63 (SCH2CH3), 15.24 (C-6). I.R: 2113.8 cm21 (N3).
Anal. Calcd for C8H15O3SN3: C, 41.19; H, 6.48; N, 18.01. Found: C, 40.88;
H, 6.61; N, 18.39.
Ethyl 4-azido-3-O-benzyl-4,6-dideoxy-1-thio-a-D-mannopyranoside (8).
A mixture of 7 (579 mg, 2.48 mmol) and dibutyltinoxide (1.20 g, 4.82 mmol)
was stirred under reflux in benzene (15 mL) with azeotropic removal of water
for 20 h. The reaction mixture was then allowed to attain rt. Benzyl bromide
(0.35 mL, 3.0 mmol) and Bu4NBr (960 mg, 3.0 mmol) were then added and the
mixture was stirred at 638C for 6 h. The mixture was concentrated under
reduced pressure and the residue dissolved in MeOH and kept at –108C
when the unwanted tin compounds were precipitated out from the mixture
and filtered off. The filtrate was concentrated to dryness and the residue was
chromatographed using 5:1 toluene-EtOAc and the product crystallized in
ether-petroleum ether to afford 8 (505 mg, 62.9%); m.p. 828C; [a]2D5 þ1208
(c 1.12, CHCl3). 1H NMR: d 7.31–7.25 (m, 4 H, aromatic protons), 5.21
(s, 1 H, H-1), 4.61, 4.56 (2 d, 2 H, J ¼ 11.4 Hz, CH2C6H4), 3.95 (d, 1 H,
J2,3 ¼ 3.2 Hz, H-2), 3.81 (m, 1 H, H-5), 3.60 (dd, 1 H, J2,3 ¼ 3.2 Hz,
J3,4 ¼ 9.7 Hz, H-3), 3.37 (t, 1 H, J ¼ 9.9 Hz, H-4), 2.51 (m, 2 H, SCH2CH3),
1.24 (d, 3 H, J5,6 ¼ 6.2 Hz, H-6), 1.19 (t, 3 H, J ¼ 7.3 Hz, SCH2CH3); 13C
NMR: d 137.40–128.60 (aromatic protons), 83.53 (C-1), 79.01, 72.48, 69.16,
67.49, 64.65 (C-4), 25.44 (SCH2CH3), 18.78 (SCH2CH3), 15.26 (C-6).
Anal. Calcd for C15H21O3N3S: C, 55.71; H, 6.54; N, 12.99. Found: C, 55.86;
H, 6.75; N, 12.77.
Ethyl 3,4,6-tri-O-acetyl-2-azido-2-deoxy-a-D-galactopyranosyl-(1 ! 2)-
4-azido-3-O-benzyl-4,6-dideoxy-1-thio-a-D-mannopyranoside
(10).
A
solution
of
3,4,6-tri-O-acetyl-2-azido-2-deoxy-b-D-galactopyranosyl

Tetrasaccharide Repeating Unit
61
trichloroacetimidate[16,17] 9 (780 mg, 1.6 mmol) and acceptor 8 (390 mg,
˚
1.2 mmol) in CH2Cl2 (15 mL) was stirred with MS 4 A (2.50 g) under N2 for
1 h. The mixture was then cooled to –258C and TESOTf (45 mL, 200 mmol)
was added dropwise. The reaction was allowed to proceed at –258C for 1.5 h
when TLC with12:1 toluene-EtOAc showed the disappearance of the acceptor
(8). The reaction was then quenched with the addition of Et3N (0.5 mL) and
the mixture was filtered through a Celite bed. The filtrate was concentrated
