Convergent synthesis of a pentasaccharide repeating unit corresponding to the cell wall O-antigen of Salmonella enterica O44

Article abstract of DOI:10.1016/j.tetasy.2013.12.005

A convergent synthetic strategy has been developed for the synthesis of a pentasaccharide fragment corresponding to the O-antigen of Salmonella enterica O44 strain. An intermediate tetrasaccharide derivative was prepared by a [2+2] block glycosylation of two disaccharide derivatives. The p-methoxybenzyl (PMB) group has been used as the in situ temporary protecting group minimizing the number of functional group manipulation steps. The application of the armed-disarmed glycosylation concept reduced the number of steps in the synthetic strategy. The glycosylation steps were highly stereoselective and high yielding.

Full text of DOI:10.1016/j.tetasy.2013.12.005

Tetrahedron: Asymmetry 25 (2014) 263–267
Contents lists available at ScienceDirect
Tetrahedron: Asymmetry
journal homepage: www.elsevier.com/locate/tetasy
Convergent synthesis of a pentasaccharide repeating unit
corresponding to the cell wall O-antigen of Salmonella enterica O44
a,
Debashis Dhara a, Pintu Kumar Mandal b, , Anup Kumar Misra
⇑
⇑
a Bose Institute, Division of Molecular Medicine, P-1/12, C.I.T. Scheme VII-M, Kolkata 700054, India
b Medicinal and Process Chemistry Division, CSIR-Central Drug Research Institute, BS-10/1, Sector 10, Jankipuram Extension, Sitapur Road, Lucknow 226031, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 18 November 2013
Accepted 5 December 2013
A convergent synthetic strategy has been developed for the synthesis of a pentasaccharide fragment cor-
responding to the O-antigen of Salmonella enterica O44 strain. An intermediate tetrasaccharide derivative
was prepared by a [2+2] block glycosylation of two disaccharide derivatives. The p-methoxybenzyl (PMB)
group has been used as the in situ temporary protecting group minimizing the number of functional
group manipulation steps. The application of the armed–disarmed glycosylation concept reduced the
number of steps in the synthetic strategy. The glycosylation steps were highly stereoselective and high
yielding.
Ó 2013 Elsevier Ltd. All rights reserved.
1. Introduction
Recently, Perepelov et al.8 reported the structure of a pentasac-
charide repeating unit of the O-polysaccharide present in the cell
Salmonellosis is a major cause of food borne illness and diar-
rheal infections, which spreads through foods and water infected
by the Salmonella bacteria.1 Mostly, young and elderly populations
as well as individuals with compromised immunity are prone to
Salmonella infections.2 Diarrhea with gastrointestinal complication
is a serious health concern in tropical countries.3 Infected poultry
products and household pets act as reservoirs of Salmonella infec-
tions.4 The common symptoms of salmonellosis include diarrhea
(bloody and mucosal), fever, stomach ache, vomiting with dehy-
dration and so on. Salmonella enterica strains are mostly responsi-
ble for the diarrheal infections among several strains of
Salmonella.5 In addition to the available therapeutics for controlling
diarrheal infections, the development of novel alternative ap-
proaches is highly essential due to the emergence of multi-drug
resistant bacteria.6 The polysaccharide antigens present in the cell
wall of Salmonella strains are closely associated with its pathoge-
nicity and play crucial roles during the initial stage of bacterial
infections. Therefore, glycoconjugates derived from the cell wall
polysaccharide could be promising for the eradication or control
of gastrointestinal infections.7 However, the quantity of the poly-
saccharides or its repeating fragments required for the preparation
of glycoconjugates to be used in several biological experiments
cannot be accessed from natural sources and hence chemical
synthesis is the best option for obtaining significant quantities of
polysaccharide fragments with adequate purity.
wall of Salmonella enterica O44, which is a pentasaccharide consist-
ing of two alpha linked -glucose moieties, two beta linked -glu-
cosamine moieties, and one alpha linked -galactose moiety.
D
D
D
During the course of the synthesis of complex oligosaccharides
for their use in the preparation of glycoconjugate derivatives, we
herein report a convergent chemical synthesis of the pentasaccha-
ride corresponding to the cell wall polysaccharide of Salmonella
enterica O44 in the form of its 2-aminoethyl glycosides. The
presence of a 2-aminoethyl group at the reducing end of the
synthesized pentasaccharide would be useful for its conjugation
with a protein or lipid (Fig. 1).
?4)-[b-D-GlcpNAc-(1?3)]-a-D-Galp-(1?3)-b-D-GlcpNAc-(1?2)-
a-D-Glcp-(1?6)-a-D-Glcp-(1?
Structure of the pentasaccharide repeating unit of the cell wall
O-antigen of Salmonella enterica O44 strain.
2. Results and discussion
The pentasaccharide 1 in the form of its 2-aminoethyl glycoside
was synthesized using a convergent [2+2] block glycosylation
strategy. The presence of three alpha linkages poses an extra
challenge during the synthetic endeavor in the stereochemical out-
come of the glycosylation steps. Suitably functionalized monosac-
charide intermediates 2,9 3,10 4,11 5, and 612 were prepared from
reducing sugars using reported reaction conditions for their use
in the construction of the desired pentasaccharide. The use of
p-methoxybenzyl (PMB) ether as an in situ removable temporary
⇑
Corresponding authors. Tel.: +91 33 25693240; fax: +91 33 2355 3886.
