Ammonium formate (6 mg) and 10% Pd/C (6 mg) were added to an ethyl acetate/MeOH (1 ml/1 ml) solution containing benzyl 4-((5-cyano-3-fluoro-6-((5-methylpyridin-3-yl)amino)pyridin-2-yl)amino)-3-(1,3-dioxoisoindolin-2-yl)piperidin-1-carboxylate (37 mg) obtained in the 1st step in a nitrogen atmosphere, followed by heating and stirring at 70° C. for 1 hour. Next, ammonium formate (30 mg) and 10% Pd/C (30 mg) were added to the solution, followed by heating and stirring at 70° C. for 1 hour. The reaction solution was cooled to room temperature and insoluble matter was removed by filtration through Celite. Filter cake was washed with ethyl acetate. The resulting filtrate was mixed with wash liquid. The obtained organic layers were washed with saturated saline and dried over anhydrous sodium sulfate. The solvent was distilled away under reduced pressure. A white solid of 6-((3-(1,3-dioxoisoindolin-2-yl)piperidin-4-yl)amino)-5-fluoro-2-((5-methylpyridin-3-yl)amino)nicotinonitrile (15 mg) was thus obtained.
