Synthesis of the blocked pentasaccharide derivative related to the repeating unit of the O-antigen from Shigella dysenteriae type 3 in the form of its allyl glycoside

Article abstract of DOI:10.1081/CAR-120023471

Starting from D-galactosamine hydrochloride, D-galactose and D-glucose, the tetrasaccharide derivative allyl 2,3,6-tri-O-benzyl-4-O-[methyl (R)-2-propanoate]-β-D-glucopyranosyl-(1→6)-2,3, 4-tri-O-benzyl-α-D-glucopyranosyl-(1→4)-2,6-di-O-benzyl-3-O-(3,4, 6-tri-O-acetyl-2-deoxy-2-phthalimido-β-D-galactopyranosyl) -α-D-galactopyranoside has been synthesized via block synthesis strategy, with one of the blocks containing a methyl (R)-2-propanoate group. Manipulation of protecting groups of this tetrasaccharide derivative followed by its reaction with a galactofuranoside donor afforded the desired pentasaccharide derivative in the form of its allyl glycoside related to the reapeating unit of Shigella dysenteriae type 3.

Full text of DOI:10.1081/CAR-120023471

Journal of Carbohydrate Chemistry
ISSN: 0732-8303 (Print) 1532-2327 (Online) Journal homepage: http://www.tandfonline.com/loi/lcar20
Synthesis of the Blocked Pentasaccharide
Derivative Related to the Repeating Unit of the
O‐Antigen from Shigella dysenteriae Type 3 in the
Form of Its Allyl Glycoside
Sujit Kumar Sarkar & Nirmolendu Roy
To cite this article: Sujit Kumar Sarkar & Nirmolendu Roy (2003) Synthesis of the Blocked
Pentasaccharide Derivative Related to the Repeating Unit of the O‐Antigen from Shigella
dysenteriae Type 3 in the Form of Its Allyl Glycoside, Journal of Carbohydrate Chemistry, 22:5,
285-296, DOI: 10.1081/CAR-120023471
To link to this article: http://dx.doi.org/10.1081/CAR-120023471
Published online: 16 Aug 2006.
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Date: 03 November 2015, At: 03:55

JOURNAL OF CARBOHYDRATE CHEMISTRY
Vol. 22, No. 5, pp. 285–296, 2003
Synthesis of the Blocked Pentasaccharide Derivative
Related to the Repeating Unit of the O-Antigen
from Shigella dysenteriae Type 3 in the
Form of Its Allyl Glycoside
*
Sujit Kumar Sarkar and Nirmolendu Roy
Department of Biological Chemistry, Indian Association for the Cultivation of
Science, Jadavpur, Calcutta, India
ABSTRACT
Starting from D-galactosamine hydrochloride, D-galactose and D-glucose, the
tetrasaccharide derivative allyl 2,3,6-tri-O-benzyl-4-O-[methyl (R)-2-propanoate]-b-
D-glucopyranosyl-(1!6)-2,3,4-tri-O-benzyl-a-D-glucopyranosyl-(1!4)-2,6-di-O-
benzyl-3-O-(3,4,6-tri-O-acetyl-2-deoxy-2-phthalimido-b-D-galactopyranosyl)-a-D-
galactopyranoside has been synthesized via block synthesis strategy, with one of the
blocks containing a methyl (R)-2-propanoate group. Manipulation of protecting
groups of this tetrasaccharide derivative followed by its reaction with a galactofurano-
side donor afforded the desired pentasaccharide derivative in the form of its allyl
glycoside related to the reapeating unit of Shigella dysenteriae type 3.
Key Words: Synthesis; Pentasaccharide repeating unit; Shigella dysenteriae type 3.
*
Correspondence: Nirmolendu Roy, Department of Biological Chemistry, Indian Association for
the Cultivation of Science, Jadavpur, Calcutta 700 032, India; E-mail: bcnr@mahendra.iacs.res.in
or nirmolendu@yahoo.com.
285
DOI: 10.1081/CAR-120023471
0732-8303 (Print); 1532-2327 (Online)
www.dekker.com
Copyright D 2003 by Marcel Dekker, Inc.

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Sarkar and Roy
INTRODUCTION
Shigella dysenteriae type 3 is a gram-negative pathogen responsible for many
intestinal diseases including dysentery. Resistance of this pathogen to antimicrobial
drugs necessitates the exploration of other approaches for controlling the diseases it
causes.[1] There are reports of the successful use of protein conjugates of synthetic
oligosaccharides as vaccines against many bacterial infections.[2] It is, therefore, rea-
sonable to explore this approach for the preparation of vaccines against Shigella
dysenteria type 3. Synthesis of oligosaccharides related to the antigen from Shigella
dysenteriae types 1,[3] 2,[4] 4[5] and 5[6] and Shigella flexneri serotypes 5a[7] and 2a[8]
have already been reported. We report herein, the synthesis of the pentasaccharide
derivative 2 related to the repeating unit 1 of the O-antigen from Shigella dysenteria
type 3. This pentasaccharide derivative in the form of its allyl glycoside can be used for
the preparation of protein conjugates.
