Solution Studies of Monosaccharide and Oligosaccharide Structure and Reactivity by NMR Spectroscopy

Saccharides are arguably the most talented molecules in the biological repertoire of molecular structures. However, the code correlating complex saccharide structure with biological function remains elusive. The saccharide code may involve more subtle physical principles involving hydration and dynamics, since saccharide oligomers are commonly considered conformationally flexible structures, especially with regard to the glycosidic bonds involved in their assembly. To date, no clear set of rules has been developed that correlates oligosaccharide primary structure with conformational preference and dynamic properties.

A large component of this work involved developing experimental and theoretical methods to prepare biologically important oligosaccharides with isotopic enrichment and to study their solution properties. The use of isotopically labeled monosaccharide precursors dramatically increases the information content of structural studies of mono- and oligosaccharides. Detailed structural studies of oligosaccharides are best conducted by experimental methods involving the use of aqueous solutions that mimic, as well as possible, the biological environment. NMR spectroscopy offers a powerful means to conduct these studies, partly based on the conformational dependencies of NMR spin-spin coupling constants involving carbon and hydrogen (JH,H, JC,H, JC,C) and other NMR parameters. In this dissertation, spin-spin coupling constants measured in these compounds are interpreted using theoretically-derived Karplus or Karplus-like relationships between molecular structure conformation and coupling magnitude.

In Chapter 2, fundamental studies of J-couplings in biologically important, isotopically labeled hexuronic acids (monosaccharide level) are presented. Chapter 3 focuses on conformational and dynamics studies of isotopically-labeled mannose-containing oligosaccharides that form part of the structures of high-mannose N-glycans of human glycoproteins (oligosaccharide level).

Concentrations of 3-deoxyglucosone (3DG) are elevated several fold above normal levels in serum and tissues of diabetic patients. 3DG can damage protein functionality and pyridoxamine (PM) can protect from 3-DG-induced protein damage. In Chapter 4, a novel protection mechanism involving PM was investigated, which includes transient adduction of 3-DG by PM followed by irreversible PM-mediated oxidative cleavage of 3-DG.

Lastly, in Chapter 5 an X-ray crystal structure of 3-deoxy-beta-D-glucopyranose is presented with a full structural analysis, including discussion of ring-puckering behavior and comparison with other structurally related sugars.