and the syrupy product was purified by column chromatography with 10:1
toluene-EtOAc to afford 10 (600 mg, 57.3%), which crystallized as fine
1
needles from hot ethanol; m.p. 968C; [a]2D5 þ115.68 (c 0.57, CHCl3). H NMR:
d 7.35–7.19 (m, 4 H, aromatic protons), 5.41 (d, 1 H, J3,4 ¼ 3.0 Hz, H-4II),
5.27 (dd, 1 H, J3,4 ¼ 3.2 Hz, J2,3 ¼ 11.3 Hz, H-3II), 5.18 (d, 1 H, J1,2 ¼ 1.1 Hz,
H-1I), 5.16 (d, 1 H, J1,2 ¼ 3.7 Hz, H-1II), 4.64, 4.59 (2 d, 2 H, J ¼ 11.7 Hz,
CH2C6H4), 4.22 (m, 1 H, H-5II), 4.01 (s, 1 H, H-2I), 3.95 (m, 2 H, H-6I), 3.78
(m, 1 H, H-5I), 3.64 (dd, 1 H, J2,3 ¼ 2.7 Hz, J3,4 ¼ 9.8 Hz, H-3I), 3.55 (t, 1 H,
J ¼ 9.7 Hz, H-4I), 3.51 (dd, 1 H, J1,2 ¼ 3.7 Hz, J2,3 ¼ 11.3 Hz, H-2II), 2.54 (m, 2
H, SCH2CH3), 2.09, 1.99, 1.98 (3 s, 9 H, 3 CH3CO), 1.55 (d, 3 H, J5,6 ¼ 6.2 Hz,
H-6I), 1.21 (t, 3 H, J ¼ 7.5 Hz, SCH2CH3); 13C NMR: d 170.84, 170.42, 170.24
(3 CH3CO), 137.69–128.34 (aromatic carbons), 99.86 (C-1I), 83.7 (C-1II),
78.65 (CH2C6H5), 76.15, 72.66, 68.16, 68.05, 67.66,64.84 (C-4I), 62.44 (C-6II),
57.76 (C-2II), 26.05 (SCH2CH3), 21.14, 21.08, 21.02 (3 CH3CO), 18.76
(SCH2CH3), 15.36 (C-6I).
Anal. Calcd for C27H36O10SN6: C, 50.94; H, 5.70. Found: C, 51.21; H, 5.92.
2-(Trimethylsilyl)ethyl 2,3-di-O-benzyl-6-O-tert-butyldiphenylsilyl-b-
D-glucopyranoside (12). To a solution of 2-(trimethylsilyl)ethyl 2,3-di-O-
benzyl-b-D-glucopyranoside 11 (2 g, 4.3 mmol) in pyridine (15 mL), tert-butyldi-
phenylsilyl chloride (1.25 mL, 4.8 mmol) was added while stirring at rt. The
reaction was monitored by TLC and after 12 h, the reaction was quenched
with methanol and the mixture was concentrated to a thick glass. Column
chromatography of the product with 5:1 toluene-EtOAc gave 12 (2.1 g, 70%);
[a]2D5 2268 (c 2.8, CHCl3). 1H NMR: d 7.55–7.10 (20 H, aromatic protons),
4.81, 4.56 (2 d, 2 H, J ¼ 11.1 Hz, CH2C6H5), 4.76, 4.59 (2 d, 2 H, J ¼ 11.4 Hz,
CH2C6H5), 4.2 (d, 1 H, J1,2 ¼ 7.2 Hz, 3.86 (t, 1 H, J ¼ 9.3 Hz, H-3), 3.83 (dd,
1 H, J1,2 ¼ 7.2 Hz, J
¼ 9.8 Hz, H-2), 3.74 (m, 1 H, H-4), 3.45 (m, 2 H,
2,3
OCH2CH2SiMe3), 3.27 (m, 3 H, H-5, H-6), 0.89 [s, 9 H, C(CH3)3], 0.82 (m, 2
H, OCH2CH2SiMe3), –0.15 [s, 9H, Si(CH3)3]; 13C NMR: d 135.6.–127.6
(aromatic carbons), 103.1 (C-1), 84.2, 81.9, 75.2, 74.8, 74.6, 71.6, 67.2, 64.4,
27.7 [SiC(CH3)3], 19.1 [SiC(CH3)3], 18.5 (CH2CH2SiMe3), –1.5 [Si (CH3)3].
Anal. Calcd for C41H54O6Si2: C, 70.44; H, 7.78. Found: C, 70.79; H, 7.32.
