Current synthetic approaches to peptide and peptidomimetic cyclization

An increasingly large number of bioactive cyclic peptides have been found in nature. The enhanced biological specificity, activity, and metabolic stability of cyclopeptides, by virtue of their conformationally constrained structural feature, have attracted much attention and made these compounds extensively studied. Cyclic peptidomimetic scaffolds and templates have been widely used to assemble various spatially defined functional groups for molecular recognition and drug discovery. These efforts are complemented optimally by NMR and X-ray based structure information, and assisted by molecular modeling based structure predictive methods. Peptide cyclization also becomes an effective and commonly employed strategy for peptide modifications. During the past several decades, great effort has been made to develop more efficient methods for the synthesis of cyclic peptides and peptidomimetics, as potential drug leads and/or as models for conformational analysis. This review is aimed at highlighting novel recently developed peptide cyclization approaches, and illustrating the profitable applications.