Synthesis of a Blocked Tetrasaccharide Related to the Repeating Unit of the Antigen from Shigella dysenteriae Type 9 in the Form of Its Methyl (R)-Pyruvate Ester and 2-(Trimethylsilyl)Ethyl Glycoside

Article abstract of DOI:10.1081/CAR-120026456

Starting from D-mannose, D-galactose and D-glucosamine hydrochloride, two disaccharide blocks were synthesized. Schmidt's inverse addition technique of tricbloroacetimidate was utilized for the construction of a disaccharide with a β-mannosidic linkage in

Full text of DOI:10.1081/CAR-120026456

Journal of Carbohydrate Chemistry
ISSN: 0732-8303 (Print) 1532-2327 (Online) Journal homepage: http://www.tandfonline.com/loi/lcar20
Synthesis of a Blocked Tetrasaccharide Related to
the Repeating Unit of the Antigen from Shigella
dysenteriae Type 9 in the Form of Its Methyl
(R)‐Pyruvate Ester and 2‐(Trimethylsilyl)Ethyl
Glycoside
Samarpita Roy & Nirmolendu Roy
To cite this article: Samarpita Roy & Nirmolendu Roy (2003) Synthesis of a Blocked
Tetrasaccharide Related to the Repeating Unit of the Antigen from Shigella dysenteriae Type 9
in the Form of Its Methyl (R)‐Pyruvate Ester and 2‐(Trimethylsilyl)Ethyl Glycoside , Journal of
Carbohydrate Chemistry, 22:7-8, 521-535, DOI: 10.1081/CAR-120026456
To link to this article: http://dx.doi.org/10.1081/CAR-120026456
Published online: 23 Feb 2007.
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Date: 21 January 2016, At: 08:01

JOURNAL OF CARBOHYDRATE CHEMISTRY
Vol. 22, Nos. 7 & 8, pp. 521–535, 2003
Synthesis of a Blocked Tetrasaccharide Related to the
Repeating Unit of the Antigen from Shigella dysenteriae
Type 9 in the Form of Its Methyl (R)-Pyruvate Ester
and 2-(Trimethylsilyl)Ethyl Glycosidey
*
Samarpita Roy and Nirmolendu Roy
Department of Biological Chemistry, Indian Association for the Cultivation
of Science, Jadavpur, Kolkata, India
ABSTRACT
Starting from D-mannose, D-galactose and D-glucosamine hydrochloride, two di-
saccharide blocks were synthesized. Schmidt’s inverse addition technique of
trichloroacetimidate was utilized for the construction of a disaccharide with a b-
mannosidic linkage in good yield. The other disaccharide had a methyl 4,6-(R)-
pyruvate ester. The two disaccharides in the appropriate form were then allowed
to react in the presence of N-iodosuccinimide (NIS) and trifluoromethanesulfonic
acid (TfOH) to give the desired tetrasaccharide derivative, 2-(trimethylsilyl)ethyl
2-acetamido-3,4,6-tri-O-benzoyl-2-deoxy-b-D-glucopyranosyl-(1 ! 3)-2-O-benzoyl-
4,6-O-[(R)-1-methoxycarbonylethylidene]-b-D-galactopyranosyl-(l ! 4)-2,3,6-tri-O-
benzyl-b-D-mannopyranosyl-(1 ! 4)-2,6-di-O-benzyl-3-O-(4-methoxybenzyl)-
b-D-galactopyranoside.
Key Words: Synthesis; Tetrasaccharide derivative; Shigella dysenteriae type 9.
yThis paper is dedicated to Professor Ge´rard Descotes on the occasion of his 70th birthday.
*
Correspondence: Nirmolendu Roy, Department of Biological Chemistry, Indian Association for
the Cultivation of Science, Jadavpur, Kolkata 700 032, India; E-mail: bcnr@mahendra.iacs.res.in.
521
DOI: 10.1081/CAR-120026456
0732-8303 (Print); 1532-2327 (Online)
www.dekker.com
Copyright D 2003 by Marcel Dekker, Inc.

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Roy and Roy
INTRODUCTION
Shigella dysenteria type 9, a gram-negative pathogen, is one of the infective agents
responsible for many intestinal diseases including dysentery. As carbohydrate-based
antibacterial vaccines found increasing interest in recent years,[1,2] it is considered
relevent to explore this approach for the preparation of vaccines against Shigella
dysenteria type 9. A considerable amount of work has already been carried out in
different laboratories,[3–8] including ours,[9,10] on the synthesis of carbohydrate haptens
related to Shigella. We report herein the synthesis of a blocked tetrasaccharide
derivative related to the repeating unit I of the antigen from Shigella dysenteriae type 9
in the form of its methyl (R)-pyruvate ester and 2-(trimethylsilyl)ethyl glycoside.[11,12]
RESULTS AND DISCUSSION
Our strategy is to synthesize the blocks DC and BA as their stable derivatives,
convert them to a suitable disaccharide donor and a disaccharide acceptor and finally
allow them to react in the presence of an appropriate promoter.
Phenyl 1-thio-b-D-galactopyranoside[13] (1) was treated with tert-butyldiphenylsilyl
chloride[14] (TBDPSCl) in pyridine to afford phenyl 6-O-tert-butyldiphenylsilyl-1-thio-
b-D-galactopyranoside (2) which upon treatment with 2,2-dimethoxypropane[15] in N,N-
dimethylformamide gave the 3,4-O-isopropylidene derivative 3. The reason for intro-
ducing the TBDPS group before the 3,4-isopropylidene moiety was to avoid the
formation of 4,6-isopropylidene derivative. Acetylation of 3 followed by removal of the
isopropylidene group from the product 4 afford phenyl 2-O-acetyl-6-O-tert-butyldi-
Scheme 1. a) TBDPSCl, Pyr, 2 h; b) DMP, CSA, DMF, 12 h; c) Ac2O, Pyr, 3 h; d) 80% AcOH,
80°C, 1 h.

Synthesis of Blocked Tetrasaccharide
523
phenylsilyl-1-thio-b-D-galactopyranoside (5) (Scheme 1). The structure of 5 was con-
1
firmed from its H and 13C NMR spectra.
The acceptor 5 with two hydroxyl groups of different reactivity was then allowed
to react with the known 3,4,6-tri-O-acetyl-2-deoxy-2-phthalimido-b-D-glucopyranosyl
trichloroacetimidate[16] (6) in the presence of triethylsilyltrifluoromethanesulfonate
(TESOTf) in dichloromethane at –20°C to afford phenyl 3,4,6-tri-O-acetyl-2-deoxy-2-
phthalimido-b-D-glucopyranosyl-(1 ! 3)-2-O-acetyl-6-O-(tert-butyldiphenylsilyl)-1-
thio-b-D-galactopyranoside (7) in 71% yield. Compound 7 has characteristic signals for
a phthalimido group, 4 acetyl groups, TBDPS and C-2 together with anomeric protons
and carbons in the NMR spectra. The formation of the 1 ! 3 linked disaccharide was
confirmed by acetylation of 7, giving a product which showed a downfield shift of
the signal for H-4C from d 4.14 to 5.39 in the corresponding 1H NMR spectrum.
Removal of TBDPS group[17] from 7 using tetrabutylammonium fluoride (TBAF)
in tetrahydrofuran gave 8, which upon treatment with a,a-dimethoxytoluene[18] and 10-
camphorsulphonic acid (CSA) in acetonitrile afforded phenyl 3,4,6-tri-O-acetyl-2-
deoxy-2-phthalimido-b-D-glucopyranosyl-(1 ! 3)-2-O-acetyl-4,6-O-benzylidene-1-thio-
b-D-galactopyranoside (9) in 88% yield. Treatment of 9 with ethylenediamine in 1-
butanol,[19] followed by reaction of the product thus formed with acetic anhydride and
pyridine, gave phenyl 2-acetamido-3,4,6-tri-O-acetyl-2-deoxy-b-D-glucopyranosyl-
(1 ! 3)-2-O-acetyl-4,6-O-benzylidene-1-thio-b-D-galactopyranoside (10) in 89% yield.
Deacetylation of 10 followed by benzoylation of the product afforded the corre-
sponding tetrabenzoate 11. Replacement of the acetyl group with benzoyl was effected
because of the greater stability of the benzoate during the pyruvate acetal formation[20]
involved in the next step. Removal of the benzylidene from 11 gave 12 which was
treated with pyruvic acid methyl ester[20,21] and borontrifluoride etherate in acetonitrile
Scheme 2. a) TESOTf, CH2Cl2, ꢀ30°C, 2 h; b) TBAF, THF, 0°C, 6 h; c) a,a-DMT, CH3CN,
camphorsulfonic acid, 2 h; d) i. n-BuOH, NH2CH2CH2NH2, 90°C, 20 h; ii. Ac2O, pyridine; e) i.
NaOMe, MeOH, 1 h; ii. BzCl, pyridine, 0°C, 4 h; f) 80% AcOH, 70°C, 1 h; g) CH3COCOOMe,
BF3.OEt2, CH3CN, 3 h.

