50.5 g of 2-((8S,10S,13S,14S,16R,17S)-16,17-dihydroxy-10,13-dimethyl-3-oxo-6,7,8,10,12,13,14,15,16,17-decahydro-3H-cyclopenta[a]phenanthren-17-yl)-2-oxoethyl acetate was dissolved in 1500 ml of acetone, 70 ml of 5% perchloric acid was added, the temperature was lowered to 0°C with stirring, and 45 g of N-bromosuccinimide was added and stirred After the reaction was completed, 50 ml of 20% sodium sulfite aqueous solution was added, the acetone was concentrated, the water was separated, filtered, and dried to obtain 62 g of Prednisone Impurity 13 (9α-bromo-11β,16α,17α,21-tetrahydroxypregnane-1,4-diene-3,20-dione-21-acetate).
