Synthesis of 1,2,3-triazolyl analog of Neisseria meningitidis A capsular polysaccharide

Article abstract of DOI:10.1080/07328303.2018.1524012

Towards constructing a stable, non-hydrolyzable linkage for Neisseria meningitidis type A (MenA) polysaccharide, the phosphate bridge of its (1→6)-linked 2-acetamido-2-deoxy-α-D-mannopyranosyl phosphate repeating unit was replaced by a triazolyl analog using Cu(I) catalyzed click reaction. The synthesis involved anomeric azidation of N-acetyl-D-mannosamine derivative from its acetate precursor using stoichiometric amount of FeCl₃ and one-pot synthesis of precursors for di- and tri- triazolyl saccharides with an azidoethyl spacer at the reducing end for bioconjugation.

Full text of DOI:10.1080/07328303.2018.1524012

Journal of Carbohydrate Chemistry
ISSN: 0732-8303 (Print) 1532-2327 (Online) Journal homepage: http://www.tandfonline.com/loi/lcar20
Synthesis of 1,2,3-triazolyl analog of Neisseria
meningitidis A capsular polysaccharide
Madhuri Vangala & Srinivas Hotha
To cite this article: Madhuri Vangala & Srinivas Hotha (2018): Synthesis of 1,2,3-triazolyl analog
of Neisseriaꢀmeningitidis A capsular polysaccharide, Journal of Carbohydrate Chemistry, DOI:
10.1080/07328303.2018.1524012
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JOURNAL OF CARBOHYDRATE CHEMISTRY
https://doi.org/10.1080/07328303.2018.1524012
Synthesis of 1,2,3-triazolyl analog of Neisseria
meningitidis A capsular polysaccharide
Madhuri Vangala
and Srinivas Hotha
Department of Chemistry, Indian Institute of Science Education and Research, Pune, India
ABSTRACT
ARTICLE HISTORY
Received 28 May 2018
Accepted 11 September 2018
Towards constructing a stable, non-hydrolyzable linkage for
Neisseria meningitidis type A (MenA) polysaccharide, the phos-
phate bridge of its (1!6)-linked 2-acetamido-2-deoxy-a-D-
mannopyranosyl phosphate repeating unit was replaced by a
triazolyl analog using Cu(I) catalyzed click reaction. The syn-
thesis involved anomeric azidation of N-acetyl-D-mannosamine
derivative from its acetate precursor using stoichiometric
amount of FeCl3 and one-pot synthesis of precursors for di-
and tri- triazolyl saccharides with an azidoethyl spacer at the
reducing end for bioconjugation.
KEYWORDS
Click chemistry; N-acetyl
D-mannosamine; Neisseria
meningitidis;
oligosaccharide
GRAPHICAL ABSTRACT
R
O
NHAc
R = TBDPS
O
BnO
BnO
NHAc
O
TBDPSO
N
BnO
BnO
O
N
NHAc
O
N
N
HO
RO
3
O
P
n= 0,1,2
NHAc
O
O
O
BnO
BnO
Na
O
HO
HO
R = H, Ac
O
N
N
Native MenA CPS
HO
N
OH
OMe
N
3
Traizolyl analogue of MenA
Introduction
Bacterial meningitis, caused by one of three pathogens Neisseria meningiti-
dis, Streptococcus pneumonia and Haemophilus influenza type b (Hib), is a
serious infection that affects the membrane surrounding brain and spinal
cord.[1] Conjugate vaccines are available for pneumococcus and Hib leaving
behind meningococcus, the major cause of meningitis in Sub-Saharan
African regions and world over.[1d,2] Serotypes A, B, C, Y and W-135 are
CONTACT Madhuri Vangala
madhurivangala99@gmail.com
Department of Chemistry, Indian Institute of
Science Education and Research, Dr. Homi Bhabha Road, Pune 411008, India.
Supplemental data for this article can be accessed on the publisher’s website.
Color versions of one or more of the figures in the article can be found online at www.tandfonline.com/lcar.
ß 2018 Taylor & Francis Group, LLC

2
M. VANGALA AND S. HOTHA
among the thirteen capsular serogroups of N. meningitidis with serotype A
(MenA) being responsible for epidemics in the ‘meningitis belt’.[1,3]
Effective vaccines were made either using purified capsular polysaccharides
(MenA-P) as the antigenic material that had limited clinical usefulness or
using MenA-P conjugates to carrier proteins, such as diptheria toxoid, tet-
anus toxoid and CRM197 (Menactra, Menveo and Nimenrin), for establish-
ing long-term immunological memory.[3a,4] The capsular polysaccharide
structure of MenA consists of repeating units of a-(1!6)-linked 2-acet-
amido-2-deoxy-a-D-mannopyranosyl phosphate residues (Figure 1, I)
majorly O-acetylated at the 3-OH position.[5]
Pozsgay and Oscarson groups independently reported the synthesis of
MenA-P fragments, where the antigenicity of glycoconjugates of these syn-
thetic molecules were demonstrated by Pozsgay group and more recently
by Chhikara and coworkers.[6] However, the instability of the bridging
anomeric phosphodiester in water[7] along with the readily hydrolyzable O-
glycosidic bond under acidic or enzymatic conditions challenged the stor-
age and formulation of MenA-P glycoconjugates. Hence, glycoconjugate
vaccines against MenA, with long shelf-life for use in the “meningitis belt”
are of immense importance. In this direction, Nicotra and Oscarson inde-
pendently reported the stable C-phosphonate analog of MenA (Figure 1,
II).[8] Subsequently, Lay et al. and Lombardi et al. showed the successful
recognition of short C-phosphonate oligomers by human polyclonal anti-
MenA serum.[9] Further, stable carbocyclic analog of MenA (Figure 1, III)
was reported by Lay and coworkers, where the glycoconjugated trimer was
O
O
NHAc
O
NHAc
O
HO
RO
HO
HO
O
P
O
O
P
II
I
Na
O
O
Na
R = H, Ac
C-phosphonate
analogue of MenA CPS
Repeating unit of MenA CPS
O
NHAc
O
O
HO
HO
NHAc
HO
HO
O
P
N
N
O
N
III
IV
Na
O
proposed
triazole analogue of MenA CPS
carba analogue of MenA CPS
Figure 1. Structures of MenA-P, its analogs and proposed triazole analog.

JOURNAL OF CARBOHYDRATE CHEMISTRY
3
noticed to elicit the anti-MenA-P antibodies indicating that the isosteric
modifications are well tolerated.[10]
Pozsgay and coworkers in their earlier report suggested that a monosac-
charide fragment of natural MenA-P exhibited the antigenicity even with-
out the phosphate group and O-acetylation at the 3-O-position.[6a] These
encouraging observations along with the literature reports on replacement
of either the phosphate group of nucleic acids[11] or the O-glycosidic linkages
of oligosaccharides[12] by the triazole linkage prompted us to synthesize a
stable analog of MenA-P. As part of our endeavors in carbohydrate chemis-
try,[13] we describe here the first synthesis of 1-azido-N-acetyl mannos-
amine derivative and its conversion into 1,4-disubstituted 1,2,3-triazole
linked mono-, di- and tri-saccharide analogs of MenA-P (Figure 1, IV)
using click reaction[14] conditions. In order to reduce the protection/depro-
tection steps, a one pot synthetic strategy was employed to make precursors
for higher oligomer synthesis with an azidoethyl spacer arm towards the
reducing end for eventual bioconjugation.
Results and discussion
Synthesis of intermediate 10 (Scheme 1) was started from methyl 4,6-O-
benzylidene a-D-glucopyranoside 2 which was conveniently prepared from
the commercially available methyl a-D-glucopyranoside 1 using benzylidene
dimethyl acetal and p-toulenesulfonic acid monohydrate in DMF.[15] The
C-2 hydroxyl group of diol 2 was selectively converted into corresponding
O-triflate and subjected to nucleophilic displacement with sodium azide in
DMF at 70 ꢀC to afford the manno-derivative 3 in a 78% yield over two
steps.[16] The spectral data and specific rotation values are in complete
agreement with that of the reported data.[16a] The resulting azide 3 was
subjected to hydrogenation over Pd/C under H2 atmosphere[17] followed by
i. Tf2O, CH2Cl2
0 oC, 1 h
i. H2, Pd/C, 5 h
ii. Ac2O, pyridine
12 h
ii. NaN3, DMF,
70 oC 12 h
PhC(OMe)2
PTSA
DMF, 60 oC, 3 h
85%
HO
HO
N3
O
O
O
Ph
Ph
O
O
O
O
HO
HO
HO
78%
(ref 16a)
90%
OH
OH
OMe
OMe
OMe
1
4
2
3
NHAc
O
TBDPSO
NaOMe
MeOH
NHAc
O
HO
NHAc
O
TBDPSCl
imidazole
O
O
Ph
PTSA
MeOH, 25 oC
1.5 h, 84%
HO
HO
AcO
AcO
AcO
15 min, 91%
DMF, 12 h, 88%
5
7
OMe
OMe
OMe
NHAc
O
AcO
AcO
AcO
TBDPSO
NHAc
O
TBDPSO
TBDPSO
NHAc
O
NHAc
O
OMe
BnBr, NaH
DMF 0 to 25 oC
Ac2O, H2SO4
0 oC, 1 h, 68%
HO
HO
6
BnO
BnO
BnO
BnO
8
OMe
1 h, 83%
9
OMe
10 OAc
Scheme 1. Synthesis of anomeric acetate derivative 10.