E-mail addresses: pintuchem06@gmail.com (P.K. Mandal), akmisra69@gmail.
com (A.K. Misra).
0957-4166/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tetasy.2013.12.005

264
D. Dhara et al. / Tetrahedron: Asymmetry 25 (2014) 263–267
OH
OH
OH
HO
O
HO
HO
O
O
HO
HO
B
OH
D
E
O
O
O
HO
NHAc
HO
O
C
O
NHAc
O
HO
HO
A
NH2
HO
1
O
OH
O
Ph
O
Ph
O
O
BnO
BnO
O
O
O
SEt
HO
SEt
BnO
N3
BnO
NPhth
OPMB
O
4
3
2
BnO OBn
OAc
O
O
AcO
AcO
SEt
PMBO
SEt
OBn
NPhth
6
5
PMB: p-methoxybenzyl
Figure 1. Structure of the synthesized pentasaccharide 1 and its synthetic intermediates.
protecting group13 allowed to perform the stereoselective glyco-
sylation as well as removal of the PMB group in one pot during
the synthesis of the disaccharide intermediate 8 and tetrasaccha-
ride intermediate 10 in excellent yield. During the synthesis, thio-
glycoside derivatives were used as glycosyl donors as well as
acceptors adopting Fraser-Reid’s concept of ‘armed–disarmed’
glycosylation.14
presence of two alpha glycosyl linkages.20 The non-participating
ability of the PMB ether at the C-2 position of compound 3 favored
the formation of the 1,2-cis glycosyl linkage and was removed in
the same pot after the glycosylation step. In another experiment,
the iodonium ion mediated stereoselective 1,2-cis glycosylation
of thioglycoside glycosyl donor 5 with a thioglycoside acceptor 4
in the presence of NIS-TfOH18,19 in a mixed solvent (CH2Cl2–Et2O;
1:1) gave the desired disaccharide thioglycoside derivative 9 in
72% yield together with a minor quantity (ꢀ8%) of the 1,2-trans
glycosyl product, which was separated by chromatography. The
presence of a benzyl ether at the C-2 position of compound 5 made
it an activated or ‘armed’ glycosyl donor while compound 4 acted
as a ‘disarmed’ glycosyl acceptor due to the presence of an
N-phthaloyl group at its C-2 potion following the Fraser-Reid’s
‘armed–disarmed’ glycosylation concept.14 The stereochemistry
at the glycosyl linkages in compound 9 was confirmed from its
spectroscopic analysis [signals at d 5.52 (d, J = 4.0 Hz, H-1D), 5.40
(d, J = 10.0 Hz, H-1C) in the 1H NMR and d 97.4 (JC1–H1 = 168.0 Hz,
C-1D), 81.7 (JC1–H1 = 155.0 Hz, C-1C) in the 13C NMR spectra]. The
appearance of JC1–H1 values 168.0 and 155.0 Hz in the 1H coupled
gated 13C NMR spectrum of compound 9 confirmed the presence
of one alpha and one beta glycosyl linkage, respectively.20 Conden-
sation of the disaccharide derivative 8 with the disaccharide thio-
Ethyl
2,4,6-tri-O-benzyl-3-O-p-methoxybenzyl-1-thio-b-
D-
galactopyranoside 5 was prepared from ethyl 1-thio-b-
D-galacto-
pyranoside 715 in 73% yield using a one-pot multistep reaction
sequence involving selective 3-O-p-methoxybenzylation via the
formation of a stannylidene acetal using dibutyltin oxide and its
regioselective opening16 using a combination of p-methoxybenzyl
chloride and tetra-n-butylammonium bromide (TBAB), followed
by benzylation of the remaining hydroxyl groups using benzyl bro-
mide and sodium hydroxide17 (Scheme 1).
OBn
BnO
OH
HO
O
O
a, b
SEt
SEt
PMBO
HO
OBn
OH
7
5
glycoside derivative
9
in the presence of an NIS-TfOH18,19
PMB: p-methoxybenzyl
combination followed by removal of the PMB group from the new-
ly formed tetrasaccharide derivative under one-pot reaction condi-
tions13 furnished the tetrasaccharide acceptor 10 in 69% yield. The
stereochemical outcome at the newly formed glycosyl linkages in
compound 10 was confirmed from its spectroscopic analysis [sig-
nals at d 5.56 (d, J = 3.5 Hz, H-1D), 5.54 (d, J = 9.0 Hz, H-1C), 4.91
(d, J = 3.5 Hz, H-1B) and 4.85 (d, J = 3.0 Hz, H-1A) in the 1H NMR
and d 100.0 (C-1B), 99.7 (C-1C), 97.0 (C-1D) and 96.5 (C-1A) in the
13C NMR spectra]. Finally, glycosylation of compound 10 with com-
pound 6 in the presence of an NIS-TfOH18,19 combination furnished
pentasaccharide derivative 11 in 67% yield. The NMR spectroscopic
analysis of compound 11 supported its formation [signals at d 5.58
(d, J = 8.5 Hz, H-1C), 5.47 (d, J = 8.5 Hz, H-1E), 5.35 (d, J = 3.5 Hz, H-
1D), 4.86 (d, J = 3.5 Hz, H-1B) and 4.62 (d, J = 3.0 Hz, H-1A) in the 1H
NMR and at d 100.0 (C-1E), 99.5 (C-1B), 99.4 (C-1C), 97.0 (C-1D) and
96.6 (C-1A) in the 13C NMR spectra]. Removal of the protecting
groups in compound 11 using a set of reactions consisting of; (a)
treatment with hydrazine followed by acetylation for the transfor-
mation of the N-phthaloyl group to an acetamido group;21 (b)
Scheme 1. Reagents and conditions: (a) (i) Bu2SnO, CH3OH, 80 °C, 3 h; (ii)
p-methoxybenzyl chloride, TBAB, DMF, 80 °C, 16 h; (b) benzyl bromide, NaOH,
DMF, room temperature, 8 h, overall 73%.
