Structure-activity relationship in clonidine-like 2,3-disubstituted 2-aryl-imino-imidazolidines.

In anaesthetized rabbits the hypotensive activity of a group of 2,3-disubstituted 2-aryl-imino-imidazolidines was estimated. Compounds with 3-bromo substituents at the phenyl moiety of the molecule are more than or as active as clonidine. Correlations between blood pressure lowering effect and lipophilicity, maximum alpha-adrenergic effects (alpha E') and -log ED50 (pD2') of blood pressure increase in spinalized rats and pKA were calculated. The results show a positive linear correlation between as well partition coefficient as alpha E' and hypotension. The relationship between pD2' and hypotensive. effect is less prominent. pKA seems to have no influence on the blood pressure effects of these compounds.