Studies on the β-Turn of Peptides. V. Turn Preference of Peptide Sequence Analyzed by Conformational Energy Calculation on Dipeptide Models and by CD Spectra of Chromophoric Derivatives

Abstract

Empirical conformational energy calculations were performed on Ac–L-Pro–D-Ala–NHCH₃ and Ac–D-Ala–L-Pro–NHCH₃. In order to study the turn tendency of the dipeptide sequences turn probabilities and average interterminal distances were calculated. Much larger turn preference of D-Ala containing sequences was indicated compared with the corresponding L-Ala containing sequences. The turn tendency of the dipeptide sequences were shown to be in the order: L-Pro–D-Ala>D-Ala–L-Pro>L-Pro–L-Ala>L-Ala–L-Pro. This order coincides with the order of the magnitude of the Cotton effects in the CD spectra of the chromophoric derivatives having 2,4-dinitrophenylglycyl and glycine-p-nitroanilide at the N- and the C-termini, respectively, of the corresponding dipeptid esequences. This agreement supports the validity of the chiroptical method to study the turn tendency of the peptide sequences using chromophoric derivatives reported earlier.