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

The use of DISAL (methyl dinitrosalicylate) glycosyl donors in efficient Le wis acid-promoted glycosylations is reported. N-Acetyl-D-glucosamine monosa ccharide acceptors are successfully glycosylated at O-6 or O-4 using benzyl - and benzoyl-protected DISAL donors in CH2Cl2 or nitromethane in the prese nce of LiClO4. The resultant disaccharides are isolated in yields ranging f rom 35 to 93%. Other Lewis acids such as FeCl3, TMSOTf, or BF3-Et2O also pr ove efficient for glycosylation of the secondary alcohol cyclohexanol. Howe ver, for the synthesis of disaccharides, the mild activation by LiClO4 give s higher yields. This approach is extended to efficient solid-phase glycosy lation of a D-glucosamine derivative anchored by the 2-amino group through a Backbone Amide Linker (BAL) to a polystyrene support.