Conformational behavior of peracetylated β-d-mannopyranosyl methanesulfonamide: implications for the mechanism of sulfonamidoglycosylation of carbohydrate derivatives Original Research Article

The conformational behavior of 2,3,4,6-tetra-O-acetyl-β-d-mannopyranosyl methanesulfonamide has been investigated from a combined theoretical and experimental point of view. The study of the conformational space of the glycosyl sulfonamide revealed that the β anomer is thermodynamically more stable than the α one. This fact suggests that the synthesis reaction could take place mainly under thermodynamic control as the main experimental product is the β-anomeric form of the sulfonamide. Several intramolecular hydrogen bonds were found in the stable conformers of the N-mannopyranosyl sulfonamide under study. A relationship was found to exist between them and the relative stability of the conformers. A detailed analysis of geometrical parameters shed light into the nature of the solid state structure of the novel 2,3,4,6-tetra-O-acetyl-β-d-mannopyranosyl methanesulfonamide in terms of exo- and endo-anomeric effects and antiperiplanar relationships. NBO calculations confirmed those findings. Calculated 1H and 13C NMR chemical shifts support previous findings concerning configuration and conformation assignments of the title sulfonamide.