Abstract

RGD-containing peptides (linear and cyclic) have been developed to target some types of cancer cells through interaction with the alpha v beta 3 Integrin. Due to their reduced conformational freedom, cyclic peptides exhibit improved metabolic stability and binding affinity/specificity to their molecular targets. However, macrocyclization is considered a significant synthetic challenge that is affected by the ring size, peptide sequence, and reaction conditions, making tetra- and pentapeptides more difficult to cyclize. In this work, we report some optimized cyclization conditions for the obtention of a cyclic RGDfK peptide that combine the use of low reaction temperature and the addition of LiCl, a combination not yet reported that resulted in a reduction of the formation of oligomers and an improvement of the cyclization efficiency.