Examination of the effect of structural variation on the N-glycosidic torsion (PhiN) among N-(beta-D-glycopyranosyl)acetamido and propionamido derivatives of monosaccharides based on crystallography and quantum chemical calculations.

GlcNAcbetaAsn linkage is conserved in the N-glycoproteins of all eukaryotes. l-Glutamine (Gln), which is a one carbon higher homolog of Asn, is never glycosylated. X-ray crystallographic study of several beta-1-N-acetamido- and propionamido derivatives of monosaccharides has earlier shown that the N-glycosidic torsion, Phi(N), is influenced to a larger extent by the structural variation of the sugar part than that of the aglycon moiety. In order to examine the influence of the carbohydrate pendent groups on the conformational preference of the N-glycosidic linkage with respect to Phi(N,) several models and analogs with gluco and manno configuration have been studied in the present work by computational chemistry. The crystal structure of XylbetaNHPr is reported here and its molecular packing compared with related analogs. The conjunction of combining Crystallographic and computational studies allows to demonstrate the strong influence that the group at C2, and environmental factors particularly inter- and intramolecular interactions involving regular hydrogen bonds and the weak C-H...O contacts, have on the energy preference of the Phi(N) torsion angle.