In 20 ml of methanol was dissolved 300 mg of (S)-3-[3-(4-amidinobenzoylamino)propyl]-4-benzyloxycarbonylaminoacetyl-2-oxopiperazine-1-acetic acid produced in Reference Example 21. To the solution was added 120 mg of 10% Pd--C, and the mixture was stirred for one hour at room temperature in hydrogen streams. The catalyst was filtered off, and the filtrate was concentrated under reduced pressure to give an oily product, which was dissolved in 5 ml of dimethylformamide. To the solution was added 5 ml of activated-ester solution in dimethylformamide which was prepared from 94 mg of N-hydroxysuccinimide and 173 mg of 4-(2-t-butoxycarbonylaminoethyl)benzoic acid in the presence of 167 mg of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride. The mixture was stirred for two hours at room temperature. The reaction mixture was concentrated to give an oily product, which was dissolved in 7 ml of trifluoroacetic acid. The solution was stirred for one hour at room temperature. The reaction mixture was concentrated under reduced pressure to give a crude product, which was purified by means of a CHP-20 column (eluted with 10% acetonitrile/water) to afford 110 mg of the titled compound as a colorless amorphous powdery product.
