PREFERRED CONFORMATION OF C-GLYCOSIDES .6. CONFORMATIONAL SIMILARITY OF GLYCOSIDES AND CORRESPONDING C-GLYCOSIDES

The conformation of the alpha-(axial)-C-glycosides 1-3 and the beta-(equatorial)-C-glycosides 4-6 were studied by H-1 NMR. Their preferred solution conformation was found to match that of the corresponding parent glycosides. The study of 2-deoxy compounds 13-16 shows that the preference is due primarily to gauche interactions around the glycosidic bond. Solvent studies indicate that electrostatic interactions and hydrogen bonds do not significantly alter the overall conformation. Temperature studies suggest that these compounds exist as an equilibrium mixture of conformers.