4
M. VANGALA AND S. HOTHA
acetylation with Ac2O in pyridine to give acetamido derivative 4 in a 90%
yield in two steps. Benzylidene deprotection under acidic conditions
(PTSA/MeOH) resulted in the isolation of 4,6-diol 5 in an 84% yield.
At this stage, the 6-OH and 4-OH groups in acetamide 5 were acetylated
to obtain compound 6, but our attempts to transform anomeric O-methyl
to O-acetyl using H2SO4 in acetic anhydride showed very poor yields. This
compelled us to revise the synthetic design and convert acetate 5 into more
reactive silyl ether. Thus, the primary hydroxyl group of diol 5 was pro-
tected as its t-butyldiphenylsilyl (TBDPS) ether using TBDPS-Cl/imidazole
ꢀ
in DMF to obtain silyl ether 7 and Zemplen deacetylation produced the
diol 8 in a 91% yield. Subsequently, the diol was alkylated with BnBr in the
presence of NaH in DMF to afford compound 9 in an 83% yield which
upon treatment with catalytic amount of H2SO4 in acetic anhydride at 0 ꢀC
for 1 h furnished the desired a-anomer 10 as the major compound in a
68% yield.
We next turned our attention to screen various Lewis acids to access
anomeric azide (Table 1). Reaction of acetate 10 and 3 equivalents of
TMSN3 in anhydrous CH2Cl2 with 10 mol% ZnCl2 did not furnish the
desired azide even after prolonged time (Table 1, entry 1). Similar observa-
tion was noticed with 10 mol% AlCl3 as well (Table 1, entry 2), which gave
only trace amounts of desired product after stirring for 24 h. On the con-
trary, 10 mol% AuCl3 or AuBr3 (Table 1, entry 3) led to 25% conversion of
Table 1. Screening of the Lewis acids for the synthesis of key intermediate 11.
TMSN3
Lewis acid
Table 1
TBDPSO
NHAc
O
BnO
BnO
10
11
N3
ORTEP diagram of compound 11
(H-atoms not shown for clarity)
Entry
Lewis acid
ZnCl2
AlCl3
AuCl3 or AuBr3
TMSOTf
FeCl3
equiv
Conversion into azide 11
time
1
2
3
4
5
6
0.1
0.1
0.1
0.5
0.5
1.0
No rxn
Trace
25%
50%
40%
2 h
24 h
3 h
3.5 h
2 h
FeCl3
100%
1 h
(78% Yield)1
Conditions: 3 eq TMSN3 in anhydrous CH2Cl2 and conversion based on TLC. 1Isolated yield after column
chromatography.

JOURNAL OF CARBOHYDRATE CHEMISTRY
5
the acetate 10 to 11 in 3 h. Furthermore, catalytic amount of TMSOTf was
ineffective but 0.5 equivalents of TMSOTf (Table 1, entry 4) led to a 50%
conversion into product in 3.5 h. However, the use of TMSOTf in stoichio-
metric quantity headed to the deprotection of TBDPS group. On the other
[18]
hand, 0.5 equivalents of FeCl3
turned out to be the most effective with
40% conversion of starting material to product in 2 h. Further, increasing
the FeCl3 amount[13b] to 1 equivalent afforded the product 11 as the major
1
compound in 1 h (78% yield). In the H NMR spectrum of compound 11,
the anomeric proton at d 5.50 ppm showed a diequatorial coupling constant
3
of J1,2 ¼ 1.6 Hz. The a-anomeric configuration of azide was ascertained by
the NOESY cross-peaks between the anomeric C1-H and C-2 acetamide
1
and C1-H and t-Bu group along with the large JC-1,H-1 ¼ 170.45 Hz cou-
1
pling constant value measured from H coupled HSQC spectral data (see
supporting information file pages S24-S30). Additionally, the structure of
azide 11 was further confirmed unambiguously by single-crystal X-ray ana-
lysis (Table 1, CCDC number 1820104).
Silyl ether moiety of thoroughly confirmed compound 11 was depro-
tected using HF.pyridine to afford alcohol 12 that was alkylated to obtain
propargyl ether 13 (80% yield) using propargyl bromide and NaH in DMF
(Scheme 2). The presence of terminal alkyne and anomeric azide in the
monosaccharide is strategically positioned to undergo intermolecular or
intramolecular azide alkyne 1,3-dipolar cycloaddition. Indeed, compound
13 was found to transform into a polar compound even when stored at
0 ꢀC, which could be either a cyclo-oligomerized or a linearly- oligomerized
cycloaddition product, and hence should be used immediately.[19] With
azido-alkyne 13 in hand, our next attempt was focused on the viability of
one pot installation of the spacer 14 and the synthesis of precursors for di-
and tri-saccharide triazolyl analogs. Thus, the spacer 14 in DMF was
treated with CuI and N,N-diisopropylethylamine and stirred for 15 min and
then azido-alkyne 13 in anhydrous DMF was introduced and stirred for
another 3 h under high dilution conditions to give 15[20] and 16 as major
products along with some unidentified products. We anticipated that the
reaction sequence would prevent the homo oligomerization of compound
13. On the other hand, reversing the sequence of addition steps or using
excessive amount of compound 14 gave the Glaser coupling product 17[21]
(confirmed by mass/IR) along with the monosaccharide 15 as the major
product. Conversely, cycloaddition of compound 11 and 13 in the presence
of catalytic amount of CuI (0.1 eq) and N,N-diisopropylethylamine (1 eq)
under dilute conditions for 2.5 h gave disaccharide 18 as the major product
along with other unidentified cycloaddition products. The structures of 1,4-
disubstuted 1,2,3-triazole compounds 15, 16 and 18 were confirmed by the
1
characteristic signals at 7.56 ppm for H5 of triazole ring in the H NMR

6
M. VANGALA AND S. HOTHA
O
NHAc
O
HF.Py
pyridine
0 oC to rt
2 h, 88%
HO
BnO
propargyl bromide
NaH
DMF, 0 oC to rt
30 min, 80%
NHAc
O
11
BnO
BnO
BnO
N3
12
13
N3
OTs
O
NHAc
O
BnO
BnO
O
N
N
NHAc
O
BnO
BnO
N
N
N
O
N
OTs
O
NHAc
O
unidentified
compounds
17
NHAc
O
CuI, DIPEA
O
BnO
BnO
NHAc
O
13
(1 eq)
BnO
BnO
DMF, rt, 2 h
BnO
BnO
14
N
N
N
(1.2 eq)
N3
N
N
15
OTs
N
16
OTs
28%
precursor for dimer
12%
precursor for trimer
OTBDPS
NHAc
O
BnO
BnO
N
N
N
unidentified
compounds
CuI, DIPEA
DMF, rt, 2.5 h
11
13
(1 eq)
(0.75 eq)
O
NHAc
O
BnO
BnO
18
N3
14%
precursor for trimer
Scheme 2. One pot synthesis of precursors for di- and tri- triazolosachharides.
spectrum and 121.8 ppm for C-5 in the 13C NMR spectrum respectively
along with good matching of HRMS spectral data. With these key precur-
sors 15, 16 and 18 in hand, we set out to make mono-, di- and tri-sacchar-
ide triazolyl analogs of MenA capsular polysaccharide which can be used to
understand the minimum fragment required for immunogenicity.
Thus, cycloaddition of compound 11 and spacer 14 in DMF using cata-
lytic CuI (0.2 eq) and N,N-diisopropylethylamine (1 eq) for 3 h gave tosyl-
ate 19 in an 82% yield (Scheme 3) which upon successive nucleophilic
displacement with NaN3 at 70 ꢀC afforded azide 20 in a 91% yield. In a
similar fashion, coupling of alkyne 15 with azide 11 under the above-men-
tioned conditions furnished 21 in an 81% yield. The latter on azidation
gave triazole-linked disaccharide 22 in an 86% yield.
In continuation, cycloaddition of either 16 and 11 with a stoichiometric
CuI (0.8 eq) or 18 and 15 with CuI (0.4 eq) and N,N-diisopropylethylamine
(1.2 eq) provided triazole-linked trisaccharide 23 in a 78% yield. The latter

JOURNAL OF CARBOHYDRATE CHEMISTRY
7
16
18
11
15
11
15
14
11
or
OTBDPS
NHAc
CuI, DIPEA
DMF, rt ,
3 h, 82%
CuI, DIPEA
DMF, rt
3 h, 81%
O
CuI, DIPEA
DMF, rt ,
BnO
BnO
3.5 h, 78%
N
N
N
OTBDPS
NHAc
O
O
OTBDPS
NHAc
O
BnO
BnO
NHAc
O
BnO
BnO
BnO
BnO
N
N
N
N
N
N
N
N
N
O
R
NHAc
O
(19)
(20)
R= OTs
R= N3
O
NaN3
NHAc
O
DMF, 70 o
12 h, 91%
C
BnO
BnO
BnO
BnO
N
N
N
N
N
N
R
R
(23)
(24)
R= OTs
R= N3
NaN3
(21)
R= OTs
NaN3
DMF, 70 o
12 h, 86%
C,
DMF, 70 o
12 h, 81%
C,
R= N3 (22)
Scheme 3. Synthesis of mono-, di- and tri- triazolosaccharides 20, 22 and 24.
combination turned out to be a certain choice as the intermediates 18 and
15 are comparatively non-polar making identification and purification of
compound 23 easier. Furthermore, applying the same set of reaction condi-
tions to tosylate 23 afforded azide 24 in a 81% yield.
In summary, anomeric azidation of N-acetyl mannopyranosyl derivative
was accomplished which would enable synthesis of various functionally
rich diverse scaffolds. The synthetic strategy is operationally simple and
needs minimum number of synthetic steps for linking the N-acetyl manno-
pyranosyl units with 1,4-disubstituted 1,2,3-triazole, providing fragments of
varied length. Our future efforts will be directed towards bioconjugation to
protein and studying the immunogenicity.
Experimental section
General methods
All reactions were carried out with distilled and dried solvents using oven-
dried glassware. All reagents were purchased from commercial sources and
1
were used without further purification unless otherwise stated. H NMR
(400 MHz), 13C (100 MHz), DEPT (135 MHz), 2 D NMR were recorded in
CDCl3 or MeOH-d4 depending on the solubility using TMS as internal
1
standard. Coupling constants (J) are given in Hertz (Hz). In H NMR spec-
tra signal multiplicity is abbreviated as s ¼ singlet, d ¼ doublet, dd ¼ doublet
of doublet, dt ¼ doublet of triplet, td ¼ triplet of doublet, t ¼ triplet,
q ¼ quartet, m ¼ multiplet, br ¼ broad. Melting points are uncorrected. IR

