Optimization of Chromeno[2,3‑<i>c</i>]pyrrol-9(2<i>H</i>)‑ones as Highly Potent, Selective, and Orally Bioavailable PDE5 Inhibitors: Structure–Activity Relationship, X‑ray Crystal Structure, and Pharmacodynamic Effect on Pulmonary Arterial Hypertension

To further explore the structure–activity relationship around the chromeno­[2,3-<i>c</i>]­pyrrol-9­(2<i>H</i>)-one scaffold, 19 derivatives as inhibitors against PDE5 were discovered. The most potent inhibitor <b>3</b> has an IC<sub>50</sub> of 0.32 nM with remarkable selectivity and druglike profile. Oral administration of <b>3</b> (1.25 mg/kg) caused comparable therapeutic effects to sildenafil (10.0 mg/kg) against pulmonary arterial hypertension. Further, different binding patterns from sildenafil were revealed in cocrystal structures, which provide structural templates for discovery of highly potent PDE5 inhibitors.