Synthesis and comparison of in vitro dual anti-infective activities of novel naphthoquinone hybrids and atovaquone.

A principal factor that contributes towards the failure to eradicate leishmaniasis and tuberculosis infections is the reduced efficacy of existing chemotherapies, owing to a continuous increase in multidrug-resistant strains of the causative pathogens. This accentuates the dire need to develop new and effective drugs against both plights. A series of naphthoquinone-triazole hybrids was synthesized and evaluated in vitro against Leishmania (L.) and Mycobacterium tuberculosis (Mtb) strains. Their cytotoxicities were also evaluated, using the human embryonic kidney cell line (HEK-293). The hybrids were found to be non-toxic towards human cells and had demonstrated micromolar cellular antileishmanial and antimycobacterial potencies. Hybrid 13, i.e. 2-{[1-(4-methylbenzyl)-1H-1,2,3-triazol-4-yl]methoxy}naphthalene-1,4-dione was the most active of all. It was found with MIC90 0.5 µM potency against Mtb in a protein free medium, and with half-maxima inhibitory concentrations (IC50) of 0.81 µM and 1.48 µM against the infective promastigote parasites of L. donavani and L. major, respectively, with good selectivity towards these pathogens (SI 22 - 65). Comparatively, the clinical naphthoquinone, atovaquone, although less cytotoxic, was found to be two-fold less antimycobacterial potent, and six- to twelve-fold less active against leishmania. Hybrid 13 may therefore stand as a potential anti-infective hit for further development in the search for new antitubercular and antileishmanial drugs. Elucidation of its exact mechanism of action and molecular targets will constitute future endeavour.