8
M. VANGALA AND S. HOTHA
spectra were recorded on a FT-IR spectrometer, and only major peaks were
reported in cmꢁ1. Optical rotations were measured on a polarimeter using
sodium light (D line 589 nm). Column chromatography was carried out
using silica gel (100–200 mesh). Mass samples were analyzed by High reso-
lution mass spectroscopy (HRMS)/MALDI-TOF using positive ion ESI-
TOF ionization sources.
Methyl 2-azido-4,6-O-benzylidene-2-deoxy-a-D-mannopyranoside (3).
To a solution of compound 2 (5 g, 17.7 mmol) in dry CH2Cl2 (50 mL) at
0 ꢀC, pyridine (2.85 mL, 35.4 mmol) was added. Triflic anhydride (3.36 mL,
20.3 mmol) was slowly added to the mixture and temperature kept at 0 ꢀC
for 1 h. The reaction mixture was quenched by adding water (15 mL) and
extracted with CH2Cl2 (50 mL ꢂ 2). The combined organic layers washed
with brine, dried over Na2SO4, filtered, concentrated and used as such
without further purification. The crude triflate compound (8 g, 25.4 mmol)
was dissolved in dry DMF (50 mL) and NaN3 (4.96 g, 76.4 mmol) is added.
The reaction mixture was stirred at 70 ꢀC for 12 h. Reaction quenched by
adding water and extracted with EtOAc (50 mL ꢂ 2) and processed as men-
tioned above to give crude mixture which was purified by column chroma-
tography to afford product 3. Thick liquid: Rf ¼ 0.5 (petroleum ether/
20
EtOAC, 80:20); Yield: (4.2 g, 78%); [a]D (Literature) ¼ þ59.1 (c 1 CHCl3);
20
1
[a]D ¼ þ64.2 (c 1 CHCl3); H NMR (400 MHz, CDCl3) d 7.51 – 7.46 (m,
2H), 7.42 – 7.36 (m, 3H), 5.58 (s, 1H), 4.70 (d, J ¼ 1.4 Hz, 1H), 4.29 – 4.23
(m, 1H), 3.98 (dd, J ¼ 4.0, 1.4 Hz, 1H), 3.90 (t, J ¼ 9.4 Hz, 1H), 3.85 – 3.73
(m, 2H), 3.39 (s, 3H), 2.62 (d, J ¼ 3.9 Hz, 1H). 13C NMR (101 MHz,
CDCl3) d 137.1, 129.5, 128.5, 126.4, 102.4, 100.2, 79.1, 68.9, 68.8, 63.7, 63.4,
55.3. DEPT NMR (135 MHz, CDCl3) d 129.4, 128.5, 126.4, 102.4, 100.1,
79.1, 68.9, 68.7, 63.7, 63.4, 55.3. IR (CHCl3) ꢀ 3470, 2108, 1380, 1064 cmꢁ1.
HRMS (TOF): [M þ Na]þ calcd for C14H17N3NaO5 330.1066,
found 330.1064.
Attention: As documented in the literature, ionic azides can react with
CH2Cl2 to form explosive azidochloromethane and/or diazidomethane.[22]
So, work up/purification for the above reaction was carried out
using EtOAc.
Methyl 2-acetamido-3-O-acetyl 4,6-O-benzylidene-2-deoxy-a-D-manno-
pyranoside (4). A solution of 3 (3.5 g, 11.4 mmol) in EtOAc (30 mL) was
stirred under an atmosphere of hydrogen in the presence of 10% Pd/C
(100 mg) for 5 h. The reaction mixture was filtered through celite using
EtOAc and concentrated in vacuo to afford crude amine as a colorless oil
which was used without further purification. To the crude solution of
amine (3 g, 10.67 mmol) in dry pyridine (15 mL) at room temperature
acetic anhydride (3.03 mL, 32.0 mmol) was added and stirred overnight.
Pyridine removed under vacuum. The mixture was diluted with EtOAc

JOURNAL OF CARBOHYDRATE CHEMISTRY
9
(75 mL), the organic layer was washed with H2O, brine, dried over Na2SO4,
filtered, concentrated and purified by column chromatography to yield the
compound 4. White solid: Rf ¼ 0.3 (EtOAC); Yield: (3.21 g, 90%);
25
[a]D ¼ þ39.6 (c 0.5, CHCl3); mp- 211–213 ꢀC; 1H NMR (400 MHz,
CDCl3) d 7.48 – 7.43 (m, 2H), 7.40 – 7.34 (m, 3H), 5.67 (d, J ¼ 9.0 Hz,
1H), 5.56 (s, 1H), 5.37 (dd, J ¼ 10.5, 4.5 Hz, 1H), 4.70 (ddd, J ¼ 9.2, 4.5,
1.4 Hz, 1H), 4.64 (d, J ¼ 1.4 Hz, 1H), 4.29 (dd, J ¼ 10.2, 4.7 Hz, 1H), 3.98
(td, J ¼ 9.9, 4.7 Hz, 1H), 3.86 – 3.74 (m, 2H), 3.40 (s, 3H), 2.07 (s, 3H),
2.02 (s, 3H). 13C NMR (101 MHz, CDCl3) d 170.1, 170.1 137.0, 129.4,
128.4, 126.3, 102.3, 101.2, 76.8, 68.9, 68.4, 63.5, 55.4, 50.8, 23.5, 21.1. DEPT
NMR (135 MHz, CDCl3) d 129.4, 128.4, 126.3, 102.3, 101.2, 76.8, 68.9, 68.4,
63.5, 55.4, 50.8, 23.5, 21.1. IR (CHCl3) ꢀ 3290, 1737, 1659, 1539, 1234,
1092 cmꢁ1. HRMS (TOF): [M þ Na]þ calcd for C18H23NNaO7 388.1372,
found 388.1366.
Methyl 2-acetamido-3-O-acetyl 2-deoxy-a-D-mannopyranoside (5).
Compound 4 (2.5 g, 6.84 mmol) was dissolved in MeOH (70 mL). p-
Toulene sulfonic acid monohydrate (260 mg, 1.36 mmol) was added and
stirred at rt for 1.5 h. Reaction quenched by adding triethylamine (0.5 mL).
MeOH removed in vacuo and the crude residue was directly adsorbed onto
silica (to avoid loss during workup) to afford 5. Thick liquid: Rf ¼ 0.1
25
1
(EtOAC); Yield: (1.58 g, 84%); [a]D ¼ þ52.0 (c 0.5, CHCl3); H NMR
(400 MHz, MeOD4) d 5.07 (dd, J ¼ 10.0, 4.5 Hz, 1H), 4.61 (d, J ¼ 1.4 Hz,
1H), 4.50 (dd, J ¼ 4.5, 1.4 Hz, 1H), 3.92 – 3.76 (m, 3H), 3.65 – 3.59 (m,
1H), 3.41 (s, 3H), 2.02 (s, 3H), 2.00 (s, 3H). 13C NMR (101 MHz, MeOD4)
d 173.4, 172.4, 101.5, 74.0, 73.9, 65.3, 61.8, 55.3, 51.5, 22.4, 21.0. DEPT
NMR (135 MHz, MeOD4) d 101.5, 74.0, 73.9, 65.3, 61.8, 55.3, 51.5, 22.4,
21.0. IR (CHCl3) ꢀ 3284, 1723, 1653, 1546, 1069 cmꢁ1. HRMS (TOF):
[M þ Na]þ calcd for C11H19NNaO7 300.1059, found 300.1053.
Methyl 2-acetamido-3-O-acetyl 2-deoxy-6-O-t-butyldiphenylsilyl-a-D-
mannopyranoside (7). Imdiazole (5.1 g, 75.78 mmol) was added to a stirred
solution of the diol 5 (7 g, 25.26 mmol) in dry DMF (45 mL) at rt. After
10 min, TBDPSCl (9.8 mL, 37.89 mmol) was added and the reaction mixture
stirred overnight under inert conditions. Solvent was removed in vacuo,
water added to the residue and extracted with EtOAc (75 mL ꢂ 2). The
combined organic layers were washed with H2O, brine, dried over Na2SO4,
filtered and concentrated. The crude residue was purified by chromatog-
raphy to yield 7. White solid: Rf ¼ 0.3 (petroleum ether/EtOAC, 20:80);
25
1
Yield: (11.4 g, 88%); [a]D ¼ þ42.4 (c 0.27, CHCl3); mp- 191–193 ꢀC; H
NMR (400 MHz, CDCl3) d 7.75 – 7.67 (m, 4H), 7.50 – 7.37 (m, 6H), 5.57
(d, J ¼ 9.3 Hz, 1H), 5.15 (dd, J ¼ 10.0, 4.1 Hz, 1H), 4.58 (d, J ¼ 0.9 Hz, 1H),
4.58 – 4.54 (m, 1H), 4.02 – 3.85 (m, 3H), 3.66 (dt, J ¼ 9.5, 3.7 Hz, 1H), 3.33
(s, 3H), 2.49 (dd, J ¼ 4.1, 1.1 Hz, 1H), 2.07 (s, 3H), 1.97 (s, 3H), 1.09 (s,

