[N+:1]([C:4]1[CH:5]=[CH:6][CH:7]=[C:8]2[C:12]=1[NH:11][C:10]([C:13]([O:15]C)=[O:14])=[CH:9]2)([O-:3])=[O:2].[OH-].[Na+].Cl>O1CCCC1.O>[N+:1]([C:4]1[CH:5]=[CH:6][CH:7]=[C:8]2[C:12]=1[NH:11][C:10]([C:13]([OH:15])=[O:14])=[CH:9]2)([O-:3])=[O:2]Methyl 7-nitroindole-2-carboxylate (13 g, 59 mmol) prepared in Preparation 8 was dissolved in a solvent mixture of tetrahydrofuran and water (1:1, 300 ml), and 1N aqueous sodium hydroxide solution (180 ml, 177 mmol) was added thereto. The mixture was stirred for 3 h at room temperature, excess 6N hydrochloric acid solution was added, and the mixture was extracted with ethyl acetate. The extract was washed with saturated sodium chloride solution, dried over anhydrous magnesium sulfate, and filtered. The filtrate was distilled under reduced pressure to give 7-nitro-1H-indole-2-carboxylic acid (12 g, Yield 99%).
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