(A) Gramicidin S and some β-turn mimics used in its analogs. (B) Ugi-reaction-derived N-alkylated peptide fragments as novel β-hairpin-stabilizing templates.

(A) Synthesis of cyclic peptide β-hairpins by on-resin Ugi macrocyclization, (B) comparison of circular dichroism spectra of bUgi-derived β-hairpins with gramicidin S, and (C) average NmR-derived structures of cyclic peptides 1 and 2

(A) Synthesis of cyclic β-hairpin structure by SPPS method involving two Ugi reactions, (B) CD spectra comparison of the double Ugi-derived β-hairpin structure and gramicidin S, and (C) average NmR-derived structure of cyclic peptide 9b