No abstract

Several 6-C-substituted 2-acetamido-2-deoxy-β-D-glucopyranosides (β-D-GlcNAc monosaccharides 1a-3a and 1,4-linked disaccharides 1b-3b) were studied by solution NMR spectroscopy. Conformational analysis of the (6S)-and (6R)-C-methyl-substituted β-D-GlcNAc monosaccharides indicates that the stereodefined methyl groups impose predictable conformational biases on the exocyclic C-5-C-6 bond, as determined by 1 H-1 H and 13 C-1 H coupling constants. Variabletemperature NMR experiments in methanol-d 4 were performed to determine ΔΔH and ΔΔS values derived from the two lowest energy conformers. These indicate that while the influence of 6-C-methyl substitution on conformational enthalpy is in accord with the classic principles of steric interactions, conformational preference in solution can also be strongly affected by other factors such as solventsolute interactions and solvent reorganization.