10
M. VANGALA AND S. HOTHA
9H). 13C NMR (101 MHz, CDCl3) d 171.1, 169.9, 135.8, 135.7, 133.1, 133.0,
130.1, 128.0, 100.2, 72.4, 71.8, 66.7, 63.7, 55.2, 50.1, 27.0, 23.4, 21.2, 19.5.
DEPT NMR (135 MHz, CDCl3) d 135.8, 135.7, 130.1, 128.0, 128.0, 100.2,
72.4, 71.8, 66.7, 63.7, 55.2, 50.1, 27.0, 23.4, 21.2. IR (CHCl3) ꢀ 3439, 3371,
1726, 1659, 1545, 1109, 744 cmꢁ1. HRMS (TOF): [M þ Na]þ calcd for
C27H37NNaO7Si 538.2237, found 538.2241.
Methyl 2-acetamido 2-deoxy-6-O-t-butyldiphenylsilyl-a-D-mannopyra-
noside (8). To a stirred solution of 7 (7.5 g, 14.55 mmol) in dry MeOH
(100 mL), sodium methoxide (589 mg, 10.91 mmol) was added and stirred
at rt. After 15 min TLC indicated complete conversion of starting material.
MeOH removed on rotary evaporator and reaction mixture diluted with
EtOAc. Organic layer washed with H2O, brine, dried over Na2SO4, filtered
and concentrated and purified by chromatography to afford compound 8.
25
Thick liquid: Rf ¼ 0.2 (EtOAC); Yield: (6.26 g, 91%); [a]D ¼ þ51.3 (c 0.24,
1
CHCl3); H NMR (400 MHz, CDCl3) d 7.79 – 7.63 (m, 4H), 7.49 – 7.31
(m, 6H), 5.93 (br s, 1H), 4.61 (s, 1H), 4.32 (dd, J ¼ 8.2, 4.3 Hz, 1H), 4.01
(dd, J ¼ 9.4, 3.4 Hz, 1H), 3.97 – 3.88 (m, 2H), 3.68 (t, J ¼ 9.4 Hz, 1H), 3.58
(dt, J ¼ 9.7, 3.7 Hz, 1H), 3.29 (s, 3H), 1.95 (s, 3H), 1.06 (s, 9H). 13C NMR
(101 MHz, CDCl3) d 171.9, 135.8, 135.7, 133.4, 133.3, 129.9, 127.8, 99.9,
72.0, 70.4, 68.4, 63.6, 55.0, 53.0, 27.0, 23.3, 19.4. DEPT NMR (135 MHz,
CDCl3) d 135.7, 135.7, 129.9, 127.8, 99.9, 72.0, 70.4, 68.4, 63.6, 55.0, 53.0,
27.0, 23.3. IR (CHCl3) ꢀ 3319, 1655, 1536, 1107, 741 cmꢁ1. HRMS (TOF):
[M þ H]þ calcd for C25H36NO6Si 474.2312, found 474.2315.
Methyl 2-acetamido 3,4-di-O-benzyl- 2-deoxy-6-O-t-butyldiphenylsilyl-
a-D-mannopyranoside (9). Compound 8 (6 g, 12.67 mmol) was dissolved
in dry DMF (52 mL) under nitrogen atmosphere. RB cooled to 0 ꢀC and
60% NaH (1.76 g, 44.3 mmol) was added under inert conditions followed
by the addition of benzyl bromide (4.52 mL, 38.03 mmol). Reaction mixture
slowly allowed to come to rt. After 1 h TLC showed complete consumption
of starting material. (note: leaving reaction for longer time can give desily-
lated product). Reaction mixture cooled to 0 ꢀC and EtOAc added followed
by addition of ice. Reaction mixture further diluted with EtOAc and
washed with H2O, brine, dried over Na2SO4, filtered and concentrated and
purified by chromatography to afford compound 9. White solid: Rf ¼ 0.2
25
(petroleum ether/EtOAC, 70:30); Yield: (6.87 g, 83%); [a]D ¼ þ20.7 (c 1,
1
CHCl3); mp- 105–106 ꢀC; H NMR (400 MHz, CDCl3) d 7.77 – 7.72 (m,
2H), 7.72 – 7.67 (m, 2H), 7.45 – 7.29 (m, 14H), 7.20 (dd, J ¼ 6.8, 2.2 Hz,
2H), 5.70 (d, J ¼ 8.8 Hz, 1H), 4.96 (d, J ¼ 10.8 Hz, 1H), 4.78 (d, J ¼ 11.1 Hz,
2H), 4.69 (dd, J ¼ 8.9, 4.5 Hz, 1H), 4.58 (d, J ¼ 10.8 Hz, 1H), 4.51 (d,
J ¼ 11.0 Hz, 1H), 4.10 (dd, J ¼ 9.4, 4.5 Hz, 1H), 4.00 (dd, J ¼ 11.1, 3.3 Hz,
1H), 3.91 (d, J ¼ 10.2 Hz, 1H), 3.81 (t, J ¼ 9.6 Hz, 1H), 3.66 (d, J ¼ 9.8 Hz,
1H), 3.32 (s, 3H), 2.02 (s, 3H), 1.09 (s, 9H). 13C NMR (101 MHz, CDCl3) d

JOURNAL OF CARBOHYDRATE CHEMISTRY
11
170.3, 138.5, 138.0, 135.9, 135.7, 133.6, 133.2, 129.9, 128.6, 128.5, 128.5,
128.0, 127.9, 127.9, 127.8, 100.0, 77.8, 75.4, 74.0, 71.7, 71.4, 62.8, 54.9, 49.3,
27.0, 23.7, 19.5. DEPT NMR (135 MHz, CDCl3) d 135.9, 135.7, 129.9,
128.6, 128.6, 128.5, 128.0, 127.9, 127.9, 127.8, 100.1, 77.8, 75.4, 74.0, 71.8,
71.4, 62.8, 55.0, 49.3, 27.0, 23.7. IR (CHCl3) ꢀ 3292, 1736, 1657, 1537, 1069,
694 cmꢁ1. HRMS (TOF): [M þ H]þ calcd for C39H48NO6Si 654.3251,
found 654.3248.
1-O-Acetyl-2-acetamido
3,4-di-O-benzyl-2-deoxy-6-O-t-butyldiphenyl-
silyl-a-D-mannopyranoside (10). To compound 9 (3 g, 4.59 mmol), acetic
anhydride (40 mL) was added and mixture cooled to 0 ꢀC. Catalytic
amount of conc. H2SO4 (400 lL) was added dropwise and reaction stirred
throughout at 0 ꢀC. After 1 h the reaction mixture was poured into ice cold
sat. aq NaHCO3 soln with stirring and left until effervescence has ceased.
The mixture extracted with EtOAc, washed with NaHCO3 sol, H2O, brine
dried over Na2SO4, filtered, concentrated and purified by chromatography
to afford compound 10 as the major product. White foam: Rf ¼ 0.3 (petrol-
25
eum ether/EtOAC, 60:40); Yield: (2.12 g, 68%); [a]D ¼ -14.1(c 0.32,
1
CHCl3); H NMR (400 MHz, CDCl3) d 7.76 – 7.66 (m, 4H), 7.47 – 7.30
(m, 14H), 7.23 (dd, J ¼ 7.2, 2.0 Hz, 2H), 6.18 (d, J ¼ 1.9 Hz, 1H), 5.74 (d,
J ¼ 8.9 Hz, 1H), 5.00 (d, J ¼ 10.6 Hz, 1H), 4.82 (d, J ¼ 11.0 Hz, 1H), 4.73
(ddd, J ¼ 9.0, 4.2, 2.1 Hz, 1H), 4.60 (dd, J ¼ 22.3, 10.8 Hz, 2H), 4.15 – 4.09
(m, 1H), 4.07 – 3.89 (m, 3H), 3.75 (d, J ¼ 9.6 Hz, 1H), 2.06 (s, 3H), 2.05 (s,
3H), 1.11 (s, 9H). 13C NMR (101 MHz, CDCl3) d 170.2, 168.5, 138.1,
137.7, 135.8, 135.6, 133.3, 132.8, 129.9, 128.6, 128.5, 128.5, 128.1, 128.0,
127.9, 127.9, 92.3, 77.3, 75.6, 73.9, 73.3, 71.5, 62.2, 48.4, 27.0, 23.5, 21.0,
19.5. DEPT NMR (135 MHz, CDCl3) d 135.8, 135.6, 129.9, 128.6, 128.5,
128.5, 128.1, 128.0, 127.9, 127.9, 92.3, 77.3, 75.6, 73.9, 73.3, 71.5, 62.2, 48.4,
27.0, 23.5, 21.0. IR (CHCl3) ꢀ 3439, 1756, 1673, 1511, 1219, 695 cmꢁ1.
HRMS (TOF): [M þ Na]þ calcd for C40H47NNaO7Si 704.3019,
found 704.3021.
1-Azido-2-acetamido-3,4-di-O-benzyl-1,2-dideoxy-6-O-t-butyldiphenyl-
silyl-a-D-mannopyranose (11). To a solution of compound 10 (2.3 g,
3.37 mmol) in dry CH2Cl2 (25 mL) TMSN3 (1.33 mL, 10.12 mmol) was
added. To the reaction FeCl3 (547 mg, 3.37 mmol) was added and stirred at
rt for 1 h. The reaction was quenched by slowly adding NaHCO3 sol or by
the addition of Et3N (200 lL). The reaction mixture was extracted with
CH2Cl2 (35 mL X 2), washed with H2O, brine, dried over Na2SO4, filtered,
concentrated and purified by chromatography to afford compound 10.
(Note: 11 can be obtained in pure form by crystallization using CH2Cl2/
hexane. Compound 11 slowly crystallizes leaving behind the impurity in
the supernatant) White solid: Rf ¼ 0.3 (petroleum ether/EtOAC, 60:40);
25
1
Yield: (1.74 g, 78%); [a]D ¼ þ45.4 (c 0.54, CHCl3); mp- 115–117 ꢀC; H

