Novel adrenoceptor antagonists with a tricyclic pyrrolodipyridazine skeleton

A still unknown tricyclic heterocyclic system (5) was synthesized from 6-hy droxy-2-methylpyridazin-3-one and its structure identified as 2,8-dichloro- 6-methylpyrrolo[1,2-b:3,4-d']dipyridazin-5(6H)-one by spectroscopic investi gations. Selective condensation of 5 with 2-[4-(2-substituted-phenyl)pipera zin-1-yl]ethylamine gave the 2-arylpiperazinylethylamino-8-chloro derivativ es 6a-c, which were investigated in binding studies toward the three alpha( 1)-adrenergic and 5-HT1A-serotonergic receptor subtypes. They displayed hig h potency on all the assays and some selectivity for alpha(1a), and old sub types.