Synthesis, in vitro activities of (2-cyclopropoxyphenyl)piperidine derivatives for alpha 1a and alpha 1d adrenergic receptor inhibitors.

An alpha 1a- and alpha 1d-adrenergic receptor (AR) selective antagonist may be a more efficacious treatment for BPH/LUTS patients and may have fewer side effects than the existing pharmaceuticals. A facile synthesis for a series of (2-cyclopropoxyphenyl)piperidine derivatives has been developed, in which aryl vinyl ether formation and subsequent cyclopropyl formation provide efficient access to key intermediate N-Boc-4-(2-cyclopropoxyphenyl)piperidine. The synthesized (2-cyclopropoxyphenyl)piperidine derivatives display high affinity and selectivity for alpha1a-AR and alpha1d-AR compared to alpha1b-AR and D2 receptor, Ki values for alpha1a-AR are 0.91 nM to 79.0 nM and alpha1d-AR are 2.0 nM to 57 nM; Ki values for alpha1b-AR are 107 nM to 839.8 nM and D2 receptor are 66.2 nM to 187.1 nM. The selectivity ratios of Ki(alpha1b)/Ki(alpha1a) are 11 to 155 fold, Ki(alpha1b)/Ki(alpha1d) are 6 to 171 fold, Ki(D2)/Ki(alpha1a) are 2 to 158 fold, and Ki(D2)/Ki(alpha1d) are 1.2 to 89 fold. Compound 17a shows improved stability in human liver microsome test (t1/2 = 18 minutes).