Synthesis of the ‘primer–adaptor’ trisaccharide moiety of Escherichia coli O8, O9, and O9a lipopolysaccharide

Described is the synthesis of the trisaccharide α-d-Manp-(1→3)-α-d-Manp-(1→3)-β-d-GlcpNAcO(CH2)8N3, the glycan portion of which corresponds to the ‘adaptor–primer’ moiety linking the O-chain and core oligosaccharide in the lipopolysaccharide of several Escherichia coli and Klebsiella pneumoniae serotypes. This report represents the first synthesis of this trisaccharide motif, and in the route involved, a key step is a [2+1] coupling of a protected Manp-(1→3)-α-d-Manp glycosyl donor with a GlcpNAc acceptor. The azido group was included in the target to facilitate future preparation of neoglycoconjugates.