Structural requirements of salicylanilides for uncoupling activity in mitochondria: Quantitative analysis of structure-uncoupling relationships

The uncoupling activities of more than 20 salicylanilides were measured in rat liver mitochondria. The activities, expressed as the minimum concentrations required for full release of state-4 respiration, ranged over three orders of magnitude. The acid dissociation constant, pK_A, and the partition coefficient between octanol and water (P_oct) of some of the salicylanilides were determined. These two parameters were found to be well expressed in terms of the Hammett constant, σ, and the hydrophobic substituent coefficient, Π, respectively. The pK_A and log P_oct values of all the salicylanilides were predicted according to these relationships. Furthermore, the capacity factor, k′, on high-performance liquid chromatography was determined on glyceryl-coated-controlled pore glass (gly-CPG). Values of log k′ correlated well with those of log P_oct. The uncoupling activities of the salicylanilides were analyzed in terms of these three parameters. Both hydrophobic and electron-withdrawing properties were found to be essential for induction of potent uncoupling activity. The correlations using log k′ were better than those using log P_oct.