Computationally designed β-turn foldamers of γ-peptides based on 2-(aminomethyl)cyclohexanecarboxylic acid



The γ-peptide β-turn structures have been designed computationally by the combination of chirospecific γ2, 3-residues of 2-(aminomethyl)cyclohexanecarboxylic acid (γAmc6) with a cyclohexyl constraint on the Cα−Cβ bond using density functional methods in water. The chirospecific γAmc6 dipeptide with the (2S,3S)-(2R,3R) configurations forms a stable turn structure in water, resembling a type II′ turn of α-peptides, which can be used as a β-turn motif in β-hairpins of Ala-based α-peptides. The γAmc6 dipeptide with homochiral (2S,3S)-(2S,3S) configurations but different cyclohexyl puckerings shows the capability to be incorporated into one of two β-turn motifs of gramicidin S. The overall structure of this gramicidin S analogue is quite similar to the native gramicidin S with the same patterns and geometries of hydrogen bonds. Our calculated results and the recently observed results may imply the wider applicability of chirospecific γ-peptides with a cyclohexyl constraint on the backbone to form various peptide foldamers. © 2012 Wiley Periodicals, Inc. Biopolymers 97:1018–1025, 2012.