Conformations of 2-C:1-N-carbonyl-2-deoxy-d-glycopyranosylamines

✍ Scribed by Zofia Urbanczyk-Lipkowska; Kinga Suwinska; Roman Luboradzki; Danuta Mostowicz; Zbigniew Kaluza; Jacek Grodner; Marek Chmielewski

• Publisher: Elsevier Science
• Year: 1994
• Tongue: English
• Weight: 616 KB
• Volume: 256
• Category: Article
• ISSN: 0008-6215
• DOI: 10.1016/0008-6215(94)84222-1

✦ Synopsis

Conformations of three derivatives of 2-C: l-Z%carbonyl-2-deoxy-o-glycopyranosylamines were investigated in the solid state, by use of X-ray. Quantitative conformational analysis (asymmetry parameters and puckering parameters), applied to the ring system in six crystallographically determined structures, revealed, for the pyranoid ring, conformations different from the initially observed half-chair conformation (H). Experimental conformations compared with molecular modelling-derived structures showed the importance of the p-lactam ring in shaping the pyranoid moiety. An entirely different hydrogen-bonding pattern, observed for molecules differing by one substituent, illustrates how easily the energy (conformation) of a molecule in solution or in the solid state could be influenced by intermolecular interactions. Substitution of the B-lactam nitrogen atom significantly changes the geometry of the four-membered ring. INTRODUCTTON Previously, we have reported the synthesis and structural studies of a new class of bicyclic &lactams'. Since X-ray studies, as well as molecular mechanics calculatiohs, have shown that the conformatioris of the pyranoid rings in the (Y-D-glmo, p-D-urabim, and /3-~-abtro derivatives remain within the calculated global energy minimum assigned to the half-chair conformation, the 'H and 13C NMR data were interpreted in terms of two interconverting half-chair forms. Not all data, however, have been entirely consistent with the accepted model and we had to consider either distortion of the half-chair geometry or a conformational equilibrium involving more than two components. In the present studies, some additional crystal structure determinations gave, even for a molecule undisturbed by the effect of substitution, conformations different from those expected from our * Part II. For Part I, see ref 1.