Ethyl 4-O-benzoyl-2-O-benzyl-1-thio-b-L-fucopyranoside (14). To
a
stirred solution of ethyl 2-O-benzyl-1-thio-b-L-fucopyranoside 13 (2.5 g,

K. Sarkar and N. Roy
62
8.4 mmol) in anhydrous DMF (16 mL), trimethylorthobenzoate (2.2 mL,
12.8 mmol) and p-TsOH (30 mg) were added. Stirring was continued at rt for
3 h and after completion of the reaction as revealed by TLC with 5:1 toluene-
EtOAc, NEt3 was added to neutralize the solution. The solution was then
concentrated and treated with 80% aqueous AcOH (10 mL) for 30 min. The
reaction mixture was concentrated and immediately purified by column chrom-
atography with 5:1 toluene-EtOAc. Crystallization of the column-purified
material in ether gave 14 (2.48 g, 73.6%); m.p. 988C; [a]2D5 256.88 (c 2.6,
CHCl3). 1H NMR: d 8.09–7.12 (m, 9 H, aromatic protons), 5.43 (d, 1 H,
J3,4 ¼ 3.1 Hz, H-4), 4.98 (d, 1 H, J1,2 ¼ 10.7 Hz, H-1), 4.67, 4.49 (2 d, 2 H,
J ¼ 9.5 Hz, CH2C6H4), 3.90 (dd, 1 H, J2,3 ¼ 9.4 Hz, J3,4 ¼ 3.2 Hz, H-3), 3.81
(m, 1 H, H-5), 3.59 (t, 1 H, J ¼ 9.4 Hz, H-2), 2.80 (m, 2 H, SCH2CH3), 1.35
(t, 3 H, J ¼ 7.4 Hz, SCH2CH3), 1.24 (d, 3 H, J ¼ 6.3 Hz, H-6); 13C NMR:
d 167.22 (CO), 138.39–128.44 (aromatic carbons), 85.24 (C-1), 79.13, 75.89,
74.41, 73.99, 73.79, 25.40 (SCH2CH3), 17.16 (SCH2CH3), 15.40 (C-6).
Anal. Calcd for C22H26O5S: C, 65.64; H, 6.51. Found: C, 65.68; H, 6.32.
Ethyl 3-O-acetyl-4-O-benzoyl-2-O-benzyl-1-thio-b-L-fucopyranoside (15).
To compound 14 (600 mg, 1.5 mmol) dissolved in pyridine (5 mL), Ac2O (2.5 mL)
was added with cooling. After 3 h at rt, solvents were evaporated and then coe-
vaporated with toluene to remove traces of pyridine. The residue was diluted
with CH2Cl2 (25 mL); washed with 1M HCl (2 ꢀ 25 mL), NaHCO3
(2 ꢀ 25 mL), and water (2 ꢀ 25 mL) in succession; dried (Na2SO4); and concen-
trated to a thick syrup. Column chromatography with 5:1 toluene-EtOAc gave
15 (580 mg, 85.8%), which crystallized from ether-petroleum ether to afford
1
pure 15; m.p. 105–1078C; [a]2D5–65.38 (c 1.9, CHCl3). H NMR: d 7.89–7.03
(10 H, aromatic protons), 5.28 (d, 1 H, J3,4 ¼ 3.1 Hz, H-4), 4.65, 4.38 (2d, 2 H,
J ¼ 10.9 Hz, CH2C6H5), 4.35 (d, 1 H, J1,2 ¼ 9.6 Hz, H-1), 3.68 (m, 1 H, H-5),
3.51 (t, 1 H, J ¼ 9.6 Hz, H-2), 2.60 (m, 2 H, SCH2CH3), 1.14 (t, 3 H,
J ¼ 7.4 Hz, SCH2CH3), 1.03 (d, 3 H, J5,6 ¼ 6.5 Hz, H-6). 13C NMR: 170.64
(COCH3), 166.47 (COC6H5), 138.28–128.23 (aromatic carbons), 85.59 (C-1),
76.55, 75.15, 73.51, 71.90, 25.53 (SCH2CH3), 21.21 (COCH3), 17.03
(SCH2CH3), 15.38 (C-6).
Anal. Calcd for C24H28O6S: C, 64.84; H, 6.35. Found: C, 64.72; H, 6.28.
2-(Trimethylsilyl)ethyl 3-O-acetyl-4-O-benzoyl-2-O-benzyl-b-L-fucopy-
ranosyl-(1 ! 4)-2,3-di-O-benzyl-6-O-tert-butyldiphenylsilyl-a-D-glucopy-
ranoside (16). A solution of the donor 15 (420 mg, 940 mmol) and the acceptor
˚
12 (550 mg, 770 mmol) in CH2Cl2 (10 mL) containing 4 A MS (1 g) was stirred at
rt for 1 h under N2. The reaction mixture was cooled to –208C and NIS (210 mg,
93 mmol) and TfOH (7 mL, 80 mmol) were added and stirring was continued at
this temperature while the reaction was monitored by TLC in 10:1 tuluene-
EtOAc. After 1 h, the concentration of the donor and the acceptor were

Tetrasaccharide Repeating Unit
63
diminished to a negligible amount and a new spot appeared in between them.
