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Conformational studies of cyclohexapeptide analogs of elastin sequences: Cyclo(Ala‐Pro‐Gly‐Ala‐Pro‐Gly)

Synthesis and conformation of a cyclohexapeptide [cyclo(L-Ala1-L-Pro2-Gly3-L-Ala4-L-Pro5-Gly6) c(APGAPG)] is reported in this paper. Conformational studies were performed using a combined approach of conformational energy calculations and 1H NMR studies in a low dielectric constant solvent, CDCl3. The results obtained from the two different methods agree reasonably well, and the minimun energy conformation derived from them is found to be stabilized by an antiparallel β-type conformation with two intramolecular hydrogen bonds between the Ala4 NH and Ala1 C O and the Ala1 NH and Ala4 C O groups. The Ramachandran map for the Ala residue in the cyclic hexapeptide reveals interesting conformational features, and its implications will be explored in more detail in future publications from this laboratory.