Study of Disaccharide Conformation by Measurements of Nuclear Overhauser Enhancement, Relaxation Rates, and ¹³C-¹H Coupling: 1,6-Anhydro-β-cellobiose Hexaacetate

Nonselective and mono-and biselective spin-lattice relaxation rates, nuclear Overhauser enhancements, and coupling constants were measured as means for determining such stereochemical features as the conformation of the glucosidic bond of 2,3,4,6,2',3'-hexa-O-acetyl-4-O-β-D-glucopyranosyl-l',6'-anhydro-β-D-glucopyranose (1) in acetone-d₆ solution. Interproton distances within each ring of 1, as well as of 2, specifically C-deuterated samples of 1, calculated from either a combination of monoselective relaxation rates and NOE experiments or mono-and biselective relaxation rates, agreed within ±0.2 Å of those found in the crystal. However, substantially different values were obtained from nonselective relaxation rate measurements. The orientation of the glucosidic bond, as deduced from interresidue spin-spin coupling (³J) between the C-l,H-4' and C-4', H-1 nuclei, is described by dihedral angles of Ψ 45-50° and of ϕ 25-30°. These values are within the region of the allowed conformation as defined by the interatomic distances H-l-H-4' and H-l-H-5' obtained from relaxation, NOE data, and by computer simulation.