Structure–activity study of retinoid agonists bearing substituted dicarba-closo-dodecaborane. Relation between retinoidal activity and conformation of two aromatic nuclei

We have investigated the structure–activity relationships of the potent retinoid agonist, 4-[4-(2-propyl-1,2-dicarba-closo-dodecaboran-1-yl)phenylamino]benzoic acid (BR403), which we have previously reported. Substitution of a methyl group on the aromatic nucleus or a methyl group on the nitrogen atom, or replacement of the amino group with ether, methylene, carboxyl or 1,1-ethylene greatly decreased the activity. The relatively planar conformation at the phenyl-N-phenyl moiety seems to play a critical role in the appearance of the biological activity.