Integrated Experimental and Theoretical Studies of Saccharide Structure

Broadly speaking the objective of this dissertation is the investigation of carbohydrate structure through an integrated theoretical and experimental approach. In addition to being the most evolutionary ancient class of biopolymer, carbohydrates have the highest potential for structural diversity. This structural diversity is manifest both in terms of primary sequence, and in a very high potential for conformational flexibility due to the high concentration of geometrically mobile dihedrals present in saccharides. The structural biology of saccharides is further complicated by a dearth of robust experimental and theoretical techniques. A large component of this work involved developing experimental and theoretical tools for the conformational analysis of carbohydrates, specifically parameterizing the conformational dependence of NMR spin-spin couplings for the interpretation of experimental couplings in structural terms. On the experimental side measurement of 13C-based spin-spin couplings necessitated the development of technologies for strategic isotopic enrichment. The couplings measured in these compounds are interpreted using theoretically derived relationships between molecular conformation and coupling magnitude. These Karplus relationships are based upon quantum mechanical density functional theory (DFT) calculations of spin-spin couplings on energetically optimized model compounds in which a particular geometric feature such as a dihedral is varied. The structural interpretations of these couplings takes the form of populational distributions about the relevant molecular dihedrals. This is applied in a modular fashion to various molecular fragments of biologically significant monosaccharides. The natural bonding orbital (NBO) method is used to dissect spin-spin coupling mechanisms based upon discreet through space and through bond orbital interactions. Lastly, an x-ray crystal structure of methyl-allolactoside is presented with a complete structural analysis including a discussion of ring-puckering behaviour. The battery of experimental and theoretical techniques presented in this dissertation set the ground work for application to a broad spectrum of biological investigations involving carbohydrate structure and function.