SCH 351591

SCH 351591 is a **potent and highly selective small molecule inhibitor of phosphodiesterase 4 (PDE4) isoenzymes**, with approximately equal specificity for PDE4 subtypes A, B, C, and D. It was investigated primarily as a potential therapeutic for asthma and chronic obstructive pulmonary disease (COPD). Preclinical toxicology data reveal dose-limiting toxicities in multiple species, including arteriopathy, myocardial inflammation, gastrointestinal effects, and reproductive toxicity. Its major active metabolite is SCH 365351. Development was led by Schering-Plough and focused on oral administration in animal studies[1][2][3][5].