Novel adrenoceptor antagonists with a tricyclic pyrrolodipyridazine skeleton.

A still unknown tricyclic heterocyclic system (5) was synthesized from 6-hydroxy-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 investigations. Selective condensation of 5 with 2-[4-(2-substituted-phenyl)piperazin-1-yl]ethylamine gave the 2-arylpiperazinylethylamino-8-chloro derivatives 6a-c, which were investigated in binding studies toward the three alpha1-adrenergic and 5-HT1A-serotonergic receptor subtypes. They displayed high potency on all the assays and some selectivity for alpha1a and alpha1d subtypes.