Synthesis of complex carbohydrates corresponding to the Lewis b blood group antigen and Vibrio cholerae polysaccharide structures

Abstract: This thesis is divided into two parts. The first part describes the syntheses of the Lewis b blood group antigen hexasaccharide and parts thereof. The Leb blood group antigen is one of the binding epitopes for the Helicobacter pylori bacteria in the human stomach. The oligosaccharides containing N-acetyl glucosamine, galactose and fucose, were synthesised as their 8-methoxycarbonyloctyl or 2-azidoethyl spacer glycosides and were conjugated to proteins using activated esters or the diethyl squarate methodology for binding studies with H. pylori. In the second part, structures from the lipopolysaccharide and capsular polysaccharide of Vibrio cholerae O139 synonym Bengal and Vibrio cholerae O22 were synthesised as 2-(4-benzyloxyamidophenyl)ethyl spacer glycosides for the study of their immunological properties. Unusual features of these oligosaccharides are the presence of a 6-membered cyclic phosphate diester and the 2,6-dideoxysugar colitose.The glycosylation reactions included halide-assisted couplings of the bromosugars of fucose and colitose, AgOTf promotion of galactosyl bromides, and DMTST or NIS promotion of thioethyl glycosides.