To a suspension of 1-(4-chlorobenzoyl)-N-hydroxy-5-methoxy-2-methyl-1H-indole-3-methanamine (500 mg, 1.45 mmol) in 30 ml of 1,4-dioxane and 15 ml of water at 0° C. is added sodium isocyanate (104 mg, 1.59 mmol) followed by 1.59 ml (1.59 mmol) of 1N hydrochloric acid. The reaction mixture is diluted with ethyl acetate and washed once with water, and finally with a saturated solution of sodium chloride. It is further dried over magnesium sulfate, filtered, and concentrated in vacuo. The crude residue is recrystallized from methylene chloride and dried to give 300 mg (53%) of pure N-(aminocarbonyl)-1-(4-chlorobenzoyl)-N-hydroxy-5-methoxy-2-methyl-1H-indole-3-methanamine (53%); mp 151.5°-154° C. dec.
