Contribution to the Chemotherapy of Human Trypanosomiasis: Design, Synthesis, and Biological Evaluation of Dimeric 2‑Nitroimidazoles against Trypanosoma cruzi Amastigotes and Bloodstream Trypanosoma brucei

Abstract

Effective and safe treatments for neglected tropical diseases caused by parasites, such as Chagas disease and sleeping sickness, remain lacking, posing a significant challenge for researchers worldwide. The rational design of dimeric compounds inspired solely by the pharmacophoric core of benznidazole (2-nitroimidazole) has proven to be a promising strategy for antiparasitic development. Thus, in the present work, it was increased the linker between the active units (2-nitroimidazole) to improve the interaction with TcNTR, facilitating the bioactivation of the longest dimers. Biological assays confirmed this, demonstrating that all compounds were active against replicative intracellular amastigotes of Trypanosoma cruzi (Tulahuen C2C4-LacZ). Notably, longer-chain dimers exhibited remarkable potency (IC₅₀ < 1.0 μM). These compounds also showed significant activity against T. b. brucei and demonstrated very low cytotoxicity in mammalian cells, highlighting their selectivity, especially among the longer-chain dimers. These findings support the development of dimeric 2-nitroimidazole derivatives as selective agents against trypanosomes.

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Chemical structures of commercial antiparasitic drugs. Azomycin is a commercial natural antibiotic. For better interpretation, the counterions were omitted.

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Structures of designed homologous dimeric derivatives of 2-nitroimidazoles (4–11).

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(A) The obtained predicted dimeric model of TcNTR and (B) its superposition with the reported AlphaFold model in graypredicted Local Distance Difference Test (pLDDT) score for residues across the full-length protein of 61.3% and 19.5%, meaning confidence of very high and high, respectively, and the superposition with the reported predicted Swiss-Model TcNTR from CL Brener in wine. (C) Superposition of the redocking calculations to FMN into the catalytic site of the crystallographic NTR from E. coli B. (D) Superposition between the obtained predicted dimeric model of TcNTR and the crystallographic NTR from E. coli B. (E) The electrostatic potential map of TcNTR docked with dimeric 2-nitroimidazoles 4–11. The best docking pose to (F) 4–6, (G) 7–9, and (H) 10 and 11 into the catalytic pocket of TcNTR in the presence of the cofactor FMN. The main amino acid residues that interact with (I) 4, (J) 6, (K) 10, and (L) 11. Blue lines, gray, orange, and green dots represent hydrogen bonds, hydrophobic interactions, π-cation interactions, and π-stacking interactions, respectively. For better interpretation, hydrogen atoms were omitted.

1. Reaction of 2-Nitroimidazole with Appropriate Dibromoalkanes (Yields of Each Derivative Are Indicated in Brackets)