New approach to the synthesis of C-glycosides, azasugars, and aza C-glycosides

Synthesis of sugar analogs in which the ring oxygen atom has been replaced by an-NR-group (azasugars) and/or the anomeric hydroxyl group has been replaced by a carbon atom (C-glycosides) has been a subject of intensive research interest in recent years. Many members of both classes of compounds are specific inhibitors of glycosidases, including enzymes involved in glycoprotein processing, glycogenolysis, and oligo- and disaccharide hydrolysis. In spite of recent developments in the synthesis of C-glycosides and azasugars, the stereospecific formation C-glycosides and aza C-glycosides remains a challenge for synthetic carbohydrate chemistry. A simple way to prepare C-glycosides and aza C-glycosides of D-arabinose and D-lyxose, that can be applied to other aldoses, is reported. The reaction involves oxidation of D-glucose diethyl dithioacetal (with spontaneous cyclization) to the corresponding ($\alpha$-D-arabinopyranosyl)-di(ethyl sufonyl)methane. Reduction to the diethyl dithioacetal of ($\alpha$-D arabinosyl) formaldehyde, and converting it to an aldhehyde provides a compound which can be modified to other desired products. Oxidation of a protected 6-amino-6-deoxy-D-galactose diethyl dithioacetal provided the corresponding azasugars