524
Roy and Roy
Scheme 3. a) Hg(OCOCF3)2, H2O, CH2Cl2, 0°C, 12 h; b) CCl3CN, K2CO3, CH2Cl2, 5 h.
to afford phenyl 2-acetamido-3,4,6-tri-O-benzoyl-2-deoxy-b-D-glucopyranosyl-(1 ! 3)-
2-O-benzoyl-4,6-O-[(R)-1-methoxycarbonylethylidene]-1-thio-b-D-galactopyranoside
(13) in 65% yield (Scheme 2) as the 6:1 (R) and (S) mixture from which a reasonable
quantity of pure (R) was separated by repeated column chromatography and utilized for
next step. The structure of 13 was confirmed from its signals for pyruvate acetal,
NHAc and anomeric protons and carbons in its NMR spectra. The (R) configuration of
13 was confirmed[21] from the 13C NMR signal of CH3 group at d 25.8. The cor-
responding (S) configuration of the pyruvate gave CH3 signal at d 18.1.
In a separate experiment, the thioethyl group in the anomeric position of the known
ethyl 4,6-O-benzylidene-2,3-di-O-benzyl-1-thio-a-D-mannopyranoside[22] (14) was re-
moved with mercury(II) trifluoroacetate[23] in moist dichloromethane and the product
15 was transformed into the donor 2,3-di-O-benzyl-4,6-O-benzylidene-a-D-mannopy-
ranosyl trichloroacetimidate[24] (16) with trichloroacetonitrile in the presence of potas-
sium carbonate (Scheme 3). About 10% of b-trichloroacetimidate was also formed as
1
revealed from the H NMR spectrum of the product.
In another experiment, benzylation of 2-(trimethylsilyl)ethyl 3,4-O-isopropylidene-
b-D-galactopyranoside (17) prepared from the known 2-(trimethylsilyl)ethyl b-D-
galactopyranoside[25] gave the dibenzyl derivative which on treatment with 80% acetic
acid afforded 19 with two free hydroxyl groups. Regioselective 4-methoxybenzylation
of 19 via the stannylene derivative[26] afforded 2-(trimethylsilyl)ethyl 2,6-di-O-benzyl-
3-O-(4-methoxybenzyl)-b-D-galactopyranoside (20) (Scheme 4). The NMR spectra of
compound 20 show characteristic signals for OCH3 and OCH2CH2Si as well as the
anomeric proton and carbon.
The mannopyranosyl trichloroacetimidate donor 16 was allowed to react with the
acceptor 20 in dichloromethane at –45°C in the presence of 0.15 equivalent of TESOTf
under inverse condition.[24] Indeed the trichloroacetimidate donor was being added to
Scheme 4. a) BnBr, NaH, DMF, 6 h; b) 80% aq AcOH, 80°C, 1 h; c) i. Bu2SnO, C6H6, reflux,
8 h; ii. 4-Methoxybenzyl chloride, TBAB, 63°C, 6 h.

Synthesis of Blocked Tetrasaccharide
525
Scheme 5. a) TESOTf, CH2Cl2, ꢀ30°C, 2 h; b) NaBH3CN, HCl.OEt2, 0°C, 10 min: c) 13, NIS,
TfOH, ꢀ10°C, 25 min.
the mixture of acceptor and TESOTf, to afford the disaccharide 2-(trimethylsilyl)ethyl
2,3-di-O-benzyl-4,6-O-benzylidene-b-D-mannopyranosyl-(1 ! 4)-2,6-di-O-benzyl-3-O-
(4-methoxybenzyl)-b-D-galactopyranoside (21) in 84% yield with 1:5 ratio of a and b
anomers. The b-anomer could be easily separated from the mixture by column chro-
matography. The structure of 21 was confirmed from the NMR signals characteristic
for benzylidene, OMBn, OSE and the anomeric regions. Moreover, the coupling con-
stants (J1,2 < 0.5 Hz, J2,3 = 3.0 Hz and J3,4 = 10.1 Hz) of the b-mannose residue in
21 support the mannose configuration.[27] Regioselective opening of the benzylidene
ring[26] of 21 afforded the disaccharide acceptor 22 (Scheme 5).
The disaccharide donor 13 was then allowed to react with the disaccharide acceptor
22 in the presense of N-iodosuccinimide (NIS) and trifluoromethanesulfonic acid[28]
(TfOH) in dichloromethane to afford the tetrasaccharide derivative 2-(trimethylsilyl)ethyl
2-acetamido-3,4,6-tri-O-benzoyl-2-deoxy-b-D-glucopyranosyl-(1 ! 3)-2-O-benzoyl-4,
6-O-[(R)-1-methoxycarbonylethylidene]-b-D-galactopyranosyl-(1 ! 4)-2,3,6-tri-O-ben-
zyl-b-D-mannopyranosyl-(1 ! 4)-2,6-di-O-benzyl-3-O-(4-methoxybenzyl)-b-D-galac-
topyranoside (23) in 66% yield (Scheme 5). Compound 23 was characterized, based
on the presence of NMR signals for NHAc, methyl pyruvate, OMBn and anome-
ric regions.
In summary, we have developed a method for the synthesis of the blocked
tetrasaccharide derivative related to the repeating unit of the O-antigen from Shigella
dysenteriae type 9 in the form of its methyl 4,6-(R)-pyruvate ester and 2-(trimeth-
ylsilyl)ethyl glycoside. It is possible to utilize this tetrasaccharide derivative for the
preparation of glycoconjugates.
EXPERIMENTAL
General. All reactions were monitored by TLC on Silica Gel G (E. Merck).
Column chromatography were performed on 100–200 mesh Silica Gel (SRL, India)

