Search for α1-adrenoceptor subtypes selective antagonists: Design, synthesis and biological activity of cystazosin, an antagonist

Two novel quinazolines (2 and 3) related to both prazosin and its open analogue 1 were synthesized, and their biological profile at α1-adrenoceptor subtypes was assessed by functional assays in rat isolated tissues, namely prostatic vas deferens (α1A), spleen (α1B) and aorta (α1D). Furthermore, the binding profile of 3 was assessed at native α2 and D2 receptors, and cloned human 5-HT1A receptors, in comparison to prazosin, (+)-cyclazosin, 1 and BMY 7383. It turned out that the cystamine-bearing quinazoline 3 (cystazosin) has a reversed affinity profile relative to (+)-cyclazosin owing to a higher affinity for α1D-adrenoceptors and a significantly lower affinity for the α1A and α1B subtypes. Furthermore, in comparison to BMY 7378, cystazosin (3) displays a much better specificity profile since it has lower affinity for D2 and 5-HT1A receptors.