X-Ray Crystallographic Investigation of Fully Acetylated N-(2-Deoxy-2-Acetamido-beta-D-Glucopyranosyl)AIkanamides as A/-Glycoprotein Linkage Region Analogs

摘要

To understand the structural significance of the linkage region of iV-glycoproteins, three title sugar amides have been prepared as analogs and their molecular assembly and crystal structures have been solved to explore the effect of acetyl protection and agly-con variation on the conformation, particularly of the iV-glycosidic linkage. Comparative analysis of these structures with those of free sugar amides reported earlier showed that conformation of the amido aglycon moiety is not altered significantly by the masking of hydroxyl groups in the form of acetate. The bifurcated antiparallel pattern involving N-H ... O and C-H ... O hydrogen bonds, a hallmark of the iV-glycoprotein models GlcNAc/^NHAc and GlcNAc/^Asn, is absent in all of the fully protected title alkanamides. The asymmetric unit of the tri-O-acetylated GlcNAc/iNHAc contains two different conformations, in one of which the double-pillared hydrogen bond network involving Cl and C2 acetamido groups is antiparallel, while it is parallel in the other. The co-occurrence of a molecular assembly motif-a double-pillared parallel and antiparallel hydrogen bonding pattern-is hitherto unknown in the crystal structures of N-glycoprotein linkage region models and analogs.