Cardioselective beta-adrenoceptor blocking actions of some 2-methoxyphenylethanolamines in guinea pig tissues

A series of new phenylethanolamines with 2-methoxy and/or 4-methyl, 4-chloro, or 4-bromo ring substituents and either N-isopropyl or N-tert butyl substituents have been synthesized and tested for beta 1- and beta 2-adrenoceptor blocking activity using isolated guinea pig atrial and tracheal preparations. Each of the disubstituted N-isopropyl derivatives was a potent antagonist, and the 2-methoxy-4-methyl derivative had a 40-fold beta 1/beta 2-receptor selectivity. Atenolol was shown to have a 32-fold selectivity in the same tests.