Effective and chemoselective glycosylations using 2,3-unsaturated sugars

Glycosyl donors containing a double bond between C2 and C3 were designed by mimicking the reaction mechanism of lysozyme-initiated hydrolysis of mucopolysaccharides. It was found that, under various glycosylation conditions, the reactivities of 2,3-unsaturated glycosyl acetates were significantly higher, while those of the corresponding 2,3-unsaturated-4-keto glycosyl acetates were much lower than those of the corresponding 2,3-dideoxy (2,3-saturated) glycosyl acetates. Based on these results, chemoselective glycosylations were effectively realized via combinatorial techniques in short-steps using three types of glycosyl donors to construct several types of deoxyoligosaccharides. Furthermore, the highly reactive 2,3-unsaturated glycosyl acetates were found to be useful in the synthesis of the O-glycosides of low reactive tertiary alcohols.