The biological action of substances related to thyroxine. 5. The relation between some of the physico-chemical properties of a series of 4-hydroxy-3:5-diiodobenzoates and their thyroxine-inhibitory actions

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Abstract
The partition coefficients of a series of alkyl and hydroxyalkyl 4-hydroxy-3,5-diiodobenzoates between 0.066 [image]-phosphate buffer of pH 7.3 and arachis oil was detd. The solubilities of the esters in the same solvents were also detd. The product of the solubilities of each ester in the two solvents correlated well with the thyroxine-inhibitory actions of the drugs. For high activity, it was necessary for the ester to be appreciably soluble in both media. Other physico-chemical properties including saponification rates and ionization constants of the phenolic hydroxy group were also examined. Some correlation was found between the former and the antithyroxine activity of the esters. All the highly active compounds were relatively rapidly hydrolyzed but the converse was not valid. It is suggested that all these esters exert their inhibitory action in the same manner, but that their variations in potency arise from differences in distr. in the animal body and in the ease of penetration of the cell membrane brought about by differences in their physico-chemical properties.