Class III antiarrhythmic activity of novel substituted 4-[(methylsulfonyl)amino]benzamides and sulfonamides.

The synthesis and Class III antiarrhythmic activity of a series of 4-[(methylsulfonyl)amino]benzamides and sulfonamides are described. Selected compounds show a potent Class III activity and are devoid of effects on conduction both in vitro (dog Purkinje fibers) and in vivo (anesthetized dogs). Compounds having a 2-aminobenzimidazole group were found to be the most potent, and one compound having this heterocycle (5, WAY-123,398) was selected for further characterization. Compound 5 was shown to have good oral bioavailability and a favorable hemodynamic profile to produce a 3-fold increase of the ventricular fibrillation threshold and to terminate ventricular fibrillation, restoring sinus rhythm in anesthetized dogs. Voltage-clamp studies in isolated myocytes show that 5 is a potent and specific blocker of the delayed rectifier potassium current (IK) at concentrations that cause significant prolongation of action potential duration.