RESULTS AND DISCUSSION
1,3,4,6-Tetra-O-acetyl-2-deoxy-2-phthalimido-b-D-galactopyranoside (3),[9] pre-
pared from D-galactosamine hydrochloride, was regioselectively de-O-acetylated at the
anomeric position with acetic hydrazide[10] in DMF to afford 4, which was then converted
to the b-trichloroacetamidate[11] donor 5 (Scheme 1). The overall method for the
1
preparation of 5 was slightly different from the one reported and its H NMR signals
matched well with the literature values.[11]

Synthesis of Pentasaccharide Derivative
287
Scheme 1. a) NH2NHAc, DMF, 50°C, 12 h; b) K2CO3, Cl3CCN, CH2Cl2, 5 h.
In another experiment, the known allyl a-D-galactopyranoside (6),[12] prepared by
refluxing D-galactose with allyl alcohol and Dowex 50W H+ resin,[13] was con-
ventionally acetonated, benzylated, and deacetonated in succession to afford the known
2,6-di-O-benzyl-a-D-galactopyranoside[12] (7) (Scheme 2).
The trichloroacetimidate donor 5 was allowed to react with the allyl glycoside
acceptor 7 in the presence of triethylsilyl trifluoromethanesulphonate[14] (TES-OTf) in
dry dichloromethane at ꢀ20°C to afford the disaccharide, allyl 3,4,6-tri-O-acetyl-2-
deoxy-2-phthalimido-b-D-galactopyranosyl-(1!3)-2,6-di-O-benzyl-a-D-galactopyrano-
side (8) in 76% yield (Scheme 3). The formation of 1!3 linked product was confirmed
by acetylation of 8 showing a downfield shift of the H-4I proton from d 4.04 to 5.41
(J=3.2 Hz). The disaccharide 8 was also characterized by its signals for allyl, three
acetyl and two anomeric protons and carbons in its NMR spectra.
In a separate experiment, ethyl 1-thioglycoside[15] of gentiobiose 9, prepared from
gentiobiose octaacetate in two steps, was treated with a,a-dimethoxybenzaldehyde[16]
and 10-camphorsulfonic acid (CSA) in DMF to afford the 4,6-O-benzylidene compound
which was benzylated to give the perbenzyl derivative 10. Regioselective opening[17] of
the benzylidene ring of 10 with sodium cyanoborohydride and HCl in ethyl ether gave
ethyl 2,3,6-tri-O-benzyl-b-D-glucopyranosyl-(1!6)-2,3,4-tri-O-benzyl-1-thio-b-D-gluco-
pyranoside (11) with a free hydroxyl group at the 4II-position. Compound 11 was
allowed to react with (S)-2-bromopropionic acid and NaH in tetrahydrofuran[18]
followed by esterification of the resulting acid with diazomethane[19] to afford the
disaccharide donor ethyl 2,3,6-tri-O-benzyl-4-O-[methyl (R)-2-propanoate]-b-D-gluco-
pyranosyl-(1!6)-2,3,4-tri-O-benzyl-1-thio-b-D-glucopyranoside (12) in 88% yield
(Scheme 4). The formation of exclusively R-product was the result of an SN-2 type
reaction.[6,18] Compound 12 was characterized by its signals for methyl ester,
SCH2CH3, CHCH3COOMe, and two anomeric protons and carbons in its NMR spectra.
The thioglycoside donor 12 was then allowed to react with the disaccharide
acceptor 8 in the presence of methyl trifluoromethanesulfonate (MeOTf)[20] in ethyl
ether at 30°C to afford allyl 2,3,6-tri-O-benzyl-4-O-[methyl (R)-2-propanoate]-b-D-
Scheme 2. a) 2,2-Dimethoxypropane, CSA, DMF, 12 h; b) BnBr, NaH, DMF, 4 h; c) 80% AcOH,
80°C, 2 h.

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Sarkar and Roy
Scheme 3. a) TES-OTf, CH2Cl2, ꢀ20°C, 30 min.
Scheme 4. a) PhCH(OCH3)2, CSA, DMF, 12 h; b) BnBr, NaH, DMF, 6 h; c) NaCNBH3, HCl in
Et2O, THF, 0°C, 45 min; d) (S)-2-bromopropionic acid, NaH, THF; e) CH2N2, Et2O; f) 8, MeOTf,
Et2O, 24 h, 25°C; g) NaOMe, MeOH, 10 min; h) t-butyldiphenylsilyl chloride (TBDPSCl),
pyridine, 12 h, 30°C.

