Glycosylation via mixed disulfide formation using glycosylthio-phthalimides and -succinimides as glycosylsulfenyl-transfer reagents

The silver salts of tetra-O-acetyl α- or -β-d-glycopyranosyl thiols 1a-4a react smoothly with N-bromophthalimide and N-bromosuccinimide to furnish glycosylthio-phthalimide (1b-4b) and -succinimide (1c-3c) derivatives. Reactions of these reagents with aliphatic, aromatic, and glycosyl thiols as well as with cysteine and glutathione result in the formation of glycosylated mixed disulfides under mild conditions and in good yields. The S-glycosyl-N-acylsulfenamides described here represent novel, convenient glycosylsulfenyl-transfer reagents in effecting glycosylation of various thiols, including sugars, amino acids and peptides, through disulfide formation and can, therefore, be useful in controlled glycosylation of proteins as well.