Optimization of Chromeno[2,3- c]pyrrol-9(2 H)-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- c]pyrrol-9(2 H)-one scaffold, 19 derivatives as inhibitors against PDE5 were discovered. The most potent inhibitor 3 has an IC₅₀ of 0.32 nM with remarkable selectivity and druglike profile. Oral administration of 3 (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.