To a suspension of 2-{[1-(cyclopropylmethyl)-2-(2,2-dimethylpropyl)-1H-benzimidazol-5-yl]sulfonyl}-2-methylpropanoic acid (Step H, 200 mg, 0.51 mmol) and di-tert-butyl dicarbonate (145 mg, 0.66 mmol) in acetonitrile (3 mL) were added ammonium bicarbonate (48 mg, 0.61 mmol) and pyridine (48 mg, 0.61 mmol) at room temperature. The mixture was stirred at room temperature for 20 h and concentrated under reduced pressure. The residue was dissolved in water (30 mL) and dichloromethane (30 mL). The aqueous layer was separated and extracted with dichloromethane (30 mL). The combined organic layers were dried over magnesium sulfate and concentrated under reduced pressure. The residue was purified by column chromatography on silica gel (hexane:ethyl acetate=1:3 as eluent) to afford the title compound (200 g, quant.) as a white solid.
