Hydroxyazole scaffold-based Plasmodium falciparum dihydroorotate dehydrogenase inhibitors: Synthesis, biological evaluation and X-ray structural studies

Abstract
Plasmodium falciparum dihydroorotate dehydrogenase (PfDHODH) has been validated as a promising target for antimalarial drug discovery, with the triazolopyrimidine-based inhibitor DSM265 currently in clinical development. In this study, we identified novel PfDHODH inhibitors based on hydroxyazole scaffolds, divided into two distinct chemical series.

The first series was developed using a scaffold-hopping approach, focusing on hydroxylated azoles. From this series, the hydroxythiadiazole compound 3 emerged as the most selective PfDHODH inhibitor, with an IC50 of 12.0 μM. The second series involved structural modifications at four positions of the hydroxypyrazole scaffold, leading to the identification of compounds 7e and 7f as potent inhibitors with IC50 values of 2.8 μM and 5.3 μM, respectively.

All three compounds (3, 7e, and 7f) demonstrated significant selectivity for PfDHODH over human DHODH (IC50 > 200 μM), low cytotoxicity, and retained micromolar efficacy against P. falciparum-infected erythrocytes. Crystallographic BAY 2402234 analysis of PfDHODH in complex with compounds 3 and 7e confirmed their binding modes, providing critical insights for future scaffold optimization.