DISAL glycosyl donors for efficient glycosylations under acidic conditions: Application to solid-phase oligosaccharide synthesis

Abstract

The use of DISAL (methyl dinitrosalicylate) glycosyl donors in efficient Lewis acid-promoted glycosylations is reported. N-Acetyl-D-glucosamine monosaccharide acceptors are successfully glycosylated at O-6 or O-4 using benzyl- and benzoyl-protected DISAL donors in CH2Cl2 or nitromethane in the presence of LiClO4. The resultant disaccharides are isolated in yields ranging from 35 to 93%. Other Lewis acids such as FeCl3, TMSOTf, or BF3·Et2O also prove efficient for glycosylation of the secondary alcohol cyclohexanol. However, for the synthesis of disaccharides, the mild activation by LiClO4 gives higher yields. This approach is extended to efficient solid-phase glycosylation of a D-glucosamine derivative anchored by the 2-amino group through a Backbone Amide Linker (BAL) to a polystyrene support.