[3-Hydrazinepyridazine derivatives. III. Synthesis and anti-hypertensive activity of new 3-(2-acylhydrazine)-pyridazine-6-alkylamino substitutes].

The synthesis of 2-(6-dialkylamino-3-pyridazinyl)hydrazinecarboxylates (II) and hydrazides (V) from the corresponding 3-chloro-6-dialkylaminopyridazines (I) is described. The 6-substituted derivatives of 2,3-dihydro-1,2,4-triazolo[4,3-b]pyridazine-3-ones (III) and 1,2,4-triazolo[4,3-b)pyridazines (VI) were obtained by thermal cyclization of (II) and (V), respectively. The new acyl derivatives were evaluated together with todralazine and budralazine as antihypertensive agents in comparison with propildazine and hydralazine. The ethoxycarbonyl compound [(II g), ISF 2469] exhibits good antihypertensive activity particularly via oral administration. Its interesting pharmacodynamic properties, including slow onset and long-lasting action, qualify it for further pharmacological and clinical studies.