Synthesis of the sialylated pentasaccharide repeating unit of the capsular polysaccharide of Streptococcus group B type VI

Article abstract of DOI:10.1016/j.carres.2021.108294

An efficient synthetic strategy has been developed for the synthesis of the sialic acid containing pentasaccharide repeating unit of the cell wall O-antigen of Streptococcus group B type VI strain involving stereoselective α-glycosylation of sialic acid thioglycoside derivative. Stereoselective glycosylation of glycosyl trichloroacetimidate derivatives and thioglycosides were carried out using perchloric acid supported over silica (HClO₄–SiO₂) as a solid acid catalyst. A panel of sialic acid donors has been screened for achieving satisfactory yield and stereochemical outcome of the glycosylation reaction.

Full text of DOI:10.1016/j.carres.2021.108294

Carbohydrate Research 502 (2021) 108294
Contents lists available at ScienceDirect
Carbohydrate Research
journal homepage: www.elsevier.com/locate/carres
Synthesis of the sialylated pentasaccharide repeating unit of the capsular
polysaccharide of Streptococcus group B type VI
Tapasi Manna, Anup Kumar Misra*
Bose Institute, Division of Molecular Medicine, P-1/12, C.I.T. Scheme VII-M, Kolkata, 700054, India
A R T I C L E I N F O
A B S T R A C T
Keywords:
An efficient synthetic strategy has been developed for the synthesis of the sialic acid containing pentasaccharide
Oligosaccharide
Glycosylation
O-antigen
repeating unit of the cell wall O-antigen of Streptococcus group B type VI strain involving stereoselective
α
-glycosylation of sialic acid thioglycoside derivative. Stereoselective glycosylation of glycosyl tri-
chloroacetimidate derivatives and thioglycosides were carried out using perchloric acid supported over silica
(HClO4–SiO2) as a solid acid catalyst. A panel of sialic acid donors has been screened for achieving satisfactory
yield and stereochemical outcome of the glycosylation reaction.
Capsular polysaccharide
Sialic acid
Streptococcus
1. Introduction
containing oligosaccharides corresponding to the CPS of type II [17] and
type V [18] applying block synthetic approach using a protected sialy-
Streptococcus agalactiae (Group B, GBS) is a Gram-positive organism,
which is the common cause of neonatal sepsis and meningitis worldwide
[1–4]. Till date, more than 10 serotypes of Streptococcus group B (GBS)
have been isolated based on the structural variations in their capsular
polysaccharides (CPSs) [5]. Most of the capsular polysaccharides of GBS
serotypes contain N-acetylneuraminic acid (Sialic acid) residue together
with other commonly available monosaccharide moieties [6]. Since
CPSs are important virulent factors which play vital roles in the initial
stage of invasion of the pathogenic bacteria to the host [7,8], it is quite
pertinent to develop glycoconjugates based on the CPS towards the
development of possible vaccine leads. Similar to other virulent strains
of GBS, type VI was found responsible for significant numbers of
neonatal infections [9]. Isolation of the oligosaccharide fragments from
the natural sources by biofermentation culture of the bacteria suffer
from several shortcomings, which include heterogeneity of the oligo-
saccharide fragments, presence of biological impurities, chances of self
infection etc. Therefore, chemical synthetic approaches are receiving
growing interest for achieving the homogeneous and pure oligosaccha-
rides free from biological impurities. They can be used in the develop-
ment of semisynthetic version of possible vaccines as well as in several
immunochemical and biophysical studies [10–13]. Earlier, synthesis of
the repeating units of the CPSs of GBS type II and VIII were reported by
Adamo et al. [14]. and Whitfield et al. [15,16] respectively. Very
recently, Guo and co-workers reported the synthesis of the sialic acid
lated galactose building block to achieve desired oligosaccharides. The
structure of the repeating unit of the CPS of GBS type VI was reported by
Jennings and co-workers in 1994 [19]. It is a pentasaccharide composed
of D-glucose, D-galactose and sialic acid in 2:2:1 ratio and the sialic acid
is linked to a D-galactose moiety at the non-reducing end through α-(2 →
3) linkage. Although the glycoconjugates derived from the penta-
saccharide repeating unit corresponding to the CPS of GBS VI is a
promising candidate aiming to the development of anti-GBS vaccine
candidate, its chemical synthesis has not been reported so far. Therefore,
it is quite pertinent to undertake the synthesis of the sialic acid con-
taining pentasaccharide using recently reported reaction conditions for
the glycosylations and functional group modifications. A straightfor-
ward sequential synthesis of the pentasaccharide corresponding to the
CPS of GBS type VI is reported herein (Fig. 1).
2. Results and discussion
Starting with D-lactose derived disaccharide acceptor (2) [20], a se-
ries of sequential stereoselective glycosylations were carried out using
suitably functionalized D-glucose, D-galactose and sialic acid thioglyco-
side and phosphate donors 3 [21], 4 [22], 5 [23], 5a [24] and 5b [25].
Compounds 2, 3, 4, 5, 5a and 5b were synthesized using multiple
numbers of reaction steps following the reaction conditions reported
earlier.
* Corresponding author.
E-mail addresses: akmisra69@gmail.com, anup@jcbose.ac.in (A.K. Misra).
https://doi.org/10.1016/j.carres.2021.108294
Received 15 January 2021; Received in revised form 10 March 2021; Accepted 10 March 2021
Available online 16 March 2021
0008-6215/© 2021 Elsevier Ltd. All rights reserved.

T. Manna and A.K. Misra
Carbohydrate Research 502 (2021) 108294
Stereoselective glycosylation of compound 2 [20] with thioglycoside
donor 3 [21] using a combination [26] of N-iodosuccinimide (NIS) and
perchloric acid supported over silica (HClO4–SiO2) [27] furnished the
trisaccharide derivative 6 in 73% yield. The formation of newly formed
glycosyl linkage was confirmed from the NMR spectroscopic analysis
(Signals at δ 4.91 (d, J = 9.0 Hz, H-1A), 4.52 (d, J = 8.5 Hz, H–1C), 4.48
(d, J = 8.0 Hz, H–1B) in 1H NMR and δ 102.9 (C-1A), 102.6 (C–1B), 102.5
(C–1C) in 13C NMR spectra). Compound 6 was subjected to a series of
functional group transformations involving (a) removal of benzylidene
acetal using p-TsOH; (b) de-O-acetylation and benzylation using benzyl
bromide and sodium hydroxide [28] and (c) oxidative removal of
p-methoxybenzyl (PMB) group using DDQ [29] to furnish trisaccharide
acceptor 7 in 62% over all yield. Stereoselective glycosylation of com-
pound 7 with D-galactose derived trichloroacetimidate derivative (4)
[22] in the presence of HClO4–SiO2 [30] furnished tetrasaccharide de-
rivative 8 in 68% yield, which was de-O-acetylated using sodium
methoxide to give the tetrasaccharide triol acceptor (9) suitable for the
glycosylation with sialic acid glycosyl donor. The stereochemistry of the
newly formed glycosidic linkages in compound 8 was confirmed from its
NMR spectral analysis [signals at δ 4.94 (d, J = 8.5 Hz, H-1D), 4.83 (d, J
= 8.5 Hz, H–1B), 4.74 (d, J = 7.5 Hz, H-1A), 4.36 (d, J = 8.0 Hz, H–1C) in
1H NMR and δ 102.8 (2 C, C-1A, C–1C), 101.8 (C–1B), 100.4 (C-1D) in 13
C
NMR spectra] (Scheme 1).
