966 mg of cesium carbonate (2.96 mmol) was added to a solution of 1.39 g of N-{(S)-2-[2,2-dimethyl-4-(5-fluoro-2-methylphenyl)-5-oxopiperazin-1-yl]-1-[(2S,4R)-4-methyl-5-oxotetrahydrofuran-2-yl]ethyl}-2-nitrobenzenesulfonamide obtained in Example (101a) (2.47 mmol) and 0.53 ml of thiophenol (content: 95%) (4.94 mmol) in acetonitrile (12 ml) under a nitrogen atmosphere at room temperature, and the mixture was stirred at the same temperature for two hours. Brine was added to the reaction mixture, followed by extraction with methylene chloride. Then, the organic layer was dried over anhydrous magnesium sulfate. After filtration, the solvent was evaporated under reduced pressure, and the residue was purified by silica gel column chromatography (elution solvent:methylene chloride/methanol=20/1-10/1). 213 mg of sodium bicarbonate (2.53 mmol) and 553 mg of di-t-butyl dicarbonate (2.53 mmol) were added to a solution of the resulting 4-{(S)-2-amino-2-[(2S,4R)-4-methyl-5-oxotetrahydrofuran-2-yl]ethyl}-5,5-dimethyl-1-(5-fluoro-2-methylphenyl)piperazin-2-one in ethyl acetate (10 ml)-water (10 ml), and the mixture was stirred at room temperature for 2.5 hours. Brine was added to the reaction mixture, followed by extraction with ethyl acetate. Then, the organic layer was dried over anhydrous magnesium sulfate. After filtration, the solvent was evaporated under reduced pressure, and the residue was purified by silica gel column chromatography (elution solvent:methylene chloride/ethyl acetate=2/1) to obtain 968 mg of the title compound (yield: 82%).
