Structure−Activity Relationships of N-Acyl Pyrroloquinolone PDE-5 Inhibitors

The discovery of the potent and selective PDE-5 inhibitory activity of a pyrroloquinolone scaffold prompted us to explore the SAR of its acyl derivatives. During the course of these studies, three structural series were found with K(i) values for PDE-5 in the subnanomolar range. Systematic modification of one of these leads produced a compound with excellent selectivity for PDE-5 over other phosphodiesterases and oral bioavailability of 15% in male rats. This compound also displayed in vivo efficacy in an anesthetized canine model of erection when dosed intravenously.