Synthesis and topical antiinflammatory properties of 17,21-bis(acetyloxy)-6beta,9-difluoro-11beta-hydroxypregna-1,4-diene-3,20-dione and related 2-halogenated compounds.

Introduction of a halogen atom at C-2 of steroid 3-ketofluorohydrins, obtained from the corresponding 5alpha,6alpha-epoxides by trans-diaxial opening with hydrofluoric acid, prevents the 6beta-fluorine atom from undergoing rearrangement to the more stable 6alpha configuration when the 5-tert-hydroxyl is split off to yield to yield a conjugated double bond. Two processes were investigated for the synthesis of 17,21-bis(acetyloxy)-6beta-fluoro-1,4,9(11)-triene-3,20-dione (24a) and the related 2-bromo compound 24b starting from the known 21-(acetyloxy)-6beta-fluoro-5alpha,11alpha,17-trihydroxypregnane-3,20-dione (13). Successive reaction with hypobromous acid, epoxidation, and fluorination converted 24a and 24b into the title compound 27a and the analogue 2-bromo compound 27b. In addition, a synthesis of 17,21-bis(acetyloxy)-2-chloro-6beta,9-difluoropregna-1,4-diene-3,20-dione (27c) is reported. The antiinflammatory activity of 17,21-bis-(acetyloxy)-6beta,9-difluoropregna-1,4-diene-3,20-dione (27a) and its 2-halogenated analogues 27b and 27c in comparison with the corresponding 6alpha,9-difluoro epimers was studied. Some 6beta-fluoro compounds displayed high topical antiinflammatory activity without systemic effects.