Guaiacoxypropanolamine derivatives of capsaicin: a new family of beta-adrenoceptor blockers with intrinsic cardiotonic properties.

A series of guaiacoxypropanolamine derivatives of capsaicin was synthesized by replacing the phenolic OH of N-nonanoylvanillamide with epichlorohydrin, followed by cleavaging the obtained epoxide compound with alkylamines. Intravenous injection of these propanolamine derivatives (1 mg/kg) in normotensive Wistar rats induced a transient fall in blood pressure but significantly reduced the heart rate for more than 30 min. These derivatives (10(-8)-10(-6) M) inhibited isoproterenol (10(-10)-10(-5) M)-induced positive chronotropic and inotropic effects in isolated guinea pig atrium. On the other hand, these derivatives (10(-5)-10(-4) M) exhibited a positive cardiotonic effect that is independent of intrinsic sympathomimetic effects. Investigation of the structure-activity relationship of these derivatives revealed that the position of the oxypropanolamine side chain and substituents of the 4-OH position play significant roles in imparting their pharmacological effects. Of the derivatives tested, the most effective one was compound 9. In conclusion, the results obtained from in vitro and in vivo studies suggested that these derivatives and compound 9 may be expected to be beta-adreneoceptor blocking agents with nonadrenergic positive chronotropic and inotropic properties.