Synthesis and conformational studies of isotopically enriched saccharides

The aims of this dissertation are to explore isotope labeling of biologically important saccharides, and establish new correlations between NMR parameters and molecular structures with a particular focus on trans-glycoside scalar couplings and their application to the studies of glycosidic linkage conformation. The work is divided into five parts.;Chapter 2 reports a novel synthesis of the disaccharide, alpha- D-Gal-(1→3)-beta-D-GalOMe, which is the main cause of antibody-mediated hyperacute rejection in xenotransplantation. This disaccharide was selectively labeled with 13C in a manner that allows accurate measurement of all available inter-residue carbon-based NMR spin-couplings sensitive to linkage conformation. These J-couplings were interpreted using Karplus-type equations derived from density functional theory (DFT) calculations and mathematical modeling.;Chapter 3 reports a simplified cyanohydrin synthetic route to prepare a series of 2-amino-2-deoxy-D-[1-13C]aldohexoses and their methyl glycosides. JCH and J CC spin-spin coupling constants involving the labeled anomeric carbon were measured and compared to those observed previously in methyl D-[1-13C]aldohexopyranosides. Theoretical J-couplings were calculated in model N-acetylated aldopyranosides by DFT to predict the effect of OH vs NHCOCH 3 substitution at C2 on JCH and JCC values in aldopyranosyl rings. The synthetic method was also modified to accommodate 15N- and 13C-labeling within the N-acetyl side-chain, methodology explored in Chapter 4.;Chapter 4 reports the preparation of, and NMR measurements of J-couplings in eight compounds: alpha and beta methyl glycosides of N-acetyl-D-glucosamine and N-acetyl- D-allosamine which were 13C labeled at C1/C3 of the pyranose ring or at the carbonyl carbon of the exocyclic NAc group. The couplings that depend on the C2-N2 torsion angle were extracted. These parameters were used to assess the N-acetyl side-chain conformation in combination with DFT parameterized equations.;Chapter 5 reports the preparation of selectively isotope labeled alpha,alpha-trehalose, which is important in cryobiology and other pharmaceutical applications, 2-deoxy derivatives. The isotope labeling strategy allowed the measurement of all trans-glycoside couplings in alpha,alpha-trehalose and its 2-deoxy derivatives. Conformational analysis based on experimental scalar couplings was performed using DFT-parametrized Karplus equations for 3J CH and 3JCC. These studies provided new experimental data to assess linkage conformation in (1,1)-linked pyranose disaccharides.;Chapter 6 reports the synthesis of a mannose-containing hexasaccharide, which is a constituent of glycoprotein CD2. The chemistry to prepare this hexasaccharide is described, including characterization by 1H and 13C NMR, and high resolution mass spectrometry. NMR characterization of intermediates provided an important reference for future synthesis of 13C isotopomers. A strategy for isotope labeling is also discussed.