Direct Dehydrative Pyridylthio-Glycosidation of Unprotected Sugars in Aqueous Media Using 2-Chloro-1,3-dimethylimidazolinium Chloride as a Condensing Agent

Various 2-pyridyl 1-thioglycosides, important synthetic intermediates and enzyme inhibitors in sugar chemistry, have been synthesized directly from the corresponding unprotected sugars in good yields by using 2-chloro-1,3-dimethylimidazolinium chloride (DMC) as dehydrative condensing agent. The reaction proceeds in aqueous media without using any protecting groups, affording 2-pyridyl 1-thioglycosides with beta-configuration selectively. According to the present method, not only unprotected monosaccharides but also unprotected oligosaccharides, such as cello-oligosaccharides, chito-oligosaccharides, malto-oligosaccharides, and glucosamine oligomers, can be converted to the corresponding 2-pyridylthio derivatives, which would greatly expand the utility of aryl 1-thioglycosides in sugar chemistry.