CONFORMATIONAL FLEXIBILITY OF CARBOHYDRATES - A FOLDED CONFORMER AT THE PHI-DIHEDRAL ANGLE OF A GLYCOSIDIC LINKAGE

The trisaccharide -Glcp-(1-->2)-beta-D-Glcp-(1-->3)-alpha-D-Glcp-OMe h as been studied by Langevin dynamics (LD) simulations and NMR spectros copy including measurement of transglycosidic (3)J(C,H) coupling const ants, (3)J(H,OH) coupling constants, temperature dependence of the che mical shift of hydroxyl protons, and 2D NOESY and T-ROESY experiments as well as their 1D DPFGSE analogues. A folded conformer at the phi(H) dihedral angle of the (1-->2)linkage observed in the LD simulation wa s corroborated by experimental NMR data, in particular spatial proximi ty of hydroxyl protons in nonadjacent sugar residues as deduced from a 2D T-ROESY experiment. The results from the present study with an ''a nti'' phi(H) conformer show that oligosaccharides exhibit large confor mational flexibility under certain conditions and that this inherent p roperty needs to be taken into account in the analysis of carbohydrate structure.