Structure−Activity Studies for a Novel Series of Bicyclic Substituted Hexahydrobenz[e]isoindole α1A Adrenoceptor Antagonists as Potential Agents for the Symptomatic Treatment of Benign Prostatic Hyperplasia

In search of a uroselective α1A subtype selective antagonist, a novel series of 6-OMe hexahydrobenz[e]isoindoles attached to a bicyclic heterocyclic moiety via a two-carbon linker was synthesized. It was found that in contrast to the previously described series of tricyclic heterocycles,1 this bicyclic series has very specific requirements for the heterocyclic attachments. The most important structural features contributing to the α1A/α1B selectivity of these compounds were identified. In vitro functional assays for the α1 adrenoceptor subtypes were used to further characterize the most selective compounds, and in vivo models of vascular vs prostatic tone were used to assess uroselectivity. Compound 48 showed the highest degree of selectivity in the radioligand binding assays (56-fold), in the in vitro functional tests (80-fold), and for in vivo prostate selectivity (960-fold).