Design and synthesis of plasmepsin I and plasmepsin II inhibitors with activity in Plasmodium falciparum-infected cultured human erythrocytes

A series of protease inhibitors targeted at the malarial enzymes plasmepsin I and II, and encompassing a basic hydroxyethylamine transition state isostere scaffold, was prepared. The substituents in the P1' position were varied and the biological activities expressed in K-i-values ranged from 60 to > 2000 nM. A more than 4-fold selectivity for either of the plasmepsins could be achieved. All of the active compounds exhibited high preference for the plasmepsins over cathepsin D, the most closely related human protease. A few active compounds were shown to inhibit parasite growth in cultured infected human erythrocytes. An ED50 value as low as 1.6 muM was observed for one of the inhibitors despite K-i values of 115 nM (Plm I) and 121 nM (Plm II).