The reaction mixture was then diluted with CH2Cl2 (30 mL) and washed suc-
cessively with water, 5% Na2S2O3, saturated NaHCO3, and water. The
organic layer was dried (Na2SO4) and concentrated and the syrupy residue
was column chromatographed with 15:1 toluene-EtOAc to give 16 (600 mg,
1
72%) as syrup; [a]2D5 –70.08 (c 1.8, CHCl3). H NMR: d 7.79–6.81 (aromatic
protons), 5.15 (dd, 1 H, J2,3 ¼ 10.7 Hz, J3,4 ¼ 3.2 Hz, H-3II), 5.07 (d, 1 H,
J3,4 ¼ 3.4 Hz, H-4II), 4.98 (d, 1 H, J1,2 ¼ 2.4 Hz, H-1II), 4.91, 4.47 (2 d, 2 H,
J ¼ 10.7 Hz, CH2C6H5), 4.87, 4.56 (2 d, 2 H, J ¼ 10.9 Hz, CH2C6H5), 4.26 (d,
1 H, J ¼ 7.7 Hz, H-1I), 1.74 (s, 3 H, COCH3), 0.94 [s, 9 H, C(CH3)3], 0.43 (d,
3 H, J ¼ 6.6 Hz, H-6II), –0.16 [s, 9 H, Si(CH3)3]. 13C NMR: d169.9 (COCH3),
165.9 (COC6H5), 138.3–127.4 (aromatic carbons), 103.0 (C-1I), 96.4 (C-1II),
83.0, 82.9, 75.8, 74.5, 73.19, 73.2, 72.2, 67.0, 64.6, 62.5, 26.7 [SiC(CH3)3], 20.7
(COCH3), 19.2 [SiC(CH3)3], 18.5 (OCH2CH2SiMe3), 15.3 (C-6II),–1.5
[Si(CH3)3]; DEPT 135 spectrum: 135.8–127.4 (aromatic carbons), 103.0 (C-1I),
96.43 (C-1II), 82.9, 75.81, 75.80 (CH2C6H5), 74.5 (CH2C6H5), 73.5, 73.24
(CH2C6H5), 73.18, 72.21, 70.15, 67.00 (C-6I), 64.60, 62.50 (OCH2CH2SiMe3),
26.74 [SiC(CH3)3], 20.70 (COCH3), 19.23 [SiC(CH3)3] 18.47 (OCH2CH2SiMe3),
15.30 (C-6II), -1.50 [Si (CH3)3].
Anal. Calcd for C63H76O12Si2: C, 69.97; H, 7.08. Found: C, 70.12; H, 7.34.
2-(Trimethylsilyl)ethyl 2-O-benzyl-a-L-fucopyranosyl-(1 ! 4)-2,3-di-O-
benzyl-6-O-tert-butyldiphenylsilyl-a-D-glucopyranoside (17). Compound
16 (600 mg, 550 mmol) was treated with 0.05 M NaOMe in MeOH (15 mL)
and stirred for 3 h. Column chromatography with 5:1 toluene-EtOAc of the
1
product gave pure 17 (430 mg, 84%); [a]2D5 –90.28 (c 0.6, CHCl3). H NMR: d
7.67–7.02 (aromatic protons), 5.16 (d, 1 H, J ¼ 3.3 Hz,. H-1II), 4.97 (d, 2 H,
J ¼ 10.9 Hz, CH2C6H5), 4.68, 4.60 (2 d, 2 H, J ¼ 10.9 Hz, CH2C6H5), 4.40 (d, 1
H, J ¼ 7.62 Hz, H-1I), 4.28 (d, 1 H, J ¼ 11.6 Hz, CH2C6H5), 4.03 (m, 1 H,
H-4II), 1.00 [s, 9 H, SiC(CH3)3], 0.86 (d, 3 H, J ¼ 6.6 Hz, H-6II), -0.01 [s, 9 H,
Si(CH3)3]. 13C NMR: d 138.40–125.20 (aromatic carbons), 103.00 (C-1I), 95.86
(C-1II), 83.20, 82.90, 76.60, 76.00, 75.40, 74.50, 73.80, 72.70, 71.40, 68.90,
67.03, 65.50, 62.90 (OCH2CH2SiMe3), 26.70 [SiC(CH3)3], 19.10 [SiC(CH3)3],
18.50 (OCH2CH2SiMe3), 15.60 (C-6II), –1.50 [Si(CH3)3].
