Triosephosphate isomerase (TIM) is an essential Trypanosoma cruzi enzyme and one of the few validated drug targets for Chagas disease. The known inhibitors of this enzyme behave poorly or have low activity in the parasite. In this work, we used symmetrical diarylideneketones derived from structures with trypanosomicidal activity. We obtained an enzymatic inhibitor with an IC50 value of 86 nm without inhibition effects on the mammalian enzyme. These molecules also affected cruzipain, another essential proteolytic enzyme of the parasite. This dual activity is important to avoid resistance problems. The compounds were studied in vitro against the epimastigote form of the parasite, and nonspecific toxicity to mammalian cells was also evaluated. As a proof of concept, three of the best derivatives were also assayed in vivo. Some of these derivatives showed higher in vitro trypanosomicidal activity than the reference drugs and were effective in protecting infected mice. In addition, these molecules could be obtained by a simple and economic green synthetic route, which is an important feature in the research and development of future drugs for neglected diseases.

Searching for prospective metal-based drugs for the treatment of Chagas disease, a new series of ten mixed-ligand oxidovanadium(IV) complexes, [V(IV)O(L-2H)(NN)], where L is a tridentate salicylaldehyde semicarbazone derivative (L1-L5) and NN is either 5-amine-1,10-phenanthroline (aminophen) or 5,6-epoxy-5,6-dihydro-1,10-phenanthroline (epoxyphen), were synthesized. The compounds were characterized in the solid state and in solution. EPR spectroscopy suggests that the NN ligands act as bidentate through both nitrogen donor atoms in an axial-equatorial mode. The stability of the complexes in solution was investigated by EPR and (51)V-nuclear magnetic resonance spectroscopies. The complexes were evaluated in vitro for their activities against Trypanosoma cruzi (T. cruzi), the parasite responsible for the disease, and their selectivity was analyzed using J-774 murine macrophages, as a mammalian model. All the complexes are more active than both the reference drug Nifurtimox and the previously reported [V(IV)O(L-2H)(NN)] complexes. In general they are more active than the corresponding free NN ligands. Complexation led to highly increased selectivities towards the parasite. In addition, the lipophilicity of the compounds was determined and correlated with the observed activity in order to perform a QSAR (quantitative structure-activity relationship) study. A clear quadratic correlation is found. This study also confirms the influence of the structure of the co-ligand on the anti-T. cruzi effect. To get insight into the mechanism of action of the compounds, the changes in biochemical pathways promoted by two of the most active and most selective complexes are studied by analyzing a few of the parasite excreted metabolites by (1)H NMR spectroscopy. The combined information suggests that the mitochondrion could be a target for these complexes. Furthermore, DNA was preliminarily evaluated as a potential target by using atomic force microscopy (AFM), which showed that the complexes display an ability to interact with this biomolecule.

ABSTRACT. As a continuation of our research and with the aim of obtaining new agents against Chagas disease, an extremely neglected disease which threatens 100 million people, eighteen new quinoxaline 1,4-di-N-oxide derivatives have been synthesized following the Beirut reaction. The synthesis of the new derivatives was optimized through the use of a new and more efficient microwave-assisted organic synthetic method. The new derivatives showed excellent in vitro biological activity against Trypanosoma cruzi. Compound 17, which was substituted with 2 fluoro groups at the 6-and 7-positions of the quinoxaline ring, was the most active and selective in the cytotoxicity assay. The electrochemical study showed that the most active compounds, which were substituted by electron-withdrawing groups, possessed a greater ease of reduction of the N-oxide groups.

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