Synthesis and conformational analysis of macrocyclic peptides consisting of both α-helix and polyproline helix segments

ABSTRACT Macrocycles are interesting molecules because their topological features and constrained properties significantly affect their chemical, physical, biological, and self‐assembling properties. In this report, we synthesized unique macrocyclic peptides composed of both an α‐helix and a polyproline segment and analyzed their conformational properties. We found that the molecular stiffness of the rod‐like polyproline segment and the relative orientation of the two different helical segments strongly affect the efficiency of the macrocyclization reaction. Conformational analyses showed that both the α‐helix and the polyproline II helix coexisted within the macrocyclic peptides and that the polyproline segment exerts significant effect on the overall helical stability and conformation of the α‐helical segment. © 2013 Wiley Periodicals, Inc. Biopolymers 101: 279–286, 2014.