Synthesis of Steroid 'Antedrugs' for Evaluation as Safe Treatments for Asthma: Practical Synthesis of the Inhaled Steroid GR250495X

The inhaled steroid antedrug candidate GR250495X was discovered at Glaxo Wellcome for the treatment of asthma. In order to fully evaluate the clinical potential of GR250495X an efficient synthesis of the drug candidate was required. Herein is described the development of an efficient and robust synthesis in which the key step is the coupling of 2(S)-mercapto-γ-butyrolactone (19) with the steroid acid (15).