A mixture of 446 mg (2.14 mmoles) of 6-guanidinohexanamide hydrochloride, 750 mg (2.57 mmoles) of N-[4-(3-aminopropyl)aminobutyl]-2,2-dihydroxyethanamide dihydrochloride, 283 mg (2.14 mmoles) of glutaric acid and 0.45 ml of water was heated at 60° C. for 24 hours. After completion of the reaction, 5 ml of water was added to the reaction mixture and the resulting mixture was purified in a manner similar to that in Example 1, using CM-Sephadex® C-25 (Na-type) and Sephadex® LH-20 to obtain 459 mg (44% yield) of a white powder of N-[4-(3-aminopropyl)aminobutyl]-2-(6-guanidinohexanamido)-2-hydroxyethanamide trihydrochloride.
