2-Butyl-3-oxo-2,3,5,6,7,8-hexahydroisoquinoline-4-carboxylic acid (4-501-05) (5 mg, 0.02 mmol) was dissolved in toluene (1 mL), and to the reaction mixture were added thionyl chloride (4.4 μL, 0.06 mmol) and catalytic amount of DMF, and the reaction mixture was reacted at 75° C. for 30 min. After concentration of the reaction mixture under reduced pressure, the residue was dissolved in methylene chloride (1 mL), and then benzylamine (6.2 μL, 0.06 mmol) was added to the reaction mixture, and the reaction mixture was stirred at room temperature for 10 min. To the reaction mixture was added diluted hydrochloric acid (1 mol/L, 3 mL), and the reaction mixture was extracted with ethyl acetate (8 mL), washed with brine (4 mL), dried over anhydrous magnesium sulfate, and evaporated under reduced pressure. The obtained residue was purified by silica gel column chromatography (toluene/ethyl acetate) to give 2-butyl-3-oxo-2,3,5,6,7,8-hexahydroisoquinoline-4-carboxylic acid benzylamide (4-501) (5 mg, 74%) as a white crystal.