In order to incorporate sialic acid in compound 9, stereoselective
glycosylation reactions have been explored using conventional sialic
acid thioglycoside (5) [23] together with a number of recently devel-
oped reaction conditions [31–38] using modified sialic acid thioglyco-
side (5a) [24] and phosphate (5b) [25] donors. Following earlier
literature reports [31–40], the glycosylation of sialic acid thioglycosides
(5, 5a and 5b) was carried out using CH3CN–CH2Cl2 mixed solvent
allowing the nitrile effect to influence the reaction intermediate towards
the formation of (2 → 3)-α-linked sialic acid glycoside. Stereoselective
glycosylation of compound 9 with thioglycoside derivative 5 and 5a in
mixed solvent of CH3CN and CH2Cl2 in the presence of a combination of
NIS and triflic acid (TfOH) [41,42] furnished inseparable mixture of (2
→ 3)-α-linked sialic acid containing pentasaccharide derivatives 10 and
Scheme 1. Reagents and conditions: (a) NIS, HClO4–SiO2, CH2Cl2, MS-4Å,
ꢀ 40 ◦C, 1 h, 73%; (b) p-TsOH, CH2Cl2–CH3OH (1:1), 0–5 ◦C, 2 h; (c) BnBr,
NaOH, THF, r t, 5 h; (d) DDQ, CH2Cl2–H2O (9:1), r t, 4 h, 62% in three steps; (e)
HClO4–SiO2, CH2Cl2, ꢀ 5 ◦C, 45 min, 68%; (f) 0.1 M CH3ONa, CH3OH, r t, 3
h, 95%.
10a respectively together with inseparable corresponding sialic acid
glycals by products 11 (~50%) and 11a (~20%) respectively. Whereas,
application of sialic acid phosphate donor (5b) using TMSOTf [25] as
promoter in a mixed solvent of CH3CN and CH2Cl2 led to the formation
of an inseparable mixture of the desired product 10a and corresponding
glycal derivative 11a (~25%). It was decided to carry out deprotection
Fig. 1. Structure of the synthesized pentasaccharide repeating unit (1) and its synthetic intermediates.
2

T. Manna and A.K. Misra
Carbohydrate Research 502 (2021) 108294
of the inseparable mixture to get pure deprotected pentasaccharide (1)
after removal of the functional groups. Therefore, hydrogenation of the
glycoside mixture (10 and 11) obtained by using the sialic acid donor 5
under a positive pressure of hydrogen in the presence of 20% Pd(OH)2–C
[43] followed by saponification using sodium methoxide led to the
deprotected pentasaccharide (1) in 40% over all yield. The other two
product mixtures (10a and 11a) obtained by using sialic acid donors 5a
and 5b subjected to a sequence of reactions involving (a) treatment with
lithium hydroxide in aqueous ethanol for the removal of 4-O,
5-N-carbonyl ring, acetyl groups and methyl ester; (b) acetylation using
acetic anhydride and pyridine; (c) hydrogenation over 20% Pd(OH)2–C
[43] and (d) de-O-acetylation using sodium methoxide to furnish desired
pentasaccharide in overall 60% and 55% yield respectively. The desired
pentasaccharide (1) was purified by column chromatography over
Sephadex LH-20 column and characterized using spectral analysis.
Although, the stereochemical outcome in the glycosylation product
could not be determined by NMR studies due to the formation of
inseparable by product, the stereochemistry of the glycosidic linkages in
the deprotected compound 1 was unambiguously confirmed by the NMR
spectral analysis [44], which clearly showed the formation of a (2 →
4.84 (d, J = 7.5 Hz, 2 H, H-1A, H–1C), 4.63 (d, J = 7.5 Hz, H–1B), 2.61
(dd, J = 13.0 Hz, 4.5 Hz, 1 H, H-3eE), 1.84 (t, J = 12.0 Hz, 1 H, H-3aE) in
1H NMR and δ 103.2 (C-1A), 103.1 (C–1C), 102.9 (C-2E), 102.8 (C–1B),
100.9 (C-1D) in 13CNMR spectra) (Scheme 2).
3. Conclusion
In conclusion, a straightforward synthetic strategy has been devel-
oped for the synthesis of the
α-linked sialic acid containing penta-
saccharide repeating unit of the Streptococcus group B type VI strain.
Perchloric acid supported over silica (HClO4–SiO2) has been used in the
stereoselective activation of glycosyl trichloroacetimidate derivatives
and glycosylation of thioglycosides. A panel of sialic acid donors have
been evaluated for the satisfactory outcome of sialic acid glycosylation
in terms of yield and stereochemical outcome. It was observed that use
of 4-O,5-N-carbonylated sialic acid thioglycoside derivative furnished
better yield with excellent stereochemical outcome in the glycosylation
reaction in comparison to the conventional per-O-acetylated sialic acid
thioglycoside donor.
3)-α-linked sialic acid glycoside (signals at δ 5.18 (d, J = 8.0 Hz, H-1D),
Scheme 2. Reagents and conditions: (a) H2, 20% Pd(OH)2–C, CH3OH, r t, 24 h; (i) 0.1 M CH3ONa, CH3OH, r t, 6 h, then H2O added, r t, 10 h, 40% in two steps; (c)
LiOH, EtOH–H2O (3:1), 80 ◦C, 12 h; (d) Ac2O, pyridine, r t, 5 h; (e) H2, 20% Pd(OH)2–C, H2, CH3OH–H2O (1:1), r t, 24 h; (f) 0.1 M CH3ONa, CH3OH, r t, 6 h, then H2O
added, r t, 10 h, (60% using donor 5a and 55% using donor 5b in three steps).