Synthesis of Pentasaccharide Derivative
289
Scheme 5. a) i. 33% HBr-AcOH, CH2Cl2, 0°C, 2 h; ii. K2CO3, Cl3CCN, CH2Cl2; b) TES-OTf,
˚
CH2Cl2, 4A MS, ꢀ30°C, 1 h.
glucopyranosyl-(1!6)-2,3,4-tri-O-benzyl-a-D-glucopyranosyl-(1!4)-2,6-di-O-benzyl-
3-O-(3,4,6-tri-O-acetyl-2-deoxy-2-phthalimido-b-D-galactopyranosyl)-a-D-galactopyra-
noside (13) (Scheme 4) in 73% yield together with traces (5%) of the b-isomer.
When the same reaction was performed in dichloromethane, the tetrasaccharide
was obtained as a (1:1) a-b mixture. The tetrasaccharide 13 was characterized by its
signals for COOCH3, CHCH3COOMe and four anomeric carbons in its 13C NMR spec-
trum. De-O-acetylation of 13 afforded 14 which upon treatment with tert-butyldi-
phenylsilyl (TBDPS) chloride[21,22] in pyridine gave the corresponding 6IV-O-TBDPS
derivative (15) as a foam in 75% yield. Formation of TBDPS ether selectively at the
6-position was also reported earlier[21,22] and was confirmed by its characteristic sharp
1
singlet at d 1.06 in the H NMR spectrum and the downfield shift of the signal of C-6IV
from d 61.2 to 62.9 in the 13C NMR spectrum.
In a separate sequence of reactions, the known 6-O-acetyl-2,3,5-tri-O-benzoyl-b-D-
galactofuranosyl acetate (16), prepared from D-galactose as described previously[23]
was converted to 6-O-acetyl-2,3,5-tri-O-benzoyl-b-D-galactofuranosyl trichloroacetimi-
date (17).[24,25] The tetrasaccharide derivative 15 was allowed to react with the donor
17 in the presence of TES-OTf, to give the desired pentasaccharide derivative, allyl
2,3,6-tri-O-benzyl-4-O-[methyl (R)-2-propanoate]-b-D-glucopyranosyl-(1!6)-2,3,4-tri-
O-benzyl-a-D-glucopyranosyl-(1!4)-2,6-di-O-benzyl-3-O-[3-O-(6-O-acetyl-2,3,5-tri-O-
benzoyl-b-D-galactofuranosyl)-6-O-tert-butyldiphenylsilyl-2-deoxy-2-phthalimido-b-D-
galactopyranosyl]-a-D-galactopyranoside (2) in 73% yield (Scheme 5). The formation
of the b-furanosidic linkage by this method has been reported earlier[23–25] and was
confirmed by the C-1V signal at d 108 in the 13C NMR spectrum. Other signals for
CH2CH=CH2, COOCH3, COCH3, CHCH3COOMe, Ph2SiC(CH3)3, anomeric protons
and carbons and also the signal for C-2IV in the NMR spectra were also characteristic
of the structure of 2.
In summary, we have synthesized a pentasaccharide derivative related to the
repeating unit of the O-antigen from Shigella dysenteriae type 3 in the form of its allyl
glycoside. The allylic moiety can be cleaved and the resulting aldehyde can be utilized
for the preparation of glycoconjugates.
EXPERIMENTAL
General. All reactions were monitored by TLC on Silica Gel G (E. Merck,
India). Column chromatography was performed on 100–200 mesh Silica Gel (SRL,

290
Sarkar and Roy
India) using 10–50 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 24°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 solvent and tetramethylsilane as internal standard unless
otherwise stated. Peaks of the 13C NMR spectra of the oligosaccharide derivatives were
confirmed by the corresponding DEPT (135) spectra. Melting points were determined
on a paraffin oil bath and are uncorrected.
3,4,6-Tri-O-acetyl-2-deoxy-2-phthalimido-b-D-galactopyranosyl Trichloroaceti-
midate (5).[11] To a solution of 3,[9] (1.4 g, 2.93 mmol) in DMF under N2, acetic
hydrazide (336 mg, 4.53 mmol) was added and the mixture was allowed to stir at 50°C.