12
M. VANGALA AND S. HOTHA
NMR (400 MHz, CDCl3) d 7.74 – 7.65 (m, 4H), 7.47 – 7.28 (m, 14H), 7.20
(dd, J ¼ 7.0, 2.4 Hz, 2H), 5.75 (d, J ¼ 7.8 Hz, 1H), 5.51 (d, J ¼ 1.6 Hz, 1H),
4.95 (d, J ¼ 10.7 Hz, 1H), 4.70 (d, J ¼ 11.1 Hz, 1H), 4.60 (d, J ¼ 10.8 Hz,
1H), 4.54 – 4.48 (m, 2H), 4.06 – 3.99 (m, 2H), 3.93 (dd, J ¼ 11.3, 1.4 Hz,
1H), 3.91 – 3.80 (m, 2H), 2.02 (s, 3H), 1.10 (s, 9H). 13C NMR (101 MHz,
CDCl3) d 170.5, 138.2, 137.5, 135.9, 135.6, 133.4, 132.9, 130.0, 128.7, 128.5,
128.5, 128.2, 127.9, 127.9, 88.7, 76.7, 75.5, 73.9, 73.4, 71.6, 62.5, 49.4, 27.0,
23.5, 19.5. DEPT NMR (135 MHz, CDCl3) d 135.9, 135.7, 130.0, 128.7,
128.6, 128.5, 128.2, 127.9, 127.9, 88.7, 76.7, 75.5, 73.9, 73.4, 71.6, 62.5, 49.4,
27.0, 23.6. IR (CHCl3) ꢀ 3305, 2111, 1659, 1101, 739, cmꢁ1. HRMS (TOF):
[M þ Na]þ calcd for C38H44N4NaO5Si 687.2979, found 687.2983.
1-Azido-2-acetamido-3,4-di-O-benzyl-1,2-dideoxy-a-D-mannopyranose
(12). Compound 11 (3.75 g, 5.64 mmol) was dissolved in pyridine (25 mL)
and cooled to 0 ꢀC. HF.pyridine(70:30) (2.5 mL) was added and reaction
mixture allowed to come to rt and stirred for 2 h. After TLC indicated the
complete consumption of starting material NaHCO3 sol was added and
extracted with EtOAc (75 mL X 2). The combined organic layer washed
with H2O, brine dried over Na2SO4, filtered, concentrated and purified by
chromatography to afford compound 12. White solid: Rf ¼ 0.2 (petroleum
25
ether/EtOAC, 20:80); Yield: (2.11 g, 88%); [a]D ¼ þ77.5 (c 0.46, CHCl3);
1
mp- 116–118 ꢀC; H NMR (400 MHz, CDCl3) d 7.40 – 7.27 (m, 10H), 6.06
(d, J ¼ 7.1 Hz, 1H), 5.49 (d, J ¼ 1.7 Hz, 1H), 4.93 (d, J ¼ 11.0 Hz, 1H), 4.65
(dd, J ¼ 11.1, 6.0 Hz, 2H), 4.50 (d, J ¼ 11.1 Hz, 1H), 4.48 – 4.41 (m, 1H),
3.99 (dd, J ¼ 9.4, 4.8 Hz, 1H), 3.87 – 3.77 (m, 3H), 3.67 (t, J ¼ 9.4 Hz, 1H),
2.04 (s, 3H). 13C NMR (101 MHz, CDCl3) d 171.0, 138.1, 137.5, 128.7,
128.6, 128.3, 128.2, 128.1, 128.0, 88.9, 76.5, 75.3, 73.2, 73.0, 71.4, 61.5, 49.6,
23.5. DEPT NMR (135 MHz, CDCl3) d 128.7, 128.6, 128.3, 128.2, 128.1,
128.0, 88.9, 76.6, 75.3, 73.2, 73.0, 71.4, 61.5, 49.6, 23.5. IR (CHCl3) ꢀ 3289,
2113, 1655, 1548, 1101, 747 cmꢁ1. HRMS (TOF): [M þ Na]þ calcd for
C22H26N4NaO5 449.1800, found 449.1805.
1-Azido-2-acetamido-3,4-di-O-benzyl-1,2-dideoxy-6-O-propargyl-a-D-
mannopyranose (13). To an ice-cold solution of compound 12 (1.76 g,
4.12 mmol) in dry DMF (35 mL), 60% NaH (181 mg, 4.54 mmol) was added
followed by addition of propargyl bromide (469 lL, 61.9 mmol) and the
reaction mixture brought to rt. After 30 min TLC indicated complete con-
sumption of starting material. Reaction cooled to 0 ꢀC and quenched by
adding cold H2O and EtOAc. Reaction mixture extracted with EtOAc
(35 mL ꢂ 2), washed with H2O, brine, dried over Na2SO4, filtered, concen-
trated and purified by chromatography to afford compound 13. (note: puri-
fication is essential to remove excess propargyl bromide which can
interfere in the next cycloaddition steps). Thick liquid: Rf ¼ 0.25 (petroleum
25
ether/EtOAC, 50:50); Yield: (1.52 g, 80%); [a]D ¼ þ78.1 (c 0.43, CHCl3);

