D-homoannulation of 17alpha,21-dihydroxy-20-keto steroids (corticosteroids)

Synthetic corticosteroids are widely used as anti-inflammatory agents. Mechanisms of their degradation continue to be studied. D-ring homoannulation is a well-known metabolic pathway for steroids in vivo. The rearrangement with aluminium trichloride of the commercial anti-inflammatory drugs hydrocortisone, cortisone and dexamethasone is here presented. The structures of the corresponding 17a-keto-17-hydroxy-D-homosteroids are established by mono- and two-dimensional NMR analysis. Inversion of the alpha-configuration of C-16 is observed in the Lewis acid assisted D-homoannulation of dexamethasone.