The iodonium ion mediated stereoselective 1,2-cis glycosylation
of compound 2 with thioglycoside derivative 3 in the presence of a
combination of N-iodosuccinimide (NIS) and trifluoromethanesul-
fonic acid (TfOH)18,19 in a mixed solvent (CH2Cl2–Et2O; 1:1) fol-
lowed by tuning the reaction conditions14 for the removal of the
PMB group in one-pot, resulted in the formation of the disaccha-
ride acceptor 8 in 74% yield together with its other isomer in a
minor quantity (ꢀ5%), which was separated by chromatography.
The NMR spectroscopic analysis of compound 8 unambiguously
confirmed its formation [signals at d 4.88 (d, J = 3.0 Hz, H-1B),
4.72 (d, J = 3.5 Hz, H-1A) in the 1H NMR and d 99.4 (JC1–H1
=
169.0 Hz; C-1B), 97.2 (JC1–H1 = 168.5 Hz; C-1A) in the 13C NMR spec-
tra]. The appearance of JC1–H1 values 168.5 and 169.0 Hz in the 1H
coupled gated 13C NMR spectrum of compound 8 confirmed the

D. Dhara et al. / Tetrahedron: Asymmetry 25 (2014) 263–267
265
saponification using sodium methoxide; and (c) removal of the
4. Experimental
benzyl ethers and benzylidene acetals as well as the reduction of
the azido group by catalytic transfer hydrogenation using triethyl-
silane and Pd-C,22 resulted in the formation of pentasaccharide 1 in
the form of its 2-aminoethyl glycoside in 57% overall yield. The for-
mation of compound 1 was confirmed by its spectroscopic analysis
[signals at d 5.35 (d, J = 3.0 Hz, H-1D), 5.00 (br s, H-1A, H-1B) and
4.88 (2 d, J = 8.0 Hz each, H-1C, H-1E) in the 1H NMR and at d
98.4 (3 C, C-1C, C-1D, C-1E), 97.9 (C-1A) and 97.8 (C-1B) in the 13C
NMR spectra] (Scheme 2).
General methods are same as reported earlier.22
4.1. Ethyl 2,4,6-tri-O-benzyl-3-O-p-methoxybenzyl-1-thio-b-D-
galactopyranoside 5
To a solution of compound 7 (2 g, 8.92 mmol) in dry CH3OH
(60 mL) was added Bu2SnO (6 g, 24.10 mmol) and the reaction
mixture was stirred at 80 °C for 3 h. The solvents were removed
under reduced pressure to give the crude stannylidene acetal
derivative. To a solution of the stannylidene acetal derivative in
dry DMF (25 mL) were added p-methoxybenzyl chloride (2.2 mL,
16.22 mmol) and TBAB (3 g, 9.30 mmol) and the reaction mixture
was allowed to stir at 80 °C for 16 h. The reaction mixture was
cooled to room temperature and benzyl bromide (6.5 mL,
54.65 mmol) followed by powdered NaOH (4 g, 100 mmol) were
added to it. After stirring the reaction mixture at room temperature
for 8 h, the solvents were removed under reduced pressure and the
crude product was dissolved in EtOAc (150 mL). The organic layer
was washed with 1 M HCl, satd NaHCO3 and water in succession,
dried (Na2SO4), and concentrated to give the crude product, which
was purified over SiO2 using hexane–EtOAc (10:1) as eluant to give
O
Ph
O
O
B
BnO
HO
O
a
2 + 3
O
BnO
BnO
A
N3
BnO
O
8
OBn
BnO
O
b
D
4 + 5
PMBO
O
O
Ph
O
BnO
C
SEt
O
pure compound 5 (4 g, 73%). Colorless oil; ½a D25
¼ þ19 (c 1.0,
ꢁ
NPhth
9
CHCl3); IR (neat): 3408, 2811, 2331, 1654, 1542, 1498, 1379,
1235, 1198, 1083, 982, 668 cmꢂ1 1H NMR (500 MHz, CDCl3): d
;
O
Ph
O
O
7.39–7.25 (m, 17H, Ar-H), 6.83 (d, J = 9.0 Hz, 2H, Ar-H), 4.94 (d,
J = 12.0 Hz, 1H, PhCH2), 4.87 (d, J = 11.0 Hz, 1H, PhCH2), 4.79 (d,
J = 11.0 Hz, 1H, PhCH2), 4.65 (br s, 2H, PhCH2), 4.59 (d, J = 11.5 Hz,
1H, PhCH2), 4.44 (d, J = 11.5 Hz, 1H, PhCH2), 4.41 (d, J = 10.0 Hz,
1H, H-1), 4.39 (d, J = 11.5 Hz, 1H, PhCH2), 3.92 (d, J = 2.5 Hz, 1H,
H-4), 3.80 (s, 3H, OCH3), 3.82-3.77 (m, 1H, H-2), 3.59–3.52 (m,
4H, H-3, H-5, H-6ab), 2.78 (m, 2H, SCH2CH3), 1.31 (t, J = 7.5 Hz,
3H, SCH2CH3); 13C NMR (125 MHz, CDCl3): d 159.2–113.8 (Ar-C),
85.3 (C-1), 83.8 (C-5), 78.4 (C-3), 77.2 (C-4), 75.7 (PhCH2), 74.4
(PhCH2), 73.6 (C-2), 73.5 (PhCH2), 72.4 (PhCH2), 68.8 (C-6), 55.2
(OCH3), 24.7 (SCH2CH3), 15.1 (SCH2CH3); ESI-MS: 637.2 [M+Na]+;
Anal. Calcd for C37H42O6S (614.27): C, 72.28; H, 6.89; found: C,
72.10; H, 7.10.
