1.34 g of (S)-6-chloro-N-[1-(4-fluorophenyl)ethyl]-4-(1-methyl-1H-pyrazol-4-yl)pyridine-2-amine synthesized by the same method as in Steps 1 and 2 of Example 4, 423 mg of 2-aminopyrazine, 154 mg of 2-dicyclohexylphosphino-2′,4′,6′-triisopropylbiphenyl, 544 mg of sodium t-butoxide and 74 mg of tris(dibenzylideneacetone)dipalladium were added in turn to 13 ml of degassed toluene, and the mixture was stirred at 100° C. for 1 hour under argon atmosphere. The reaction solution was diluted with ethyl acetate. The solution was washed with water and then dried over magnesium sulfate. The solvent was distilled off under reduced pressure, and the obtained residue was purified by silica gel column chromatography to obtain 1.26 g of (S)—N2-[1-(4-fluorophenyl)ethyl]-4-(1-methyl-1H-pyrazol-4-yl)-N6-(pyrazin-2-yl)pyridine-2,6-diamine as pale yellow powder. Subsequently, 1.0 g of the obtained (S)—N2-[1-(4-fluorophenyl)ethyl]-4-(1-methyl-1H-pyrazol-4-yl)-N6-(pyrazin-2-yl)pyridine-2,6-diamine was dissolved in 1 ml of methanol, and 300 mg of maleic acid was added. The reaction solution was added with 6 ml of ethyl acetate, and stirred at room temperature for 2 hours. The precipitated solid was filtered to obtain 1.1 g of the objective compound as white powder.
