To a stirred solution of methyl 4-chloro-2-[(3,5-dichloropyridin-2-yl)amino]-1-(4-hydroxybutyl)-1H-benzimidazole-7-carboxylate (Reference example 165, 2.45 g, 5.52 mmol) and triethylamine (1.92 mL, 13.8 mmol) in tetrahydrofuran (30 mL) was added methanesulfonyl chloride (513 μL, 6.62 mol) at 0° C. After 15 min, the reaction mixture was diluted with ethyl acetate, washed with brine, dried over sodium sulfate, filtered, and concentrated in vacuo. The residue was dissolved in N,N-dimethylformamide (55 mL) and potassium carbonate (2.29 g, 16.6 mmol) was added. After being stirred for 1 h at 80° C., the reaction mixture was diluted with ethyl acetate, washed with water and brine, dried over sodium sulfate, filtered and concentrated in vacuo. The resulting solid was washed with diisopropyl ether to give the title compound as a colorless solid (2.24 g, 5.26 mmol, 95%).