3

T. Manna and A.K. Misra
Carbohydrate Research 502 (2021) 108294
4. Experimental
reaction mixture was diluted with H2O (100 mL) and extracted with
CH2Cl2 (100 mL). The organic layer was successively washed with satd.
NaHCO3 (50 mL) and H2O (50 mL), dried (Na2SO4) and concentrated. To
a solution of the crude product in CH2Cl2–H2O (30 mL; 9:1) was added
DDQ (500 mg, 2.20 mmol) and the reaction mixture was stirred at room
temperature for 4 h. The reaction mixture extracted with CH2Cl2 (100
mL) and the organic layer was washed with H2O (50 mL), dried
(Na2SO4) and concentrated. The crude product was purified over SiO2
using hexane-EtOAc (8:1) as eluant to give pure compound 7 (1.0 g,
4.1. General methods
All reactions were monitored by thin layer chromatography over
silica gel coated TLC plates. The spots on TLC were visualized by
warming ceric sulphate (2% Ce(SO4)2 in 2 N H2SO4) sprayed plates in
hot plate. Silica gel 230–400 mesh was used for column chromatog-
raphy. NMR spectra were recorded on Bruker Avance 500 MHz using
CDCl3 as solvent and TMS as internal reference unless stated otherwise.
Chemical shift value is expressed in δ ppm. The complete assignment of
proton and carbon spectra was carried out by using a standard set of
NMR experiments, e.g. 1H NMR, 13C NMR, 13C DEPT 135, 2D COSY and
2D HSQC etc. ESI-MS were recorded on a Thermo Scientific Orbitrap
Velos Pro TM mass spectrometer. Optical rotations were recorded in a
Jasco P-2000 spectrometer. Commercially available grades of organic
solvents of adequate purity are used in all reactions. HClO4–SiO2 was
prepared following the reported method [27].
62%). Yellow oil; [
α]
D ꢀ 17 (c 1.0, CHCl3); 1H NMR (500 MHz, CDCl3): δ
7.42–6.73 (m, 49 H, Ar–H), 5.06 (d, J = 11.5 Hz, 1 H, PhCH), 4.97 (d, J
= 11.5 Hz, 1 H, PhCH), 4.92–4.88 (m, 2 H, 2 PhCH), 4.85 (d, J = 8.5 Hz,
1 H, H–1B), 4.80 (d, J = 12.0 Hz, 1 H, PhCH), 4.78 (d, J = 8.5 Hz, 1 H, H-
1A), 4.69 (br s, 2 H, 2 PhCH), 4.63–4.39 (m, 11 H, 11 PhCH), 4.38 (d, J =
8.5 Hz, 1 H, H–1C), 4.25 (d, J = 8.0 Hz, 1 H, H–4B), 4.01 (t, J = 9.0 Hz, 1
H, H–4C), 3.85 (t, J = 9.0 Hz, 1 H, H-4A), 3.77 (br s, 2 H, H-6aA, H-6aB),
3.75 (s, 3 H, OCH3), 3.72–3.54 (m, 8 H, H-2A, H-3A, H–3B, H–3C, H-5A,
H–5B, H-6bA, H-6bB), 3.47–3.32 (m, 4 H, H–2C, H–5C, H-6abC), 3.15 (t, J
= 9.0 Hz, 1 H, H–2B), 2.41 (br s, 1 H, OH); 13C NMR (125 MHz, CDCl3): δ
155.3–114.5 (Ar–C), 102.9 (C-1A), 102.8 (C–1B), 102.5 (C–1C), 83.0 (C-
4A), 82.3 (C-3A), 81.7 (C–5C), 81.6 (C–5B), 80.4 (C–3B), 77.2 (C–4C),
76.7 (C–4B), 76.6 (C-5A), 75.8 (PhCH2), 75.3 (C-2A), 75.2, (2 PhCH2),
74.8 (C–3C), 74.5, 74.0 (2 PhCH2), 73.9 (C–2C), 73.4, 73.3, 73.2, 72.9 (4
PhCH2), 71.2 (C–2B), 69.2 (C-6A, C–6B), 68.2 (C–6C), 55.5, (OCH3);
HRMS [M+1]+: Calcd. for C88H92O17: 1421.6413; found 1421.6394.
4.2. p-Methoxyphenyl [2-O-acetyl-4,6-O-benzylidene-3-O-(p-
methoxybenzyl)-β-D-glucopyranosyl]-(1 → 3)-(2,6-di-O-benzyl-β-D-
galactopyranosyl)-(1 → 4)-2,3,6-tri-O-benzyl-β-D-glucopyranoside
(6)
To a solution of compound 2 (1.5 g, 1.67 mmol) and compound 3
(0.87 g, 1.83 mmol) in anhydrous CH2Cl2 (20 mL) was added MS-4Å (2
g) and it was cooled to ꢀ 40 ◦C under argon. To the cooled reaction
mixture were added NIS (430 mg, 1.91 mmol) and HClO4–SiO2 (25 mg)
and the reaction mixture was allowed to stir at same temperature for 1 h.
The reaction mixture was filtered and washed with CH2Cl2 (50 mL). The
organic layer was successively washed with 5% Na2S2O3 (50 mL), satd.
NaHCO3 (50 mL) and water (50 mL), dried (Na2SO4) and concentrated.
The crude product was purified over SiO2 using hexane-EtOAc (4:1) as
4.4. p-Methoxyphenyl (2,3,4-tri-O-acetyl-6-O-benzyl-β-D-
galactopyranosyl)-(1 → 3)-(2,4,6-tri-O-benzyl-β-D-glucopyranosyl)-
(1 → 3)-(2,4,6-tri-O-benzyl-β-D-galactopyranosyl)-(1 → 4)-2,3,6-
tri-O-benzyl-β-D-glucopyranoside (8)
A solution of compound 7 (0.8 g, 0.56 mmol) and compound 4 (0.34
g, 0.63 mmol) in anhydrous CH2Cl2 (10 mL) was cooled to ꢀ 5 ◦C under
argon. To the cooled reaction mixture was added HClO4–SiO2 (50 mg)
and the reaction mixture was allowed to stir at same temperature for 45
min. The reaction mixture was filtered and washed with CH2Cl2 (50 mL).
