A conformational study of alpha-D-Manp-(1-->2)-alpha-D-Manp-(1-->O)-L-Ser by NMR 1H,1H T-ROESY experiments and molecular-dynamics simulations.

The conformational preference of alpha-D-Manp-(1-->2)-alpha-D-Manp-(1-->O)-L-Ser has been investigated by one-dimensional (1)H,(1)H T-ROESY experiments and molecular-dynamics simulations with CHARMM22 type of force fields and water as explicit solvent. Proton-proton distances were obtained from the simulations and subsequently experimentally determined distances could be derived. Measurements were performed on the title compound as well as on selectively deuterium-substituted analogues synthesized as part of this study to alleviate possible NMR spectroscopic difficulties. A very good agreement was present between the separate NMR experiments. In the subsequent analysis a key nuclear Overhauser effect between the anomeric protons in the two sugar residues was used to assess the conformational dynamics revealed by the molecular simulations. The combined results support a model in which two states are significantly populated as a result of flexibility around the bond defined by the glycosidic torsion angle psi.