To a 5L reactor were added 80 g of (S)-4-ethyl-4-hydroxy-1H-pyrano[3',4':6,7]indolizino[1,2-b]quinoline-3,14(4H,12H)-dione (camptothecin), 840 g of glacial acetic acid, and 368 g of concentrated sulfuric acid, and mechanical stirring was initiated until complete dissolution. Subsequently, 80 g of propionaldehyde was slowly added and 102 g of hydrogen peroxide was added dropwise. The reaction temperature was controlled in the range of -5 to 5°C for 10 minutes. After completion of the reaction, 10 kg of pure water was added to the system and stirring was continued for 2 hours. The precipitate was collected by filtration to give 72.5 g of (S)-4,11-diethyl-4-hydroxy-1H-pyrano[3',4':6,7]indolo[1,2-b]quinoline-3,14(4H,12H)-dione (7-ethylcamptothecin) in 95.4% yield.
