A conformational study of the vicinally branched trisaccharide beta-D-glcp-(1 --> 2)[beta-D-glcp-(1 --> 3)]alpha-D-Manp-OMe by nuclear Overhauser effect spectroscopy (NOESY) and transverse rotating-frame Overhauser effect spectroscopy (TROESY) experiments: comparison to Monte Carlo and Langevin dynamics simulations.

The trisaccharide beta-D-Glcp-(1 --> 2)[beta-D-Glcp-(1 --> 3)]alpha-D-Manp-OMe, a model for branching regions in oligosaccharides, has been investigated by one-dimensional DPFGSE (1)H, (1)H nuclear Overhauser effect spectroscopy (NOESY) and transverse rotating-frame Overhauser effect spectroscopy (TROESY) experiments at 30 degrees C in water and in the solvent mixture water : dimethyl sulfoxide (7 : 3). Cross-relaxation rates were obtained from the nmr experiments and interpreted as proton-proton distances. From Metropolis Monte Carlo and Langevin dynamics simulations, distances were calculated and compared to those obtained from experiment. Using the previously determined dynamics from carbon-13 nmr relaxation measurements of the trisaccharide in the solvent mixture, intraresidue proton distances could be obtained that were in excellent to reasonable agreement with those calculated from simulations. In water, the isolated spin-pair approximation was used for comparison of interproton distances. The experimentally derived distances in both solvents showed that the trans-glycosidic distances were shorter between the anomeric proton of the glucosyl group and the proton at the linkage position, respectively, than to the proton on the adjacent carbon on the mannosyl residue. The interresidue distances calculated from the computer simulations, performed with three different force fields, namely HSEA, PARM22, and CHEAT95, resulted in the reverse order in all cases but one. Copyright 1999 John Wiley & Sons, Inc.