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 H-1-H-1 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- alpha-D-galactopyranose was good, thereby confirming an S-0(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-beta-D-glucopyranoyl)-alpha-D-galacto-pyranose and 1,2,3,4,6-penta-O-acetyl-alpha-D-galactopyranose provided S-0(2) and C-4(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.