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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)
Author(s) -
Bielinski Henryk,
Ciarkowski Jerzy
Publication year - 1986
Publication title -
biopolymers
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.556
H-Index - 125
eISSN - 1097-0282
pISSN - 0006-3525
DOI - 10.1002/bip.360250505
Subject(s) - cndo/2 , chemistry , conformational isomerism , side chain , epimer , stereochemistry , ring (chemistry) , crystallography , molecule , polymer , organic chemistry
Conformational energy calculations, aimed at verification of the suitability of the semiempirical molecular orbital CNDO/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; cyclo (Glycyl‐L‐Alanyl), cyclo (Glycyl‐L‐Valyl), and both epimers of cyclo ‐di‐(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 cyclo (Gly‐Val) for assuming a folded conformation with one of the side chain γ‐methyl groups sticking over the DOP ring.