Chemoenzymic synthesis of oligosaccharide fragments of the capsular polysaccharide of Streptococcus pneumoniae type 14

Abstract

The chemoenzymic synthesis is described of β-D-Galp-(1→4)-β-D-Glcp-(1→6)-[(β-D-Galp)-(1→4)]-β-D-GlcpNAc-(1→3)-β-D-Galp-(1→O(CH₂)₆NH₂) 20 and β-D-Galp-(1→4)-β-D-Glcp-(1→6)-[(β-D-Galp)-(1→4)]-β-D-GlcpNAc-(1→3)-β-D-Galp-(1→4)-β-D-Glcp-(1→O(CH₂)₆NH₂) 21, representing penta- and hexasaccharide fragments of the Streptococcus pneumoniae type 14 capsular polysaccharide. In a chemical approach the intermediate tetra- and pentasaccharide fragments 18 and 19, respectively, were synthesised, wherein the non-terminal N-acetyl-β-D-glucosamine residues were not yet galactosylated. Both intermediates were found to be good acceptor substrates for bovine milk β-1,4-galactosyltransferase. The title oligosaccharides form suitable compounds for conjugation with carrier proteins, to be tested as potential vaccines in animal models.