ABSTRACT
Conformational studies have been carried out on hydrogenbonded all-trans cyclic pentapeptide backbone· Application of a combination of grid search and energy minimization on this system has resulted in obtaining 23 minimum energy conformations, which are characterized by unique patterns of hydrogen bonding comprising of ßand γ-turns. A study of the minimum energy conformations vis-a-vis non-planar deviation of the peptide units reveals that non-planarity is an inherent feature in many cases· A study on conformational clustering of minimum energy conformations shows that the minimum energy conformations fall into 6 distinct conformational families· Preliminary comparison with available X-ray structures of cyclic pentapeptide indicates that only some of the minimum energy conformations have formed crystal structures· The set of minimum energy conformations worked out in the present study can form a consolidated database of prototypes for hydrogen bonded backbone and be useful for modelling cyclic pentapeptides both synthetic and bioactive in nature·
ABSTRACT
Cyclic peptides form an interesting class of compounds for study by conformational analysis, by virtue of their unique conformational features and biological properties. The small cyclic peptides having 3–6 peptide units in their ring, show a variety of conformational characteristics such as occurrence of cis peptide units, flexibility of peptide dimension and variety in hydrogen bonding. The different possible conformations of cyclic triand hexa-peptides are given and certain specific conformational features are discussed for cyclic tetra and pentapeptides. For higher cyclic peptides, the hydrogen bonding requirement for stability of the backbone of the ring, is seen to be kept to a minimum. These various features and their significance are examined and discussed in the light of energy minimization studies and analysis of available experimental data.