Development of new NMR techniques for conformational analysis of ¹³C-enriched oligosaccharides

Abstract

The three-dimensional conformations of various oligosaccharides have been investigated using high-resolution nuclear magnetic resonance measurements and molecular dynamics calculations. A fundamental problem with such studies is the lack of structural restraints across the glyosidic linkage as well as the short-range nature of these restraints. In this thesis this problem has been addressed by developing new techniques that increase the total number of structural parameters for inclusion in the molecular modelling simulations. The measurement of inter-glycosidic heteronuclear NOEs is described and four 1H- NOEs were measurable in a model disaccharide with appropriate 13C and 2H enrichment. NMR studies were also carried out with a series of oligosaccharides dissolved in a dilute liquid crystalline medium. This resulted in a degree of molecular alignment for the oligosaccharides that in turn allowed the measurement of dipole-dipole coupling constants. These were incorporated in dynamic simulated annealing calculations in order to verify their usefulness in structural calculations. The three-dimensional structure and dynamics of Gal?1-4Glc were investigated using the additional restraints mentioned above, as well as 13C-13C trans-glycosidic long-range coupling constants and 1H-1H NOEs. It was shown that the conformation cannot be represented by a single structure, but is best represented by a dynamic model. Other techniques developed in this thesis include the measurement of three-bond scalar coupling constants to probe the existence of inter-glycosidic hydrogen bonding, and the direct measurement of bond angles using relaxation via cross-correlated dipolar couplings. Finally the bound-state conformation of 13C-enriched Sialyl Lewis-x in association with E-selectin was investigated using a three-dimensional nuclear Overhauser effect 13C-1H heteronuclear single quantum correlation experiment.