After 12 h, the reaction mixture was diluted with EtOAc, washed with 5% NaCl and
water, dried (Na2SO4) and concentrated to a thick syrup. Column chromatography of
the product gave 3,4,6-tri-O-acetyl-2-deoxy-2-phthalimido-b-D-galactopyranose (4)
(1.1 g, 83.6%) as revealed by NMR. To a solution of 4 (600 mg, 1.34 mmol) in CH2Cl2
(5 mL), anhydrous K2CO3 (0.68 g, 5.0 mmol) and trichloroacetonitrile (0.69 mL,
6.80 mmol) were added. The mixture was stirred at room temperature under N2 for
5 h, then filtered through a Celite bed. The filtrate was diluted with CH2Cl2, washed
successively with water, aqueous NaHCO3 and water. The organic layer was dried
(Na2SO4) and concentrated. Column chromatography of the resulting syrup with 1:1
petroleum-ether (60–80°C)-EtOAc containing 0.1% Et3N gave pure 5 (585 mg, 74
%); [a]D25+27° (c 1.2, CHCl3). H NMR d 8.63 (s, 1H, C=NH), 7.85–7.72 (m, 4H,
1
Phth), 6.58 (d, 1H, J1,2=8.9 Hz, H-1), 5.95 (dd, 1H, J2,3=11.5 Hz, J3,4=3.4 Hz,
H-3), 5.56 (d, 1H, J3,4=3.3 Hz, H-4), 4.83 (dd, 1H, J1,2=9 Hz, J2,3=11.4 Hz, H-2),
4.32–4.23 (m, 3H, H-5, H-6), 2.24, 2.07, 1.88 (3 s, 9H, COCH3).
Allyl 3,4,6-Tri-O-acetyl-2-deoxy-2-phthalimido-b-D-galactopyranosyl-(1
!3)-
A solution of the donor 5 (445 mg,
0.77 mmol) and the acceptor 7 (200 mg, 0.50 mmol) in dichloromethane (3 mL)
2,6-di-O-benzyl-a-D-galactopyranoside (8).
˚
containing 4A MS (300 mg) was stirred at ꢀ20°C for 1 h under argon. TES-OTf (17
mL, 0.08 mmol) was then added and the mixture stirred for 30 min when TLC showed
a major spot in between the donor and the acceptor. The reaction was quenched with
Et3N, and the mixture was diluted with CH2Cl2, and the filtrate was washed with water,
saturated NaHCO3 and water in succession, dried and concentrated. Column chroma-
tography of the product with toluene-EtOAc (3:1) gave pure 8 (292 mg, 76%) as an
1
amorphous solid; [a]D25+17.6° (c 0.8, CHCl3). H NMR d 7.70–7.56 (m, 4H, Phth),
7.26–6.95 (m, 10 H, aromatic protons), 5.82 (dd, 1H, J2,3=11.5 Hz, J3.4=3.4 Hz, H-3II),
5.73 (m, 1H, CH2CH=CH2), 5.44 (d, 1H, J1,2=8.5 Hz, H-1II), 5.42 (d, 1H, J3,4=4 Hz,
H-4II), 5.16–5.04 (m, 2H, CH2CH=CH2), 4.59–4.41 (m, 4H, 2 CH2C6H5), 4.44 (d, 1H,
J
1,2=3.8 Hz, H-1I), 4.04 (d, 1H, J3,4=3.2 Hz, H-4I), 2.16, 1.91, 1.78, (3 s, 9 H, 3
COCH3). 13C NMR d 169.4, 169.2, 168.7 (3 COCH3), 167.0, 166.7 [N(CO)2C6H4],
137.3–122.4 (aromatic carbons), 132.7 (CH2CH=CH2), 117.1 (CH2CH=CH2), 98.3
(C-1II), 95.1 (C-1I), 79.0, 73.6, 72.4, 72.1, 70.0, 68.4 (CH2CH=CH2), 68.1, 67.2 (C-6I),
66.6, 65.7, 60.6 (C-6II), 50.4 (C-2II), 19.7, 19.6, 19.4 (3 COCH3). The DEPT (135)
spectrum of 8 clearly showed the presence of 7 CH and 5 CH2 carbons in the region
between d 90 and d 60 as expected.

Synthesis of Pentasaccharide Derivative
291
Anal. Calcd for C43H47O15N: C, 63.15; H, 5.79; N, 1.71. Found: C, 63.02; H, 5.69;
N, 1.73.
Conventional acetylation of 8 gave the corresponding 4I-O-acetyl compound which
1
showed H NMR signals at d 7.76–7.64 (m, 4H, Phth), 7.31–7.02 (m, 10 H, aromatic
protons), 5.88 (dd, 1H, J2,3=11.6 Hz, J3,4=3.5 Hz, H-3II), 5.83–5.73 (m, 1H,
CH2CH=CH2), 5.51 (d, 1H, J1,2=8.3 Hz, H-1II), 5.45 (d, 1H, J3,4=3.2 Hz, H-4II), 5.42
(d, 1H, J3,4=3.2 Hz, H-4I), 5.21–5.10 (m, 2H, CH2CH=CH2), 4.52 (d, 1H, J1,2=3.9 Hz,
H-1I), 4.49, 4.43 (2d, 2H, J=11.9 Hz, CH2Ph), 4.29, 3.93 (2d, 2H, J=12.6 Hz, CH2Ph),
4.11 (dd, 1H, J2,3=10 Hz, J3,4=3.5 Hz, H-3I), 3.56 (dd, 1H, J1,2=3.7 Hz, J2,3=10 Hz,
H-2I), 2.21, 2.08, 2.04, 1.85 (4s, 12H, 4 OCOCH3).
