Purification of oligosaccharides having a free reducing-end from glycopeptide sources

A hydrazinolysis-N-reacetylation procedure, modified by the inclusion of a mild acid-hydrolysis step after N-acetylation, was used to prepare, in overall yields of 60-70%, pure oligosaccharides containing a reducing D-GlcNAc residue from glycopeptide sources. Three types of asparagine-linked glycopeptides were treated: a high-mannose type, a complex-type not containing sialic acid, and a complex-type containing sialic acid, linked both alpha-(2----3) and alpha-(2----6) to beta-D-Galp residues. After the hydrazinolysis-N-reacetylation procedure, there was often contamination of the reducing oligosaccharides with glycopeptide that remained intact through the procedure, as well as minor oligosaccharide products, altered in the nature of the residue at the reducing end. Oligosaccharides having a reducing D-GlcNAc residue were purified by standard liquid chromatography and high-pressure liquid chromatography (l.c.) 360-MHz 1H-n.m.r. was valuable in establishing common structural reporter signals which enabled major products to be identified at stages during the production of free reducing oligosaccharides, and their purity to be assessed.