Evaluation of the Anti- Leishmania mexicana and - Trypanosoma brucei Activity and Mode of Action of 4,4'-(Arylmethylene)bis(3-methyl-1-phenyl-1 H -pyrazol-5-ol).

Trypanosomiasis and leishmaniasis are neglected infections caused by trypanosomatid parasites. The first-line treatments have many adverse effects, high costs, and are prone to resistance development, hence the necessity for new chemotherapeutic options. In line with this, twenty five 4,4'-(arylmethylene)bis(1 H -pyrazol-5-ols) derivatives were synthesized and evaluated in vitro for their anti-trypanosomatid activity. Ten and five compounds from this series showed IC 50 ≤ 10 µM against the promastigote and the bloodstream stage of Leishmania mexicana and Trypanosoma brucei brucei , respectively. Overall, derivatives with pyrazole rings substituted with electron-withdrawing groups proved more active than those with electron-donating groups. The hits proved moderately selective towards L. mexicana and T. brucei (selectivity index, SI, compared to murine macrophages = 5-26). The exception was one derivative displaying an SI (>111-189) against T. brucei that surpassed, by >6-fold, the selectivity of the clinical drug nifurtimox (SI = 13-28.5). Despite sharing a common scaffold, the hits differed in their mechanism of action, with halogenated derivatives inducing a rapid and marked intracellular oxidative milieu in infective T. brucei . Notably, most of the hits presented better absorption, distribution, metabolism, and excretion (ADME) properties than the reference drugs. Several of the bioactive molecules herein identified represent a promising starting point for further improvement of their trypanosomatid potency and selectivity.