526
Roy and Roy
using 15–20 times (by weight) of the crude product. The organic extracts were dried
over anhydrous Na2SO4. All solvents were distilled and/or dried before use and all
evaporations were conducted at or below 40°C under reduced pressure unless stated
otherwise. Optical rotations were measured at 25°C with a Perkin-Elmer 241 MC
polarimeter. The 1H and 13C NMR spectra were recorded with a Bruker DPX 300
spectrometer using CDCl3 as the solvent and tetramethylsilane as internal standard
1
unless otherwise stated. H NMR data of the unassigned signals are not listed. Melting
points were determined in a paraffin oil bath and are uncorrected.
Phenyl 6-O-tert-butyldiphenylsilyl-1-thio- -D-galactopyranoside (2). To a so-
lution of phenyl 1-thio-b-D-galactopyranoside (1) (2.7 g, 9.9 mmol) in pyridine (16
mL), tert-butyldiphenylsilyl chloride (3.8 mL, 14.9 mmol) was added. The reaction
mixture was stirred for 3 h at 25°C, and then concentrated under reduced pressure.
Column chromatography of the residue in 1:1 toluene-EtOAc gave 2 (3.6 g, 73%) as an
25
1
amorphous solid, Rf = 0.5, [a]D ꢀ 13.8 (c 1.0, CHCl3). H NMR: d 7.75–7.26 (m,
15H, aromatic protons), 4.53 (d, 1H, J = 9.6 Hz, H-1), 4.14 (d, 1H, J3,4 = 2.4 Hz, H-4),
3.96 (m, 2H, H-6), 3.72 (t, 1H, J = 9.1 Hz, H-2), 3.05, 2.83 (2 bs, 3H, 3 OH), 1.08 (s,
9H, [Ph2SiC(CH3)3].
Anal. Calcd for C28H34O5SiS: C, 65.84; H, 6.71. Found: C, 65.72; H, 6.69.
Phenyl 6-O-tert-butyldiphenylsilyl-3,4-O-isopropylidene-1-thio- -D-galactopy-
ranoside (3). To a solution of 2 (5 g, 9.8 mmol) in DMF (25 mL), 2,2-
dimethoxypropane (1.80 mL, 14.6 mmol) and 10-camphorsulfonic acid (100 mg) were
added. The mixture was stirred at room temperature for 12 h. The reaction was
quenched with Et3N, concentrated to a syrup which upon column chromatography (3:1
25
toluene-EtOAc), gave 3 (4.2 g, 77.9%) as a foam, Rf = 0.82, [a]D + 7.4 (c 0.7,
1
CHCl3). H NMR: d 7.63–7.14 (m, 15H, aromatic protons), 4.37 (d, 1H, J1,2 = 10.2
Hz, H-1), 4.18 (dd, 1H, J2,3 = 5.4 Hz, J3,4 = 1.3 Hz, H-3), 3.99 (t, 1H, J = 6.7 Hz, H-5),
3.93–3.80 (m, 3H, H-4,H-6), 3.48 (dd, 1H, J2,3 = 7.1 Hz, J1,2 = 10.1 Hz, H-2), 2.72
(bs, 1H, OH), 1.32, 1.24 (2s, 6H, C(CH3)2, 0.98 [s, 9H, (CH3)3CSiPh2]. 13C NMR: d
136.1–128.1 (aromatic carbons), 110.6 [C(CH3)2], 88.6 (C-1), 79.5, 78.3, 77.1, 75.4,
73.7, 63.4 (C-6), 28.6, 26.8 [C(CH3)3], 27.2 [Ph2SiC(CH3)3], 19.6 [Ph2SiC(CH3)3].
Anal. Calcd for C31H38O5SiS: C, 67.60; H, 6.95. Found: C, 67.82; H, 7.12.
Phenyl 2-O-acetyl-6-O-tert-butyldiphenylsilyl-3,4-O-isopropylidene-1-thio- -D-
galactopyranoside (4). To a solution of 3 (4 g, 7.26 mmol) in pyridine (8 mL),
acetic anhydride (5 mL) was added and the mixture was stirred for 3 h. The reaction
mixture was concentrated under vacuum and co-evaporated twice with toluene. Column
chromatography of the syrupy material with 5:1 toluene-EtOAc gave 4 (4 g, 93%),
25
Rf = 0.80, [a]D + 30.3 (c 2.2, CHCl3). 1H NMR: d 7.71–7.21 (m, 15H, aromatic
protons), 5.04 (dd, 1H, J2,3 = 7.3 Hz, J1,2 = 10.2 Hz, H-2), 4.61 (d, 1H, J = 10.3 Hz, H-
1), 4.28 (dd, 1H, J3,4 = 5.1 Hz, J4,5 = 1.3 Hz, H-4), 4.17 (dd, 1H, J2,3 = 7.1 Hz,
J3,4 = 5.5 Hz, H-3), 3.93 (m, 1H, H-5), 2.11 (s, 3H, OCOCH3), 1.50, 1.32 [2 s, 6H,
C(CH3)2], 1.06 [s, 9H, Ph2SiC(CH3)3]; 13C NMR: d 169.8 (OCOCH3), 135.7–125.4
(aromatic carbons), 110.6 [C(CH3)2], 86.2 (C-1), 77.3, 77.1, 73.5, 71.6, 63.0 (C-6),
27.8, 21.6 [C(CH3)3], 26.9 [Ph2SiC(CH3)3], 21.2 (OCOCH3), 19.3 [Ph2SiC(CH3)3].
Anal. Calcd for C33H40O6SiS: C, 66.85; H, 6.80. Found: C, 66.67; H, 6.92.