JOURNAL OF CARBOHYDRATE CHEMISTRY
13
1H NMR (400 MHz, CDCl3) d 7.40 – 7.27 (m, 10H), 5.85 (d, J ¼ 7.8 Hz,
1H), 5.48 (d, J ¼ 1.7 Hz, 1H), 4.91 (d, J ¼ 10.8 Hz, 1H), 4.67 (dd, J ¼ 10.9,
6.9 Hz, 2H), 4.52 – 4.46 (m, 2H), 4.25 (dd, J ¼ 15.9, 2.4 Hz, 1H), 4.14 (dd,
J ¼ 15.9, 2.4 Hz, 1H), 4.00 – 3.89 (m, 3H), 3.77 – 3.68 (m, 2H), 2.41 (t,
J ¼ 2.4 Hz, 1H), 2.05 (s, 3H); 13C NMR (101 MHz, CDCl3) d 170.7, 138.3,
137.5, 128.6, 128.5, 128.3, 128.1, 128.0, 128.0, 89.2, 79.4, 76.6, 75.4, 75.3,
73.3, 72.4, 71.4, 67.9, 58.7, 49.5, 23.6. DEPT NMR (135 MHz, CDCl3) d
128.6, 128.5, 128.3, 128.1, 128.0, 128.0, 89.2, 76.6, 75.4, 73.3, 72.4, 71.4,
67.9, 58.7, 49.5, 23.6. IR (CHCl3) ꢀ 3287, 2111, 1656, 1543, 1095, 695 cmꢁ1.
HRMS (TOF): [M þ Na]þ calcd for C25H28N4NaO5 487.1957,
found 487.1962.
[1-(2-Acetamido 3,4-di-O-benzyl-2-deoxy-6-O-propargyl-a-D-mannopyr-
anosyl)-1H-1,2,3-triazol-4-yl]ethyl p-tolylsulfonate (15). To a solution of
14 (579 mg, 2.58 mmol) in dry DMF (8 mL), CuI (147 mg, 0.775 mmol) and
DIPEA (540 lL, 3.10 mmol) with respect to 14 were added under nitrogen
atmosphere and stirred for 15 min. Then purified 13 (1 g, 2.15 mmol) dis-
solved in 18 mL of dry DMF was added. After 2 h, water was added and
reaction mixture extracted with CH2Cl2 (50 mL ꢂ 3). The combined organic
layers dried over Na2SO4, concentrated and purified by column chromatog-
raphy to afford 15 and 16. (Note: RM stopped after 2 h to avoid higher
oligomerisation). Compound 15: Thick liquid: Rf ¼ 0.3 (petroleum ether/
25
1
EtOAC, 20:80); Yield: (415 mg, 28%); [a]D ¼ þ31.4 (c 0.3, CHCl3); H
NMR (400 MHz, CDCl3) d 7.73 (d, J ¼ 8.3 Hz, 2H), 7.57 (s, 1H), 7.37 –
7.27 (m, 12H), 6.11 (d, J ¼ 6.1 Hz, 1H), 6.07 (d, J ¼ 2.9 Hz, 1H), 5.25 – 5.19
(m, 1H), 4.83 (d, J ¼ 11.1 Hz, 1H), 4.66 (d, J ¼ 11.1 Hz, 1H), 4.62 (s, 2H),
4.47 (dd, J ¼ 8.3, 4.9 Hz, 1H), 4.30 – 4.23 (m, 2H), 4.20 (dd, J ¼ 15.9,
2.3 Hz, 1H), 4.12 (dd, J ¼ 16.0, 2.4 Hz, 1H), 3.89 – 3.79 (m, 2H), 3.63 (dd,
J ¼ 10.5, 2.7 Hz, 1H), 3.52 – 3.47 (m, 1H), 3.08 (t, J ¼ 6.7 Hz, 2H), 2.41 (br
s, 4H), 1.98 (s, 3H). 13C NMR (101 MHz, CDCl3) d 170.8, 145.1, 143.3,
138.0, 137.3, 132.7, 130.0, 128.7, 128.5, 128.4, 128.3, 127.9, 122.1, 84.4, 79.2,
77.1, 75.4, 74.6, 73.4, 72.8, 72.0, 68.7, 67.5, 58.6, 48.5, 25.8, 23.3, 21.7.
DEPT NMR (135 MHz, CDCl3) d 130.0, 128.7, 128.5, 128.4, 128.3, 127.9,
122.1, 84.5, 77.1, 74.6, 73.4, 72.8, 72.0, 68.7, 67.5, 58.6, 48.5, 25.8, 23.4,
21.7. IR (CHCl3) ꢀ 3287, 1667, 1359, 1099, 747 cmꢁ1. HRMS (TOF):
[M þ H]þ calcd for C36H41N4O8S 689.2645, found 689.2630.
Compound (16): Pale yellow liquid: Rf ¼ 0.2 (pure EtOAC); Yield:
25
(297 mg, 12%); [a]D ¼ þ34.2 (c 0.27, CHCl3); 1H NMR (400 MHz,
CDCl3) d 7.76 (s, 1H), 7.71 (d, J ¼ 8.2 Hz, 2H), 7.56 (s, 1H), 7.36 – 7.22
(m, 22H), 6.91 (br s, 1H), 6.13 – 6.04 (m, 2H), 5.93 (d, J ¼ 3.0 Hz, 1H),
5.40 – 5.33 (m, 1H), 5.15 – 5.08 (m, 1H), 4.79 (d, J ¼ 11.1 Hz, 2H), 4.74 (d,
J ¼ 12.2 Hz, 1H), 4.69 – 4.62 (m, 3H), 4.59 (d, J ¼ 4.9 Hz, 2H), 4.54 (dd,
J ¼ 11.1, 2.7 Hz, 2H), 4.46 – 4.36 (m, 2H), 4.29 – 4.21 (m, 2H), 4.13 (qd,

14
M. VANGALA AND S. HOTHA
J ¼ 16.0, 2.4 Hz, 2H), 3.90 (d, J ¼ 8.3 Hz, 1H), 3.88 – 3.79 (m, 3H), 3.73 –
3.67 (m, 1H), 3.66 – 3.59 (m, 2H), 3.50 – 3.44 (m, 1H), 3.07 (t, J ¼ 6.7 Hz,
2H), 2.41 (br s, J ¼ 3.0 Hz, 4H), 2.05 (s, 3H), 1.91 (s, 3H). 13C NMR
(101 MHz, CDCl3) d 171.0, 170.8, 145.1, 143.2, 138.1, 137.9, 137.6, 137.2,
132.7, 130.0, 128.8, 128.6, 128.6, 128.5, 128.4, 128.4, 128.3, 128.1, 128.0,
127.9, 123.0, 122.0, 84.9, 84.3, 79.2, 77.2, 77.1, 75.4, 74.6, 74.5, 74.4, 73.9,
72.8, 72.6, 72.1, 72.0, 68.8, 68.1, 67.5, 64.6, 58.7, 48.7, 48.0, 25.9, 23.3, 23.3,
21.7. DEPT NMR (135 MHz, CDCl3) d 130.1, 128.8, 128.6, 128.6, 128.5,
128.4, 128.4, 128.1, 128.0, 128.0, 127.9, 123.0, 122.0, 84.9, 84.3, 77.2, 77.1,
74.6, 74.5, 74.4, 73.9, 72.8, 72.6, 72.1, 72.0, 68.8, 68.1, 67.5, 64.6, 58.7, 48.7,
48.0, 25.8, 23.3, 23.3, 21.7. IR (CHCl3) ꢀ 3282, 1665, 1363, 1099 cmꢁ1.
HRMS (TOF): [M þ H]þ calcd for C61H69N8O13S 1153.4705,
found 1153.4722.
Compound (18): Compounds 11 (1 g, 1.50 mmol) and 13 (524 mg,
1.12 mmol) were taken together in a RB and dry DMF (25 mL) was added
under N2 atmosphere. CuI (21.4 mg, 0.112 mmol) and DIPEA (196 lL,
1.12 mmol) with respect to 13 were added at rt and stirred for 2.5 h. TLC
indicated consumption of 13 and formation of polar spots along with some
amount of 11. Water was added to the mixture and extracted into CH2Cl2
(25 mL X 3). The combined organic layers dried over Na2SO4, concentrated
and purified by column chromatography to afford 18. (Note: RM stopped
after 2.5 h to avoid higher oligomerisation). White foam: Rf ¼ 0.4 (petrol-
25
eum ether:EtOAC 40:60); Yield: (237 mg, 14%); [a]D ¼ þ8.7 (c 0.2,
1
CHCl3); H NMR (400 MHz, CDCl3) d 7.70 (s, 1H), 7.65 – 7.60 (m, 4H),
7.42 (td, J ¼ 7.3, 1.5 Hz, 2H), 7.38 – 7.31 (m, 10H), 7.30 – 7.28 (m, 4H),
7.28 – 7.21 (m, 10H), 7.14 – 7.08 (m, 1H), 6.03 (d, J ¼ 4.7 Hz, 1H), 5.87 (d,
J ¼ 7.4 Hz, 1H), 5.38 (d, J ¼ 1.6 Hz, 1H), 5.15 – 5.08 (m, 1H), 4.86 (d,
J ¼ 10.9 Hz, 1H), 4.78 (d, J ¼ 11.8 Hz, 2H), 4.72 (d, J ¼ 11.1 Hz, 1H), 4.67 –
4.60 (m, 3H), 4.58 (d, J ¼ 4.6 Hz, 1H), 4.54 – 4.45 (m, 3H), 4.30 (dd,
J ¼ 6.8, 4.4 Hz, 1H), 3.99 – 3.92 (m, 4H), 3.91 – 3.87 (m, 3H), 3.75 (d,
J ¼ 11.7 Hz, 1H), 3.68 – 3.62 (m, 1H), 2.11 (s, 3H), 1.86 (s, 3H), 1.06 (s,
9H). 13C NMR (101 MHz, CDCl3) d 171.1, 170.5, 145.1, 138.4, 137.9, 137.7,
137.1, 135.7, 135.6, 133.1, 133.0, 130.0, 128.8, 128.6, 128.5, 128.4, 128.3,
128.0, 128.0, 127.9, 127.9, 127.8, 127.7, 122.4, 89.7, 83.8, 77.1, 76.8, 75.7,
75.3, 74.1, 73.8, 73.3, 72.2, 72.0, 71.4, 68.6, 64.6, 62.0, 48.9, 48.5, 26.9, 23.4,
23.2, 19.4. DEPT NMR (135 MHz, CDCl3) d 135.7, 135.5, 130.0, 128.8,
128.5, 128.4, 128.4, 128.3, 128.0, 127.9, 127.9, 127.8, 127.8, 127.7, 122.4,
89.7, 83.8, 77.1, 76.9, 75.7, 75.3, 74.1, 73.8, 73.3, 72.2, 72.0, 71.4, 68.6, 64.6,
62.0, 48.9, 48.5, 26.9, 23.4, 23.2. IR (CHCl3) ꢀ 3279, 2112, 1661, 1542,
1104 cmꢁ1. HRMS (TOF): [M þ Na]þ calcd for C63H72N8NaO10Si
1151.5038, found 1151.5043.

