¹H–¹H internuclear distance measurements in carbohydrates: proton transient nuclear Overhauser enhancement and spin-lattice relaxation in (¹³C)- and (²H)-substituted compounds

Abstract

Proton transient nuclear Overhauser enhancement (TnOe) and spin-lattice relaxation times (T 1 ) have been used to evaluate the conformations of several monosaccharides and disaccharides containing ( 13 C) and ( 2 H) substitution. Absolute 1 H– 1 H internuclear distances were determined by TnOe and DESERT (deuterium substitution effects on relaxation times) experiments on conformationally rigid methyl β-D-galactopyranoside and α- and β-D-xyloses, respectively. The DESERT method was extended to examine O-glycoside conformation in two blood-group disaccharides that were prepared enzymically with ( 13 C) and (or) ( 2 H) substitution. Preferred disaccharide conformations deduced from these distance measurements are compared to those determined from 13 C– 13 C and 13 C– 1 H spin coupling constants, theoretical calculations, and crystallographic studies. Keywords: TnOe, DESERT, carbohydrate conformation.