1,3,4,6-Tetra-O-acetyl-2-chloroacetamido-2-deoxy-β-D-glucopyranose as a glycosyl donor in syntheses of oligosaccharides

Article abstract of DOI:10.1016/0008-6215(90)84083-7

1,3,4,6-Tetra-O-acetyl-2-chloroacetamido-2-deoxy-β-D-glucopyranose was tested as a glycosyl donor for oligosaccharide synthesis via ferric chloride-catalyzed coupling reaction.Glycosyl acceptors tried (6 in all) were O-benzyl-protected D-galactosides having free OH groups at positions 3 and 4, respectively, and similarly protected glycosides of D-glucose and 2-acetamido-2-deoxy-D-glucose unsubstituted on O-4.Existing syntheses of all the acceptors were improved, in four instances by exploitation of Garegg and Hultberg's cyanoborohydride procedure for the conversion 4,6-O-benzylidene -> 6-O-benzyl .Good to excellent yields of β-linked disaccharides were obtained from the galactoside and glucoside acceptors, but with allyl 2-acetamido-3,6-di-O-benzyl-2-deoxy-α-D-glucopyranoside, stereoselectivity was lost (α:β-ratio 1:2).Allyl and benzyl 2-acetamido-3,6-di-O-benzyl-2-deoxy-β-D-glucopyranosides gave, respectively, the allyl and benzyl β-glycosides of the donor as major products.A mechanism is proposed for this transglycosidation reaction.The N-chloroacetyl groups in the disaccharide products were readily converted into N-acetyl by reduction with zinc-acetic acid.