Methanesulfonic acid (250 μL) was added to a solution of 6-{[4-(cyclopropylsulfanyl)phenyl](hydroxy)methyl}-3-(trifluoromethyl)pyridin-2(1H)-one (40 mg) in cyclopentanol (500 μL), and the mixture was stirred at 100° C. for six hours. Water was added to the reaction solution, followed by extraction with ethyl acetate. The organic layer was dried over magnesium sulfate, after which the solvent was evaporated under reduced pressure. The residue was purified by preparative HPLC (Waters Sunfire 19×150 mm 5 μm, rate: 20 mL/min, eluent: A=acetonitrile, B=0.1% trifluoroacetic acid solution, gradient: 10 to 90%) to give the title compound as a colorless amorphous (25 mg, 52%).
