Synthesis of oligosaccharides of bacterial origin containing heptoses, uronic acids and fructofuranoses as synthetic challenges

Abstract

In this article, syntheses of bacterial oligosaccharides containing additional synthetic challenges are presented. In the first part, syntheses of L-glycero-D-manno-heptopyranosyl-containing oligosaccharides are reported. Synthesis of the heptose trisaccharide structures from the core region of lipopolysaccharides from Salmonella and Haemophilus bacteria are described together with larger fragments containing hexoses as well. In the second part, development of reactive β-selective glucuronic acid thioglycoside donors is presented. These donors, promoted by DMTST, are used to prepare disaccharide structures corresponding to the repeating unit of the capsular polysaccharide from Streptococcus pneumoniae type 3 and to parts of the capsular polysaccharide of Cryptococcus neoformans. In the third and last part, stereoselective synthesis of α - and β-D-fructofuranosides using thioglycoside donors are discussed. With participating benzoyl groups and DMTST as promoter, excellent yields of α-linked fructofuranosyl disaccharides are obtained. Application of the internal aglycon delivery approach, with the aglycon tethered to the β-face of the fructofuranosyl thioglycoside donor as part of a 3-O-p-methoxybenzylidene acetal, produced stereospecifically high yields of β-linked fructofuranosyl disaccharides, inter alia, structures from the Haemophilus influenzae type e capsular polysaccharide, after activation of the tethered intermediates with DMTST.