ABSTRACT
A series of 9-mer and 13-mer amide-bridged cyclic peptides derived from the linear prototype Ac-PKIIQSVGIS-Nle-K-Nle-NH2 (Toro et al. ChemBioChem2013) has been designed and synthesized by introduction of the lactam between amino acid side chains that are separated by one helical turn (i, i+4). All of these compounds were tested in vitro as both dimerization and enzyme inhibitors of Leishmania infantum trypanothione reductase (Li-TryR). Three of the 13-mer cyclic peptide derivatives (3, 4 and 6) inhibited the oxidoreductase activity of Li-TryR in the low micromolar range and they also disrupted enzyme dimerization. Cyclic analogues 3 and 4 were more resistant to proteases than was the linear prototype. Furthermore, the most potent TryR inhibitors in the linear and cyclic series displayed potent in vitro activity against Leishmania infantum upon conjugation with cationic cell-penetrating peptides. To date, these conjugated peptides can be considered the first example of TryR dimerization inhibitors that are active in cell culture.
