Trifluoroacetic anhydride (80 μL) was added to a solution of (2S,4S)-1-[2-[(4-ethoxycarbonylbicyclo[2.2.2]oct-1-yl)amino]ac etyl]-4-fluoropyrrolidine-2-carboxamide (100 mg) in tetrahydrofuran (1 mL). The mixture was stirred at room temperature for 2 hours and then at 40° C. for 1.5 hours. Subsequently, additional trifluoroacetic anhydride (40 μL) was added and the mixture was further stirred for 30 minutes. A saturated aqueous sodium bicarbonate solution (5 mL) was then added and the reaction mixture was extracted with ethyl acetate (2×10 mL). The ethyl acetate extracts were combined, washed with saturated brine (5 mL), dried over anhydrous sodium sulfate, and concentrated under reduced pressure. The resulting residue was purified on an aminated silica gel column (eluant=ethyl acetate:methanol=30:1) to give (2S,4S)-1-[2-[(4-ethoxycarbonylbicyclo[2.2.2]oct-1-yl)amino]ac etyl]-4-fluoropyrrolidine-2-carbonitrile as a colorless solid (63.7 mg, 67% yield). This compound was identical to the compound obtained in Example 7.
