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 α1-adrenergic and 5-HT(1A)-serotonergic receptor subtypes. They displayed high potency on all the assays and some selectivity for α(1a) and α(1d) subtypes.