Ethyl 2,3-Di-O-benzyl-4,6-O-benzylidene-b-D-glucopyranosyl-(1
!6)-2,3,4-tri-
Ethyl 1-thio-gentiobioside (9) (0.6 g,
O-benzyl-1-thio-b-D-glucopyranoside (10).
1.55 mmol), obtained from gentiobiose octaacetate by thioglycosidation[15] followed
by deacetylation of the product with NaOMe was dissolved in DMF (5 mL) and a,
a-dimethoxytoluene (0.35 mL, 2.3 mmol) and p-TsOH (25 mg) were added to it. The
reaction mixture was stirred at room temperature for 12 h when TLC showed optimum
conversion. The reaction was quenched with Et3N and the mixture was concentrated to
a syrup. Column chromatography of the crude material with 19:1 EtOAc-EtOH gave
pure 9 (545 mg, 74%) as a solid mass; [a]D25+15.2° (c 0.3, MeOH). To a cold solution
of 9 (500 mg, 1.05 mmol) in DMF (7.5 mL) was added NaH (0.4 g, 8 mmol, 50% oil
coated) and benzyl bromide (1 mL, 8 mmol), and the mixture was stirred at room
temperature for 6 h. Methanol (0.5 mL) was then added to decompose the excess of
NaH, the mixture was diluted with dichloromethane (25 mL) and filtered. The filtrate
was washed with water (3ꢁ20 mL), dried (Na2SO4), and concentrated. The crude
product was chromatographed with 10:1 toluene-EtOAc and crystallized from ethanol
1
to give 10 (925 mg, 95%); mp 186°C ; [a]D25+18.9° (c 1.6, CHCl3). H NMR d 7.39–
7.21 (m, 30H, aromatic protons), 5.57 (s, 1H, CHC6H5), 4.82 (d, 1H, J1,2=9.3 Hz,
H-1I), 4.43 (d, 1H, J1,2=9.9 Hz, H-1II), 2.66 (m, 2H, SCH2CH3), 1.20 (t, 3H, J=7.4 Hz,
SCH2CH3). 13C NMR d 138.5–126.0 (aromatic carbons), 104.1 (C-1II), 101.1
(CHC6H5), 86.6 (C-1I), 84.9, 82.0, 81.8, 81.5, 80.8, 79.1, 78.2, 75.7, 75.5, 75.2,
75.0, 75.0, 68.9, 68.8 (C-6II), 66.0 (C-6I), 24.9 (SCH2CH3), 15.0 (SCH2CH3).
Anal. Calcd for C56H60O10S: C, 70.70; H, 6.54. Found: C, 70.57; H, 6.56.
Ethyl 2,3,6-Tri-O-benzyl- -D-glucopyranosyl-(1
!6)-2,3,4-tri-O-benzyl-1-thio- -
To a solution of 10 (200 mg, 0.2 mmol) and NaBH3CN (110
D-glucopyranoside (11).
˚
mg, 1.8 mmol) in THF (10 mL) containing MS 3 A (300 mg) was added HCl in ether
at 0°C drop-wise until the solution became acidic and evolution of H2 ceased. After
stirring for another 45 min at 0–10° C, the mixture was diluted with CH2Cl2 and
filtered through a Celite bed. The filtrate was washed with water, saturated NaHCO3
and water in succession. The organic layer was dried (Na2SO4), concentrated and
column chromatographed with 10:1 toluene-EtOAc to give pure 11 (160 mg, 80%) as a
25
1
glass; [a]D ꢀ3.9° (c 1, CHCl3). H NMR d 7.37–7.20 (m, 30H, aromatic protons),
4.81 (d, 1H, J1,2=10.5 Hz, H-1I), 4.43 (d, 1H, J1,2=9.6 Hz, H-1II), 2.65 (m, 2H,
SCH2CH3), 1.19 (t, 3H, J=7.8 Hz, SCH2CH3). 13C NMR d 138.4–127.6 (aromatic
carbons), 103.8 (C-1II), 86.5 (C-1I), 84.7, 84.0, 81.8, 81.5, 79.0, 78.2, 75.7, 75.4, 75.2,
74.9, 74.6, 73.9, 73.6, 71.6, 70.2, 68.7 (C-6I, C-6II), 24.8 (SCH2CH3), 14.9 (SCH2CH3).
