Structure-activity analysis of imino-pyrimidinone-fused pyrrolidines aids the development of dual plasmepsin V and plasmepsin X inhibitors.

A library of known aspartic protease inhibitors was screened to identify compounds that inhibit plasmepsin V from Plasmodium vivax. This screen revealed compounds with an imino-pyrimidinone-fused pyrrolidine (IPF) scaffold that exhibited sub-micromolar inhibitory activity against plasmepsin V. Further screening of IPF analogs against the related aspartic protease plasmepsin X showed inhibitory activity, while a third aspartic protease, plasmepsin IX, was not significantly inhibited. Modifications to the P1 biaryl region of the IPF scaffold differentially modulated inhibition of both plasmepsin V and X. Notably, analogs with potent plasmepsin X inhibitory activity successfully blocked the growth of Plasmodium falciparum in vitro. X-ray structures of IPF analogs in complex with plasmepsin V provided insights into their binding mode and revealed avenues to further improve IPF potency and selectivity between plasmepsin V and X. This understanding of how these compounds interact with the active sites of plasmepsin V and X will serve as a foundation for the future design of dual inhibitors targeting these proteases.