In 10 ml of N,N-dimethylformamide was dissolved 1.00 g of 1-(2,4-dimethoxybenzyl)-2,3-dioxopiperazine, and 0.17 g of sodium hydride (60%, oil) was added to the solution, followed by stirring at 50° C. for 30 minutes. Then, the reaction mixture was cooled to room temperature, after which 1.48 g of 1-bromo-3-(4-benzyloxycarbonylamidinophenoxy)propane was added thereto and the resulting mixture was stirred overnight at the same temperature. The solvent was distilled off under reduced pressure and the resulting residue was purified by a silica gel column chromatography (eluent; chloroform:methanol=20:1) to obtain 1.76 g of 4-[3-(4-benzyloxycarbonylamidinophenoxy)propyl]-1-(2,4-dimethoxybenzyl)-2,3-dioxopiperazine as colorless crystals.
