PREFERRED CONFORMATION OF C-GLYCOSIDES .10. SYNTHESIS AND CONFORMATIONAL-ANALYSIS OF CARBON TRISACCHARIDES

A flexible and efficient synthesis of the carbon trisaccharide 2 related to the Type II O(H) blood group determinant has been developed. This route was applied to the synthesis of the trisaccharides 3, 4, and 5. The preferred solution conformations of compounds 2-5 were determined on the basis of vicinal coupling constants in the H-1 NMR spectrum. Each of the four trisaccharides adopts a distinct and well-defined solution conformation in accord with the predictions made on the basis of the preference of the C-glycosidic bond for the ''exo-anomeric'' conformation and the analysis of 1,3-diaxial-like interactions around the C-aglyconic bond.