ANALYSIS OF CONFORMATIONALLY RESTRICTED MODELS FOR THE (1-]6)-BRANCH OF ASPARAGINE-LINKED OLIGOSACCHARIDES BY NMR-SPECTROSCOPY AND HSEA CALCULATION

The conformational preferences of the trisaccharide, beta-D-GlcpNAc-(1 --> 2)-alpha-D-Manp-(1 --> 6)-beta-D-GlcpOR (1) have been investigated by n.m.r.-spectroscopy and HSEA calculation. The fixed omega-angle bicyclic analogs 2 and 3, models for the gt and gg rotamers, respectively, of 1, were furthermore examined with the same techniques in an attempt to deduce which of the conformations accessible to 1 was recognized and glycosylated by the enzyme GlcNAc-transferase-V, which acts on a component of the (1 --> 6)-arm of glycoproteins. Only the gg bicyclic 3 was found to be reactive with the enzyme and this study concludes, based on conformational analysis, that 1 as well as the natural Asn-linked oligosaccharide are recognized by GlcNAc-transferase-V in only one of the two local minimum energy conformations energetically accessible to these molecules in their gg rotamer.