O
O
O
B
Ph
BnO
BnO
O
C
c
O
O
8 + 9
NPhth
HO
BnO
O
BnO
BnO
D
A
O
N3
BnO
OBn
10
O
d
6
O
Ph
O
O
O
O
O
O
B
Ph
BnO
BnO
OAc
C
O
O
O
AcO
AcO
NPhth
E
O
O
BnO
BnO
D
A
O
NPhth
N3
BnO
4.2. 2-Azidoethyl (3-O-benzyl-4,6-O-benzylidene-a-D-glucopyr-
BnO
OBn
O
11
anosyl)-(1?6)-2,3,4-tri-O-benzyl- -glucopyranoside 8
a-D
e, f, g, h
To a solution of compound 2 (1.4 g, 2.69 mmol) and compound
3 (1.5 g, 2.87 mmol) in anhydrous CH2Cl2–Et2O (20 mL; 1:1) was
added MS 4 Å (2 g) and the reaction mixture was cooled to
ꢂ45 °C under argon. To the cooled reaction mixture was added
1
NIS (700 mg, 3.11 mmol) followed by TfOH (20 lL) and then al-
Scheme 2. Reagents and conditions: (a) N-iodosuccinimide (NIS), TfOH, MS 4 Å,
CH2Cl2–Et2O (1:1), ꢂ45 °C, 45 min, then 0 °C, 1 h, 74%; (b) NIS, TfOH, MS 4 Å,
CH2Cl2–Et2O (1:1), ꢂ35 °C, 30 min, 72%; (c) NIS, TfOH, MS 4 Å, CH2Cl2, ꢂ30 °C,
30 min, then 0 °C, 1 h, 69%; (d) NIS, TfOH, MS 4 Å, CH2Cl2, ꢂ25 °C, 20 min, 67%; (e)
NH2NH2ꢃH2O, EtOH, 80 °C, 8 h; (f) acetic anhydride, pyridine, room temperature,
1 h; (g) 0.1 M CH3ONa, CH3OH, room temperature, 2 h; (h) Et3SiH, 20% Pd(OH)2-C,
CH3OH–EtOAc (3:1), room temperature, 10 h, over all 57%.
lowed to stir at ꢂ45 °C for 45 min. The reaction mixture was
warmed up to 0 °C and stirred at 0 °C for 1 h. The reaction mixture
was filtered through a CeliteÒ bed and washed several times with
CH2Cl2 (50 mL). The organic layer was washed with 5% aq Na2S2O3,
satd NaHCO3 and water in succession, dried (Na2SO4), and concen-
trated. The crude product was purified over SiO2 using hexane–
EtOAc (4:1) as eluant to give pure compound 8 (1.7 g, 74%). Color-
3. Conclusion
less oil; ½a 2D5
þ 33 (c 1.0, CHCl3); IR (neat): 3021, 2927, 2847, 1734,
ꢁ
1535, 1323, 1133, 1079, 782, 698 cmꢂ1; 1H NMR (500 MHz, CDCl3):
d 7.47–7.46 (m, 2H, Ar-H), 7.45–7.23 (m, 23H, Ar-H), 5.52 (s, 1H,
PhCH), 4.97 (d, J = 11.0 Hz, 1H, PhCH2), 4.92 (d, J = 12.0 Hz, 2H,
PhCH2), 4.88 (d, J = 3.0 Hz, 1H, H-1B), 4.79 (dd, J = 12.0 Hz, 3H,
PhCH2), 4.72 (d, J = 3.5 Hz, 1H, H-1A), 4.65 (d, J = 11.0 Hz, 1H,
PhCH2), 4.57 (d, J = 11.0 Hz, 1H, PhCH2), 4.19–4.16 (m, 1H, H-6aB),
In summary, a pentasaccharide repeating unit of the cell wall O-
polysaccharide of Salmonella enterica O44 strain in the form of its
2-aminoethyl glycoside has been synthesized in excellent yield
and the stereochemical outcome was established by using a con-
vergent synthetic scheme involving a one-pot glycosylation and
protecting group manipulations as well as ‘armed–disarmed’ gly-
cosylation. The use of a PMB group as the in situ removable tempo-
rary protecting group for the hydroxyl groups reduced the number
of steps and increased the overall yield of the synthetic strategy.
