Quantum chemical studies on the conformational structure of bacterial peptidoglycan. V. PCILO Calculations on β(1 → 4) linked disaccharide of N-acetyl-glucosamine and N-acetyl muramic acid

The glycan moiety of the bacterial peptidoglycan consists of alternatingly β(1 → 4) linked disaccharides of N-acetylglucosamine (NAG) and its 3-O-D lactic derivative, N-acetyl β-D-muramic acid (NAM). PCILO conformational energy calculations have been carried out for NAG–NAM and NAM–NAG disaccharides to see whether or not the glycan strands possess a chitinlike structure as suggested by earlier workers. In agrement with recent experimental findings, the present results also suggest that the chitinlike structure is energetically disallowed. Furthermore, the bulky N-acetyl substituents at C₂ positions of the two sugar molecules are found to be relatively less important in stabilizing mutual orientations of the two pyranosyl rings.