10-Aminocamptothecin (50 mg, 0.138 m-mol) is dissolved in a 10% aqueous solution of sulfuric acid (5 ml). To this solution in a salted ice bath is added dropwise slowly an aqueous solution of sodium nitrite (9.5 mg, 0.138 m-mol) with stirring. After the addition of sodium nitrite, the mixture is further stirred for 10 minutes in a salted ice bath. To the reaction mixture is added conc. sulfuric acid (1 ml), and the whole is boiled under reflux for 2 hours. The reaction mixture is diluted with ice water (200 ml) and chloroform (200 ml) is added. The mixture is shaken in a separating funnel and the resultant emulsion is filtered through celite. The chloroform phase containing camptothecin formed as by-product by side reactions is dried over magnesium sulfate, filtered and evaporated until dryness under reduced pressure whereby camptothecin (8 mg) is recovered. On the other hand, a solid on the celite, which is insoluble in chloroform-water, is taken up in 20% MeOH-CHCl3 (200 ml) and the solution is evaporated until dryness under reduced pressure whereby 28 mg (yield: 66.5% ) of the title compound is obtained as light yellow crystals. M.P. (with decomp.) 270°-272° C. (from pyridine-methanol)
