α<sub>1</sub>-Adrenoceptor Antagonists. 6. Structural Optimization of Pyridazinone−Arylpiperazines. Study of the Influence on Affinity and Selectivity of Cyclic Substituents at the Pyridazinone Ring and Alkoxy Groups at the Arylpiperazine Moiety
compounds were tested for their affinity toward alpha(1)- and alpha(2)-AR and toward the 5-HT(1A) receptor. alpha(1)-AR affinity data are in the subnanomolar range, with 3 showing an affinity of 0.052 nM, about 5-fold higher than prazosin. None of the studied compounds was found to be alpha(1)/alpha(2) selective, but 8 showed an interesting 5-HT(1A)/alpha(1) affinity ratio of 119.