Boc-Phe-OH (4 g, 15 mmole), H-Arg-OBzl.TosOH (8.9 g, 15 mmole) and HOBt (2.1 g, 15.75 mmole) were dissolved in DMF (25 ml), and WSCI (12.9 ml, 15.75 mmole) was added dropwise thereto while cooling, and the thus-obtained mixture (pH=4) was stirred overnight. To the reaction solution, AcOEt (300 ml) was added thereto, and the solution was washed with 1N HCl, water and 5% NaHCO3 and water, in order, and dried with Na2SO4 . AcOEt was distilled off under reduced pressure, and the thus-obtained residue was treated with ethyl acetate, ether, and n-hexane to give an oily substance. The substance was obtained by decantation and treated with ethyl acetate and hexane to give precipitates of the object product (6.89 g, 60%).
