Glycosyl azides as building blocks in convergent syntheses of oligomeric lactosamine and Lewis(x) saccharides

Oligosaccharides containing type 2 lactosamine repeating units, e.g. neo-lacto-octaose and trimeric Lewis(x) derivatives, are constructed using neo-lactosamine azide building blocks. The azido group provides a favorable protection of the anomeric position which is stable to versatile protecting group manipulations and glycosylation reactions. On the other hand, glycosyl azides can be converted into glycosyl fluorides via a 1,3-dipolar cycloaddition with di-tert-butyl acetylenedicarboxylate and subsequent treatment of the resulting N-glycosyl triazoles with hydrogen fluoride-pyridine complex. Activation of the lactosamine fluorides with Lewis acids affords the possibility to extend the oligosaccharide chain with disaccharide units. Suitable protecting group combinations within the galactose and the glucosamine portion of the lactosamine unit enable selective deprotection reactions and, subsequently, chain extension or branching, e.g. to yield Lewis(x) structures. Copyright (C) 1997 Elsevier Science Ltd.