Convergent synthesis of the tetrasaccharide repeating unit related
to the O-antigenic polysaccharide of Escherichia coli 78
Sajal K. Maity
, Amarendra Patra
, Rina Ghosh
Department of Chemistry, Jadavpur University, Kolkata 700 032, India
Department of Chemistry, University College of Science and Technology, University of Calcutta, Kolkata 700 009, India
Received 30 December 2009
Received in revised form 12 February 2010
Accepted 12 February 2010
Available online 17 February 2010
E. coli 78
Cell wall polysaccharide
A convergent synthesis of the tetrasaccharide repeating unit of the O-antigenic cell wall polysaccharide
of Escherichia coli 78, as the corresponding methyl glycoside (I), is being reported. It involved stereo-
selective glycosidation of a
-linked mannodisaccharide acceptor with a
-linked glucosamine based
disaccharide thioglycoside donor, which were prepared from the corresponding functionalised mono-
saccharide based glycosyl donors and acceptors. The resulting tetrasaccharide derivative was ﬁnally
converted to (I) by selective deprotection and also by global protection and deprotection techniques.
Ó 2010 Elsevier Ltd. All rights reserved.
Escherichia coli, a group of gram negative bacteria generally
conﬁned to intestinal lumen, causes human gastroenteritis;
also infect immune-suppressed host.
Three general clinical syn-
dromes effected by pathogenic clones of E. coli are urinary tract
infection, sepsis or meningitis, and enteric or diarrheal disease.
About one third of isolated enterotoxic strains of E. coli (ETEC) in-
clude serogroups of O6, O8, and O78. ETEC are associated with
pediatric diarrhea in developing countries, severe cholera like
disease in epidemic cholera zones and ‘travellers’ diarrhea’.
Structure of the O-antigenic cell wall polysaccharide of E. coli 78
(Fig. 1) was established by Jansson et al.
analysis, partial solvolysis with liquid hydrogen ﬂuoride and also by
1D- and 2D-NMR spectroscopy.
Carbohydrates of bacterial cell wall play important role during
host infection and subsequent immune response in the host. Sub-
stantial amounts of bacterial polysaccharides or oligosaccharides
are necessary for extensive biological evaluation and biochemical
studies of bacterial strains. Though, oligosaccharides can be isolated
from the native sources, the meager amount obtained by isolation
can not meet the quantity required for their detailed biological
studies. Oligosaccharides or their modiﬁed forms are, however,
obtainable in large quantities by chemical synthesis.
In continuation to our research based on carbohydrate syn-
and also as part of our ongoing research programme to the
synthesis of oligosaccharides for developing serological markers
toward a variety of bacterial strains, we present herein the conver-
gent synthesis (Schemes 1–3) of the tetrasaccharide repeating unit,
of the O-antigenic polysaccharide of E. coli 78 as its methyl glycoside
(I). To the best of our knowledge, this is the ﬁrst synthesis of the
tetrasaccharide related to this strain.
Figure 1. Structure of the O-antigenic polysaccharide of E. coli 78.
Scheme 1. Reagents and conditions: (a) Ac
O (1.2 equiv), pyridine, DMAP, CH
1 h, 99%; (b) NaCNBH
(12 equiv), HCl/Et
O, THF, 4 Å MS, 0
C, 40 min, 94%;
(c) 1 (1.0 equiv), BSP, Tf
O, TTBP, CH
, 4 Å MS, Ar, À78
C, 30 min, 75%.
Corresponding author. Fax: þ91 033 24146266; e-mail addresses: ghosh_rina@
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Tetrahedron 66 (2010) 2809–2814