Based on some structural analogies with leflunomide and brequinar, two well-known inhibitors of dihydroorotate dehydrogenase (DHODH), a new series of products was designed, by joining the substituted biphenyl moiety to the 4-hydroxy-1,2,5-oxadiazol-3-yl scaffold through an amide bridge. The compounds were studied for their DHODH inhibitory activity on rat liver mitochondrial/microsomal membranes. The activity was found to be closely dependent on the substitution pattern at the biphenyl system; the most potent products were those bearing two or four fluorine atoms at the phenyl adjacent to the oxadiazole ring. A molecular modeling study suggested that these structures might have a brequinar-like binding mode. The greater potency of fluorinated analogs may depend partly on enhanced interactions with the hydrophobic ubiquinone channel, and partly on the role of fluorine in stabilizing the putative bioactive conformation.
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