Design, synthesis, biophysical and antiprotozoal evaluation of new promising 2,9-bis[(substituted-aminomethyl)]-4,7-phenyl-1,10-phenanthroline derivatives by targeting G-quadruplex

A series of new 2,9-bis[(substituted-aminomethyl)]-4,7-phenyl-1,10-phenanthroline derivatives was designed, synthesized, and evaluated in vitro against three protozoan parasites (Plasmodium falciparum, Leishmania donovani and Trypanosoma brucei brucei). Biological results showed antiprotozoal activity with IC₅₀ values in the sub and mM range. In addition, the in vitro cytotoxicity of these original molecules was assessed with human HepG2 cells. The substituted diphenylphenanthroline 1l was identified as the most potent antiplasmodial candidate with a ratio of cytotoxic to antiparasitic activities of 505.7 against the P. falciparum CQ-resistant strain W2. Against the promastigote forms of L. donovani, the phenanthrolines 1h, 1j, 1n and 1o were found the most active compounds with IC₅₀ from 2.52 to 4.50 mM. The phenanthroline derivative 1o was also identified as the most potent trypanosomal candidate with a selectivity index (SI) of 91 on T. brucei brucei strain. Moreover, as the telomeres of the parasites P. falciparum and Trypanosoma could be considered as possible targets of this kind of nitrogen heterocyclic derivatives, their ability to stabilize the parasitic telomeric G-quadruplexes have been determined through the FRET melting assay and by native mass spectrometry.