Novel and potent inhibitors of Plasmodium falciparum plasmepsin II were 
identified by post-processing the results of a docking screening with BEAR, a 
recently reported procedure for the refinement and rescoring of docked ligands 
in virtual screening. FRET substrate degradation assays performed on the 30 most 
promising compounds resulted in 26 inhibitors with IC(50) values ranging from 
4.3 nM to 1.8 microM.Herein we report the discovery of novel and potent 
inhibitors of Plasmodium falciparum plasmepsin II using GRID computing 
infrastructures. These compounds were identified by post-processing the results 
of a large docking screen of commercially available compounds using an automated 
procedure based on molecular dynamics refinement and binding free-energy 
estimation using MM-PBSA and MM-GBSA. Among the best-scored compounds, four 
highly populated and promising chemical classes were identified: 
N-alkoxyamidines, guanidines, amides, and ureas and thioureas. Thirty hit 
compounds representative of each class were selected on the basis of their 
favourable binding free energies and molecular interactions with key active site 
residues. These were experimentally validated using an inhibition assay based on 
FRET substrate degradation. Remarkably, 26 of the 30 tested compounds proved to 
be active as plasmepsin II inhibitors, with IC(50) values ranging from 4.3 nM to 
1.8 microM.