Design and Synthesis of Novel α1a Adrenoceptor-Selective Dihydropyridine Antagonists for the Treatment of Benign Prostatic Hyperplasia

We report the synthesis and evaluation of novel α1a adrenoceptor subtype-selective antagonists. Systematic modification of the lipophilic 4,4-diphenylpiperidinyl moiety of the dihydropyridine derivatives 1 and 2 provided several highly selective and potent α1a antagonists. From this series, we identified the 4-(methoxycarbonyl)-4-phenylpiperidine analogue SNAP 5540 (−) [(−)-63] for further characterization. When examined in an isolated human prostate tissue assay, this compound was found to have a Ki of 2.8 nM, in agreement with the cloned human receptor binding data (Ki = 2.42 nM). Further evaluation of the compound in isolated dog prostate tissue showed a Ki of 3.6 nM and confirmed it to be a potent antagonist (Kb = 1.6 nM). In vivo, this compound effectively blocked the phenylephrine-stimulated increase in intraurethral pressure (IUP) in mongrel dogs, at doses which did not significantly affect the arterial pressure (diastolic blood pressure, DBP), with a DBP Kb/IUP Kb ratio of 16. In addition, (−)-63 ...