Synthesis and Structure-Activity Relationships of New 2-Phenoxybenzamides with Antiplasmodial Activity

The 2-phenoxybenzamide 1 from the Medicines for Malaria Venture Malaria Box Project has shown promising multi-stage activity against different strains of P. falciparum. It was successfully synthesized via a retrosynthetic approach. Subsequently, twenty-one new derivatives were prepared and tested for their in vitro activity against blood stages of the NF54 strain of P. falciparum. Several insights into structure-activity relationships were revealed. The antiplasmodial activity and cytotoxicity of compounds strongly depended on the substitution pattern of the anilino partial structure as well as on the size of substituents. The diaryl ether partial structure had further impacts on the activity. Additionally, several physicochemical and pharmacokinetic parameters were calculated (log P, log D-7.(4) and ligand efficiency) or determined experimentally (passive permeability and CYP3A4 inhibition). The tert-butyl-4-{4-[2-(4-fluorophenoxy)-3-(trifluoromethyl)benzamido]phenyl}piperazine-1-carboxylate possesses high antiplasmodial activity against P. falciparum NF54 (PfNF54 IC50 = 0.2690 mu M) and very low cytotoxicity (L-6 cells IC50 = 124.0 mu M) resulting in an excellent selectivity index of 460. Compared to the lead structure 1 the antiplasmodial activity was improved as well as the physicochemical and some pharmacokinetic parameters.

Automated summary

The study synthesized and tested twenty-one derivatives, revealing structure-activity relationships and discussing the impact of substitution patterns and size on antiplasmodial activity and cytotoxicity. An optimized compound showed improved antiplasmodial activity, low cytotoxicity, and enhanced physicochemical and pharmacokinetic parameters compared to the lead structure.