3.99 (t, J = 9.5 Hz, 1H, H-3A), 3.85–3.74 (m, 4H, H-3B, H-5B, H-6aA
,
OCH2), 3.70–3.65 (m, 4H, H-2B, H-5A, H-6bB, OCH2), 3.60–3.49 (m,
3H, H-2A, H-4B, H-6bA), 3.48–3.34 (m, 3H, H-4A, CH2N3); 13C NMR

266
D. Dhara et al. / Tetrahedron: Asymmetry 25 (2014) 263–267
(125 MHz, CDCl3): d 128.9–126.1 (Ar-C), 101.3 (PhCH), 99.4 (C-1B),
97.2 (C-1A), 81.8 (C-4B), 81.7 (C-3A), 80.2 (C-2A), 78.6 (C-2B), 77.4
(C-4A), 75.7 (PhCH2), 74.9 (PhCH2), 74.5 (PhCH2), 73.3 (PhCH2),
72.6 (C-5A), 70.1 (C-3B), 68.9 (C-6B), 67.2 (C-6A), 66.8 (OCH2), 62.9
(C-5B), 50.6 (CH2N3); ESI-MS: 882.3 [M+Na]+; Anal. Calcd for
1H, PhCH), 5.05 (d, J = 11.0 Hz, 1H, PhCH2), 4.92 (d, J = 12.0 Hz,
1H, PhCH2), 4.91 (d, J = 3.5 Hz, 1H, H-1B), 4.88–4.86 (m, 2H, PhCH2),
4.85 (d, J = 3.0 Hz, 1H, H-1A), 4.84 (d, J = 11.5 Hz, 2H, PhCH2), 4.77
(d, J = 12.0 Hz, 1H, PhCH2), 4.60 (d, J = 1.5 Hz, 1H, PhCH2), 4.56
(dd, J = 12.0 Hz, 3H, PhCH2), 4.47–4.45 (m, 1H, H-2C), 4.32–4.28
(m, 2H, H-6abB), 4.20 (dd, J = 12.0 Hz, 2H, PhCH2), 4.19–4.17 (m,
1H, H-6aD), 4.09 (t, J = 9.5 Hz, 1H, H-3A), 4.04 (d, J = 11.5 Hz, 1H,
PhCH2), 3.93–3.82 (m, 5H, H-2D, H-3C, H-3D, H-4D, H-6bD),
3.79–3.60 (m, 10H, H-2A, H-2B, H-3B, H-4A, H-4B, H-4C, H-5A,
H-5B, H-6abA), 3.53–3.45 (m, 1H, CH2N3), 3.44–3.37 (m, 5H, H-5C,
H-5D, H-6abC, CH2N3), 3.40–3.37 (m, 1H, OCH2), 2.89–2.83 (m, 1H,
C49H53N3O11 (859.37): C, 68.44; H, 6.21; found: C, 68.27; H, 6.35.
4.3. Ethyl (2,4,6-tri-O-benzyl-3-O-p-methoxybenzyl-
pyranosyl)-(1?3)-4,6-O-benzylidene-2-deoxy-2-N-phthalimido-
1-thio-b- -glucopyranoside 9
a-D-galacto-
D
To a solution of compound 4 (1.3 g, 2.94 mmol) and compound
5 (1.9 g, 3.09 mmol) in anhydrous CH2Cl2–Et2O (20 mL; 1:1) was
added MS 4 Å (2 g) and the reaction mixture was cooled to
ꢂ35 °C under argon. To the cooled reaction mixture was added
OCH2); 13C NMR (125 MHz, CDCl3):
d 167.8, 167.4 (Phth),
138.5–126.1 (Ar-C), 101.9 (PhCH), 101.3 (PhCH), 100.0 (C-1B),
99.7 (C-1C), 97.0 (C-1D), 96.5 (C-1A), 83.0 (C-3A), 82.3 (C-3D), 81.9
(C-2A), 80.2 (C-4B), 79.7 (C-4A), 78.1 (C-2B), 76.5 (C-4D), 75.8
(PhCH2), 75.7 (C-3C), 75.6 (C-2D), 74.9 (PhCH2), 74.8 (PhCH2), 73.6
(PhCH2), 73.1 (PhCH2), 72.7 (PhCH2), 72.4 (C-5A), 71.0 (PhCH2),
70.3 (C-5D), 69.4 (C-3B), 69.2 (C-5C), 68.9 (C-6B), 68.7 (C-6D),
67.9 (C-6C), 67.7 (C-6A), 66.8 (OCH2), 65.6 (C-4C), 62.4 (C-5B),
55.4 (C-2C), 50.6 (CH2N3); MALDI-MS: 1693.6 [M+Na]+; Anal. Calcd
for C97H98N4O22 (1670.67): C, 69.69; H, 5.91; found: C, 69.52; H,
6.10.
