Regiospecific Syntheses of N-Acetyllactosamine Derivatives and Application Toward a Highly Practical Synthesis of Lewis X Trisaccharide

An efficient methodology for regiospecific glycosylation was developed by using 6-O-tert-butyldiphenylsilyl N-acetylglucosamine derivatives 3 and 5 which bear two free hydroxyl groups as acceptors. The regiospecificity was attributed to the presence of the tert-butyldiphenylsilyl group at the O-6 position of the N-acetylglucosamine derivatives. Glycosylation of suitably protected galactoside donors 10-14 with acceptors 3 and 5 gave only β (1→4) linked disaccharides 15-19 in good yields. Fucosylation of disaccharide 18 led to Lewis X (Lex) trisaccharide 21 in high yield.