Anal. Calcd for C54H70O10Si2: C, 69.34; H, 7.54. Found: C, 69.57; H, 7.40.
2-(Trimethylsilyl)ethyl 3,4,6-tri-O-acetyl-2-azido-2-deoxy-a-D-galacto-
pyranosyl-(1 ! 2)-4-azido-3-O-benzyl-4,6-dideoxy-a-D-mannopyranosyl-
(1 ! 3)-2-O-benzyl-a-L-fucopyranosyl-(1 ! 4)-2,3-di-O-benzyl-6-O-tert-
butyldiphenylsilyl-b-D-glucopyranoside (18). NIS (58 mg, 260 mmol) and
TfOH (3 mL, 30 mmol) were added to the stirred mixture of the acceptor 17
˚
(200 mg, 210 mmol), the donor 10 (163 mg, 200 mmol), 4 A molecular sieves
(100 mg), and CH2Cl2 (3mL) at (208C under N2 as described for compound 16.

K. Sarkar and N. Roy
64
The reaction was monitored by TLC (10:1 toluene-ethyl acetate) and after
45 min, the spots for the donor and the accepter almost disappeared and a
spot for the product appeared prominently. The reaction mixture was worked
up as described for compound 16. Column chromatography of the crude
product with 15 : 1 toluene-EtOAc afforded 18 (180 mg, 57%) and another
tetrasaccharide derivative 19 (25 mg, 7.8%).
For compound 18: [a]2D5 þ3.58 (c 0.01, CHCl3). 1H NMR: 7.53–6.99 (aromatic
protons, 30 H), 5.23 (d, 1 H, J ¼ 3.2 Hz, H-4IV), 5.14 (m, 1 H, H-3IV), 5.12 (s, 1 H,
H-1II), 4.87 (s, 1 H, H-1III), 4.83 (s, 2 H, CH2Ph), 4.79 (s, 1 H, H-1IV), 4.52 (m, 2 H,
CH2Ph), 4.50 (m, 1 H, H-3II), 4.46 (m, 2 H, CH2Ph), 4.23 (d, 1 H, J ¼ 7.6 Hz, H-1I),
4.16 (m, 2 H, CH2Ph), 3.95 (dd, 1 H, J ¼ 0.5 Hz, J ¼ 12.8 Hz, H-5IV), 3.87 (bs, 1 H,
H-4II), 3.85 (m, 2 H, H-6IV), 3.81 (s, 1 H, H-2III), 3.75 (m, 1 H, H-2I), 3.55 (dd, 1 H.,
J ¼ 3.6 Hz, J ¼ 9.9 Hz, H-3III), 2.76 (m, 2 H, OCH2CH2SiMe3), 1.94, 1.82, 1.73 (3
s, 9 H, 3 COCH3), 1.07 (d, 3 H, J ¼ 7.1 Hz, H-6III), 0.87 [s, 9 H, SiC(CH3)3], 0.86
(m, 2 H, OCH2CH2SiMe3), 0.73 (d, 3 H, J ¼ 6.4 Hz, H-6II), –0.15 [s, 9 H, Si(CH3)3;
13C NMR: d170.30, 169.80, 169.20 (3 COCH3), 135.80–127.30 (aromatic
carbons), 102.90 (C-1I), 97.90 (C-1IV), 97.20 (C-1III), 96.20 (C-1II), 83.08, 82.85,
80.90, 78.70, 76.00, 75.00, 74.40, 74.10, 72.90, 72.80, 72.50, 72.10, 71.40, 70.60,
67.50, 67.40, 66.90, 66.30, 65.30, 63.80 (C-4III), 62.70 (OCH2CH2SiMe3), 61.40
(C-6IV), 57.60 (C-2IV), 26.90 [SiC(CH3)3], 20.40 (3 COCH3), 19.20 [SiC(CH3)3],
18.50 (OCH2CH2SiMe3), 18.20 (C-6III), 15.60 (C-6II), –1.50 [Si(CH3)3]; DEPT
135 Spectrum: d 136.10–127.60 (aromatic carbons), 103.20 (C-1I), 98.2
0(C-1IV), 97.50 (C-1III), 96.50 (C-1II), 83.30, 83.10, 81.10, 79.00, 77.30, 76.20,
75.20 (CH2), 74.70 (CH2), 74.30, 73.10, 73.00 (CH2), 72.80, 72.30 (CH2),
71.70, 70.80, 67.80, 67.60, 67.20 (C-6I), 66.60, 65.50, 64.10 (C-4III), 62.90
(OCH2CH2SiMe3), 61.70 (C-6IV), 57.90 (C-2IV), 27.00 [SiC(CH3)3], 20.70 (3
COCH3), 18.70 (OCH2CH2SiMe3), 18.50 (C-6III), 15.90 (C-6II), –1.20 [Si(CH3)3].
