N,N′-carbonyldiimidazole (45.8 g) was added at a time to a solution of 45.0 g of 6-carboxy-1-(2-chlorobenzyl)-2-methylbenzimidazole in 950 ml of N,N-dimethylformamide, and the mixture was stirred at room temperature for 1 hour. Subsequently, 47.1 g of benzenesulfonamide and 35.0 g of diazabicycloundecene were added thereto, and the mixture was stirred at 100° C. for 70 hours. The reaction solution was cooled, and the solvent was distilled off under reduced pressure. To the residue were added 300 ml of water and 200 ml of methanol. Further, 60.7 g of 35% hydrochloric acid were added thereto to adjust the solution to a pH of 5.5. The crystals precipitated were separated through filtration, washed with 200 ml of a mixed solution of methanol and water (at a ratio of 1:1), and dried to obtain 38.4 g of 6-benzenesulfonylcarbamoyl-1-(2-chlorobenzyl)-2-methylbenzimidazole. Water was added to the filtrate. The crystals precipitated were separated through filtration, washed with water, and dried. The amount of the crystals was 13.3 g. The crystals were combined, and were dissolved by being heated with the addition of 3300 ml of acetone and 900 ml of water. From this solution, 200 ml of the solvent were distilled off while being heated, and the residue was cooled. The crystals precipitated were separated through filtration, and were dried to give 33.8 g of 6-benzenesulfonylcarbamoyl-1-(2-chlorobenzyl)-2-methylbenzimidazole (163).