Synthesis of Blocked Tetrasaccharide
527
Phenyl 2-O-acetyl-6-O-tert-butyldiphenylsilyl-1-thio- -D-galactopyranoside (5).
A solution of 4 (2 g, 3.37 mmol) in 80% acetic acid (20mL) was stirred at 80°C. After
1 h when TLC showed complete conversion, solvents were evaporated off. Column
chromatography with 3:1 toluene-EtOAc gave 5 (1.71 g, 92%) as a foamy product,
25
1
Rf = 0.64, [a]D + 13.6 (c 3.3, CHCl3). H NMR: d 7.65–7.01 (m, 15H, aromatic
protons), 4.97 (t, 1H, J = 9.7 Hz, H-2), 4.54 (d, 1H, J = 10.0 Hz, H-1), 4.04 (d, 1H,
J = 2.0 Hz, H-4), 3.88, 3.87 (2 bs, 2H, H-6), 3.54 (d, 1H, J = 7.6 Hz, H-3), 3.47 (t, 1H,
J = 5.0 Hz, H-5), 3.03, 2.85 (2 bs, 1H, 3-OH, 4-OH), 2.06 (s, 3H, OCOCH3), 0.99 [s,
9H, Ph2SiC(CH3)3]; 13C NMR: d 171.34 (OCOCH3), 136.1–125.7 (aromatic carbons),
86.6 (C-1), 78.3, 74.3, 71.5, 70.3, 64.3 (C-6), 27.2 [Ph2SiC(CH3)3], 21.5 (OCOCH3),
19.6 [Ph2SiC(CH3)3].
Anal. Calcd for C30H36O6SiS: C, 65.18; H, 6.56. Found: C, 64.95; H, 6.78.
Phenyl 3,4,6-tri-O-acetyl-2-deoxy-2-phthalimido- -D-glucopyranosyl-(1 ! 3)-2-
ꢀ
O-acetyl-6-O-tert-butyldiphenylsilyl-1-thio- -D-galactopyranoside (7). To a solu-
˚
tion of 5 (1.07 g, 1.94 mmol) in CH2Cl2 (10 mL) was added 4 A molecular sieve (2.5
g) and stirred for 2 h under N2 at ꢀ30°C. To this solution was added TESOTf (80 mL,
0.35 mmol) and 3,4,6-tri-O-acetyl-2-deoxy-2-phthalimido-b-D-glucopyranose trichloro-
acetimidate (6) (1.35 g, 2.32 mmol) and the reaction mixture was allowed to stir for 30
min at that temperature. The mixture was then diluted with CH2Cl2 (25 mL), filtered
and the filtrate washed successively with saturated NaHCO3 solution and water, dried
(Na2SO4) and concentrated. Column chromatography of the resulting syrup with 10:1
25
toluene-EtOAc gave 7 (1.33 g, 71%) as a white amorphous solid, Rf = 0.70, [a]D
1
+ 18.8 (c 2.0, CHCl3). H NMR: d 7.84–7.73 [m, 4H, N(CO)2C6H4], 7.72–7.16 (m,
15H, aromatic protons), 5.75 (t, 1H, J = 9.2 Hz, H-3D), 5.54 (d, 1H, J = 8.4 Hz, H-1D),
5.15 (t, 1H, J = 9.6 Hz, H-4D), 5.09 (t, 1H, J = 9.7 Hz, H-2C), 4.53 (d, 1H, J = 10.1 Hz,
H-1C), 4.36 (dd, 1H, J1,2 = 8.5 Hz, J2,3 = 10.7 Hz, H-2D), 4.14 (bs, 1H, H-4C), 3.97–
3.85 (m, 3H, H-5D, H-6C), 3.72 (dd, 1H, H-5C), 2.66 (bs, 1H, 4-OH), 2.02, 1.99, 1.84,
1.57 (4 s, 12 H, OCOCH3), 1.05 [s, 9H, Ph2SiC(CH3)3]; 13C NMR: d 171.0, 170.6,
169.8, 169.5 (4 COCH3), 136.1–127.8 (aromatic carbons), 98.8 (C-1D), 87.3 (C-1C),
82.1, 79.1, 78.3, 72.5, 70.8, 69.1, 68.7, 63.5, 62.2 (C-6C, C-6D), 54.8 (C-2D), 27.2
[Ph2SiC(CH3)3], 21.1, 21.0, 20.8, 20.7 (4 COCH3), 19.6 [Ph2SiC(CH3)3].
Anal. Calcd for C50H55O15SiNS: C, 61.90; H, 5.71; N, 1.44. Found: C, 61.65; H,
5.78; N, 1.45.
Phenyl 3,4,6 tri-O-acetyl-2-deoxy-2-phthalimido- -D-glucopyranosyl-(1 ! 3)-2-
ꢀ
O-acetyl-1-thio- -D-galactopyranoside (8). Tetrabutylammonium fluoride (75.3 mg,
0.29 mmol) in THF (0.2 mL) was added to a solution of 7 (380 mg, 0.39 mmol) in
THF (1 mL) at 0°C, then the temperature was slowly raised to 25°C. After 6 h, the
solution was concentrated. Column chromatography of the residue with 1:1 toluene-
25
1
EtOAc gave 8 (202 mg, 74%), Rf = 0.26, [a]D + 26.3 (c 2.4, CHCl3). H NMR: d
7.85–7.72 [m, 4H, N(CO)2C6H4], 7.40–7.14 (m, 5H, aromatic protons), 5.72 (t, 1H,
J = 9.2 Hz, H-3D), 5.56 (d, 1H, J = 8.0 Hz, H-1D), 5.12 (t, 1H, J = 9.6 Hz, H-4D), 5.07
(t, 1H, J = 9.4 Hz, H-2C), 4.57 (d, 1H, J = 9.9 Hz, H-1C), 4.25 (bs, 1H, H-4C), 4.32–
4.17 (m, 2H, H-6D), 3.90 (m, 2H, H-6C), 3.76 (m, 1H, H-5D), 3.58 (t, 1H, J = 5.7 Hz,
H-5C), 2.09, 2.02, 1.84, 1.50 (4 s, 12 H, OCOCH3); 13C NMR: d 170.8, 170.2, 169.4,
169.1 (4 COCH3), 134.5–123.8 (aromatic carbons), 98.4 (C-1D), 86.5 (C-1C), 81.7,

528
Roy and Roy
78.3, 72.1, 70.4, 68.9, 68.5, 62.1, 61.9 (C-6C, C-6D), 54.4 (C-2D), 20.8, 20.6, 20.4, 20.2
(4 COCH3).
Anal. Calcd for C34H37O15NS: C, 58.36; H, 5.32; N, 2.00. Found: C, 58.03; H,
5.50; N, 1.90.
Phenyl 3,4,6-tri-O-acetyl-2-deoxy-2-phthalimido- -D-glucopyranosyl-(1 ! 3)-2-
ꢀ
O-acetyl-4,6-O-benzylidene-1-thio- -D-galactopyranoside (9). To a solution of
8 (200 mg, 0.29 mmol) in dry acetonitrile (1.5 mL) were added at room temperature
benzaldehyde dimethylacetal (51.5 mL, 0.34 mmol) and 10-camphorsulfonic acid (30
mg) and the mixture was allowed to stir for 2 h. The reaction was quenched with Et3N,
and solvents were evaporated under reduced pressure. Column chromatography of the
syrupy product with 3:1 toluene-EtOAc gave 9 (206.2 mg, 88%) as a glassy material,
25
1
Rf = 0.55, [a]D ꢀ 19.5 (c 1.0, CHCl3). H NMR: d 7.83–7.70 [m, 4H, N(CO)2C6H4],
7.49–7.16 (m, 10H, aromatic protons), 5.70 (dd, 1H, J2,3 = 9.2 Hz, J3,4 = 10.7 Hz, H-
3D), 5.57 (d, 1H, J = 8.4 Hz, H-1D), 5.51 (s, 1H, PhCH), 5.17 (t, 1H, J = 9.7 Hz, H-4D),
5.11 (t, 1H, J = 9.7 Hz, H-2C), 4.55 (d, 1H, J = 9.8 Hz, H-1C), 4.35 (m, 2H, H-6D),
4.39 (d, 1H, J = 2.2 Hz, H-4C), 3.85 (m, 2H, H-6C), 3.47 (bs, 1H, H-5C), 2.09, 2.03,
1.82, 1.69 (4 s, 12 H, OCOCH3); 13C NMR: d 170.6, 170.2, 169.4, 168.9 (4 COCH3),
137.7–123.6 (aromatic carbons), 100.9 (CHPh), 99.0 (C-1D), 85.8 (C-1C), 79.4, 75.7,
72.0, 70.6, 70.1, 69.0, 68.8, 68.1 (C-6C), 61.7 (C-6D), 54.4 (C-2D), 20.9, 20.6, 20.6,
20.4 (4 COCH3).
Anal. Calcd for C41H41O15NS: C, 60.06; H, 5.04; N, 1.70. Found: C, 60.26; H,
5.12; N, 1.61.
Phenyl 2-acetamido-3,4,6-tri-O-acetyl-2-deoxy- -D-glucopyranosyl-(1 ! 3)-2-
ꢀ
O-acetyl-4,6-O-benzylidene-1-thio- -D-galactopyranoside (10). To compound 9
(180 mg, 0.22 mmol) dissolved in n-butanol (5 mL) was added to ethylenediamine
(1 mL) under N2 atmosphere. The solution was stirred at 90°C for 20 h. Solvents were
removed under reduced pressure by co-evaporation twice with toluene to give a yellow
syrup. Acetic anhydride (2 mL) and pyridine (2 mL) were then added and stirring was
continued at rt. After 14 h, the solution was concentrated to a syrup, which was purified
by column chromatography using 1:1 toluene-EtOAc to give 10 (143 mg, 89%) as a
25
1
thick glass, Rf = 0.21, [a]D ꢀ 1.5 (c 1.1, CHCl3). H NMR: d 7.60–7.15 (m, 10H,
aromatic protons), 5.73 (t, 1H, J2,3 = J3,4 = 9.9 Hz, H-3D), 5.70 (bs, 1H, NHCOCH3),
5.48 (s, 1H, PhCH), 5.28 (d, 1H, J = 8.1 Hz, H-1D), 5.23 (t, 1H, J3,4 = J4,5 = 9.7 Hz, H-
4D), 4.97 (t, 1H, J1,2 = J2,3 = 9.8 Hz, H-2C), 4.58 (d, 1H, J = 9.8 Hz, H-1C), 4.26 (bs,
1H, H-4C), 4.21 (m, 2H, H-6D), 3.12 (m, 1H, H-5C), 2.35 (s, 3H, NHCOCH3), 2.13,
2.07, 2.01, 1.98 (4 s, 12 H, OCOCH3); 13C NMR: d 170.9 (NHCOCH3), 170.6, 170.0,
169.7, 169.7 (4 COCH3), 137.9–125.3 (aromatic carbons), 101.3 (CHPh), 99.6 (C-1D),
85.4 (C-1C), 78.2, 76.0, 71.7, 70.6, 70.1, 69.2, 69.1, 68.2(C-6C), 62.0 (C-6D), 56.9
(C-2D), 23.3 (NHCOCH3), 21.3, 20.9, 20.7, 20.6 (4 COCH3).
Anal. Calcd for C35H41O14NS: C, 57.44; H, 5.64; N, 1.91. Found: C, 57.60; H,
5.81; N, 1.77.
Phenyl 2-acetamido-3,4,6-tri-O-benzoyl-2-deoxy- -D-glucopyranosyl-(1 ! 3)-2-
ꢀ
O-benzoyl-4,6-O-benzylidene-1-thio- -D-galactopyranoside (11). To a solution of
10 (140 mg, 0.19 mmol) in dry methanol (4.5 mL), 0.5M methanolic NaOMe (0.5 mL)

