To 3.8 g of 1-benzyl-6-chloro-2-[1-(3-chloro-propyl)indol-5-ylaminocarbonyl]benzimidazole was added 100 mg of dimethylformamide, further added 1.4 g of 1H-1,2,3,4-tetrazol, 2.2 g of potassium carbonate and 7.2 g of sodium iodide, the mixture was heated and stirred at 100° C. for 2 days. Water was added to the reaction mixture, and extracted with ethyl acetate, the extract was washed with water and an aqueous solution saturated with sodium chloride. The washed extract was dried with anhydrous magnesium sulfate, and the solvent was removed by distillation under reduced pressure. The residue thus obtained was subjected to a silica gel column chromatography (eluent: ethyl acetate/n-hexane=1/1), after separation of isomers, there were obtained 1.1 g of 1-benzyl-6-chloro-2-{1-[3-(1,2,3,4-tetrazol-1-yl)propyl]indol-5-ylaminocarbonyl}benzimidazole (A) as in form of colorless needle crystals by recrystallization from ethyl acetate-n-hexane, and 0.9 g of 1-benzyl-6-chloro-2-{1-[3-(1,2,3,4-tetrazol-2-yl)-propyl]indol-5-ylaminocarbonyl}benzimidazole (B) as in the form of pale yellow needle crystals by recrystallization from dichloromethane-n-hexane.
