Novel Selective and Low-Toxic Inhibitor of CPB2.8ΔCTE (CPB) One Important Cysteine Protease for Virulence.

Leishmaniasis is a highly prevalent, yet neglected disease caused by protozoan parasites of the genus . In the search for newer, safer, and more effective antileishmanial compounds, we herein present a study of the mode of action in addition to a detailed structural and biological characterization of [-benzoyl-'-benzyl-″-(4-tertbutylphenyl)guanidine]. X-ray crystallography and extensive NMR experiments revealed that nearly exclusively adopts the conformation stabilized by an intramolecular hydrogen bond. The investigated guanidine showed selective inhibitory activity on cysteine protease CPB2.8ΔCTE (CPB) with ~73% inhibition and an IC of 6.0 µM. This compound did not show any activity against the mammalian homologues cathepsin L and B. has been found to be nontoxic toward both organs and several cell lines, and no signs of hepatotoxicity or nephrotoxicity were observed from the analysis of biochemical clinical plasma markers in the treated mice. Docking simulations and experimental NMR measurements showed a clear contribution of the conformational parameters to the strength of the binding in the active site of the enzyme, and thus fit the differences in the inhibition values of compared to the other guanidines. Furthermore, the resulting data render suitable for further development as an antileishmanial drug.