NIS (700 mg, 3.11 mmol) followed by TfOH (15 lL) and then al-
lowed to stir at ꢂ35 °C for 30 min. The reaction mixture was fil-
tered through a CeliteÒ bed and washed several times with
CH2Cl2 (50 mL). The organic layer was washed with 5% aq Na2S2O3,
satd NaHCO3 and water in succession, dried (Na2SO4), and
concentrated. The crude product was purified over SiO2 using hex-
ane–EtOAc (4:1) as eluant to give pure compound 9 (2.1 g, 72%).
Colorless oil; ½a D25
¼ þ25 (c 1.0, CHCl3); IR (neat): 3418, 2911,
ꢁ
2769, 2211, 1664, 1498, 1411, 1379, 1255, 1063, 982, 668 cmꢂ1
;
4.5. 2-Azidoethyl (3,4,6-tri-O-acetyl-2-deoxy-2-N-phthalimido-b-
1H NMR (500 MHz, CDCl3): d 7.89–7.77 (m, 2H, Ar-H), 7.56–7.54
(m, 2H, Ar-H), 7.53–6.79 (m, 24H, Ar-H), 5.52 (d, J = 4.0 Hz, 1H,
H-1D), 5.40 (d, J = 10.0 Hz, 1H, H-1C), 5.36 (s, 1H, PhCH), 4.89–
4.85 (m, 1H, PhCH2), 4.72 (d, J = 11.0 Hz, 1H, PhCH2), 4.68 (d,
J = 11.0 Hz, 1H, PhCH2), 4.57 (d, J = 11.0 Hz, 1H, PhCH2), 4.51–4.47
(m, 2H, H-2C, PhCH2), 4.39 (d, J = 11.0 Hz, 1H, PhCH2), 4.36–4.34
(m, 1H, H-6aD), 4.19 (d, J = 11.0 Hz, 1H, PhCH2), 3.90–3.56 (m, 7H,
H-2D, H-3C, H-3D, H-4C, H-4D, H-6bD, PhCH2), 3.78 (s, 3H, OCH3),
3.56 (br s, 1H, H-5D), 3.34–3.32 (m, 1H, H-5C), 3.25–3.23 (m, 1H,
H-6aC), 2.81–2.78 (m, 1H, H-6bC), 2.72–2.64 (m, 2H, SCH2CH3),
1.94 (t, J = 7.4 Hz, 1H, SCH2CH3); 13C NMR (125 MHz, CDCl3): d
167.9, 167.4 (Phth), 159.1–113.5 (Ar-C), 101.7 (PhCH), 97.4
(C-1D), 83.1 (C-3D), 81.7 (C-1C), 77.8 (C-3C), 75.4 (C-4D), 74.9
(C-2D), 74.7 (PhCH2), 73.3 (C-5D), 72.9 (PhCH2), 72.6 (PhCH2), 71.8
(PhCH2), 70.2 (C-4C), 69.5 (C-5C), 68.8 (C-6D), 67.5 (C-6C), 55.2
(OCH3), 54.2 (C-2C), 23.9 (SCH2CH3), 14.9 (SCH2CH3); ESI-MS:
1016.3 [M+Na]+; Anal. Calcd for C58H59NO12S (993.38): C, 70.07;
H, 5.98; found: C, 69.90; H, 6.16.
D
-glucopyranosyl)-(1?3)-(2,4,6-tri-O-benzyl-
syl)-(1?3)-(4,6-O-benzylidene-2-deoxy-2-N-phthalimido-b-
glucopyranosyl)-(1?2)-(3-O-benzyl-4,6-O-benzylidene- -glu-
copyranosyl)-(1?6)-2,3,4-tri-O-benzyl- -glucopyranoside 11
a-D-galactopyrano
D
-
a
-D
a-D
To a solution of compound 10 (1.2 g, 0.72 mmol) and compound
6 (380 mg, 0.79 mmol) in anhydrous CH2Cl2 (10 mL) was added MS
4 Å (1 g) and the reaction mixture was cooled to ꢂ25 °C under
argon. To the cooled reaction mixture was added NIS (190 g,
0.84 mmol) followed by TfOH (5 lL) and then allowed to stir at
ꢂ25 °C for 20 min. The reaction mixture was filtered through a Cel-
iteÒ bed and washed several times with CH2Cl2 (50 mL). The organ-
ic layer was washed with 5% aq Na2S2O3, satd NaHCO3 and water in
succession, dried (Na2SO4), and concentrated. The crude product
was purified over SiO2 using hexane–EtOAc (4:1) as eluant to give
pure compound 11 (1 g, 67%). Colorless oil; ½a D25
¼ þ18 (c 1.0,
ꢁ
CHCl3); IR (neat): 3019, 2418, 2210, 1849, 1628, 1415, 1322,
1122, 1042, 988, 756, 668 cmꢂ1 1H NMR (500 MHz, CDCl3): d
;
7.63–6.93 (m, 51H, Ar-H), 6.62–6.60 (m, 2H, Ar-H), 5.82 (dd,
J = 10.2, 10.2 Hz, 1H, H-3E), 5.58 (d, J = 8.5 Hz, 1H, H-1C), 5.47 (d,
