Virtual Screening and Optimization Yield Low-Nanomolar Inhibitors of the Tautomerase Activity of <i>Plasmodium falciparum</i> Macrophage Migration Inhibitory Factor

The <i>Plasmodium falciparum</i> orthologue of the human cytokine, macrophage migratory inhibitory factor (<i>Pf</i>MIF), is produced by the parasite during malaria infection and modulates the host’s immune response. As for other MIF orthologues, <i>Pf</i>MIF has tautomerase activity, whose inhibition may influence the cytokine activity. To identify small-molecule inhibitors of the tautomerase activity of <i>Pf</i>MIF, virtual screening has been performed by docking 2.1 million compounds into the enzymatic site. Assaying of 17 compounds identified four as active. Substructure search for the most potent of these compounds, a 4-phenoxypyridine analogue, identified four additional compounds that were purchased and also shown to be active. Thirty-one additional analogues were then designed, synthesized, and assayed. Three were found to be potent <i>Pf</i>MIF tautomerase inhibitors with <i>K</i>_i of ∼40 nM; they are also highly selective with <i>K</i>_i > 100 μM for human MIF