Anal. Calcd for C56H62O10S: C, 72.54; H, 6.74. Found: C, 72.48; H, 6.80.

292
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Sarkar and Roy
Ethyl 2,3,6-Tri-O-benzyl-4-O-[methyl (R)-2-propanoate]-b-D-glucopyranosyl-
To a solution of 11
!6)-2,3,4-tri-O-benzyl-1-thio-b-D-glucopyranoside (12).
(1.2 g, 1.3 mmol) in tetrahydrofuran (40 mL) was added NaH (60% oil coated, 345
mg, 8.6 mmol). The mixture was then stirred for 1 h at 65°C and a solution of (S)-2-
bromopropionic acid (645 mL, 7.0 mmol) in THF (5 mL) was added with vigorous
stirring. After 2 h, a suspension of NaH (1.5 g) in THF was added and stirring was
continued overnight at 65°C. The reaction mixture was then cooled to room tem-
perature, quenched with MeOH (5 mL), diluted with CH2Cl2 (50 mL) and filtered. The
filtrate was washed with water, dried (Na2SO4) and concentrated to a syrup. Column
chromatography with 10:1 toluene-EtOAc containing 0.01% AcOH gave the product as
a carboxylic acid. The product was dissolved in ether (10 mL) and an ethereal
diazomethane solution (5 mL) was added to it dropwise until the yellow color of
diazomethane persists. Excess diazomethane was decomposed by adding dilute AcOH.
The solvent was evaporated and traces of AcOH removed by co-evaporation with
toluene. Column chromatography with 12:1 toluene-EtOAc gave pure 12 (1.14 g,
88.3%); [a]D25+25.6° (c 3.1, CHCl3). 1H NMR d 7.37–7.20 (m, 30 H, aromatic
protons), 4.70 (d, 1H, J1,2=10.4 Hz, H-1I), 4.14 (d, 1H, J1,2=10.9 Hz, H-1II), 3.58 (s,
3H, COOCH3), 2.64 (m, 2H, SCH2CH3), 1.32 (d, 3H, J=6.8 Hz, CHCH3COOMe), 1.18
(t, 3H, J=7.6 Hz, SCH2CH3). 13C NMR d 173.9 (COOCH3), 138.9–127.8 (aromatic
carbons), 104.2 (C-1II), 87.0 (C-1I), 85.3, 84.9, 82.7, 82.2, 79.5, 78.6, 77.5, 76.2, 76.1,
76.0, 75.9, 75.4, 75.2, 75.1, 73.8, 69.7, 69.2 (C-6I, C-6II), 52.1 (COOCH3), 25.3
(SCH2CH3), 19.5 (CHCH3COOMe), 15.4 (SCH2CH3). DEPT (135) spectrum of 12
clearly showed the presence of 9 CH and 9 CH2 carbons in the region between d 85
and d 60 as expected.
Anal. Calcd for C60H68O12S: C, 71.12; H, 6.76. Found: C, 71.18; H, 6.62.
Allyl 2,3,6-Tri-O-benzyl-4-O-[methyl (R)-2-propanoate]-b-D-glucopyranosyl-
(1
!6)-2,3,4-tri-O-benzyl-a-D-glucopyranosyl-(1!4)-2,6-di-O-benzyl-3-O-(3,4,6-tri-
O-acetyl-2-deoxy-2-phthalimido-b-D-galactopyranosyl)-a-D-galactopyranoside (13).
