Sodium Hydroxide → 1-phenyl-1H-pyrazole-4-carboxylic acid

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1-Phenyl-1H-pyrazole-4-carboxylic acid ethyl ester (4.1 g) synthesized in Reference Example 16 was dissolved in methanol (40 mL) and tetrahydrofuran (40 mL), aqueous sodium hydroxide solution (1 mol/L, 40 mL) was added, and the mixture was stirred at 60° C. for one hour. The reaction mixture was concentrated under reduced pressure, aqueous hydrochloric acid solution (1 mol/L, 50 mL) was added, and the precipitated solid was filtrated. The solid was dissolved in ethyl acetate, and dried over anhydrous sodium sulfate. The solvent was evaporated under reduced pressure to give 1-phenyl-1H-pyrazole-4-carboxylic acid (2.5 g) as a white solid. This carboxylic acid (8.72 g) and 2-{[4-(2-aminoethyl)-1,3-thiazol-2-yl]thio}-2-methylpropionic acid tert-butyl ester (14 g) synthesized in Example 7 were dissolved in N,N-dimethylformamide (225 mL), N-(3-dimethylaminopropyl)-N′-ethylcarbodiimide (EDC) hydrochloride (10.65 g) and 1-hydroxybenztriazole (HOBt) monohydrate (10.62 g) were successively added thereto, and the mixture was stirred at room temperature for 6 hr. Water was added to the reaction mixture, and the mixture was extracted with ethyl acetate. The organic layer was washed with saturated brine and dried over anhydrous sodium sulfate. The solvent was evaporated under reduced pressure, and the residue was purified by silica gel chromatography (elution solvent; hexane:ethyl acetate=1:1) to give the title compound (16.2 g) as a white solid.

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