Synthesis and Conformational Studies of Novel Cyclic Peptides Constrained into a 3₁₀ Helical Structure by a Heterochiral d-Pro-l-Pro Dipeptide Template

An acyclic tripeptide based on a heterochiral d-pro-l-pro template shows a propensity to exist as a 310 helical conformation and can be cyclized, via ring-closing metathesis, to the corresponding cyclic tetrapeptides without disrupting the helical conformations in CDCl3 as well as in DMSO-d6 solutions. The detailed conformational studies were carried out by using NMR spectroscopy, X-ray crystallography, molecular dynamic simulations, and circular dichroism spectroscopy.