This paper reports on the synthesis and pharmacological activity of 6-aryl-4,5-dihydro-3(2H)-pyridazinone derivatives. The compounds exhibit an aggregation inhibiting action on human platelets in vitro and on rat platelets under ex vivo conditions, as well as a hypotensive action on rats. The strongest pharmacological effects were found with dihydropyridazinones, which have a 6-[p-[(chloroalkanoyl)amino]phenyl] substituent, together with a methyl group in the 5-position. The antiaggregation activity of compounds of this type is in vitro up to 16000 times and ex vivo up to 370 times greater than that of acetylsalicylic acid; the hypotensive action is up to 40 times as great as that of the comparative substance dihydralazine.

No abstract

The synthesis and pharmacological activity of new 6-heteroaryl-3-hydrazinopyridazines with antihypertensive action are described. The introduction of pyrrole, pyrazole, imidazole, triazole, tetrazole, thiophene, indole, and carbazole heterocyclic rings into the 6 position of the pyridazine nucleus has been carried out by three different methods of synthesis. The hypotensive action has been examined on normotensive and spontaneously hypertensive rats by comparison with dihydralazine (I). 6-Imidazol-1-yl derivatives have proved particularly active. Of these derivatives, 3-hydrazino-6-(2-methylimidazol-1-yl)pyridazine (7c) achieves 4.9 times the activity of dihydralazine when administered orally to spontaneously hypertensive rats. The LD50 values of 7c and dihydralazine are very similar.

The synthesis of a series of (E)-1-amino-3-[2-(2-isoxazolylethenyl)phenoxyl-2-propanols is described. These compounds were found to have beta- and alpha-adrenergic blocking properties, as well as hypotensive and antihypertensive properties. The beta-adrenoceptor antagonism of all these compounds was more pronounced than their alpha-sympatholytic and hypotensive activity. 3a was 16 times more potent than labetalol in beta-adrenergic receptor blockade and was effective in lowering blood pressure in acute trials on spontaneously hypertensive rats at a dosage of 15 mg/kg. Structure-activity considerations showed that antihypertensive potency was more sensitive to structural variations than beta-adrenoceptor antagonistic activity. However, in general, those compounds having the most potent beta-adrenoceptor blocking activity also lowered blood pressure most effectively.

No abstract