J = 8.5 Hz, 1H, H-1E), 5.35 (d, J = 3.5 Hz, 1H, H-1D), 5.34 (s, 1H,
PhCH), 5.10 (t, J = 8.5 Hz, 1H, H-4E), 5.06 (d, J = 11.0 Hz, 1H, PhCH2),
4.92 (d, J = 11.0 Hz, 1H, PhCH2), 4.87 (s, 1H, PhCH), 4.86
(d, J = 3.5 Hz, 1H, H-1B), 4.84 (d, J = 11.0 Hz, 1H, PhCH2), 4.79 (d,
J = 11.5 Hz, 1H, PhCH2), 4.72 (dd, J = 11.0 Hz, 2H, PhCH2), 4.62
(d, J = 3.0 Hz, 1H, H-1A), 4.55 (d, J = 11.0 Hz, 1H, PhCH2), 4.39 (dd,
J = 8.5 Hz, 1H, H-2C), 4.35–4.28 (m, 3 H, H-2E, H-6aE, H-5E), 4.22
(d, J = 11.5 Hz, 1H, PhCH2), 4.32–3.88 (m, 10H, H-2D, H-3C, H-3D,
H-4D, H-6abB, H-6bE, PhCH2), 3.83–3.51 (m, 18H, H-2B, H-3A, H-3B,
H-4C, H-5A, H-5C, H-5D, H-6abA, H-6abC, H-6abD, PhCH2, CH2N3),
3.52–3.43 (m, 2H, H-4A, H-5B), 3.36–3.33 (m, 2H, H-2A, H-4B),
2.98–2.94 (m, 1H, OCH2), 2.79–2.73 (m, 1H, OCH2); 13C NMR
(125 MHz, CDCl3): d 170.1, 170.0, 169.9 (3 COCH3), 167.6, 167.3
(Phth), 167.2 (2C, Phth), 148.2–123.0 (Ar-C), 101.3 (PhCH), 100.9
(PhCH), 100.0 (C-1E), 99.5 (C-1B), 99.4 (C-1C), 97.0 (C-1D), 96.6 (C-
1A), 82.5 (C-3A), 82.4 (C-4B), 81.9 (C-2A), 80.1 (C-4A), 78.4 (C-3D),
78.1 (C-2B), 76.5 (C-5E), 76.4 (C-4D), 75.8 (PhCH2), 74.9 (PhCH2),
74.8 (PhCH2), 74.6 (C-2D), 73.9 (C-3C), 73.5 (PhCH2), 73.1 (PhCH2),
72.8 (PhCH2), 72.6 (C-5A), 71.3 (C-5D), 70.6 (C-3B), 70.5 (PhCH2),
70.2 (C-3E), 69.0 (C-4E), 68.9 (C-6B), 68.5 (C-6D), 67.9 (C-6C), 67.7
(C-6A), 67.0 (OCH2), 66.9 (C-5C), 65.7 (C-4C), 62.3 (C-5B), 61.9
4.4. 2-Azidoethyl (2,4,6-tri-O-benzyl-
3)-(4,6-O-benzylidene-2-deoxy-2-N-phthalimido-b-
anosyl)-(1?2)-(3-O-benzyl-4,6-O-benzylidene- -glucopyrano-
syl)-(1?6)-2,3,4-tri-O-benzyl- -glucopyranoside 10
a
-
D
-galactopyranosyl)-(1?
D
-glucopyr-
a-D
a-D
To a solution of compound 8 (1.2 g, 1.39 mmol) and compound
9 (1.5 g, 1.51 mmol) in anhydrous CH2Cl2 (20 mL) was added MS
4 Å (2 g) and the reaction mixture was cooled to ꢂ30 °C under
argon. To the cooled reaction mixture was added NIS (360 mg,
1.6 mmol) followed by TfOH (15 lL) and then allowed to stir at
ꢂ30 °C for 30 min. The reaction mixture was warmed up to 0 °C
and stirred at 0 °C for 1 h. The reaction mixture was filtered
through a CeliteÒ bed and washed several times with CH2Cl2
(50 mL). The organic layer was washed with 5% aq Na2S2O3, satd
NaHCO3 and water in succession, dried (Na2SO4), and
concentrated. The crude product was purified over SiO2 using hex-
ane–EtOAc (4:1) as eluant to give pure compound 10 (1.6 g, 69%).
Colorless oil; ½a D25
¼ þ28 (c 1.0, CHCl3); IR (neat): 3087, 2856,
ꢁ
1732, 1719, 1625, 1520, 1375, 1239, 1173, 1097, 1072, 989, 911,
823, 755, 698 cmꢂ1 1H NMR (500 MHz, CDCl3): d 7.69–7.24 (m,
;
35H, Ar-H), 7.14–6.92 (m, 14H, Ar-H), 5.56 (d, J = 3.5 Hz, 1H,
H-1D), 5.54 (d, J = 9.0 Hz, 1H, H-1C), 5.34 (s, 1H, PhCH), 5.06 (s,

D. Dhara et al. / Tetrahedron: Asymmetry 25 (2014) 263–267
267
(C-6E), 55.5 (C-2C), 55.0 (C-2E), 50.5 (CH2N3), 20.8 (COCH3), 20.6
Acknowledgments
(COCH3), 20.4 (COCH3); MALDI-TOF-MS: 2110.7 [M+Na]+; Anal.