To a mixture of the disaccharide donor 12 (200 mg, 0.18 mmol) and the acceptor 8
˚
(144 mg, 0.18 mmol) in Et2O containing 4A MS (400 mg), was added MeOTf (0.1 mL,
0.9 mmol). The mixture was stirred under argon at 25°C for 24 h when TLC showed a
major spot in between the donor and the acceptor. The reaction was then quenched
with triethylamine (1 h), filtered through a Celite bed and the filtrate was concentrated
to a syrup. Column chromatography of the crude product with 3:1 toluene-EtOAc gave
1
13 as a thick glass (230 mg, 73%): [a]D25+14.1° (c 1.4, CHCl3). H NMR d 7.42–6.80
(m, 44 H, aromatic protons), 5.80 (dd, 1H, J2,3=3.2 Hz, J4,5=11.4 Hz, H-3IV), 5.71 (m,
1H, CH2CH=CH2), 5.42 (d, 1H, J1,2=8.4 Hz, H-1IV), 5.38 (d, 1H, J3,4=3.1 Hz, H-4IV),
5.12–5.01 (m, 2H, CH2CH=CH2), 4.94 (d, 1H, J1,2=2.7 Hz, H-1II), 4.86 (d, 1H,
J
1,2=11 Hz, H-1III), 4.50 (d, 1H, J3,4=3.3 Hz, H-4I), 4.37 (d, 1H, J1,2=3.5 Hz, H-1I),
3.50 (s, 3H, COOCH3), 1.98, 1.89,1.67 (3 s, 9H, 3 COCH3), 1.24 (d, 3H, J=9.6 Hz,
CHCH3COOMe). 13C NMR d 173.9 (COOCH3), 171.3, 170.7, 170.2 (3 COCH3),
168.1, 167.6 [N(CO)2C6H5], 140.0–123.9 (aromatic carbons), 134.4 (CH2CH=CH2),
118.4 (CH2CH=CH2), 104.9 (C-1III), 101.2 (C-1II), 98.0 (C-1IV), 96.3 (C-1I), 85.0,
83.2, 82.2, 80.1, 79.2, 78.1, 77.0, 76.0, 75.9, 75.5, 75.4, 75.2, 74.6, 74.1, 74.0, 73.4,
73.4, 72.2, 71.1, 71.0, 70.5, 69.9, 69.5, 69.1, 68.8 (C-6I, C-6III, C-6II), 68.3, 67.0, 61.8
(C-6IV), 52.1 (COOCH3), 51.8 (C-2IV), 21.1, 21.0, 20.9 (3 OCOCH3), 19.5 (CHCH3

Synthesis of Pentasaccharide Derivative
293
COOMe). DEPT (135) spectrum of 13 clearly showed the presence of 15 CH and 13 CH2
carbons in the region between d 90 and d 60 as expected.
Anal. Calcd for C101H109O27N: C, 68.57; H, 6.21; N, 0.79. Found: C, 68.49; H,
6.12; N, 0.78.
Allyl 2,3,6-Tri-O-benzyl-4-O-[methyl (R)-2-propanoate]-b-D-glucopyranosyl-
(1
!6)-2,3,4-tri-O-benzyl-a-D-glucopyranosyl-(1!4)-2,6-di-O-benzyl-3-O-(6-O-tert-
butyldiphenylsilyl-2-deoxy-2-phthalimido-b-D-galactopyranosyl)-a-D-galactopy-
Compound 13 (200 mg) was deacetylated with 0.2 M NaOMe ac-
ranoside (15).
cording to a conventional method to afford the trihydroxy compound 14 in quantitative
yield; [a]D25+12.3° (c 1.7, CHCl3). The product (142 mg, 0.09 mmol) was dissolved in
pyridine (1 mL) and tert-butyldiphenylsilyl chloride (27 mL, 0.1 mmol) was added. The
reaction mixture was stirred at 25°C for 12 h when TLC showed the reaction to
be almost complete. The reaction was quenched with MeOH and the mixture was
concentrated to a thick glass. Column chromatography of the product with 5:1 toluene-
EtOAc gave pure 14 (122 mg, 75%); [a]D25+8.26° (c 2.0, CHCl3). 1H NMR d 7.70–7.54
(m, 4H, Phth), 7.43–6.96 (m, 50H, aromatic protons), 5.85 (m, 1H, CH2CH=CH2), 5.26
(d, 1H, J1,2=8 Hz, H-1IV), 5.23–5.10 (m, 2H, CH2CH=CH2), 4.99 (d, 1H, J1,2=10.8 Hz,
H-1III), 4.94 (d, 1H, J1,2=3 Hz, H-1II), 4.52 (d, 1H, J1,2=4.1 Hz, H-1I), 3.56 (s, 3H,
COOCH3), 1.26 (d, 3H, J=6.3 Hz, CHCH3COOMe), 1.06 [s, 9H, Ph2SiC(CH3)3]. 13C
NMR d 173.9 (COOMe), 168.6, 168.5 [N(CO)2C6H4], 135.9 (CH2=CH-CH2), 139.7–
127.6 (aromatic carbons), 118.3 (CH2=CH-CH2), 103.6 (C-1III), 101.9 (C-1II), 98.6
(C-1IV), 96.5 (C-1I), 85.4, 82.7, 81.8, 80.4, 80.1, 78.4, 78.3, 77.2, 76.1, 75.8, 75.7, 75.5,
75.3, 75.1, 74.4, 73.9, 73.8, 73.3, 73.2, 72.2, 70.5, 70.4, 68.7, 68.6, 67.6, 62.9 (C-6IV)
55.4 (COOCH3), 52.0 (C-2IV), 27.3 Ph2SiC(CH3)3, 19.6 (CHCH3COOMe). DEPT (135)
spectrum of 15 clearly showed the presence of 15 CH and 13 CH2 carbons in the region
between d 90 and d 60 as expected.
Anal. Calcd for C111H121O24NSi: C, 70.87; H, 6.48; N, 0.74. Found: C, 70.76; H,
6.42; N, 0.72.