The organic layer was successively washed with satd. NaHCO3 (50 mL)
and water (50 mL), dried (Na2SO4) and concentrated. The crude product
was purified over SiO2 using hexane-EtOAc (5:1) as eluant to give pure
eluant to give pure compound 6 (1.6 g, 73%). Yellow oil; [α]D ꢀ 7 (c 1.0,
CHCl3); 1H NMR (500 MHz, CDCl3): δ 8.65–6.83 (m, 38 H, Ar–H), 5.62
(s, 1 H, PhCH), 5.20 (m, J = 10.5 Hz, 1 H, PhCH), 5.08 (t, J = 8.5 Hz, 1 H,
H–2C), 5.07 (d, J = 11.5 Hz, 1 H, PhCH), 4.95 (d, J = 11.0 Hz, 1 H,
PhCH), 4.91 (d, J = 9.0 Hz, 1 H, H-1A), 4.88–4.82 (m, 3 H, 3 PhCH), 4.68
(d, J = 12.0 Hz, 1 H, PhCH), 4.63 (d, J = 12.0 Hz, 1 H, PhCH), 4.59 (d, J
= 12.0 Hz, 1 H, PhCH), 4.52 (d, J = 8.5 Hz, 1 H, H–1C), 4.48 (d, J = 8.0
Hz, 1 H, H–1B), 4.45 (d, J = 12.0 Hz, 1 H, PhCH), 4.44 (d, J = 12.0 Hz, 1
H, PhCH), 4.31 (d, J = 12.0 Hz, 1 H, PhCH), 4.22–4.21 (m, 1 H, H-6aA),
4.12 (d, J = 2.5 Hz, 1 H, H–4B), 4.06 (t, J = 9.0 Hz, 1 H, H–4C), 3.81 (br s,
6 H, 2 OCH3), 3.79–3.74 (m, 5 H, H-3A, H–3B, H-6bA, H-6abB), 3.70 (t, J
= 6.5 Hz, 2 H, H-4A, H–5C), 3.63 (dd, J = 7.5 Hz, 2.5 Hz, 2 H, H–3C, H-
compound 8 (0.69 g, 68%). Yellow oil; [
α]
D ꢀ 10 (c 1.0, CHCl3); 1H NMR
(500 MHz, CDCl3): δ 7.30–6.67 (m, 54 H, Ar–H), 5.33 (br s, 1 H, H-4D),
5.06 (t, J = 9.0 Hz, 1 H, H-2D), 4.98 (d, J = 12.0 Hz, 1 H, 1 PhCH), 4.96
(d, J = 12.0 Hz, 1 H, PhCH), 4.94 (d, J = 8.5 Hz, H-1, H-1D), 4.92–4.85
(m, 3 H, 3 PhCH), 4.83 (d, J = 8.5 Hz, 1 H, H–1B), 4.80 (dd, J = 9.0 Hz,
2.5 Hz, 1 H, 2 H-3D), 4.74 (d, J = 7.5 Hz, 1 H, H-1A), 4.67 (d, J = 11.0 Hz,
1 H, PhCH), 4.61–4.57 (m, 2 H, 2 PhCH), 4.52–4.45 (m, 5 H, 5 PhCH),
4.40–4.37 (m, 5 H, 5 PhCH), 4.36 (d, J = 8.0 Hz, 1 H, H–1C), 4.34 (d, J =
11.0 Hz, 1 H, PhCH), 4.26 (brs, 1 H, H–4B), 4.15–4.12 (m, 2 H, 2 PhCH),
3.92 (t, J = 9.0 Hz, 1 H, H–4C), 3.86 (t, J = 9.0 Hz, 1 H, H-4A), 3.76–3.73
(m, 1 H, H-6aA), 3.72–3.65 (m, 2 H, H-6abD), 3.67 (s, 3 H, 3 OCH3),
3.62–3.58 (m, 4 H, H–3B, H–3C, H-6aB, H-6bA), 3.52–3.48 (m, 4 H, H-3A,
H-5A, H–5B, H-6bB), 3.41–3.37 (m, 3 H, H-2A, H–2C, H–5C), 3.28–3.22
(m, 3 H, H-5D, H-6abC), 3.18 (t, J = 8.5 Hz, 1 H, H–2B), 1.90 (s, 3 H,
COCH3), 1.88 (s, 3 H, COCH3), 1.70 (s, 3 H, COCH3); 13C NMR (125
MHz, CDCl3): δ 169.8, 169.7, 169.1 (3 COCH3), 155.2–114.4 (Ar–C),
102.8 (C-1A, C–1C), 101.8 (C–1B), 100.4 (C-1D), 83.3 (C-5D), 83.1 (C–5B),
82.3 (C–2C), 81.5 (C-2A), 80.6 (C-4A), 80.5 (C–3C), 76.6 (C–4C), 75.7
(PhCH2), 75.6 (C–5C), 75.4 (C-3A), 75.3, 75.1, 74.9, 74.5 (4 PhCH2),
74.4 (C-5A), 73.7 (C–2B), 73.5, 73.4, 73.3, 73.1, 72.6 (5 PhCH2), 71.6 (C-
3D), 71.2 (C–3B), 69.8 (C-2D, C–4B), 69.0 (C–6B), 68.9 (C–6C), 68.1 (C-
6A), 67.6 (C-4D), 66.6 (C-6D), 55.5, (OCH3), 20.7, 20.6 (3 COCH3);
HRMS [M+1]+: Calcd. for C107H114O25: 1799.7727; found 1799.7712.
6
6
aC), 3.57–3.49 (m, 3 H, H–2B, H-5A, H–5B), 3.42–3.39 (m, 2 H, H-2A, H-
bC), 2.12 (s, 3 H, COCH3); 13C NMR (125 MHz, CDCl3): δ 168.6
(COCH3), 159.2–113.6 (Ar–C), 102.9 (C-1A), 102.6 (C–1B), 102.5
(C–1C), 101.3 (PhCH), 82.6 (C-4A), 81.4 (C-3A, C–5C), 78.2 (C–5B), 77.8
(C–3B), 76.8 (C–4C), 75.6 (PhCH2), 75.3 (C–4B), 75.2, 75.1 (2 PhCH2),
75.0 (C-2A), 74.9 (C-5A), 73.7 (PhCH2), 73.4 (C–2C), 73.2, 73.1 (2
PhCH2), 72.9 (C–3C), 68.6 (C–6B), 68.4 (C–6C), 68.1 (C-6A), 65.9 (C–2B),
55.5, 55.1 (2 OCH3), 21.0 (COCH3); HRMS [M+1]+: Calcd. for
C
77H82O19: 1311.5528; found 1311.5510.
