Approaches to cyclic peptide β-turn mimics

The beta -turn is a common recognition feature between peptide ligands and their macromolecular targets. The cyclization of a short peptide segment with a linker is one method of imitating this conformation. The first part of this review discusses tethering strategies which have resulted in the development of mimetics for the enkephalins and somatostatin as well as in the discovery of antagonists for targets such as thrombin, the CD4 protein on T lymphocytes, the integrins, and other receptors involved in inflammatory diseases. The second portion of this review describes the application of aminocaproic acid (Aca) as a tether in cyclic peptide beta -turn mimics. Alkyl substituents on Aca may influence the beta -turn preference of the dipeptide. The synthesis of the substituted Aca linkers and their incorporation into the macrocycles is highlighted.