JOURNAL OF CARBOHYDRATE CHEMISTRY
15
[1-(2-Acetamido 3,4-di-O-benzyl-2-deoxy-6-O-t-butyldiphenylsilyl-a-D-
mannopyranosyl)-1H-1,2,3-triazole-4-yl]ethyl p-tolylsulfonate (19). To a
solution of azido compound 11 (750 mg, 1.12 mmol) and 14 (303 mg,
1.35 mmol) in dry DMF (15 mL), CuI (43 mg, 0.225 mmol) was added fol-
lowed by addition of DIPEA (196 lL, 1.12 mmol) and stirred at rt for 3 h.
After TLC showed complete consumption of starting material, water is
added and extracted with EtOAc (25 mL X 3). The combined organic layers
washed with H2O, brine, dried over Na2SO4, filtered, concentrated and
purified by chromatography to afford compound 19. Thick liquid: Rf ¼ 0.5
25
(petroleum ether/EtOAC, 20:80); Yield: (822 mg, 82%); [a]D ¼ þ18.2
1
(c 0.61, CHCl3); H NMR (400 MHz, CDCl3) d 7.72 (d, J ¼ 8.1 Hz, 2H),
7.69 – 7.62 (m, 4H), 7.52 (s, 1H), 7.46 – 7.27 (m, 16H), 7.23 – 7.19 (m,
2H), 6.05 (d, J ¼ 3.3 Hz, 1H), 5.91 (dd, J ¼ 7.0, 3.0 Hz, 1H), 5.24 – 5.18 (m,
1H), 4.83 (d, J ¼ 11.1 Hz, 1H), 4.64 – 4.55 (m, 3H), 4.39 (dd, J ¼ 7.7,
4.5 Hz, 1H), 4.31 – 4.20 (m, 2H), 3.98 – 3.92 (m, 2H), 3.91 – 3.85 (m, 1H),
3.47 (s, 1H), 3.06 (t, J ¼ 6.8 Hz, 2H), 2.39 (s, 3H), 1.96 (s, 3H), 1.07 (s, 9H);
13C NMR (101 MHz, CDCl3) d 170.6, 145.0, 143.1, 137.9, 137.3, 135.8,
135.6, 133.2, 132.9, 132.8, 130.0, 128.8, 128.6, 128.5, 128.4, 128.0, 127.9,
127.9, 121.8, 84.0, 77.1, 75.3, 74.5, 72.4, 72.1, 68.7, 62.1, 48.5, 26.9, 25.8,
23.4, 21.7, 19.4. DEPT NMR (135 MHz, CDCl3) d 135.8, 135.6, 130.0,
128.8, 128.6, 128.5, 128.4, 128.0, 127.9, 127.9, 121.8, 84.0, 77.1, 75.3, 74.5,
72.4, 72.1, 68.7, 62.1, 48.5, 26.9, 25.8, 23.4, 21.7. IR (CHCl3) ꢀ 3287, 1668,
1362, 1104, 698 cmꢁ1. HRMS (TOF): [M þ H]þ calcd for C49H57N4O8SSi
889.3666, found 889.3669.
1-(20-Acetamido 30,40-di-O-benzyl-20-deoxy-60-O-t-butyldiphenylsilyl-a-
D-mannopyranosyl)-1H-1,2,3-triazole-4-ethyl azide (20). To a solution of
tosylate 19 (650 mg, 0.731 mmol) in dry DMF (12 mL), NaN3 (142 mg,
2.19 mmol) was added and stirred the reaction at 70 ꢀC for 12 h. The mix-
ture was diluted with H2O and extracted with EtOAc (25 mL ꢂ 3). The
combined organic layer washed with H2O, brine, concentrated and purified
by chromatography to afford 20. Thick liquid: Rf ¼ 0.2 (petroleum ether/
25
1
EtOAC, 40:60); Yield: (505 mg, 91%); [a]D ¼ þ19.8 (c 0.24, CHCl3); H
NMR (400 MHz, CDCl3) d 7.69 – 7.63 (m, 4H), 7.60 (s, 1H), 7.47 – 7.42
(m, 2H), 7.41 – 7.30 (m, 12H), 7.24 – 7.21 (m, 2H), 6.10 (d, J ¼ 3.9 Hz,
1H), 5.95 (d, J ¼ 6.9 Hz, 1H), 5.26 – 5.20 (m, 1H), 4.83 (d, J ¼ 11.2 Hz, 1H),
4.66 – 4.56 (m, 3H), 4.43 (dd, J ¼ 7.5, 4.5 Hz, 1H), 3.98 – 3.88 (m, 3H),
3.62 – 3.54 (m, 3H), 2.98 (t, J ¼ 6.9 Hz, 2H), 1.95 (s, 3H), 1.08 (s, 9H). 13C
NMR (101 MHz, CDCl3) d 170.5, 144.6, 137.8, 137.2, 135.8, 135.6, 133.2,
133.0, 129.9, 128.8, 128.5, 128.5, 128.4, 128.0, 127.9, 127.8, 127.8, 121.5,
83.9, 77.1, 75.4, 74.3, 72.4, 72.1, 62.2, 50.5, 48.5, 26.9, 25.7, 23.3, 19.4.
DEPT NMR (135 MHz, CDCl3) d 135.8, 135.6, 129.9, 128.8, 128.5, 128.5,
128.4, 128.0, 127.9, 127.8, 127.8, 121.5, 83.9, 77.1, 75.4, 74.3, 72.4, 72.1,

16
M. VANGALA AND S. HOTHA
62.2, 50.5, 48.5, 26.9, 25.7, 23.3. IR (CHCl3) ꢀ 3286, 2100, 1664, 1104,
750 cmꢁ1. HRMS (TOF): [M þ H]þ calcd for C42H50N7O5Si 760.3643,
found 760.3644.
Compound (21). Compound 11 (300 mg, 0.451 mmol) and 15 (310 mg,
0.451 mmol) were dissolved in dry DMF (10 mL). CuI (17 mg, 0.090 mmol)
and DIPEA (78.6 lL, 0.451 mmol) were added at rt. Reaction mixture
stirred for 3 h under an atmosphere of N2. After TLC indicated consump-
tion of starting materials, water was added and extracted with CH2Cl2
(35 mL X 3). The combined organic layer washed with brine, dried over
Na2SO4, concentrated and purified by chromatography to afford 21. (note:
solubility of triazolyl sachharides is more in CH2Cl2 than in EtOAc). White
25
foam: Rf ¼ 0.25 (pure EtOAC); Yield: (494 mg, 81%); [a]D ¼ þ33.2
1
(c 0.14, CHCl3); H NMR (400 MHz, CDCl3) d 7.76 (d, J ¼ 2.9 Hz, 2H),
7.74 (s, 1H), 7.69 – 7.62 (m, 4H), 7.58 (s, 1H), 7.48 – 7.42 (m, 2H), 7.41 –
7.31 (m, 16H), 7.30 – 7.23 (m, 10H), 6.89 (d, J ¼ 8.0 Hz, 1H), 6.05 (d,
J ¼ 4.7 Hz, 1H), 5.94 (d, J ¼ 2.7 Hz, 1H), 5.86 (d, J ¼ 7.6 Hz, 1H), 5.45 –
5.39 (m, 1H), 5.16 – 5.09 (m, 1H), 4.82 (dd, J ¼ 11.1, 8.3 Hz, 2H), 4.76 (d,
J ¼ 12.2 Hz, 1H), 4.71 (d, J ¼ 11.2 Hz, 1H), 4.67 – 4.50 (m, 6H), 4.44 (dd,
J ¼ 8.6, 4.7 Hz, 1H), 4.38 – 4.33 (m, 1H), 4.33 – 4.25 (m, 2H), 4.02 – 3.85
(m, 5H), 3.73 – 3.64 (m, 2H), 3.47 (d, J ¼ 8.3 Hz, 1H), 3.07 (t, J ¼ 6.7 Hz,
2H), 2.41 (s, 3H), 2.04 (s, 3H), 1.85 (s, 3H), 1.05 (s, 9H); 13C NMR
(101 MHz, CDCl3) d 171.0, 170.5, 145.1, 144.9, 143.2, 138.2, 137.8, 137.7,
137.1, 135.8, 135.6, 133.2, 133.0, 132.8, 130.0, 130.0, 128.8, 128.7, 128.6,
128.5, 128.4, 128.1, 128.0, 128.0, 127.9, 127.9, 127.9, 122.6, 122.0, 85.0, 83.8,
77.2, 77.1, 75.8, 74.7, 74.4, 74.1, 72.8, 72.2, 72.1, 71.9, 68.8, 68.1, 64.6, 62.0,
48.6, 48.0, 26.9, 25.9, 23.3, 23.2, 21.7, 19.4. DEPT NMR (135 MHz, CDCl3)
d 135.8, 135.6, 130.0, 130.0, 128.8, 128.7, 128.6, 128.5, 128.1, 128.0, 128.0,
127.9, 127.9, 122.6, 122.0, 85.1, 83.8, 77.2, 77.1, 75.8, 74.7, 74.4, 74.1, 72.8,
72.2, 72.1, 71.9, 68.8, 68.1, 64.6, 62.0, 48.6, 48.0, 26.9, 25.9, 23.3, 23.2, 21.7.
IR (CHCl3) ꢀ 3282, 1664, 1364, 1104 cmꢁ1; HRMS (TOF): [M þ H]þ calcd
for C74H85N8O13SSi 1353.5726, found 1353.5728.
Compound (22): To a solution of compound 21 (460 mg, 0.34 mmol) in
dry DMF (8 mL), NaN3 (66 mg, 1.02 mmol) was added and stirred at 70 ꢀC
for 12 h. DMF removed under reduced pressure. Water was added to the
residue and extracted with CH2Cl2 (30 mL ꢂ 3). The combined organic
layer washed with brine, dried over Na2SO4, concentrated and purified by
chromatography to afford 22. White foam: Rf ¼ 0.25 (pure EtOAC); Yield:
25
(357 mg, 86%); [a]D ¼ þ35.6 (c 0.19, CHCl3); 1H NMR (400 MHz,
CDCl3) d 7.73 (s, 1H), 7.66 – 7.60 (m, 4H), 7.59 (s, 1H), 7.45 – 7.40 (m,
2H), 7.38 – 7.21 (m, 24H), 6.87 (d, J ¼ 7.3 Hz, 1H), 6.05 (d, J ¼ 4.8 Hz, 1H),
5.98 (d, J ¼ 3.0 Hz, 1H), 5.88 (d, J ¼ 7.6 Hz, 1H), 5.41 – 5.31 (m, 1H), 5.13
– 5.05 (m, 1H), 4.79 (d, J ¼ 9.6 Hz, 2H), 4.69 (dd, J ¼ 15.0, 11.7 Hz, 2H),