4.3. p-Methoxyphenyl (2,4,6-tri-O-benzyl-β-D-glucopyranosyl)-(1
→ 3)-(2,4,6-tri-O-benzyl-β-D-galactopyranosyl)-(1 → 4)-2,3,6-tri-
O-benzyl-β-D-glucopyranoside (7)
To a solution of compound 6 (1.5 g, 1.14 mmol) in CH2Cl2–CH3OH
(20 mL; 1:1) was added p-TsOH (200 mg) and the reaction mixture was
stirred at 0–5 ◦C for 2 h. The reaction mixture was quenched with Et3N
(1 mL) and the solvents were removed under reduced pressure. To a
solution of the crude product in DMF (15 mL) was added benzyl bromide
(1 mL, 8.42 mmol) followed by powdered NaOH (0.5 g, 12.5 mmol) and
the reaction mixture was stirred at room temperature for 5 h. The
4

T. Manna and A.K. Misra
Carbohydrate Research 502 (2021) 108294
4.5. p-Methoxyphenyl (6-O-benzyl-β-D-galactopyranosyl)-(1 → 3)-
(2,4,6-tri-O-benzyl-β-D-glucopyranosyl)-(1 → 3)-(2,4,6-tri-O-
benzyl-β-D-galactopyranosyl)-(1 → 4)-2,3,6-tri-O-benzyl-β-D-
glucopyranoside (9)
5A), 2.61 (dd, J = 13.0 Hz, 4.5 Hz, 1 H, H-3eE), 2.17 (s, 3 H, COCH3), 1.84
(t, J = 12.0 Hz, 1 H, H-3aE); 13C NMR (125 MHz, D2O): δ 175.5
(NHCOCH3), 174.7 (COOH), 154.7–115.0 (Ar–C), 103.2 (C-1A), 103.1
(C–1C), 102.9 (C-2E), 102.8 (C–1B), 100.9 (C-1D), 84.3 (C–3C), 77.9
(C–3B), 77.4 (C-4A), 77.2 (C–5B), 75.4 (C-5D), 75.0 (C-5A), 74.8 (C–5C),
74.5 (C-3A), 74.1 (C-2A), 73.3 (C-6E), 72.9 (C-8E), 72.6 (C–2C), 71.6 (C-
2D), 71.4 (C-3D), 69.9 (C–2B, C–4B), 68.5 (C-7E), 68.0 (C-4E), 67.9 (C-4D),
66.1 (C–4C), 63.3 (C-9E), 60.9.(C–6B, C-6D), 60.6 (C–6C), 59.8 (C-6A),
55.7, (OCH3), 52.0 (C-5E), 40.6 (C-3E), 22.1 (COCH3); HRMS [M]+:
Calcd. for C42H64NNaO30: 1085.3411; found 1085.3392. The depro-
tected glycal derivative (side product) could not be isolated during
column chromatography.
A solution of compound 8 (0.6 g, 0.33 mmol) in 0.1 M CH3ONa in
CH3OH (20 mL) was stirred at room temperature for 3 h and neutralized
with Dowex 50 W X8 (H+) resin. The reaction mixture was filtered and
concentrated under reduced pressure to give compound 9 (525 mg,
95%). Colorless oil; [
α]
D ꢀ 25 (c 1.0, CHCl3); 1H NMR (500 MHz, CDCl3):
δ 7.37–6.73 (m, 54 H, Ar–H), 5.08 (d, J = 11.0 Hz, 1 H, PhCH), 5.02 (d, J
= 11.0 Hz, 1 H, PhCH), 4.93–4.89 (m, 2 H, 2 PhCH), 4.90 (d, J = 8.5 Hz,
1 H, H-1D), 4.80 (d, J = 8.0 Hz, 1 H, H–1B), 4.77 (d, J = 8.5 Hz, 1 H, H-
1A), 4.70 (brs, 2 H, 2 PhCH), 4.59–4.36 (m, 14 H, 14 PhCH), 4.34 (d, J =
8.5 Hz, 1 H, H–1C), 4.27 (d, J = 2.0 Hz, 1 H, H–4B), 3.98 (t, J = 9.0 Hz, 1
H, H–4C), 3.86 (t, J = 9.0 Hz, 1 H, H-4A), 3.83–3.81 (m, 2 H, H-
6abD),3.75–3.74 (m, 2 H, H-6abA), 3.72 (s, 3 H, OCH3), 3.36–3.64 (m, 4
H, H–3B, H–3C, H-6abB), 3.59–3.52 (m, 5 H, H-3A, H-3D, H-4D, H–5B,
H–5C), 3.43–3.40 (m, 5 H, H-2A, H–2C, H-5A, H-6abC), 3.38–3.31 (m, 3 H,
H–2B, H-2D, H-5D); 13C NMR (125 MHz, CDCl3): δ 138.7–114.5 (Ar–C),
104.7 (C-1A), 102.9 (C–1C), 102.8 (C–1B), 102.5 (C-1D), 83.0 (C-5D),
82.7 (C–5B), 82.2 (C–2C), 81.7 (C-2A), 81.6 (C-4A), 80.5 (C–3C), 77.6
(C–4C), 75.7 (C–5C), 75.4 (PhCH2), 75.3 (C-3A), 75.2, 75.1, 74.8 (3
PhCH2), 74.6 (C-5A), 74.5 (PhCH2), 73.8 (C–2B), 73.7 (C–3B), 73.5, 73.4,
73.3, (3 PhCH2), 73.3 (C-3D), 73.2 (PhCH2), 73.0 (C-2D), 72.9 (PhCH2),
71.1.(C–4B), 69.1 (C-6A), 69.0 (C–6B), 68.9 (C–6C), 68.3 (C-4D), 68.2 (C-
6D), 55.5, (OCH3); HRMS [M+1]+: Calcd. for C101H108O22: 1673.7410;
found 1673.7394.
