197 mg of cesium carbonate (0.61 mmol) was added to a solution of 299 mg of N-{(S)-2-[4-(2-chlorophenyl)-2,2-dimethyl-5-oxopiperazin-1-yl]-1-[(2S,4S)-4-isopropyl-5-oxotetrahydrofuran-2-yl]ethyl}-2-nitrobenzenesulfonamide obtained in Example (1l) (0.50 mmol) and 0.11 ml of thiophenol (content: 95%) (1.00 mmol) in N,N-dimethylformamide (5 ml) under a nitrogen atmosphere at room temperature, and the mixture was stirred at the same temperature for one hour. 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). 0.21 ml of triethylamine (1.51 mmol) and 132 mg of di-t-butyl dicarbonate (0.61 mmol) were added to a solution of the resulting 4-{(S)-2-amino-2-[(2S,4S)-4-isopropyl-5-oxotetrahydrofuran-2-yl]ethyl}1-(2-chlorophenyl)-5,5-dimethylpiperazin-2-one in methylene chloride (5 ml), and the mixture was stirred at room temperature for 15 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/ethyl acetate=2/1) to obtain 205 mg of the title compound (yield: 80%).
