7.13 g of N,N'-dibenzyloxycarbonyl histidine, 3.00 g of 4-phenylpiperazine and 16.1 g of N-hydroxybenzotriazole were dissolved in 100 ml of tetrahydrofuran, and to the mixture was added 3.84 g of DCC (dicyclohexylcarbodiimide), and the whole was stirred at a room temperature for three hours. An insoluble matter was filtered off, the filtrate was concentrated under a reduced pressure, and to the concentrate was added 200 ml of ethyl acetate to reform crystals, which were then filtered off. The filtrate was sequentially washed with 20% potassium carbonate aqueous solution and saturated sodium chloride aqueous solution, dried over magnesium sulfate, and concentrated under a reduced pressure. The resulting residue was dissolved in 60 ml of methanol, and after an addition of a 10% ammonium-methanol solution and stirring at a room temperature for 30 minutes, the solution was concentrated under a reduced pressure to obtain a residue, which was then subjected to silica gel chromatography and eluted with chloroform/methanol (50:1 to 10:1) to obtain 6.61 g of the title compound in a colorless amorphous form.