4.6.2. Glycosylation of compound 9 with Sialic acid donor 5a
To a solution of compound 9 (100 mg, 0.06 mmol) and compound 5a
(62 mg, 0.12 mmol) in anhydrous CH3CN–CH2Cl2 (5 mL; 5:1 v/v) was
added MS-3Å (0.2 g) and it was cooled to ꢀ 40 ◦C under argon. To the
cooled reaction mixture were added NIS (55 mg, 0.24 mmol) and TfOH
(5 μL) and the reaction mixture was allowed to stir at same temperature
for 5 h. The reaction mixture was filtered and washed with CH2Cl2 (25
mL). The organic layer was successively washed with 5% Na2S2O3 (25
mL), satd. NaHCO3 (25 mL) and water (25 mL), dried (Na2SO4) and
concentrated. The crude product was passed through a short pad of SiO2
using toluene-acetone (6:1) as eluant to give glycosylated product (10a)
together with sialic acid glycal derivative (11a). To a solution of the
product mixture in EtOH–H2O (5 mL; 3:1) was added LiOH (30 mg, 1.25
mmol) and the reaction was stirred at 80 ◦C for 12 h. The reaction
mixture was cooled to room temperature, neutralized with 10% HCl and
concentrated. A solution of the crude product in pyridine (1 mL) and
acetic anhydride (1 mL) was stirred at room temperature for 5 h and
concentrated. The crude product mixture was extracted with EtOAc (3
× 20 mL) and the organic layer was concentrated. To a solution of the
product obtained in CH3OH (5 mL) was added 20% Pd(OH)2–C (25 mg)
and it was stirred under a positive pressure of H2 at room temperature
for 24 h. The reaction mixture was filtered through a Celite bed and
concentrated under reduced pressure. A solution of the product in 0.1 M
CH3ONa in CH3OH (10 mL) was stirred at room temperature for 6 h and
then H2O (0.2 mL) was added to the reaction mixture and allowed to stir
at room temperature for 10 h and neutralized with Dowex 50 W X8 (H+)
resin and concentrated under reduced pressure. The deprotected prod-
uct was passed through a column of Sephadex LH-20 column using
CH3OH–H2O (6:1) as eluant to give pure compound 1 (40 mg, 60%).
White powder. The analytical data was identical with the compound 1,
obtained earlier. The deprotected glycal derivative (side product) could
not be isolated during column chromatography.
4.6. p-Methoxyphenyl [sodium(5-acetamido-3,5-dideoxy-D-glycero-α-D-
galacto-2-nonulopyranosyl)onate]-(2 → 3)-(β-D-galactopyranosyl)-(1 →
3)-(β-D-glucopyranosyl)-(1 → 3)-(β-D-galactopyranosyl)-(1 → 4)-β-D-
glucopyranoside (1)
4.6.1. Glycosylation of compound 9 with sialic acid donor 5
To a solution of compound 9 (500 mg, 0.298 mmol) and compound 5
(435 mg, 0.74 mmol) in anhydrous CH3CN–CH2Cl2 (10 mL; 5:1 v/v) was
◦
added MS-3Å (1 g) and it was cooled to ꢀ 40 C under argon. To the
cooled reaction mixture were added NIS (330 mg, 1.46 mmol) and TfOH
(25 μL) and the reaction mixture was allowed to stir at same temperature
for 5 h. The reaction mixture was filtered and washed with CH2Cl2 (50
mL). The organic layer was successively washed with 5% Na2S2O3 (50
mL), satd. NaHCO3 (50 mL) and water (50 mL), dried (Na2SO4) and
concentrated. The crude product was passed through a short pad of SiO2
using hexane-EtOAc (1:1) as eluant to give glycosylated product (10)
together with sialic acid glycal derivative (11). To a solution of the
product mixture in CH3OH (5 mL) was added 20% Pd(OH)2–C (50 mg)
and it was stirred under a positive pressure of H2 at room temperature
for 24 h. The reaction mixture was filtered through a Celite bed and
concentrated under reduced pressure. A solution of the product in 0.1 M
CH3ONa in CH3OH (10 mL) was stirred at room temperature for 6 h and
then H2O (0.2 mL) was added to the reaction mixture and allowed to stir
at room temperature for 10 h and neutralized with Dowex 50 W X8 (H+)
resin. The reaction mixture was filtered and passed through a short
column of Dowex 50 W X8 (Na+) resin and concentrated under reduced
pressure. The deprotected product was passed through a column of
Sephadex LH-20 column using CH3OH–H2O (6:1) as eluant to give pure
4.6.3. Glycosylation of compound 9 with Sialic acid donor 5b
To a solution of compound 9 (100 mg, 0.06 mmol) and compound 5b
(75 mg, 0.12 mmol) in anhydrous CH3CN–CH2Cl2 (5 mL; 3:1 v/v) was
added MS-3Å (0.2 g) and it was cooled to ꢀ 40 ◦C under argon. To the
cooled reaction mixture was added TMSOTf (15 μL) and the reaction
mixture was allowed to stir at same temperature for 5 h. The reaction
mixture was filtered and washed with CH2Cl2 (25 mL). The organic layer
was successively washed with satd. NaHCO3 (25 mL) and water (25 mL),
dried (Na2SO4) and concentrated. The crude product was passed
through a short pad of SiO2 using toluene-acetone (6:1) as eluant to give
glycosylated product (10a) together with sialic acid glycal derivative
(11a). To a solution of the product mixture in EtOH–H2O (5 mL; 3:1) was
added LiOH (30 mg, 1.25 mmol) and the reaction was stirred at 80 ◦C for
12 h. The reaction mixture was cooled to room temperature, neutralized
with 10% HCl and concentrated. A solution of the crude product in
pyridine (1 mL) and acetic anhydride (1 mL) was stirred at room tem-
perature for 5 h and concentrated. The crude product mixture was
extracted with EtOAc (3 × 20 mL) and the organic layer was concen-
trated. To a solution of the product obtained in CH3OH (5 mL) was
added 20% Pd(OH)2–C (25 mg) and it was stirred under a positive
compound 1 (128 mg, 40%). White powder; [
α]
D ꢀ 19 (c 1.0, H2O); 1H
NMR (500 MHz, D2O): δ 7.25–7.10 (m, 4 H, Ar–H), 5.18 (d, J = 8.0 Hz, 1
H, H-1D), 4.84 (d, J = 7.5 Hz, 2 H, H-1A, H–1C), 4.63 (d, J = 7.5 Hz, 1 H,
H–1B), 4.38 (d, J = 2.5 Hz, 1 H, H-4D), 4.31 (d, J = 2.5 Hz, 1 H, H–4B),
4.30–4.28 (m, 1 H, H–5C), 4.12–4.02 (m, 5 H, H-3D, H-6aA, H-6aC, H-5E,
H-8E), 3.97–3.92 (m, 6 H, H–3B, H–3C, H-9aE, H-6bA, H-6aB, H-6bC), 3.93
(s, 3 H, OCH3), 3.90–3.83 (m, 8 H, H–2B, H-2D, H–5B, H-5D, H-6bB, H-
6
abD, H-9bE), 3.81–3.73 (m, 4 H, H–2C, H-4E, H-6E, H-7E), 3.72–3.67 (m,
2 H, H-4A, H–4C), 3. 67–3.63 (m, 2 H, H-2A, H-3A), 3.62–3.56 (m, 1 H, H-
5

T. Manna and A.K. Misra
Carbohydrate Research 502 (2021) 108294
[15] E. Eichler, H.J. Jennings, D.M. Whitfield, Synthesis of a single repeat unit of type
VIII group B streptococcus capsular polysaccharide, J. Carbohydr. Chem. 16 (1997)
385–411.
pressure of H2 at room temperature for 24 h. The reaction mixture was
filtered through a Celite bed and concentrated under reduced pressure.
