A mixture of 5-{[(1R,2S)-2-(1,3-dioxo-1,3-dihydro-2H-isoindol-2-yl)cyclopentyl]oxy}-6-ethyl-3-({4-[4-(4-methylpiperazin-1-yl)piperidin-1-yl]phenyl}amino)pyrazine-2-carboxamide (322 mg), hydrazine monohydrate (99 mg), tetrahydrofuran (6.44 mL), and ethanol (6.44 mL) was stirred at 80° C. overnight. The insoluble matter was separated by filtration and the filtrate was concentrated under reduced pressure. The obtained residue was purified by silica gel column chromatography (NH2 type: eluent; chloroform:methanol=99:1-97:3) to obtain 5-{[(1R,2S)-2-aminocyclopentyl]oxy}-6-ethyl-3-({4-[4-(4-methylpiperazin-1-yl)piperidin-1-yl]phenyl}amino)pyrazine-2-carboxamide (117 mg) as a pale yellow solid.
