254 mg of 3-amino-5-(4-fluorophenyl)-4-(4-pyridyl)pyrazole was suspended in 20 ml of tetrahydrofuran, and 306 mg of triethylamine was added thereto. Then, 5 ml of a tetrahydrofuran solution containing 464 mg of phenylacetyl chloride was added dropwise thereto, followed by stirring at room temperature for 3 hours. After the addition of water, the reaction mixture was extracted with ethyl acetate. After the organic layer was washed with water and dried over anhydrous magnesium sulfate, the solvent was distilled off under reduced pressure. After the resulting residue was dissolved in a mixture composed of 20 ml of methanol and 2 ml of a 2 mol/L sodium hydroxide solution and stirred for 1 hour, the precipitated crystals were collected by filtration. Moreover, the crystals thus obtained were suspended in a mixture composed of 20 ml of methanol and 2 ml of a 2 mol/L sodium hydroxide solution, and heated under reflux for 5 hours. The reaction mixture was concentrated under reduced pressure and then purified by column chromatography using 20 g of silica gel [with an elution solvent comprising chloroform-methanol (30:1)]. Thus, 80 mg (22% yield) of the title compound was obtained as colorless crystals.
