To 2-((4-cyanophenyl)amino)-4-(propylamino)pyrimidine-5-carboxylic acid (C5, 297 mg), 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride (383 mg) and 1-hydroxybenzotriazole monohydrate (270 mg), N,N-dimethylformamide (7.5 mL) was added at room temperature, and the mixture was stirred at 50° C. for 1 hour and 20 minutes. The reaction mixture was cooled to room temperature, and then N,N-diisopropylethylamine (697 μL) and (S)-tert-butyl (1-((3-aminophenyl)amino)-1-oxopropan-2-yl)(methyl)carbamate (B9, 323 mg) were added to the mixture at room temperature, and the mixture was stirred at the same temperature for 30 minutes, and then further stirred at 50° C. for 1 hour and 30 minutes. The reaction mixture was cooled to room temperature, and then saturated aqueous sodium hydrogencarbonate and ethyl acetate were added to the mixture. The organic layer was separated, washed successively with water and saturated aqueous sodium chloride, and then dried over anhydrous sodium sulfate, and the solvent was evaporated under reduced pressure. The obtained residue was purified by silica gel column chromatography (eluent, 40 to 10% hexane in ethyl acetate) to obtain (S)-tert-butyl (1-((3-(2-((4-cyanophenyl)amino)-4-(propylamino)pyrimidine-5-carboxamido)phenyl)amino)-1-oxopropan-2-yl)(methyl)carbamate (C8, 325 mg).
