90.0 g of methyl 1-(1-benzyloxycarbonylpiperidin-4-yl)-1H-indole-6-carboxylate was dissolved in a mixed solution consisting of 760 ml of methanol and 200 ml of tetrahydrofuran. Thereafter, 92 ml of a 5 N sodium hydroxide aqueous solution was added to the reaction solution, and the mixture was then heated to a temperature between 60° C. and 70° C. After completion of the reaction, the reaction solution was cooled, and 65.0 g of ammonium chloride was added thereto, followed by concentration under a reduced pressure. A 5% KHSO4 aqueous solution was added to the residue, so as to adjust pH to be 5 to 6, followed by extraction with ethyl acetate. The organic layer was washed with water and a saturated sodium chloride solution, and then dried over anhydrous magnesium sulfate. After removing the drying agent by filtration, the organic layer was concentrated under a reduced pressure. Thereafter, the residue was solidified, and then collected from a mixed solvent consisting of hexane and t-butylmethyl ether by filtration, so as to obtain 75.6 g of the subject compound.
