STRAIGHTFORWARD SYNTHESIS OF (1-]2)-LINKED PSEUDO AZA-C-DISACCHARIDESBY THE NOVEL CYCLOADDITION OF ENANTIOPURE CYCLIC NITRONES TO GLYCALS

The novel, highly stereoselective, intermolecular cycloaddition reacti on of enantiopure cyclic nitrones 8 to 1,2-glycals 9 opens the way to a straightforward synthesis of a broad class of new (1-->2)-linked pse udo aza-C-disaccharides 6, suitable substrates for selective inhibitio n of glycosidase enzymes. The cycloadditions occur with high stereocon trol, displaying preferential interaction between the bottom face of t he glycal and the face of the nitrone anti to the substituent on C-3, with the reagents approaching in an exo fashion. The cycloadditions pr oduced tricyclic isoxazolidines 7 that represent nonreducing pseudo az a-C-disaccharides stable to hydrolytic conditions. The target pseudo a za-disaccharides 6 were obtained by sequential deprotection of the hyd roxyl groups and isoxazolidine ring-opening.