The 7-(5-azidomethyl-2-oxooxazolidin-3-yl)-3-(2-trifluoromethylphenyl)-2H-isoquinolin-1-one (50.0 mg, 0.116 mmol) obtained in Example 1-30 was dissolved in tetrahydrofuran (387 μl). Thereafter, triphenylphosphine (33.6 mg, 0.128 mmol) and water (20.9 μl) were added to the obtained solution, and the obtained mixture was then stirred at 40° C. for 14 hours. Thereafter, 1 N hydrochloric acid (0.5 ml) was added to the reaction solution, followed by washing with ethyl acetate. A 1 N sodium hydroxide aqueous solution (1.0 ml) was added to the residual water layer, followed by extraction with ethyl acetate. The extract was washed with a saturated saline solution, and was then dried over anhydrous sodium sulfate, followed by concentration under reduced pressure. The obtained residue was purified by column chromatography using Bond Elut (registered trademark) NH2 (Varian; 1g), so as to obtain 7-(5-aminomethyl-2-oxooxazolidin-3-yl)-3-(2-trifluoromethylphenyl)-2H-isoquinolin-1-one (45.8 mg; yield: 98%) in the form of a colorless foaming substance.
