N-Arylpiperazinyl-N‘-propylamino Derivatives of Heteroaryl Amides as Functional Uroselective α1-Adrenoceptor Antagonists

Novel arylpiperazines were identified as α1-adrenoceptor (AR) subtype-selective antagonists by functional in vitro screening. 3-[4-(ortho-Substituted phenyl)piperazin-1-yl]propylamines were derivatized with N,N-dimethyl anthranilamides, nicotinamides, as well as carboxamides of quinoline, 1,8-naphthyridine, pyrazolo[3,4-b]pyridine, isoxazolo[3,4-b]pyridine, imidazo[4,5-b]pyridine, and pyrazolo[1,5-a]pyrimidines. Strips of rabbit bladder neck were employed as a predictive assay for antagonism in the human lower tract. Rings of rat aorta were used as a “negative screen” for the test antagonists. Binding to α1-ARs was relatively sensitive to size and electronic features of the arylpiperazine portion of the antagonists and permissive to these features on the heteroaryl carboxamide side. These structure−affinity findings were exploited to produce nicotinamides (e.g. 13ii and 25x) and pyrazolo[3,4-b]pyridines (e.g. 37f and 37y) ligands with nanomolar affinity at the α1-AR subtype prevalent in the human lower urinary tract (pA 2 values: 8.8, 10.7, 9.3, and 9.9, respectively) and displaying 2−3 orders of magnitude selectivity over the α1D-AR.