A solution of the product in 0.1 M CH3ONa in CH3OH (10 mL) was
stirred at room temperature for 6 h and then H2O (0.2 mL) was added to
the reaction mixture and allowed to stir at room temperature for 10 h
and neutralized with Dowex 50 W X8 (H+) resin and concentrated under
reduced pressure. The deprotected product was passed through a col-
umn of Sephadex LH-20 column using CH3OH–H2O (6:1) as eluant to
give pure compound 1 (35 mg, 55%). White powder. The analytical data
was identical with the compound 1, obtained earlier. The deprotected
glycal derivative (side product) could not be isolated during column
chromatography.
[16] E. Eichler, H.J. Jennings, M. Gilbert, D.M. Whitfield, Synthesis of a desialylated
hexasaccharide of type VIII Group B Streptococcus capsular polysaccharide,
Carbohydr. Res. 319 (1999) 1–16.
[17] L. Shao, H. Zhang, Y. Li, G. Gu, F. Cai, Z. Guo, J. Gao, Chemical synthesis of the
repeating unit of type II group B streptococcus capsular polysaccharide, J. Org.
Chem. 83 (2018) 5920–5930.
[18] J. Gao, Z. Guo, Chemical synthesis of the repeating unit of type V group B
Streptococcus capsular polysaccharide, Org. Lett. 18 (2016) 5552–5555.
[19] G. Kogan, D. Uhrin, J.-B. Brisson, L.C. Paoletti, D.L. Kasper, C. von Hunolstein,
G. Orefici, H.J. Jennings, Structure of the type VI group B Streptococcus capsular
polysaccharide determined by high resolution NMR spectroscopy, J. Carbohydr.
Chem. 13 (1994) 1071–1078.
´
´ ´
´
´
´
[20] A. Borbas, M. Csavas, L. Szilagyi, G. Majer, A. Liptak, Replacement of carbohydrate
sulfates by sugar C-sulfonic acid derivatives, J. Carbohydr. Chem. 23 (2004)
133–146.
Declaration of competing interest
[21] C. Mukherjee, A.K. Misra, Total synthesis of an antigenic heptasaccharide motif
found in the cell-wall lipooligosaccharide of Mycobacterium gordonae strain 989,
Glycoconj. J. 25 (2008) 817–826.
The authors declare that they have no known competing financial
interests or personal relationships that could have appeared to influence
the work reported in this paper.
[22] P.K. Mandal, A.K. Misra, Concise synthesis of the pentasaccharide O-antigen
corresponding to the Shiga toxin producing Escherichia coli O171, Bioorg. Chem. 38
(2010) 56–61.
[23] P. Sengupta, A.K. Misra, M. Suzuki, M. Fukuda, O. Hindsgaul, Chemoenzymatic
synthesis of sialylated oligosaccharides for their evaluation in a
polysialyltransferase assay, Tetrahedron Lett. 44 (2003) 6037–6042.
[24] M.D. Farris, C. De Meo, Application of 4,5-O,N-oxazolidinone protected thiophenyl
Acknowledgement
T. M. thanks UGC, New Delhi for providing Senior Research
Fellowship. The work is supported by SERB, India (Project No. CRG/
2019/000352 dated January 23, 2020) (AKM) and Bose Institute.
sialosyl donor to the synthesis of α-sialosides, Tetrahedron Lett. 48 (2007)
1225–1227.
[25] C.-H. Hsu, K.-C. Chu, Y.-S. Lin, J.-L. Han, Y.-S. Peng, C.-T. Ren, C.-Y. Wu, C.-
H. Wong, Highly alpha-selective sialyl phosphate donors for efficient preparation
of natural sialosides, Chem. Eur J. 16 (2010) 1754–1760.
Appendix A. Supplementary data
[26] C. Mukherjee, A.K. Misra, Glycosylation and pyranose-furanose isomerization of
carbohydrates using HClO4-SiO2: synthesis of oligosaccharides containing
galactofuranose, Synthesis (2007) 683–692.
Supplementary data to this article can be found online at https://doi.
org/10.1016/j.carres.2021.108294.
[27] A.K. Chakraborti, R. Gulhane, Perchloric acid adsorbed on silica gel as a new,
highly efficient, and versatile catalyst for acetylation of phenols, thiols, alcohols,
and amines, Chem. Commun. (2003) 1896–1897.
[28] S.K. Madhusudan, G. Agnihotri, D.S. Negi, A.K. Misra, Direct one-pot conversion of
acylated carbohydrates into their alkylated derivatives under heterogeneous
reaction conditions using solid NaOH and a phase transfer catalyst, Carbohydr.
Res. 340 (2005) 1373–1377.
References
[1] K.A. Simonsen, A.L. Anderson-Berry, S.F. Delair, H.D. Davis, Early-onset neonatal
sepsis, Clin. Microbial. Rev. 27 (2014) 21–47.
[29] P.G.M. Wuts, in: D. Crich (Ed.), Handbook of Reagents for Organic Synthesis:
Reagents for Glycoside, Nucleotide, and Peptide Synthesis, Wiley, Chichester,
2005, pp. 425–428.
[2] H.C. Maisey, K.S. Doran, V. Nizet, Recent advances in understanding the molecular
basis of group B Streptococcus virulence, Expet Rev. Mol. Med. 10 (2009) e27,
https://doi.org/10.1017/S1462399408000811.
[30] B. Mukhopadhyay, S.V. Maurer, N. Rudolph, R.M. van Well, D.A. Russell, R.
A. Field, From solution phase to “on-column” chemistry: trichloroacetimidate-
based glycosylation promoted by perchloric acid-silica, J. Org. Chem. 70 (2005)
9059–9062.
[3] P. Melin, Neonatal group B streptococcal disease: from pathogenesis to preventive
strategies, Clin. Microbiol. Infect. 17 (2011) 1294–1303.
[4] L. Rajagopal, Understanding the regulation of Group B Streptococcal virulence
factors, Future Microbiol. 4 (2009) 201–221.
[31] B. Jones, A. Behm, M. Shadrick, S.A. Geringer, S. Escopy, M. Lohman, C. De Meo,
Comparative study on the effects of picoloyl groups in sialylations based on their
substitution pattern, J. Org. Chem. 84 (2019) 15052–15062.
