Betamethasone-17-valerate (I) was treated with acidic or alkaline solution to investigate its stability in the pharmaceutical preparation. 9α-Fluoro-11β, 17α-dihydroxy-16β-methyl-21-valeroxypregna-1, 4-diene-3, 20-dione (II), a rearrangement product of I, was isolated when I was warmed at 40°C in alkaline medium. Compound II and 9α-fluoro-11β, 17α, 21-trihydroxy-16β-methylpregna-1, 4-diene-3, 20-dione (III), a degradation product of I, were obtained on heating at 100°C. The structure determination of these products was also described.
