Structural analysis of the solution conformation of methyl 4-O-beta-D-glucopyranosyl-alpha-D-glucopyranoside by molecular mechanics and ab initio calculation, stochastic dynamics simulation, and NMR spectroscopy

Unambiguous determination of the solution conformation of carbohydrates is an important current research challenge. In general, we wish to test the hypothesis that the connecting linkages of these molecules may have significantly greater flexibility than in the crystalline state. In this study we specifically focus on the conformation of the disaccharide methyl 4-O-beta-D-glucopyranosyl-alpha-D-glucopyranoside using 1D and 2D NOESY experiments and molecular modeling. In particular we attempt to discover if ''folded'' conformations of this molecule exist in addition to the more expected crystalline ''extended'' conformations. The modeling calculations, both ab initio and molecular mechanics, indicate that the folded conformations are low in energy and can reasonably be expected to exist in solution if solvent effects, which are difficult to predict accurately, are not too large. The NMR data do not support the existence of the folded conformations in solution as a major population. Minor populations of folded conformations cannot, however, be clearly ruled out by the data. We assert that the glycosidic linkage flexibility hypothesis is not yet disproven for this linkage.