[5] M.J. Cieslewicz, D. Chaffin, G. Glusman, D. Kasper, A. Madan, S. Rodrigues,
J. Fahey, M.R. Wessels, C.E. Rubens, Structural and genetic diversity of group B
Streptococcus capsular polysaccharides, Infect. Immun. 73 (2005) 3096–3103.
[6] F. Berti, R. De Ricco, R. Rappuoli, Role of O-acetylation in the immunogenicity of
bacterial polysaccharide vaccines, Molecules 23 (2018) 1340, https://doi.org/
10.3390/molecules23061340Molecules.
[32] S. Escopy, S.A. Geringer, C. De Meo, Combined effect of the picoloyl protecting
group and triflic acid in sialylation, Org. Lett. 19 (2017) 2638–2641.
[33] C.-S. Yu, K. Niikura, C.-C. Lin, C.-H. Wong, The thioglycoside and glycosyl
phosphite of 5-azido sialic acid: excellent donors for the α-glycosylation of primary
[7] L.R.K. Brooks, G.I. Mias, Streptococcus pneumoniae’s virulence and host immunity:
aging, diagnostics, and prevention, Front. Immunol. 9 (2018) 1366, https://doi.
org/10.3389/fimmu.2018.01366.
hydroxy groups. Angew. Chem. Int. Ed. 40 (20010 2900-2903.
´
[34] J. Chen, T. Hansen, Q. Ju Zhang, D.-Y. Liu, Y. Sun, H. Yan, J.D.C. Codee, R.
R. Schmidt, J.-S. Sun, 1-Picolinyl-5-azido thiosialosides: versatile donors for the
stereoselective construction of sialyl linkages, Angew. Chem. Int. Ed. 58 (2019)
2–11.
[8] J. Sarowska, B. Futoma-Koloch, A. Jama-Kmiecik, M. Frej-Madrzak, Ksiazczyk,
M. Bugla-Ploskonska, I. Choroszy-Krol, Virulence factors, prevalence and potential
transmission of extraintestinal pathogenic Escherichia coli isolated from different
sources: recent reports, Gut Pathog. 11 (2019). Article number: 10.
[9] C. von Hunolstein, S. D’Ascenzi, B. Wagner, J. Jelinkova, G. Alfarone, S. Recchia,
M. Wagner, G. Orefici, Immunochemistry of capsular type polysaccharide and
virulence properties of type VI Streptococcus agalactiae (Group B Streptococci),
Infect. Immun. 61 (1993) 1272–1280.
[35] X.S. Ye, X. Huang, C.-H. Wong, Conversion of the carboxy group of sialic acid
donors to a protected hydroxymethyl group yields an efficient reagent for the
synthesis of the unnatural beta-linkage, Chem. Commun. (2001) 974–975.
[36] Y.-F. Wu, Y.-F. Tsai, Assistance of the C-7,8-picoloyl moiety for directing the
glycosyl acceptors into the
Lett. 19 (2017) 4171–4174.
[37] G.B. Shelke, B.-R. Chen, S.-A. Yang, T.-M. Kuo, Y.-L. Syu, Y.-C. Ko, S.-Y. Luo, Mild
α-orientation for the glycosylation of sialyl donors, Org.
[10] K.R. Harale, J.K. Rout, M.K. Chhikara, D.S. Gill, A.K. Misra, Synthesis and
immunochemical evaluation of a novel Neisseria meningitides serogroup A
tetrasaccharide and its conjugate, Org. Chem. Front. 4 (2017) 2348–2357.
[11] C.-X. Huo, D. Dhara, S.M. Baliban, S.T. Nick, Z. Tan, R. Simon, A.K. Misra,
X. Huang, Synthetic and immunological studies of Salmonella Enteritidis O-antigen
tetrasaccharides as potential anti-Salmonella vaccines, Chem. Commun. 55 (2019)
4519–4522.
and highly α-selective O-sialylation method based on pre-activation: access to
Gangliosides Hp-s1, DSG-A, and their analogues, Asian J. Org. Chem. 6 (2017)
1556–1560.
[38] H. Tanaka, Y. Nishiura, T. Takahashi, Stereoselective synthesis of α(2,9) di- to
tetrasialic acids, using a 5,4-N,O-carbonyl protected thiosialoside, J. Org. Chem. 74
(2009) 4383–4386.
[12] A.E. Zarei, H.A. Almehdar, E.M. Redwan, Hib vaccines: past, present, and future
perspectives, J. Immunol. Res. 2016 (2016) 7203587.
[39] H. Ando, M. Ishida, M. Kiso, Synthesis of sialic acid containing carbohydrates, in:
H.M.I. Osborn (Ed.), Best Synthetic Methods, Academic Press, Oxford, 2003,
pp. 277–310.
[13] F. Micoli, L.D. Bino, R. Alfini, F. Carboni, M.R. Romano, R. Adamo, Glycoconjugate
vaccines: current approaches towards faster vaccine design, Expet Rev. Vaccine 18
(2019) 881–895.
[40] D.K. Ress, R.J. Linhardt, Sialic acid donors: chemical synthesis and glycosylation,
Curr. Org. Synth. 1 (2004) 31–46.
[14] V. Cattaneo, F. Carboni, D. Oldrini, R. De Ricco, N. Donadio, I.M. Y Ros, F. Berti,
R. Adamo, Synthesis of Group B Streptococcus type III polysaccharide fragments for
evaluation of their interactions with monoclonal antibodies, Pure Appl. Chem. 89
(2016), https://doi.org/10.1515/pac-2016-0918.
[41] G.H. Veeneman, S.H. van Leeuwen, J.H. van Boom, Iodonium ion promoted
reactions at the anomeric centre. II an efficient thioglycoside mediated approach
toward the formation of 1,2-trans linked glycosides and glycosidic esters,
Tetrahedron Lett. 31 (1990) 1331–1334.
6

T. Manna and A.K. Misra
Carbohydrate Research 502 (2021) 108294
[42] P. Konradsson, U.E. Udodong, B. Fraser-Reid, Iodonium promoted reactions of
disarmed thioglycosides, Tetrahedron Lett. 31 (1990) 4313–4316.
[43] W.M. Pearlman, Noble metal hydroxides on carbon nonpyrophoric dry catalysts,
Tetrahedron Lett. 8 (1967) 1663–1664.
[44] N. Komura, K. Kato, T. Udagawa, S. Asano, H.-N. Tanaka, A. Imamura, H. Ishida,
M. Kiso, H. Ando, Constrained sialic acid donors enable selective synthesis of
α
-glycosides, Science 364 (2019) 677–680.
7