19.7 g of N-(tert-butoxycarbonyl)tyrosine, 12.5 g of N-phenylpiperazine and 16.1 g of N-hydroxybenzotriazole were dissolved in 100 ml of tetrahydrofuran, and to the solution was added dropwise a solution of 18.7 g of DCC in 50 ml of tetrahydrofuran for 20 minutes with ice cooling, and the mixture was stirred for one hour. The reaction mixture was filtered to remove insoluble matter, which was then washed with 300 ml of ethyl acetate, and the filtrates were combined and concentrated under a reduced pressure. The resulting residue was dissolved in 500 ml of ethyl acetate, and the solution was washed three times with saturated sodium bicarbonate aqueous solution and once with saturated sodium chloride aqueous solution, dried over magnesium sulfate, and concentrated under a reduced pressure. The resulting residue was applied to a silica gel column and eluted with ethyl acetate/hexane (1:2 to 1:1) to collect desired fractions, which were then combined and concentrated under a reduced pressure. Resulting residue was dissolved in 100 ml of ethyl acetate, and the solution was allowed to stand overnight in a refrigerator and then filtered to remove insoluble matter. The filtrate was concentrated under a reduced pressure, subjected to azeatropic distillation with benzene and dried under a reduced pressure to obtain 40.0 g of the title compound in a colorless amorphous form.
