Conformational Mobility of Oligosaccharides: Experimental Evidence for the Existence of an Anti Conformer of the Galpl−3Glcpl−OMe Disaccharide

A hydrogen bond between the Glc OH(4) and Gal OH(2) groups of the title disaccharide, manifested by the doubling of their H NMR signals in a partially deuteriated sample in Me2SO solution, proves the existence of an anti conformer, Le., one with the anomeric and transglycosidic aglyconic C−H bonds tumed away from each other by −180. This conformer is at equilibrium with the predominating normal syn conformation(s), as shown by the analysis of several interresidue NOEs, and confirmed by molecular mechanics and molecular dynamics calculation