Synthesis of N-glycan oxazolines: donors for endohexosaminidase catalysed glycosylation.

Oxazoline mono-, di-, tri- and hexasaccharides, corresponding to the core components of N-linked glycoprotein high mannose glycans, are synthesised as potential glycosyl donors for endohexosaminidase catalysed glycosylation of glycopeptides and glycoprotein remodelling. The crucial beta-D-Manp-(1-->4)-D-GlcpNAc linkage is synthesised via epimerisation of gluco disaccharide substrates by sequential triflation and nucleophilic substitution. Oxazolines are formed directly from the anomeric OPMP protected N-acetyl glucosamine derivatives. Efficient endohexosaminidase catalysed glycosylation of a synthetic beta-D-GlcpNAcAsn glycosyl amino acid is demonstrated with the trisaccharide oxazoline donor.