4-Aryl Pyrrolidines as a Novel Class of Orally Efficacious Antimalarial Agents. Part 1: Evaluation of 4-Aryl- N-benzylpyrrolidine-3-carboxamides

Identification of novel chemotypes with antimalarial efficacy is imperative to combat the rise of Plasmodium species resistant to current antimalarial drugs. We have used a hybrid target-phenotype approach to identify and evaluate novel chemotypes for malaria. In our search for drug-like aspartic protease inhibitors in publicly available phenotypic antimalarial databases, we identified GNF-Pf-4691, a 4-aryl-N-benzylpyrrolidine-3-carboxamide, as having a structure reminiscent of known inhibitors of aspartic proteases. Extensive profiling of the two terminal aryl rings revealed a structure-activity relationship in which relatively few substituents are tolerated at the benzylic position, but the 3-aryl position tolerates a range of hydrophobic groups and some heterocycles. Out of this effort, we identified (+)-54b (CWHM-1008) as a lead compound. 54b has EC ₅₀ values of 46 and 21 nM against drug-sensitive Plasmodium falciparum 3D7 and drug-resistant Dd2 strains, respectively. Furthermore, 54b has a long half-life in mice (4.4 h) and is orally efficacious in a mouse model of malaria (qd; ED ₉₉ ∼ 30 mg/kg/day). Thus, the 4-aryl-N-benzylpyrrolidine-3-carboxamide chemotype is a promising novel chemotype for malaria drug discovery.