Synthesis of Blocked Tetrasaccharide
529
was added. After 1 h at 25°C, the solution was neutralized with Dowex 50 (H+) resin,
filtered and the filtrate was concentrated to dryness to give the de-O-acetylated product
in quantitative yield. To a stirred solution of the product in pyridine (800 mL), benzoyl
chloride (110 mL, 0.95 mmol) was added at 0°C and the mixture was allowed to stir for
4 h. Excess benzoyl chloride was then decomposed by the addition of water (1 mL).
Stirring was continued for another 30 min. The mixture was then concentrated under
vacuum to a small volume, diluted with CH2Cl2, washed successively with a saturated
aq NaHCO3 solution and water. The organic layer was collected, dried (Na2SO4) and
concentrated. Column chromatography of the residue with 5:1 toluene-EtOAc gave
25
1
pure 11 (145.5 mg, 93%) as a thick glass, Rf = 0.85, [a]D + 1.3 (c 0.8, CHCl3). H
NMR: d 8.14–7.19 (m, 30H, aromatic protons), 6.10 (t, 1H, J2,3 = J3,4 = 9.8 Hz, H-3D),
5.56 (d, 1H, J = 7.3 Hz, H-1D), 5.48 (t, 1H, J = 9.8 Hz, H-4D), 5.46 (t, 1H, J = 8.0 Hz,
H-2C), 5.38 (s, 1H, PhCH), 4.73 (d, 1H, J = 9.8 Hz, H-1C), 4.41 (d, 1H, J = 3.1 Hz, H-
4C), 4.11 (m, 1H, H-5D), 2.35 (s, 3H, NHCOCH3); 13C NMR: d 171.8 (NHCOCH3),
166.0, 165.7, 165.3, 165.0 (4 COC6H5), 133.8–126.7 (aromatic carbons), 101.1
(CHPh), 100.8 (C-1D), 85.3 (C-1C), 80.4, 75.9, 71.9, 71.2, 70.2, 69.8, 68.9, 68.5 (C-6C),
62.5 (C-6D), 56.9 (C-2D), 22.3 (NHCOCH3).
Anal. Calcd for C55H49O14NS: C, 67.40; H, 5.03; N, 1.42. Found: C, 67.27; H,
5.27; N, 1.37.
Phenyl 2-acetamido-3,4,6-tri-O-benzoyl-2-deoxy- -D-glucopyranosyl-(1 ! 3)-2-
ꢀ
O-benzoyl-1-thio- -D-galactopyranoside (12). A solution of 11 (105 mg, 0.11 mmol)
in 80% acetic acid (1.05 mL) was heated at 70°C for 1 h. Solvents were evaporated off.
Column chromatography of the residue with 2:1 toluene-EtOAc gave 12 (77.4 mg,
25
81%), Rf = 0.44, [a]D ꢀ 1.0 (c 1.5, CHCl3). 1H NMR: d 7.99–7.15 (m, 25H,
aromatic protons), 5.77 (d, 1H, J = 8.9 Hz, NHCOCH3), 5.76 (t, 1H, J = 10.8 Hz, H-
3D), 5.45 (t, 1H, J = 9.9 Hz, H-4D), 5.41 (t, 1H, J = 9.7 Hz, H-2C), 5.20 (d, 1H, J = 8.1
Hz, H-1D), 4.79 (d, 1H, J = 10.1 Hz, H-1C), 4.58 (dd, 1H, J2,3 = 12.3 Hz, J3,4 = 2.7 Hz,
H-3C), 4.24 (d, 1H, J = 2.7 Hz, H-4C), 4.05 (m, 1H, H-5D), 3.84 (m, 1H, H-5C), 1.13 (s,
3H, NHCOCH3); 13C NMR: d 171.5 (NHCOCH3), 166.6, 166.5, 165.7, 165.6 (4
COC6H5), 133.9–128.2 (aromatic carbons), 101.3 (C-1D), 87.0 (C-1C), 82.6, 78.4, 72.5,
72.1, 70.1, 69.9, 69.3, 63.1, 62.8 (C-6C, C-6D), 56.3 (C-2D), 22.7 (NHCOCH3).
Anal. Calcd for C48H45O14NS: C, 64.63; H, 5.08; N, 1.57. Found: C, 64.50; H,
4.90; N, 1.40.
Phenyl 2-acetamido-3,4,6-tri-O-benzoyl-2-deoxy- -D-glucopyranosyl-(1 ! 3)-2-
ꢀ
O-benzoyl-4,6-O-[(R)-1-methoxycarbonylethylidene]-1-thio- -D-galactopyranoside
(13). To a solution 12 (100 mg, 0.11 mmol) in acetonitrile (0.3 mL), BF3ꢁ OEt2 (28.4
mL, 0.22 mmol) and methyl pyruvate (20.3 mL, 0.22 mmol) were added, and the mixture
was stirred under N2 for 3 h at room temperature. The reaction mixture was then diluted
with CH2Cl2 and poured into an aq NaHCO3 solution. The organic layer was separated
and the aqueous layer was extracted twice with CH2Cl2. Concentration of the combined
organic layers gave a foamy product which on chromatography with 1:1 toluene-EtOAc
25
afforded 13 (47.6 mg, 45%), Rf = 0.72, [a]D ꢀ 30.8 (c 0.5, CHCl3) together with 25
1
mg of the corresponding (R) and (S) mixture. H NMR of 13: d 8.00–7.20 (m, 25H,
aromatic protons), 5.82 (t, 1H, J = 9.9 Hz, H-3D), 5.75 (d, 1H, J = 8.3 Hz, NHCOCH3),
5.41 (t, 1H, J = 9.7 Hz, H-4D), 5.38 (t, 1H, J = 9.4 Hz, H-2C), 5.27 (d, 1H, J = 8.2 Hz,

