Straightforward synthesis of the pentasaccharide repeating unit of the cell wall O -antigen of Escherichia coli O43 stra
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ORIGINAL ARTICLE
Straightforward synthesis of the pentasaccharide repeating unit of the cell wall O-antigen of Escherichia coli O43 strain Pradip Shit 1 & Anup Kumar Misra 1 Received: 21 April 2020 / Revised: 23 May 2020 / Accepted: 18 June 2020 # Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract A concise synthetic strategy has been developed for the synthesis of the pentasaccharide repeating unit of the cell wall O-antigen of Escherichia coli O43 strain involving stereoselective β-D-mannosylation and α-L-fucosylation using corresponding trichloroacetimidate intermediates and perchloric acid supported over silica (HClO4-SiO2) as glycosylation promoter. The yield and stereoselectivity of the glycosylations were very good. Keywords Oligosaccharide . Glycosylation . O-antigen . Diarrhea . E. coli
Introduction Diarrhoeal outbreaks associated with gastrointestinal infections are serious health concern in the developing countries due to the lack of adequate sanitation [1]. In the recent past, it became severe health hazard in the developed countries also due to the intake of contaminated food and water [2]. Most frequently found bacteria causing enteric infections are Shigella [3], Salmonella [4], Vibrio Cholerae [5], enteropathogenic Escherichia coli (E. coli) [6], Campylobacter jejuni [7] etc. Among several enteropathogenic microbes causing diarrhoeal infections, pathogenic Escherichia coli (E. coli) strains are important. E. coli is a Gram-negative, facultative anaerobic pathogen predominantly found in the gastrointestinal tract of humans [8]. Despite their harmless existence in the gut flora and beneficial contribution, a certain species of E. coli acquired virulence factors and causes severe intestinal and urinary infections in humans and animals [9, 10]. They are associated with gastrointestinal infections, particularly “traveller’s diarrhoea” [11] and classified in several sub-types such as, enteropathogenic E. coli (EPEC), enterohemorrhagic E. coli (EHEC), enterotoxigenix E. coli (ETEC), enteroinvasive E. coli (EIEC), enteroaggregative E. coli (EAEC), diffusely adherent E. coli (DAEC) etc. [12].
* Anup Kumar Misra [email protected] 1
Division of Molecular Medicine, Bose Institute, P-1/12, C.I.T. Scheme VII M, Kolkata 700054, India
Among different sub-classes, shiga-toxin (ST) producing EHEC strains are associated with diarrhoeal diseases with life threatening complications such as haemorrhagic colitis [13]. Shiga-toxin producing E. coli O43 strain belongs to EHEC and has been responsible for several diarrhoeal outbreaks in the past [14]. Because of the important role of the cell wall polysaccharides of the pathogenic bacterial strains during the initial stage of infection to the host, a large number of polysaccharides from several bacterial strains have been characterized. Recently, the structure of the repeating unit of the Oantigenic polysaccharide of E. coli O43 has been reported by Perepelov et al [15]. It is a pentasaccharide composed of one β-N-acetyl-D-galactosamine, two
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