Membrane-bound pyrophosphatases (mPPases) regulate energy homeostasis in pathogenic protozoan parasites and lack human homologues, which makes them promising targets in e.g. malaria. Yet only few nonphosphorus inhibitors have been reported so far. Here, we explore an isoxazole fragment hit, leading to the discovery of small mPPase inhibitors with 6–10 μM IC50 values in the Thermotoga maritima test system. Promisingly, the compounds retained activity against Plasmodium falciparum mPPase in membranes and inhibited parasite growth.

Inhibition of membrane-bound pyrophosphatase (mPPase) with small molecules offer a new approach in the fight against pathogenic protozoan parasites. mPPases are absent in humans, but essential for many protists as they couple pyrophosphate hydrolysis to the active transport of protons or sodium ions across acidocalcisomal membranes. So far, only few nonphosphorus inhibitors have been reported. Here, we explore the chemical space around previous hits using a combination of screening and synthetic medicinal chemistry, identifying com-pounds with low micromolar inhibitory activities in the Thermotoga maritima mPPase test system. We furthermore provide early structure-activity relationships around a new scaffold having a pyrazolo[1,5-a]pyrimidine core. The most promising pyrazolo[1,5-a]pyrimidine congener was further investigated and found to inhibit Plasmodium falciparum mPPase in membranes as well as the growth of P. falciparum in an ex vivo survival assay.

Cooperative molecular contacts play an important role in protein structure and ligand binding. Here, we constructed a PostgreSQL database that stores structural information in the form of atomic environments and allows flexible mining of molecular contacts. Taking the Ser‐His‐Asp/Glu catalytic triad as a first test case, we demonstrate that the presence of a carboxylate oxygen atom in the vicinity of a His is associated with shorter Ser‐OH..N‐His bond in the PDB30 subset. We prospectively mine catalytic triads in unannotated proteins, suggesting catalytic functions for unannotated proteins. As a second test case, we demonstrate that this database system can include ligand atoms, represented by Sybyl atom types, by evaluating the proportion of counter‐ions for ligand carboxylate oxygens.