Synthesis and X-ray crystallographic investigation of N-(3-deoxy-3-acetamido-β-D-glycopyranosyl)alkanamides as analogs of N-glycoprotein linkage region.

As part of our ongoing program aimed at understanding the structural significance of GlcNAcβAsn linkage conserved in all eukaryotic N-glycoproteins, the present study reports on the synthesis and X-ray crystal structures of N-(3-deoxy-3-acetamido-β-D-glycopyranosyl)acetamide (Glc3NAcβNHAc) and the corresponding propionamide (Glc3NAcβNHPr). Comparative analysis of these structures with those of the corresponding GlcNAc (C2 acetamido) compounds showed that the bifurcated anti-parallel pattern involving N-H…O and C-H…O hydrogen bonds, the hallmark feature of the N-glycoprotein models, GlcNAcβNHAc and GlcNAcβAsn, is absent in both the C3 acetamido analogs. The extended (anti) conformation of the amido aglycon moiety as defined by χ(2) seen in the case of C2 acetamido derivative, GlcNAcβNHPr, turns into gauche for the C3 acetamido analog (Glc3NAcβNHPr). This observation is consistent with the earlier work on the critical role of the C2-NHAc group of GlcNAcβAsn in controlling χ(2) at the linkage region of N-glycoproteins.