This compound, with CAS number 73205-13-7, is a specified impurity of Fluticasone Propionate, a potent synthetic glucocorticoid corticosteroid. Its chemical name is [(6S,9R,11S,13S,16R,17R)-6,9-difluoro-11-hydroxy-10,13,16-trimethyl-17-methylsulfanylcarbonyl-3-oxo-6,7,8,11,12,14,15,16-octahydrocyclopenta[a]phenanthren-17-yl] propanoate. It is structurally related to the active pharmaceutical ingredient (API) and is formed during the synthesis or storage of Fluticasone Propionate. As a pharmaceutical impurity, its primary and critical application is in the quality control and regulatory compliance of Fluticasone Propionate drug products. It is used as a reference standard (impurity standard) in analytical methods, such as high-performance liquid chromatography (HPLC), to identify, quantify, and monitor this specific impurity to ensure the drug's purity, safety, and efficacy. Fluticasone Propionate itself is a key API used in inhaled medications for the treatment of asthma and allergic rhinitis. The control of this impurity is mandated by pharmacopoeial standards (e.g., USP, EP) and regulatory guidelines (e.g., ICH Q3A/B). Its availability as a characterized standard is essential for pharmaceutical manufacturers to develop validated analytical procedures and to meet the stringent requirements for drug approval and batch release.