conformational analisys of amino suger.

Abstract

"NMR-2JCH index" analysis developed by Oikawa and co-workers is a simple and reliable technique for identification of various saccharides, and the improved application toward elucidation for the primary sequence and three-dimensional structure of biologically important oligosaccharides is strongly expected. In the latest extension of the 2JCH index analysis to various aminosugars and their N-acetyl derivatives, we have observed that only 2JC4,H5 value of alpha-galactosamin (a-GalN) is peculiarly different from those of the others. In order to explain the problem, we have performed various computational conformational analyses of a-GalN and the N-acetyl derivative (a-GalNAc) by using CONFLEX conformational search method. In this study, various theoretical levels with solvent effects have been also examined for exact predictions of NMR coupling constants on the pyranosyl ring of 20 a-GalN conformers found by CONFLEX. Finally, it is noted that the calculated 2JCH values of theromodynamical conformational mixture based on the Bolzmann law using conformational energies and 2JCH values at b3pw91/6-311+G(2d,p)// b3pw91/6-31+G** level calculation in water, can represent the experimental values within 1.3 Hz RMSD. We are now investigating the origin of the remarkable differences of 2JCH values between a-GalN and a-GalNAc.