Conformational Flexibility of Carbohydrates: A Folded Conformer at the φ Dihedral Angle of a Glycosidic Linkage

Abstract

The trisaccharide β-d-Glcp-(1→2)-β-d-Glcp-(1→3)-α-d-Glcp-OMe has been studied by Langevin dynamics (LD) simulations and NMR spectroscopy including measurement of transglycosidic 3JC,H coupling constants, 3JH,OH coupling constants, temperature dependence of the chemical shift of hydroxyl protons, and 2D NOESY and T-ROESY experiments as well as their 1D DPFGSE analogues. A folded conformer at the φH dihedral angle of the (1→2)-linkage observed in the LD simulation was corroborated by experimental NMR data, in particular spatial proximity of hydroxyl protons in nonadjacent sugar residues as deduced from a 2D T-ROESY experiment. The results from the present study with an “anti” φH conformer show that oligosaccharides exhibit large conformational flexibility under certain conditions and that this inherent property needs to be taken into account in the analysis of carbohydrate structure.