JOURNAL OF CARBOHYDRATE CHEMISTRY
17
4.65 – 4.57 (m, 4H), 4.57 – 4.43 (m, 3H), 4.35 – 4.29 (m, 1H), 4.00 – 3.87
(m, 4H), 3.84 (dd, J ¼ 11.2, 3.9 Hz, 1H), 3.71 – 3.50 (m, 5H), 2.98 (t,
J ¼ 6.9 Hz, 2H), 2.01 (s, 3H), 1.84 (s, 3H), 1.05 (s, 9H); 13C NMR
(101 MHz, CDCl3) d 171.0, 170.6, 144.9, 144.7, 138.1, 137.7, 137.6, 137.1,
135.8, 135.6, 133.1, 133.0, 130.0, 128.8, 128.7, 128.6, 128.6, 128.4, 128.4,
128.1, 128.0, 128.0, 127.9, 127.9, 127.8, 122.6, 121.7, 84.8, 83.8, 77.2, 77.1,
75.8, 74.5, 74.4, 74.1, 72.8, 72.2, 72.1, 72.0, 68.1, 64.5, 62.0, 50.5, 48.6, 48.2,
26.9, 25.7, 23.3, 23.2, 19.4. DEPT NMR (135 MHz, CDCl3) d 135.8, 135.6,
130.0, 128.8, 128.7, 128.6, 128.6, 128.5, 128.4, 128.1, 128.1, 128.0, 127.9,
127.9, 127.8, 122.6, 121.7, 84.8, 83.8, 77.2, 77.1, 75.8, 74.6, 74.4, 74.1, 72.8,
72.2, 72.1, 72.0, 68.1, 64.5, 62.0, 50.5, 48.6, 48.2, 26.9, 25.7, 23.3, 23.2. IR
(CHCl3) ꢀ 3390, 2100, 1665, 1102 cmꢁ1; HRMS (TOF): [M þ H]þ calcd for
C67H78N11O10Si 1224.5702, found 1224.5706.
Compound (23): Compound 18 (320 mg, 0.283 mmol) and 15 (195 mg,
0.283 mmol) were dissolved in dry DMF (10 mL). CuI (21.6 mg,
0.113 mmol) and DIPEA (49.3 lL, 0.283 mmol) were added at rt. Reaction
mixture stirred for 3.5 h under an atmosphere of N2. The reaction mixture
is processed as described for compound 21 to afford the purified com-
pound 23. Pale yellow foam: Rf ¼ 0.2 (EtOAC run twice); Yield: (401 mg,
25
1
78%); [a]D ¼ þ39.4 (c 0.65, CHCl3); H NMR (400 MHz, CDCl3) d 7.78 –
7.70 (m, 4H), 7.66 – 7.59 (m, 4H), 7.57 (s, 1H), 7.45 – 7.39 (m, 3H), 7.38 –
7.31 (m, 14H), 7.30 – 7.21 (m, 21H), 6.99 – 6.85 (m, 1H), 6.05 (d,
J ¼ 4.6 Hz, 1H), 5.99 (d, J ¼ 3.3 Hz, 1H), 5.95 (d, J ¼ 2.9 Hz, 1H), 5.92 (br s,
1H), 5.38 (br s, 1H), 5.31 (br s, 1H), 5.13 – 5.07 (m, 1H), 4.85 – 4.71 (m,
5H), 4.70 – 4.47 (m, 13H), 4.44 – 4.37 (m, 2H), 4.34 – 4.29 (m, 1H), 4.29
– 4.22 (m, 2H), 4.00 – 3.82 (m, 7H), 3.64 (t, J ¼ 9.5 Hz, 3H), 3.52 – 3.47
(m, 1H), 3.06 (t, J ¼ 6.7 Hz, 2H), 2.40 (s, 3H), 2.04 (s, 3H), 1.97 (s, 3H),
1.84 (s, 3H), 1.05 (s, 9H). 13C NMR (101 MHz, CDCl3) d 170.9, 170.9,
170.5, 145.0, 143.1, 138.0, 137.9, 137.7, 137.6, 137.4, 137.0, 135.7, 135.5,
133.1, 132.9, 132.7, 130.0, 129.9, 128.7, 128.6, 128.5, 128.4, 128.4, 128.3,
128.1, 128.0, 128.0, 127.9, 127.9, 127.8, 127.8, 122.8, 122.5, 121.9, 84.9, 84.8,
83.8, 77.1, 77.0, 75.8, 75.8, 74.7, 74.6, 74.5, 74.4, 74.0, 72.7, 72.6, 72.1, 71.9,
71.9, 68.7, 68.1, 68.0, 64.5, 64.4, 61.9, 48.5, 48.1, 47.9, 26.9, 25.8, 23.2, 23.1,
23.1, 21.6, 19.3. DEPT NMR (135 MHz, CDCl3) d 135.7, 135.5, 130.0,
129.9, 128.7, 128.6, 128.5, 128.4, 128.4, 128.3, 128.1, 128.0, 128.0, 127.9,
127.9, 127.8, 127.8, 122.8, 122.5, 121.9, 84.8, 84.8, 83.7, 77.1, 77.0, 75.8,
75.8, 74.7, 74.6, 74.5, 74.4, 74.0, 72.7, 72.6, 72.1, 71.9, 71.9, 68.7, 68.1, 68.0,
64.5, 64.4, 61.9, 48.5, 48.1, 47.9, 26.9, 25.8, 23.2, 23.1, 23.1, 21.6. IR
(CHCl3) ꢀ 3384, 1707, 1662, 1101 cmꢁ1. MALDI (TOF): [M þ Na]þ calcd
for C99H112N12NaO18SSi 1841.1858, found 1841.0696.
Compound (24): To a solution of compound 23 (220 mg, 0.121 mmol)
in dry DMF (5 mL), NaN3 (23 mg, 0.363 mmol) was added and stirred at

18
M. VANGALA AND S. HOTHA
70 ꢀC for 12 h. The reaction mixture is processed as described for 22 to
afford the purified compound 24. White foam: Rf ¼ 0.2 (EtOAC run
25
1
twice); Yield: (165 mg, 81%); [a]D ¼ þ45.5 (c 0.38, CHCl3); H NMR
(400 MHz, CDCl3) d 7.78 – 7.71 (m, 2H), 7.62 (t, J ¼ 8.2 Hz, 5H), 7.45 –
7.39 (m, 2H), 7.38 – 7.28 (m, 23H), 7.26 – 7.21 (m, 11H), 6.95 (br s,
1H), 6.05 (d, J ¼ 3.7 Hz, 1H), 6.01 – 5.88 (m, 3H), 5.35 (br s, 1H), 5.30
(br s, 1H), 5.09 (br s, 1H), 4.83 – 4.67 (m, 6H), 4.66 – 4.53 (m, 10H),
4.51 – 4.39 (m, 3H), 4.33 – 4.28 (m, 1H), 4.00 – 3.83 (m, 7H), 3.70 (br s,
1H), 3.66 – 3.55 (m, 6H), 2.98 (t, J ¼ 6.9 Hz, 2H), 2.02 (s, 3H), 1.96 (s,
3H), 1.84 (s, 3H), 1.05 (s, 9H). 13C NMR (101 MHz, CDCl3) d 171.0,
170.5, 145.0, 144.8, 144.7, 138.0, 138.0, 137.7, 137.6, 137.5, 137.0, 135.7,
135.5, 133.1, 132.9, 130.0, 128.8, 128.6, 128.5, 128.4, 128.3, 128.1, 128.1,
128.0, 127.9, 127.9, 127.8, 122.8, 122.6, 121.7, 84.8, 84.6, 83.7, 77.2, 77.1,
77.0, 75.9, 75.8, 74.7, 74.5, 74.5, 74.4, 74.0, 72.7, 72.6, 72.1, 72.0, 72.0,
71.9, 68.0, 64.5, 64.4, 62.0, 50.5, 48.6, 48.1, 48.1, 26.9, 25.7, 23.2, 23.1,
19.3. DEPT NMR (135 MHz, CDCl3) d 135.7, 135.5, 129.9, 128.8, 128.6,
128.4, 128.4, 128.3, 128.1, 128.0, 128.0, 127.9, 127.9, 127.8, 122.8, 122.5,
121.7, 84.8, 84.6, 83.7, 77.2, 77.1, 77.0, 75.9, 75.8, 74.6, 74.5, 74.4, 74.4,
74.0, 72.7, 72.6, 72.2, 72.0, 72.0, 71.9, 68.0, 64.5, 64.4, 62.0, 50.5, 48.6,
48.1, 48.1, 26.9, 25.7, 23.2, 23.1. IR (CHCl3) ꢀ 3395, 2102, 1660, 1544,
1105 cmꢁ1. MALDI (TOF): [M þ Na]þ calcd for C92H105N15NaO15Si
1712.0168, found 1711.8669.
Acknowledgments
Authors thank Prof. Krishna N Ganesh, IISER Tirupati for the encouragement and guid-
ance. MV thanks DST SERB, India for Fast Track research grant (SB/FT/CS-159/2012).
ORCID
Madhuri Vangala
http://orcid.org/0000-0002-4424-3181
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