Calcd for C117H117N5O31 (2087.77): C, 67.26; H, 5.64; found: C,
67.10; H, 5.82.
D.D. thanks CSIR, New Delhi for providing a Junior Research Fel-
lowship. This work was supported by CSIR, New Delhi [Project No.
02(0038)/11/EMR-II] and Bose Institute, Kolkata.
4.6. 2-Aminoethyl (2-acetamido-2-deoxy-b-
D-glucopyranosyl)-
(1?3)-( -galactopyranosyl)-(1?3)-(2-acetamido-2-deoxy-b-D-
glucopyranosyl)-(1?2)-(a-D-glucopyranosyl)-(1?6)-a-D-glucopy
a
-
D
References
ranoside 1
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To a solution of compound 11 (700 mg, 0.34 mmol) in EtOH
(15 mL) was added NH2NH2ꢃH2O (0.5 mL, 10.31 mmol) and the
reaction mixture was stirred at 80 °C for 8 h. The solvents were
removed under reduced pressure and a solution of the crude prod-
uct in acetic anhydride and pyridine (5 mL; 1:1) was kept at room
temperature for 1 h. The reaction mixture was evaporated and
co-evaporated with toluene (3 ꢄ 20 mL) under reduced pressure.
A solution of the acetylated product in 0.1 M CH3ONa in CH3OH
(10 mL) was stirred at room temperature for 2 h, neutralized with
Dowex 50W X8 (H+), filtered, and concentrated. To a solution of the
de-O-acetylated product and 20% Pd(OH)2-C (100 mg) in CH3OH–
EtOAc (10 mL; 3:1) was added dropwise Et3SiH (2 mL, 12.52 mmol)
over 30 min and the reaction mixture was allowed to stir at room
temperature for 10 h. The reaction mixture was filtered through a
Celite bed and washed with CH3OH (50 mL) and the combined fil-
trate was evaporated under reduced pressure to give a product,
which was passed through a Sephadex LH-20 column using CH3-
OH–H2O (3:1) as eluant to give pure compound 1 (185 mg, 57%).
Glass; ½a 2D5
ꢁ
¼ þ8 (c 1.0, H2O); IR (KBr): 3435, 2946, 1617, 1397,
1155, 1096, 667 cmꢂ1
;
1H NMR (500 MHz, D2O): d 5.35 (d,
J = 3.0 Hz, 1H, H-1D), 5.00 (br s, 2H, H-1A, H-1B), 4.88 (2 d,
J = 8.0 Hz each, 2H, H-1C, H-1E), 4.16–4.00 (m, 2H, H-4D, H-5A),
3.96–3.70 (m, 6H, H-2C, H-2D, H-3C, H-5D, H-6aA, H-6aB), 3.68–
3.50 (m, 14H, H-2E, H-3A, H-3B, H-3D, H-4C, H-5B, H-6bA, H-6bB, H-
13. Bhattacharyya, S.; Magnusson, B. G.; Wellmar, U.; Nilsson, U. J. J. Chem. Soc.,
Perkin Trans 1 2001, 886–890.
14. (a) Fraser-Reid, B.; Lopez, J. C. Top. Curr. Chem. 2011, 301, 1–29; (b) Mootoo, D.
R.; Konradsson, P.; Udodong, U.; Fraser-Reid, B. J. Am. Chem. Soc. 1988, 110,
5583–5584.
6abC, H-6abD, H-6abE), 3.48–3.15 (m, 8H, H-2A, H-2B, H-3E, H-4A, H-
15. Lemieux, R. U. Can. J. Chem. 1951, 29, 1079–1091.
5C, H-5E, OCH2), 3.14–3.00 (m, 2H, H-4B, H-4E), 2.99–2.92 (m, 2H,
NCH2), 2.12, 2.11 (2 s, 6H, 2 COCH3); 13C NMR (125 MHz, D2O): d
176.0, 175.9 (2 COCH3), 98.4 (3C, C-1C, C-1D, C-1E), 97.9 (C-1A),
97.8 (C-1B), 75.9 (C-2B), 75.8 (C-3D), 73.0 (3 C, C-3C, C-5D, C-5E),
71.5 (3 C, C-4D, C-5A, C-5C), 71.1 (3 C, C-2A, C-2D, C-3E), 70.6 (3 C,
C-3A, C-3B, C-5B), 69.6 (2 C, C-4A, C-4B), 66.1 (C-4C), 63.7 (C-6A),
60.7 (3 C, C-6B, C-6C, OCH2), 60.4 (2 C, C-6D, C-6E), 59.9 (C-4E),
56.8 (C-2C), 54.2 (C-2E), 39.3 (NCH2), 23.2 (2 C, 2 COCH3); ESI-
MS: 976.3 [M+Na]+; Anal. Calcd for C36H63N3O26 (953.37): C,
45.33; H, 6.66; found: C, 45.16; H, 6.80.
16. Eis, M. J.; Ganem, B. Carbohydr. Res. 1988, 176, 316–323.
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