Stereoselective synthesis of glycosides and anomeric azides of glucosamine

Abstract

The β-azide of O-acetyl protected N-acetyl glucosamine is efficiently accessible via a phasetransfer-catalyzed reaction of the corresponding glycosyl chloride with sodium azide. The azido group revealed to be a useful anomeric protection for modifications of the protecting group pattern of the glucosamine unit. Exchange of the O-acyl groups by 4-methoxybenzylidene and 4-methoxybenzyl (Mpm) protection delivered regioselectively blocked glucosaminyl azide derivatives. In contrast, the N-phthaloyl protected glucosaminyl azide was obtained quantitatively from the corresponding glycosyl fluoride via a boron trifluoride-promoted reaction with trimethylsilyl azide. N-Phthaloyl glucosaminyl fluoride was also revealed to be useful in the synthesis of β-glucosamine glycosides and saccharides. Chitobiosyl azide 21 carrying a selectively removable 6-O-Mpm protection was synthesized from the O-acetyl protected N-phthaloyl glucosaminyl bromide and N-acetylglucosaminyl azide 13 as an acceptor selectively deblocked at O-4.