Synthesis of oligosaccharides corresponding to Streptococcus pneumoniae type 9 capsular polysaccharide structures.

Two trisaccharides, alpha-D-Galp-(1-->3)-beta-D-ManpNAc-(1-->4)-beta-D-Glcp and alpha-D-Glcp-(1-->3)-beta-D-ManpNAc-(1-->4)-beta-D-Glcp, corresponding to structures from Streptococcus pneumoniae capsular polysaccharides type 9A, L, V and type 9N, respectively, have been synthesised as 2-aminoethyl glycosides and as protected TMSE glycosides. Ethyl thioglycosides were used as glycosyl donors and NIS/TfOH (in CH(2)Cl(2) for beta-linkages) and DMTST (in Et(2)O for alpha-linkages) as promoters in the glycosylations. The beta-ManNAc motif was introduced at the disaccharide level by azide displacement of a 2-O-triflate with beta-D-gluco configuration. The protecting group patterns allow continued syntheses of larger structures.