For compound 19: [a]2D5 þ6.28 (c 0.7, CHCl3). 1H NMR: d 7.51–6.85 (aromatic
protons, 30 H), 5.18 (d, 1 H, J ¼ 1.9 Hz, H-4IV), 5.09 (dd, 1 H, J ¼ 2.8 Hz,
J ¼ 11.3 Hz, H-3IV), 5.02 (d, 1 H, J ¼ 2.9 Hz, H-1II), 4.93 (s, 1 H, H-1III), 4.88
(d, 1 H, J ¼ 3.8 Hz, H-1IV), 4.84, 4.82 (2d, 2 H, J ¼ 10.8 Hz, CH2Ph), 4.83 (s, 1
H, H-4II), 4.55, 4.51 (2 s, 2 H, CH2Ph), 4.40 (bs, 2 H, CH2Ph), 4.20 (d, 1 H,
J ¼ 6.6 Hz, H-1I), 4.01 (m, 2 H, CH2Ph), 3.94 (t, 1 H, J ¼ 6.5 Hz, H-5IV), 3.85
(d, 1 H, J ¼ 8.6 Hz, H-3I), 3.83 (m, 1 H, H-3II), 3.02 (m, 2 H, OCH2CH2SiMe3)
1.94, 1.87, 1.73 (3 s, 9 H, 3 COCH3), 1.23 (d, 3 H, J ¼ 6.3 Hz, H-6III), 0.88 [s, 9
H, SiC(CH3)3] 0.84 (m, 2 H, OCH2CH2SiMe3), 0.56 (d, 3 H, J ¼ 6.3 Hz, H-6II)
–0.15 [s, 9 H, Si (CH3)3]; 13C NMR: d 170.20, 169.80, 169.60 (3 COCH3),
135.90–127.30 (aromatic carbons), 103.00 (C-1I), 99.85 (C-1IV), 99.00 (C-1III),
95.50 (C-1II), 82.80, 82.50, 75.8000, 75.40, 75.30, 74.40, 74.20, 73.00, 72.20,
71.90, 68.00, 67.50, 67.40, 67.00, 66.90, 65.00, 63.80 (C-4III), 62.10
(OCH2CH2Si), 61.7000 (C-6IV), 57.30 (C-2IV), 26.8000 [SiC(CH3)3], 20.80,
20.50, 20.40 (3 COCH3), 19.20 [SiC(CH3)3], 18.50 (C-6III), 18.40 (OCH2CH2Si),
15.30 (C-6II),–1.50 [Si(CH3)3]; DEPT 135 Spectrum: d 136.10–127.50 (aromatic

Tetrasaccharide Repeating Unit
65
carbons), 103.10 (C-1I), 100.00 (C-1IV), 99.19 (C-1III), 95.70 (C-1II), 83.00, 82.70,
77.50, 77.20, 75.90, 75.50, 75.40 (CH2C6H5), 74.60 (CH2C6H5), 74.40, 73.20
(CH2C6H5), 72.30, 72.10, 72.00, 68.10, 67.60, 67.10 (C-6I), 67.00, 65.20, 63.90
(C-4III), 62.30 (OCH2CH2SiMe3), 61.90 (C-6IV), 57.40 (C-2IV), 26.90 [SiC(CH3)3],
20.90, 20.65, 20.63 (3 COCH3), 18.70 (C-6III), 18.60 (OCH2CH2Si), 15.50 (C-6II),
–1.30 [Si(CH3)3].
