A mixture of 102 mg of (±)-2-(1-naphthylmethylcarbamoyl)-3-phenylpropionic acid and 50 mg of 1,1'-carbonyldiimidazole was added to 5 ml of dichloromethane, and the mixture was stirred for 40 minutes at room temperature. The reaction mixture was added to a solution of 202 mg of L-histidyl-L-leucinal semicarbazone.2p-toluenesulfonic acid salt and 0.09 ml of triethylamine in 3 ml of N,N-dimethylformamide, and the mixture was stirred overnight at room temperature. The reaction mixture was concentrated under reduced pressure, and a 5% aqueous sodium bicarbonate solution was added to the residue. The mixture was extracted with ethyl acetate, dried and concentrated under reduced pressure. The residue was purified by preparative silica gel thin layer chromatography (developing solvent: lower layer of chloroform/methanol/water=8/3/1 by volume) to obtain 24 mg of N-[(±)-2-(1-naphthylmethylcarbamoyl)-3-phenylpropionyl]-L-histidyl-L-leucinal semicarbazone as a white powder.
