Synthesis and Conformational Analysis of 6-C-Methyl-Substituted 2-Acetamido-2-deoxy-beta-D-glucopyranosyl Mono-and Disaccharides

摘要

Several 6-C-substituted 2-acetamido-2-deoxy-beta-D-glucopyranosides(beta-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 beta-D-GlcNAc monosaccharides indicates that the stereodefined methyl groups impose predictable conformational biases on the exocyclic C-5-C-6 bond,as determined by ~1H-~1H and ~(13)C-~1H coupling constants.Variable-temperature NMR experiments in methanol-d4 were performed to determine AAH and DELTADELTAS 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 solvent-solute interactions and solvent reorganization.