Anal. Calcd for C79H100O20N6Si2: C, 62.84; H, 6.67; N, 5.57. Found for 18:
C, 62.58; H, 6.82; N, 5.48. Found for 19: C, 62.61; H, 6.79; N, 5.42.
2-(Trimethylsilyl)ethyl 3,4,6-tri-O-acetyl-2-azido-2-deoxy-a-D-galacto-
pyranosyl-(1 ! 2)-4-azido-3-O-benzyl-4,6-dideoxy-a-D-mannopyranosyl-
(1 ! 3)-2-O-benzyl-4-O-aetyl-a-L-fucopyranosyl-(1 ! 4)-2,3-di-O-benzyl-
6-O-tert-butyldiphenylsilyl-b-D-glucopyranoside (18A). Compound 18
was acetylated as described for compound 15 to give 18A.1H NMR: d 7.53–
6.99 (aromatic protons, 30 H), 5.14 (d, 1 H, J ¼ 2.6 Hz, H-4II), 5.09 (d, 1 H,
J ¼ 3.5 Hz, H-4IV), 5.03 (dd, 1 H, J ¼ 3.2 Hz, J ¼ 7.7 Hz, H-3IV), 5.02 (s, 1 H,
H-1II), 4.88, 4.82 (2d, 2 H, J ¼ 11.1 Hz, CH2Ph), 4.80 (s, 1 H, H-1III), 4.69
(d, 1 H, J ¼ 3.1 Hz, H-1IV), 4.58 (dd, 1 H, J ¼ 3.2 Hz, J ¼ 6.96 Hz, H-3II), 4.51,
4.46 (2d, 2 H, J ¼ 11.0 Hz, CH2Ph), 4.41 (m, 2 H, CH2Ph), 4.24 (d, 1 H,
J ¼ 6.5 Hz, H-1I), 4.2 (bs, 2 H, CH2Ph), 4.08 (d, 1 H, J ¼ 6.4 Hz, H-5IV), 3.99
(dd, 1 H, J ¼ 8.6 Hz, J ¼ 10.9 Hz, H-2I), 3.92 (dd, 2 H, J ¼ 3.5 Hz, J ¼ 10.1 Hz,
H-6IV), 3.79 (s, 1 H, H-2III), 2.92 (m, 2 H, OCH2CH2Si), 1.94, 1.91, 1.83, 1.66
(4 s, 12 H, 4 COCH3), 1.14 (d, 3 H, J ¼ 6 Hz, H-6III), 0.87 (m, 2 H,
OCH2CH2Si), 0.59 (d, 3 H, J ¼ 6.6 Hz, H-6II), –0.15 [s, 9 H, Si(CH3)3].
2-(Trimethylsilyl)ethyl 3,4,6-tri-O-acetyl-2-azido-2-deoxy-a-D-galacto-
pyranosyl-(1 ! 2)-4-azido-3-O-benzyl-4,6-dideoxy-a-D-mannopyranosyl-
(1 ! 4)-2-O-benzyl-3-O-aetyl-a-L-fucopyranosyl-(1 ! 4)-2,3-di-O-benzyl-
6-O-tert-butyldiphenylsilyl-b-D-glucopyranoside (19A). Compound 19
1
was acetylated as described for compound 15 to give 19A. H NMR: d 7.50–
6.88 (30 H, aromatic protons), 5.12 (s, 2 H, H-1III, H-4IV), 5.05 (dd, 1 H,
J ¼ 3.2 Hz, J ¼ 11.4 Hz, H-3IV), 5.02 (d, 1 H, J ¼ 3.1 Hz, H-1II), 4.92 (s, 1 H,
H-1IV), 4.86 (dd, 1 H, J ¼ 8.1 Hz, J ¼ 4.4 Hz, H-3II), 4.81 (s, 2 H, CH2Ph), 4.68
(d, 1 H, J ¼ 3.0 Hz, H-4II), 4.55, 4.51 (2 s, 2 H, CH2Ph), 4.41, 4.39 (2d, 2 H,
J ¼ 5.3 Hz, CH2Ph), 4.22 (d, 1 H, J ¼ 7.3 Hz, H-1I), 4.06 (bs, 2 H, CH2Ph), 3.06
(d, 2 H, J ¼ 8.9 Hz, OCH2CH2Si), 1.94, 1.86, 1.80, 1.75 (4 s, 12 H, 4 COCH3),
1.18 (d, 3 H, J ¼ 6 Hz, H-6III), 0.89 (m, 2 H, OCH2CH2Si), 0.38 (d, 3 H,
J ¼ 6.3 Hz, H-6II), –0.15 [s, 9 H, Si(CH3)2].
