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-Pro(L)(c)-L-Pro-NHMe (D-Pro(L)(c) =a proline/leucine chimera) show that it possesses a water stable type 11' beta-turn structure. The isopropyl side chain of D-Pro(L)(c) compares with the leucine side chain of a typical type I beta-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' beta-turns and incorporate the side chain functionalities on both the i + 1 and i + 2 positions of beta-turns. (C) 2003 Elsevier Ltd. All rights reserved.