Beta-adrenoceptor studies. 2. Effects of alkyl substitution on beta-adrenoceptor blocking, antiarrhythmic, and local anesthetic activities of 1,1'-(o-phenylenedioxy)bis(3-isopropylamino-2-propanol).

A series of bis(2-hydroxy-3-isopropylaminopropyl) ethers of nuclear-substituted catechols (1-7) has been synthesized and examined in vitro for beta-adrenoceptor blocking activity, antagonism of ouabain-induced arrhythmias, and local anesthetic activity. Both tracheal and right atrial beta-adrenoceptor blocking activity are markedly decreased by alkyl substitution in position 3 of parent catechol diether 1. Substitution in position 4 still lowers the affinity to cardiac arrhythmias and local anesthetic activity increases with introduction of alkyl substituents in the 3 as well as in the 4 position. In contrast with biological activities, the partition coefficient 1-octanol-phosphate buffer, pH 7.40, of 1 did not change significantly by 3- and 4-methyl substitution. Stepwise multiple regression analyses were performed using log P or pi values in combination with pKa(m), E8, or sigma. With cardiac beta-adrenoceptor blocking activity the optimal equation contained E8 and pi parameters, tracheal activity appeared to depend mainly on the E8 parameter, whereas for antiarrhythmic and local anesthetic activities the lipophilicity of the substituents appeared to be the determinant factor.