6-O-Acetyl-2,3,5-tri-O-benzoyl-b-D-galactofuranosyl Trichloroacetimidate (17).
6-O-Acetyl-2,3,5-tri-O-benzoyl-b-D-galactofuranose (250 mg, 0.47 mmol) was prepared
from 16[23] (335 mg, 0.58 mmol) according to the method described previously[24,25]
25
which was converted to the trichloroacetimidate donor 17 (262 mg, 83%); [a]D ꢀ23.8°
1
(c 1.5, CHCl3). H NMR d 8.67 (s, 1H, CONHCCl3), 8.03–7.18 (m, 15H, aromatic
protons), 6.60 (s, 1H, H-1), 5.88 (m, 1H, H-5), 5.65 (s, 1H, H-2), 5.68 (d, 1H, J3,4=4 Hz,
H-3), 4.69 (t, 1H, J=3.8 Hz, H-4), 4.51–4.37 (m, 2H, H-6), 1.91 (s, 3H, COCH3).
Allyl 2,3,6-Tri-O-benzyl-4-O-[methyl (R)-2-propanoate]-b-D-glucopyranosyl-
(1
!6)-2,3,4-tri-O-benzyl-a-D-glucopyranosyl-(1!4)-2,6-di-O-benzyl-3-O-[3-O-(6-O-
acetyl-2,3,5-tri-O-benzoyl-b-D-galactofuranosyl)-6-O-tert-butyldiphenylsilyl-2-
A mixture
deoxy-2-phthalimido-b-D-galactopyranosyl]-a-D-galactopyranoside (2).
˚
of 15 (86.6 mg, 0.05 mmol) and 4A MS in CH2Cl2 (2 mL) was stirred for 1 h at 25°C
under argon. The mixture was then cooled to ꢀ20°C and TES-OTf (2 mL, 0.01 mmol)
was added upon stirring. After 5 min, the donor 17 (38.6 mg, 0.06 mmol) in CH2Cl2 (1
mL) was added and stirring was continued. The reaction was monitored by TLC and
after 1 h the reaction was quenched with triethylamine. The reaction mixture was

294
Sarkar and Roy
diluted with CH2Cl2, filtered and washed successively with saturated NaHCO3 and
water. The organic layer was dried (Na2SO4) and concentrated to a thick glass. Column
chromatography with toluene-EtOAc (5:1) gave pure 2 (80 mg, 72.6%); [a]D25+8.3° (c
1.2, CHCl3). 1H NMR d 7.95–6.87 (m, 69H, aromatic protons), 5.78 (m, 1H,
CH2CH=CH2), 5.22 (d, 1H, J=6.5 Hz, H-1IV), 5.19 (bs, 1H, H-1V), 5.17–5.05 (m, 2H,
CH2CH=CH2), 4.88 (d, 1H, J1,2=10.9 Hz, H-1III), 4.61 (d, 1H, J1,2=3.0 Hz, H-1II), 4.54
(d, 1H, J1,2=2.9 Hz, H-1I), 3.38 (s, 3H, COOCH3), 1.82 (s, 3H, COCH3), 1.17 (d, 3H,
J=6.4 Hz, CHCH3COOMe), 0.96 [s, 9H, Ph2SiC(CH3)3]. 13C NMR d 173.7 (COOCH3),
170.7 (COCH3), 169.3, 168.0, 166.0 (3 COC6H5), 165.9, 165.1 [N(CO)2C6H4], 134.4
(CH2CH=CH2), 138.8–127.6 (aromatic carbons), 118.4 (CH2CH=CH2), 108.3 (C-1V),
103.9 (C-1III), 101.9 (C-1II), 98.0 (C-1IV), 96.4 (C-1I), 85.1, 82.8, 82.6, 81.9, 81.1, 80.5,
76.4, 75.9, 75.8, 75.5, 75.3, 74.9, 74.6, 73.9, 73.7, 73.4, 73.2, 72.4, 70.7, 69.7, 69.3, 68.5 (C-
6I, C-6II, C-6III), 63.8, 62.9 (C-6IV, C-6V), 52.4 (COOCH3), 51.9 (C-2IV), 27.2
[Ph2SiC(CH3)3], 21.0 (COOCH3), 19.6 (CHCH3COOMe). DEPT (135) spectrum of 2
clearly showed the presence of 20 CH and 14 CH2 carbons in the region between d 90 and d
60 as expected.
Anal. Calcd for C140H145O33NSi: C, 70.27; H, 5.90; N, 0.58. Found: C, 70.17; H,
5.86; N, 0.61.
ACKNOWLEDGMENT
Financial support from the Department of Science and Technology, New Delhi,
India (Project No. SP/S1/G14/95) is thankfully acknowledged.
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Received December 31, 2002
Accepted April 24, 2003