N-[(2R,3R)-3-Hydroxybutan-2-yl]-5-(3-{[(2S)-1-methoxypropan-2-yl]oxy}-5-[(tripropan-2-ylsilyl)oxy]phenyl)-1H-pyrrole-2-carboxamide (722 mg, 1.39 mmol) synthesized in Example (109a) was dissolved in tetrahydrofuran (30 mL), and anhydrous methanesulfonic acid (430 mg, 2.47 mmol) and triethylamine (1.20 mL, 8.61 mmol) were added, and stirring was carried out at 50° C. overnight under nitrogen atmosphere. The reaction solution was brought back to room temperature, and a saturated aqueous ammonium chloride solution (50 mL) was added, followed by extraction with methylene chloride (50 mL). The organic layer was washed with saturated brine, and subsequently dried over anhydrous magnesium sulfate. The solvent was distilled off under reduced pressure, and the resulting residue was purified using silica gel column chromatography (elution solvent: ethyl acetate/hexane=40%-70%) to afford the desired compound (700 mg, yield 100%) as a yellow liquid.
