To a suspension of 4-(propylamino)-2-((2-(pyridin-4-yl)ethyl)amino)pyrimidine-5-carboxylic acid (A3, 301 mg) in N,N-dimethylformamide (3 mL), 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride (211 mg) and 1-hydroxybenzotriazole monohydrate (162 mg) were added at room temperature, and the mixture was stirred at the same temperature for 2 hours. To the reaction mixture, a solution of N,N-diisopropylethylamine (511 μL) and tert-butyl (2-((3-aminophenyl)amino)-2-oxoethyl)carbamate (B1, 292 mg) in N,N-dimethylformamide (2 mL) was added at room temperature, and the mixture was stirred at the same temperature for 5 hours. To the reaction mixture, saturated aqueous sodium chloride and ethyl acetate were added. The organic layer was separated, washed with saturated aqueous sodium chloride, and then dried over anhydrous magnesium sulfate, and the solvent was evaporated under reduced pressure. The obtained residue was purified by silica gel column chromatography (eluent, 100 to 93% ethyl acetate in methanol) to obtain oily tert-butyl (2-oxo-2-((3-(4-(propylamino)-2-((2-(pyridin-4-yl)ethyl)amino)pyrimidine-5-carboxamido)phenyl)amino)ethyl)carbamate (B2, 437 mg).
