Structure-enabled enhancement of potency in a metronidazole–benznidazole hybrid: design, synthesis, and evaluation of antitrypanosomal activity of a benzylamide-linked 5-nitroimidazole

Benznidazole (1) remains the primary antiparasitic drug used clinically for Chagas disease, underscoring the need to discover novel treatments targeting Trypanosoma cruzi (T. cruzi) infection. In this sense, the present work reports the in silico design of a novel hybrid (3) containing the 5-nitroimidazole core from the commercial antiparasitic drug metronidazole (2) and the N-benzylacetamide moiety from 1. These structural motifs were designed to target T. cruzi nitroreductase type I (TcNTR) for activation and to boost intracellular drug levels (lipophilicity). The in silico predictions suggested that the presence of the N-benzylacetamide moiety might enhance the anti-T. cruzi activity of 2 and improve the drug-likeness. To validate the predictions, hybrid 3 was synthesized with a yield of 53% and structurally characterized (melting point, 1H and 13C NMR, and HRMS). The in vitro assays of hybrid 3 against T. cruzi amastigotes (Tulahuen strain C2C4 LacZ) supported the in silico predictions, showing a lower IC50 for 3 (67.73 ± 8.98 µM) than for 2 (>100 µM). Despite hybrid 3 having an activity 45-fold lower than that of 1, the results provide insights for future hybrid optimization.