5-Nitroindazole-based compounds: further studies for activity optimization as anti-Trypanosoma cruzi agents

In this study, a new series of eleven 5-nitroindazole derivatives (10-20) and a related 6-nitroquinazoline (21) was synthesized and tested in vitro against different forms of the kinetoplastid parasite Trypanosoma cruzi, etiological agent of Chagas disease. Among these compounds, derivatives 11-14 and 17 showed trypanocidal profiles on epimastigotes (IC₅₀ = 1.00-8.75 µM) considerably better than that of the reference drug benznidazole, BZ (IC₅₀ = 25.22 µM). Furthermore, the lack of cytotoxicity observed for compounds 11, 12, 14, 17 and 18 over L929 fibroblasts, led to a notable selectivity (SI) on the extracellular replicative form of the parasite: SI_EPI > 12.41 to > 256 µM. Since these five derivatives overpassed the cut-off value established by BZ (SI_EPI ≥ 10), they were moved to a more specific assay against the intracellular and replicative form of T. cruzi, i.e, amastigotes. These molecules were not as active as BZ (IC₅₀ = 0.57 µM) against this parasite form; however, all of them showed remarkable IC₅₀ values lower than 7 µM. Special mention deserve compounds 12 and 17, whose SI_AMA were > 246.15 and > 188.23, respectively. The results compiled in the present work, point to a positive impact over the trypanocidal activity of the electron withdrawing substituents introduced at position 2 of the N-2 benzyl moiety of these compounds, especially fluorine, i.e., derivatives 12 and 17. These outcomes, supported by the in silico prediction of good oral bioavailability and suitable risk profile, reinforce the 5-nitroindazole scaffold as an adequate template for preparing potential antichagasic agents.