Conformation of dioxopiperazines, II. CNDO/2 quantum mechanical calculations on conformational preferences in cyclo (glycyl-L-alanyl), cyclo(glycyl-L-valyl), and both epimers of cyclo-di-(alanyl)

✍ Scribed by Henryk Bielinski; Jerzy Ciarkowski

• Publisher: Wiley (John Wiley & Sons)
• Year: 1986
• Tongue: English
• Weight: 757 KB
• Volume: 25
• Category: Article
• ISSN: 0006-3525
• DOI: 10.1002/bip.360250505

✦ Synopsis

Conformational energy calculations, aimed at verification of the suitability of the semiempirical molecular orbital CND0/2 method for conformational elucidations in cyclic dipeptides formed from amino acids with aliphatic side chains, have been carried out. The results obtained for four dioxopiperazines [DOP cycZdGlycy1-L-Alanyl), cy-cZo(Glycy1-L-Valyl), and both epimers of cycbdi-(Alanyl)] point out very good agreement with experimental premises. The latter include (1) the preference of the cis-peptide bonds for being nonplanar, which results in twisted-boat conformations of the DOP ring;

(2) greater stability of conformers with a side chain oriented axially over those with a side chain oriented equatorially; (3) the preference of cycZo(G1y-Val) for assuming a folded conformation with one of the side chain y-methyl groups sticking over the DOP ring.