Design of Peptide Models for β-Hairpins and Equilibrating Helix-Hairpin Structures

It is well established that synthetic peptides containing a centrally positioned Type-I or Type-II β-turn can form well folded peptide hairpins (1). Earlier studies from this laboratory have established that D-Pro-Xxx segments nucleate β-hairpin structures, with formation of a central Type-II β-turn (2). The octapeptide (Boc-Leu-Phe-Val-Aib-D-Ala-Leu-Phe- Val-OMe) is a rare example of a synthetic peptide hairpin, containing a central Type-I β-turn. Hairpins with Type-I turns are considerably more twisted than their Type-II counterparts. The Aib-Xxx segment has also been shown to adopt a Type-I β-turn structure, resulting in incorporation into the centre of a long synthetic, helical peptide (3) (Figures 1,2).