Conformation of the Galactose Ring Adopted in Solution and in Crystalline Form as Determined by Experimental and DFT 1H NMR and Single-Crystal X-ray Analysis

The solution-state conformations of various galactose derivatives were determined by comparison of the experimental 1H−1H vicinal coupling constants to those calculated using density functional theory (DFT) at the B3LYP/cc-pVTZ//B3LYP/6-31G(d,p) level of theory. The agreement between the experimental and calculated vicinal coupling constants for 1,2:3,4-di-O-isopropylidene-α-d-galactopyranose was good, thereby confirming an O S 2 skew conformation for it and its derivatives on the basis of their similar observed couplings. Single-crystal X-ray analysis of 1,2:3,4-di-O-isopropylidene-6-O-(3,4,6-tri-O-acetyl-2-deoxy-2-N-phthalimido-β-d-glucopyranosyl)-α-d-galactopyranose and 1,2,3,4,6-penta-O-acetyl-α-d-galactopyranose provided O S 2 and 4 C 1 conformations, respectively, for the galactose ring in the solid state. The solid-state structures proved to be suitable starting structures for further DFT structure refinement or for immediate calculation of the coupling constants.