Cyclic peptides––Small and big and their conformational aspects.

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.