Synthesis and renal vasodilator activity of 2-chlorodopamine and N-substituted derivatives

A four-step synthesis of 2-chlorodopamine (2b) is presented as well as methods for the syntheses of the N-methyl, ethyl, and n-propyl analogues (2c-e). Compounds 2b and 2c were essentially equipotent to dopamine for increasing renal blood flow in anesthetized dogs that had been treated with the alpha-adrenergic antagonist phenoxybenzamine. The increases in renal blood flow were blocked by the DA1 antagonist (R)-(+)-8-chloro-2,3,4,5-tetrahydro-3-methyl-5-phenyl-1H-3-benzazepine. Compounds 2d and 2e were significantly less potent than dopamine in the same model; the increases in renal blood flow were attenuated by propranolol and blocked by a combination of propranolol and (R)-(+)-8-chloro-2,3,4,5-tetrahydro-3-methyl-5-phenyl-1H-3-benzazepine. The significance of an o-chloro substituent on dopamine analogues for the activation of the DA1 receptor is briefly discussed.