530
Roy and Roy
H-1D), 4.63 (d, 1H, J = 9.7 Hz, H-1C), 4.32 (d, 1H, J = 2.7 Hz, H-4C), 4.08 (m, 1H, H-5D),
3.72 (s, 3H, COOCH3), 1.47 (s, 3H, NHCOCH3), 1.22 [s, 3H, C(CH3)COOCH3]; 13C
NMR: d 170.1 (NHCOCH3),169.1 (COOCH3) 164.9, 164.8, 164.3, 164.1 (4 COC6H5),
135.7–127.0 (aromatic carbons), 100.3 [C(CH3)COOCH3], 97.4 (C-1D), 84.7 (C-1C),
79.3, 71.1, 71.0, 70.8, 70.3, 69.1, 68.1, 67.1, 67.0, 64.2, 62.5 (C-6C, C-6D), 54.8 (C-2D),
51.6 (COOCH3), 25.8 [C(CH3)COOCH3], 22.5 (NHCOCH3).
Anal. Calcd for C52H49O16NS: C, 63.99; H, 5.06; N, 1.43. Found: C, 63.80; H,
5.28; N, 1.56.
2,3-Di-O-benzyl-4,6-O-benzylidene- , -D-mannopyranose (15). To a stirred so-
lution of ethyl 2,3-di-O-benzyl-4,6-O-benzylidene-1-thio-a-D-mannopyranoside (14)
(1.1 g, 2.23 mmol) in CH2Cl2 (14.38 mL), water (360 mL) and (CF3CO2)2Hg (1.04 g,
2.45 mmol) were added at 0°C. The mixture was stirred at rt for 12 h. The contents
were then diluted with CH2Cl2 and filtered through a Celite bed. The organic layer was
washed successively with water, 5% KI solution and water, dried (Na2SO4) and
concentrated. Column chromatography with 3:1 toluene:EtOAc gave 15 (715 mg, 71
25
1
%), Rf = 0.62, [a]D ꢀ 9.2 (c 0.6, CHCl3). H NMR : d 7.54–7.25 (m, 15H, aromatic
protons), 5.65 (s, 1H, CHC6H5).
Anal. Calcd for C27H28O6: C, 72.30; H, 6.29. Found: C, 72.05; H, 6.19.
2,3-Di-O-benzyl-4,6-O-benzylidene- , -D-mannopyranosyl trichloroacetimidate
(16). To a solution of 15 (700 mg, 1.56 mmol) in CH2Cl2 (7 mL) was added K2CO3
(775 mg) and trichloroacetonitrile (782 mL) and the mixture was vigorously stirred for
5 h at room temperature under N2. The mixture was filtered through a Celite bed,
washed with CH2Cl2, dried (Na2SO4), and concentrated to a syrup. Column chro-
matography with 1:1 petroleum ether (60–80°C)-EtOAc (containing 0.1% triethyl-
25
1
amine) gave 16 (675 mg, 73%) as a foam, Rf = 0.90, [a]D + 72.5 (c 1.5, CHCl3). H
NMR (a-isomer): d 8.67 [s, 1H, OCNHCCl3], 7.51–7.25 (m, 15H, aromatic protons),
1
5.83 (s, 1H, H-1), 5.62 (s, 1H, CHC6H5), 3.52 (m, 1H, H-5); H NMR (b-isomer): 8.57
[s, 1H, OCNHCCl3], 7.51–7.25 (m, 15H, aromatic protons), 6.26 (s, 1H, H-1), 5.66 (s,
1H, CHC6H5), 3.52 (m, 1H, H-5).
Anal. Calcd for C29H28O6NCl3: C, 58.74; H, 4.75; N, 2.36. Found: C, 58.56; H,
4.97; N, 2.18.
2-(Trimethylsilyl)ethyl 3,4-O-isopropylidene- -D-galactopyranoside (17). To a
solution of 2-(trimethylsilyl)ethyl b-D-galactopyranoside[24] (3.8 g, 13.6 mmol) in DMF
(3mL), 2,2-dimethoxypropane (2.5 mL, 20.3 mmol) was added followed by the addition
of 10-camphorsulfonic acid (100 mg). The reaction was conducted as described for
compound 3 and monitored by TLC (3:1 toluene-EtOAc), giving 17 (2.7 g, 63.8%) as a
syrup, Rf = 0.46, [a]D25 + 5.3 (c 3.8, CHCl3). 1H NMR: d 4.03 (d, 1H, J = 8.3 Hz, H-1),
3.99 (dd, 1H, J2,3 = 5.6 Hz, J3,4 = 1.8 Hz, H-3), 3.69 [m, 2H, OCH2CH2Si(CH3)3], 3.45–
3.31 (m, 2H, H-5, H-6), 2.62, 2.25 (2 bs, 2H, 2-OH, 6-OH), 1.34, 1.17 [2 s, 6H, C(CH3)2],
0.83 [m, 2H, OCH2CH2Si(CH3)3], ꢀ 0.15 [s, 9H, OCH2CH2Si(CH3)3]. 13C NMR: d 110.8
[C(CH3)2], 102.2 (C-1), 79.3, 74.3, 74.0, 73.8, 67.7 [OCH2CH2Si(CH3)3], 62.7 (C-6),
28.5, 26.8 [C(CH3)2], 18.7 [OCH2CH2Si(CH3)3], ꢀ 1.0 [OCH2CH2Si(CH3)3].
Anal. Calcd for C14H28O6Si: C, 52.47; H, 8.80. Found: C, 52.65; H, 8.61.

