2-((3-Methyl-4-(3-benzylaminopropylthio)-2-pyridyl)methylthio)-1H-benzimidazole (2.0 g) was dissolved in dimethylformamide (25 ml) and thereto were added ethyl bromoacetate (0.834 g) and potassium carbonate (0.984 g). The mixture was stirred at 40°-50° C. for 1 hour. The reaction mixture was poured into water and extracted with ethyl acetate. The extract was washed with water, dried and concentrated under reduced pressure. The residue was subjected to column chromatography and eluted with chloroform-methanol to give 2-((3-methyl-4-(3-(N-benzyl-N-ethoxycarbonylmethylamino)propylthio)-2-pyridyl)methylthio)-1H-benzimidazole.
