Prolinoamino acids as a tool to stabilize β-turns with the side chain of natural amino acids

Molecular mechanics calculations, X-ray, FT-IR, and NMR analysis performed on Piv-d-Procl-l-Pro-NHMe (d-Procl=a proline/leucine chimera) show that it possesses a water stable type II′ β-turn structure. The isopropyl side chain of d-Procl compares with the leucine side chain of a typical type I β-turn found in a protein (taken from the PDB). Thus cis-3-substituted prolines with the appropriate side chain can be used to mimic type I, II or II′ β-turns and incorporate the side chain functionalities on both the i+1 and i+2 positions of β-turns.