2-(Trimethylsilyl)ethyl
2-acetamido-2-deoxy-a-D-galactopyranosyl-
(1 ! 2)-4-acetamido-4,6-dideoxy-a-D-mannopyranosyl-(1 ! 3)-a-L-fuco-
pyranosyl-(1 ! 4)-b-D-glucopyranoside (21). Tetrabutylammoniumfluor-
ide (36 mg, 140 mmol) in 0.3 mL THF was added to a solution of 18 (103mg,

K. Sarkar and N. Roy
66
68 mmol) in THF at 08C with stirring. The mixture was then allowed to attain rt
and after 12 h, the solution was concentrated. Column chromatography of the
residue with 5:1 toluene-EtOAc gave pure compound 20 (45 mg, 51.5%). A
solution of 20 (45mg, 35 mmol) in aldehyde-free methanol (2 mL) containing
acetic anhydride (0.1 mL) was stirred with 10% Pd on charcoal under
hydrogen for 3 d when all the starting material was transformed into a clean,
slower-moving compound as observed in the TLC. The mixture was filtered
through a Celite bed, the filtrate was concentrated to a syrup, and the
product was treated with 0.05 M NaOMe in methanol as described in the case
of compound 17. The deacetylated product was dissolved in water and filtered
through Sep-Pak C-18 cartridge and concentrated to dryness to afford pure
1
compound 21 (16 mg, 56%). [a]2D5 þ528 (c 0.01, H2O). H NMR (D2O): d5.08
(s, 1 H, H-1III), 4.81 (bs, 1 H, H-1IV), 4.69 (d, 1 H, J ¼ 4.2 Hz, H-1II), 4.30 (d,
1 H, J ¼ 7.9 Hz, H-1I), 3.09 (m, 2H, OCH2CH2SiMe3), 1.86, 1.83 (2 s, 6 H,
2 NHCOCH3), 1.08, 1.02 (2d, 6 H, J ¼ 6 Hz, H-6II, H-6III), 0.85 (m, 2H,
OCH2CH2SiMe3), -0.15 [Si(CH3)3]; 13C NMR: d175.90 (2 NHCOCH3), 102.50
(C-1I), 100.50 (C-1IV), 99.20 (C-1III), 97.20 (C-1II), 78.30, 76.70, 76.20, 75.80,
74.60, 72.90, 72.50, 71.20, 70.40, 69.50, 69.40, 69.10, 68.10, 67.90 (C-6I),
67.60, 67.50, 61.90 (OCH2CH2 SiMe3), 61.10 (C-6IV), 54.00 (C-4III), 51.30 (C-
2IV), 23.20, 23.10 (2 NHCOCH3), 18.60 (OCH2CH2SiMe3), 17.70 (C-6III), 16.30
(C-6II), –1.50 [Si(CH3)3]; DEPT 135 Spectrum: d 102.50 (C-1I), 100.50 (C-1IV),
99.10 (C-1III), 97.10 (C-1II), 78.30, 76.70, 76.20, 75.80, 74.60, 72.90, 72.50,
71.20, 70.40, 69.50, 69.40, 69.10, 68.10, 67.90 (C-6I), 67.60, 67.50, 61.80
(OCH2CH2 SiMe3), 61.10 (C-6IV), 54.00 (C-4III), 51.30 (C-2IV), 23.20, 23.10 (2
NHCOCH3), 18.60 (OCH2CH2SiMe3), 17.70 (C-6III), 16.30 (C-6II), –1.50
[Si(CH3)3].
Anal. Calcd for C33H60O19N2Si: C, 48.52; H, 7.40; N, 3.43. Found: C, 48.38;
H, 7.58; N, 3.25.
ACKNOWLEDGEMENT
Financial support by the Council of Scientific and Industrial research, New
Delhi, (Project No. 01/1536/98/EMR-II) is thankfully acknowledged.
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