To the obtained tert-butyl 2-(4-fluoroanilino)-4-(1-methyl-1H-indol-5-yl)benzoate were added dioxane 1.5 mL, methanol 1.5 mL and 2.0 mol/L sodium hydroxide aqueous solution 0.29 mL, and it was stirred at 50° C. for 2 hours. After the reaction mixture was cooled to room temperature, 2.0 mol/L sodium hydroxide aqueous solution 0.20 mL was added to it, and it was stirred at 55° C. for 1 hour and 30 minutes. Subsequently, 2.0 mol/L sodium hydroxide aqueous solution 0.29 mL was added, it was stirred at 55° C. for 1 hour and 20 minutes, 2.0 mol/L sodium hydroxide aqueous solution 0.29 mL was added, it was stirred at 55° C. for 1 hour, 2.0 mol/L sodium hydroxide aqueous solution 0.29 mL was added, and it was stirred at 55° C. for 1 hour. After the reaction mixture was cooled to room temperature, toluene and water were added to it. The water layer was separated and collected, it was adjusted to pH3.4 with 1.0 mol/L hydrochloric acid after washing with toluene, and ethyl acetate was added to it. The organic layer was separated and collected,dried over anhydrous magnesium sulfate after washing with saturated sodium chloride aqueous solution, and the solvent was removed under reduced pressure. Diisopropyl ether was added to the obtained residue, solid matter was filtrated to give 2-(4-fluoroanilino)-4-(1-methyl-1H-indol-5-yl)benzoic acid 37 mg of a pale yellow solid.