Synthesis of Blocked Tetrasaccharide
531
2-(Trimethylsilyl)ethyl 2,6-di-O-benzyl-3,4-O-isopropylidene- -D-galactopyra-
noside (18). To a cold solution of 17 (2.5 g, 7.8 mmol) in DMF (10 mL), NaH
(1.87 g, 39.0 mmol) and benzyl bromide (2.8 mL, 23.4 mmol) were added. The mixture
was stirred at room temperature for 3 h. The reaction was quenched with MeOH, diluted
with water and repeatedly extracted with ether. The organic layer was washed with water,
dried (Na2SO4), and concentrated. Column chromatography with 8:1 toluene-EtOAc gave
18 (3.38 g, 86.7%) as a thick syrup, Rf = 0.71, [a]D25 + 18.5 (c 2.7, CHCl3). 1H NMR: d
7.24–7.05 (m, 10H, aromatic protons), 4.69 (2d, 2H, J = 11.8 Hz, CH2Ph), 4.46 (2d, 2H,
J = 11.8 Hz, CH2Ph), 4.12 (d, 1H, J = 8.0 Hz, H-1), 3.24 (m, 1H, H-5), 1.21, 1.18 [2s, 6H,
C(CH3)2], 0.90 (t, 2H, J = 8.4 Hz, OCH2CH2SiMe3), ꢀ0.15 [s, 9H, OCH2CH2Si(CH3)3].
13C NMR: d 138.8–127.9 (aromatic carbons), 110.3 [C(CH3)2], 102.8 (C-1), 80.2, 79.5,
74.3, 74.1, 74.0, 72.6, 70.1 (OCH2CH2SiMe3), 67.6 (C-6), 28.2, 26.8 [C(CH3)2], 18.9
(OCH2CH2SiMe3), ꢀ1.5 [OCH2CH2Si(CH3)3].
Anal. Calcd for C28H40O6Si: C, 67.16; H, 8.05. Found: C, 67.30; H, 7.88.
2-(Trimethylsilyl)ethyl 2,6-di-O-benzyl- -D-galactopyranoside (19). A solution
of 18 (2.4 g, 4.79 mmol) in 80% aq acetic acid (24 mL) was heated at 80°C for 1 h.
Solvents were then evaporated off. Column chromatography with 3:1 toluene-EtOAc
25
1
gave 19 (2.04 g, 92.8%) as a syrup, Rf = 0.42, [a]D + 5.2 (c 3.0, CHCl3). H NMR: d
7.31–7.18 (m, 10H, aromatic protons), 4.89, 4.62 (2d, 2H, J = 11.5 Hz, CH2Ph), 4.49
(s, 2H, CH2Ph), 4.29 (d, 1H, J = 7.3 Hz, H-1), 3.94 (dd, 1H, J1,2 = 7.0 Hz, J2,3 = 10.7 Hz,
H-2), 3.83 (d, 1H, J = 2.4 Hz, H-4), 3.67 [m, 2H, OCH2CH2Si(CH3)3], 2.89 (bs, 2H, 3-OH,
4-OH), 0.96 [m, 2H, OCH2CH2Si(CH3)3], ꢀ0.04 [s, 9H, OCH2CH2Si(CH3)3]. 13C NMR:
d 138.6–127.5 (aromatic carbons), 110.0 (CMe2), 103.1 (C-1), 79.3, 74.5, 73.5, 73.3, 73.2,
69.4, 69.0 (2CH2Ph), 67.3 (C-6), 18.5 [OCH2CH2Si(CH3)3], ꢀ1.5 [OCH2CH2Si(CH3)3].
Anal. Calcd for C25H36O6Si: C, 65.18; H, 7.87. Found: C, 65.02; H, 7.65.
2-(Trimethylsilyl)ethyl 2,6-di-O-benzyl-3-O-(4-methoxybenzyl)- -D-galactopyr-
anoside (20). To a solution of 19 (1.1 g, 2.38 mmol) in benzene (50 mL), and
Bu2SnO (653 mg, 2.6 mmol) was added and the mixture was refluxed for 8 h in a
Dean-Stark apparatus. The solution was cooled, 4-methoxybenzyl chloride (387 mL,
2.86 mmol) and Bu4NBr (920 mg, 2.86 mmol) were added, and the reaction was
allowed to continue at 63°C for 6 h. The benzene solution was concentrated, MeOH
was added and the mixture was kept at –5°C for 2 h. The tin compound precipitated
out and filtered off. The filtrate was concentrated and the syrupy product was purified
by column chromatography with 4:1 toluene-EtOAc to afford 20 (1.02 g, 74.5%) as a
glass, Rf = 0.65, [a]D ꢀ 1.1 (c 1.7, CHCl3). 1H NMR: d 7.22–7.09 (m, 10H, aromatic
25
protons), 7.07, 6.65 (2 d, 4H, J = 6.7 Hz, CH2C6H4OCH3), 4.72, 4.53 (2d, 2H, J = 11.0
Hz, CH2Ph), 4.46 (s, 2H, CH2C6H4OCH3), 4.38 (s, 2H, CH2Ph), 4.16 (d, 1H, J = 7.7
Hz, H-1), 3.78 (d, 1H, J = 3.4 Hz, H-4), 3.58 [s, 3H, CH2C6H4OCH3), 3.65–3.51 [m,
2H, OCH2CH2Si(CH3)3], 3.38 (m, 3H, H-5, H-6), 0.87 [t, 2H, J = 8.4 Hz,
OCH2CH2Si(CH3)3], ꢀ0.15 [s, 9H, OCH2CH2Si(CH3)3]; 13C NMR: d 159.3–113.8
(aromatic carbons), 103.1 (C-1), 80.2, 79.0, 75.1, 73.6, 73.1, 71.9, 69.2, 67.2 (CH2Ph),
66.8 (C-6), 55.2 (CH2C6H4OCH3), 18.4 [OCH2CH2Si(CH3)3], ꢀ1.5 [OCH2CH2-
Si(CH3)3].
Anal. Calcd for C33H44O7Si: C, 68.24; H, 7.63. Found: C, 68.10; H, 7.59.

532
Roy and Roy
2-(Trimethylsilyl)ethyl 2,3-di-O-benzyl-4,6-O-benzylidene- -D-mannopyrano-
syl-(1 ! 4)-2,6-di-O-benzyl-3-O-(4-methoxybenzyl)- -D-galactopyranoside
ꢀ
(21). To a solution of the acceptor 20 (180 mg, 0.31 mmol) in CH2Cl2 (1.6 mL) was
˚
added 4 A molecular sieves (300 mg) and the suspension stirred for 2 h at ꢀ30°C. To
this mixture was added TESOTf (12.6 mL, 0.06 mmol) and the trichloroacetimidate
donor 16 (220 mg, 0.73 mmol) and the solution was allowed for stir for 30 min at that
temperature. The reaction mixture was then diluted with CH2Cl2 (25 mL) and washed
successively with saturated NaHCO3 and water. The organic phase was collected, dried
(Na2SO4) and concentrated to a syrup. Column chromatography of the residue with
25
10:1 toluene-EtOAc gave pure disaccharide 21 (223 mg, 70%), Rf = 0.66, [a]D ꢀ23.5
25
(c 2.0, CHCl3) together with 45 mg (14%) of the corresponding a anomer (21a), [a]D
1
+ 126.5 (c 0.7, CHCl3). H NMR of 21: d 7.33–7.05 (m, 25H, aromatic protons), 6.97,
6.61 (2d, 4H, J = 8.4 Hz, CH3OC6H4CH2), 5.41 (s, 1H, CHC6H5), 4.76 (d, 1H, J = 3.0
Hz, H-2B), 4.78, 4.67 (2d, 2H, J = 12.4 Hz,CH2Ph), 4.77, 4.52 (2d, 2H, J = 11.0
Hz,CH2Ph), 4.53, 4.33 (2d, 2H, J = 11.2 Hz,CH2Ph), 4.59 (bs, 1H, H-1B), 4.36 (s, 2H,
CH3OC6H4CH2 ), 4.21 (d, 1H, J = 7.6 Hz, H-1A), 3.85 (dd, 1H, J2,3 = 3.0 Hz,
J3,4 = 10.1 Hz, H-3B) 3.54 (s, 3H, CH2C6H4OCH3), 3.50 [m, 2H, OCH2CH2Si(CH3)3],
0.88 [m, 2H, OCH2CH2Si(CH3)3], ꢀ0.15 [s, 9H, OCH2CH2Si(CH3)3]; 13C NMR: d
138.6–125.9 (aromatic carbons), 103.3 (C-1A), 102.3 (C-1B), 101.2 (CHPh), 81.5, 79.3,
78.3, 78.2, 75.1, 74.9, 74.3, 73.3, 73.3, 73.2, 73.1, 71.9, 69.4, 68.4 (OCH2CH2SiMe3),
67.5, 67.1 (C-6A, C-6B), 55.1 (CH2C6H4OCH3), 18.4 (OCH2CH2SiMe3), ꢀ1.5
[OCH2CH2Si(CH3)3]. 1H NMR of 21a: d 7.35–6.62 (m, 25H, aromatic protons),
6.99, 6.63 (2d, 4H, J = 8.2 Hz, CH2C6H4OMe), 5.45 (s, 1H, CHPh), 4.68 (bs, 1H, H-
1B), 4.16 (d, J = 7.6 Hz, H-1A), 3.59 (s, 3H, C6H4OCH3), 0.74 (m, 2H,
OCH2CH2SiMe3), ꢀ0.18 [s, 9H, OCH2CH2Si(CH3)3]; 13C NMR: d 159.0, 138.2–
126.0 (aromatic carbons), 103.7 (C-1A), 101.1 (CHPh), 101.0 (C-1B), 79.5, 79.2, 78.7,
77.0, 74.9, 74.3, 73.8, 73.6, 73.2, 72.6, 72.2, 72.1, 72.1, 68.8, 68.0, 64.4 (C-6A, C-6B),
55.1 (CH2C6H4OCH3), 18.5 (OCH2CH2SiMe3), ꢀ1.5 [OCH2CH2Si(CH3)3].
Anal. Calcd for: C60H70O12Si (21): C, 71.26; H, 6.97; Found: C, 71.08; H, 7.10.
2-(Trimethylsilyl)ethyl 2,3,6-tri-O-benzyl- -D-mannopyranosyl-(1 ! 4)-2,6-di-
ꢀ
O-benzyl-3-O-(4-methoxybenzyl)- -D-galactopyranoside (22). To a vigorously
stirred suspension of 21 (180 mg, 0.18 mmol) and NfsaBH3CN (100 mg, 1.60 mmol)
˚
in THF (5 mL) containing 3 A molecular sieves (100 mg), a saturated ethereal HCl
solution was added dropwise at 0°C until the solution was acidic and evolution of H2
ceased. The solution was stirred for another 10 min, when TLC indicated almost total
conversion of the starting material. The reaction mixture was diluted with CH2Cl2 and
filtered through a Celite bed. The filtrate was washed successively with water, saturated
aq NaHCO3 (3 ꢂ 30 mL) and water. The organic phase was dried (Na2SO4), con-
centrated and column chromatographed with 10:1 toluene-EtOAc to give 22 (126.3 mg,
25
1
70.0%) as a thick syrup, Rf = 0.40, [a]D ꢀ 30.3 (c1.3, CHCl3). H NMR: d 7.38–
7.03 (m, 25H, aromatic protons), 7.00, 6.62 (2d, 4H, J = 8.4 Hz, CH3OC6H4CH2),
4.57 (s, 1H, H-1B), 4.59 (d, 2H, J = 11.7 Hz,CH2Ph), 4.51 (d, 1H, J = 11.7 Hz,
CH2Ph), 4.38 (d, 1H, J = 11.8 Hz,CH2Ph), 4.31 (d, 1H, J = 11.8 Hz,CH2Ph), 4.32 (s,
2H CH3OC6H4CH2), 4.22 (d, 1H, J = 7.4 Hz, H-1A), 3.94 (bs, 1H, H-4A), 3.61[m, 2H,
OCH2CH2Si(CH3)3], 3.54 (s, 3H, CH3OC6H4CH2 ), 3.15 (m, 1H, H-5A), 3.09 (dd, 1H,
J = 2.4 Hz, J = 9.4Hz, H-5B), 2.47 [bs, 1H, 4-OH), 0.89 [m, 2H, OCH2CH2-

Synthesis of Blocked Tetrasaccharide
533
Si(CH3)3)], ꢀ0.15 [s, 9H, OCH2CH2Si(CH3)3]; 13C NMR: d 159.4 (CH2C6H4OCH3),
139.0–127.4 (aromatic carbons), 103.5 (C-1A), 102.0 (C-1B), 81.9, 81.6, 79.6, 75.5,
75.1, 73.9, 73.8, 73.7, 73.5, 73.1, 72.7, 71.1, 70.9, 70.3 (OCH2CH2SiMe3), 68.4, 67.4,
(C-6A, C-6B), 55.3 (CH2C6H4OCH3), 18.6 [OCH2CH2Si(CH3)3], ꢀ1.3 [OCH2CH2-
Si(CH3)3].
Anal. Calcd for: C60H72O12Si: C, 71.11; H, 7.16. Found: C, 70.95; H, 7.34.
2-(Trimethylsilyl)ethyl 2-acetamido-3,4,6-tri-O-benzoyl-2-deoxy- -D-glucopy-
ranosyl-(1 ! 3)-2-O-benzoyl-4,6-O-[(R)-1-methoxycarbonylethylidene]- -D-galacto-
ꢀ
pyranosyl-(1 ! 4)-2,3,6-tri-O-benzyl- -D-mannopyranosyl-(1 ! 4)-2,6-di-O-ben-
ꢀ
ꢀ
zyl-3-O-(4-methoxybenzyl)- -D-galactopyranoside (23). To a solution of the donor
13 (112 mg, 0.12 mmol) and the acceptor 22 (100 mg, 0.10 mmol) in dry CH2Cl2 (3
˚
mL), 4 A molecular sieves (300 mg) was stirred under N2 for 2 h. The mixture was
then cooled to ꢀ10°C, NIS (34.5 mg, 0.15 mmol) and TfOH (1.5 mL, 0.01 mmol) were
added, and the mixture was allowed to stir for 25 min at this temperature. The reaction
mixture was then diluted with CH2Cl2 (25 mL) and filtered through a Celite bed. The
filtrate was washed successively with 10% aq Na2S2O3, saturated aq NaHCO3 and
water, dried (Na2SO4) and concentrated. Column chromatography of the resulting
syrupy product with 3:1 toluene-EtOAc gave 23 (122.4 mg, 66%) as a foam, Rf = 0.63,
25
1
[a]D ꢀ2.5 (c 0.6, CHCl3). H NMR: d 7.84–7.04 (m, 45H, aromatic protons), 6.95,
6.63, (2d, 4H, J = 8.4 Hz, CH3OC6H4CH2), 5.70 (t, 1H, J = 9.9 Hz, H-3D), 5.14 (d, 1H,
J = 8.2 Hz, H-1C), 4.71 (bs, 1H, H-1B), 4.56 (d, 1H, J = 7.9 Hz, H-1A), 4.07 (d, 1H,
J = 3.4 Hz, H-4C), 3.75 (d, 1H, J = 3.3 Hz, H-4A), 3.60 (s, 3H CH3OC6H4CH2), 3.55
(s, 3H, COOCH3), 1.44 (s, 3H, NHCOCH3), 1.10 [s, 3H, C(CH3)COOCH3], 0.89 [m,
2H, OCH2CH2Si(CH3)3], ꢀ0.15 [s, 9H, OCH2CH2Si(CH3)3]; 13C NMR: d 170.6
(COOCH3), 170.2 (NHCOCH3), 165.9, 165.8, 165.1, 165.0 (4 COC6H5), 138.8–126.6
(aromatic carbons), 103.2 (C-1A), 101.6 (C-1C), 101.4 (C-1B), 100.9 [C(CH3)COOCH3],
98.3 (C-1D), 81.1, 79.4, 78.7, 75.4, 75.2, 74.9, 73.7, 73.6, 73.2, 73.0, 72.9, 72.7, 71.9,
71.7, 71.2, 70.6, 70.3 (CH2), 70.2, 69.9, 69.3 (OCH2CH2SiMe3), 69.0, 67.1 (one CH2 of
C-6), 66.9, 65.4, 64.7, 63.3 (three CH2 of C-6), 55.7 (CH2C6H4OCH3), 55.2
(COOCH3), 52.4 (C-2D), 25.8 [C(CH3)COOCH3], 22.3 (NHCOCH3), 18.4 [OCH2CH2
Si(CH3)3], ꢀ1.5 [OCH2CH2Si(CH3)3]. DEPT (135) Spectrum of 23: d 103.2 (C-1A),
101.6 (C-1C), 101.4 (C-1B),100.8 (C-1D), 81.1, 79.4, 78.7, 75.5, 75.1 (5 CH carbons),
74.9 (CH2), 73.7, 73.5 (2 CH carbons), 73.2, 73.1 (2 CH2 carbons), 72.9, 72.8 (2 CH
carbons), 72.7 (CH2), 71.9, 71.7 (2 CH carbons), 71.1 (CH2), 70.5 (CH), 70.3 (CH2),
69.8, 69.7 (2 CH carbons), 69.0 (OCH2CH2SiMe3), 67.5 (CH), 67.1 (one CH2 of C-6),
65.4 (CH), 65.1, 64.7, 63.3 (three CH2 of C-6), 55.7 (CH2C6H4OCH3), 55.1
(COOCH3), 52.4 (C-2D), 25.8 [C(CH3)COOCH3], 22.3 (NHCOCH3), 18.4 [OCH2CH2
Si(CH3)3], ꢀ1.5 [OCH2CH2Si(CH3)3].
Anal. Calcd for: C106H115O28NSi: C, 67.75; H, 6.16; N, 0.75. Found: C, 67.49; H,
6.02; N, 0.73.
ACKNOWLEDGMENT
Financial support from the Department of Science and Technology, New Delhi,
India (Project No. SP/S1/G14/95) is thankfully acknowledged.

534
Roy and Roy
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Received February 11, 2003
Accepted June 17, 2003