FC1C(O[C:9]([CH:11]2[CH2:15][C:14](=[O:16])[NH:13][CH2:12]2)=[O:10])=C(F)C(F)=C(F)C=1F.[NH:21]1[CH2:26][CH2:25][NH:24][CH2:23][CH2:22]1.C(Cl)Cl>C1COCC1>[N:21]1([C:9]([CH:11]2[CH2:12][NH:13][C:14](=[O:16])[CH2:15]2)=[O:10])[CH2:26][CH2:25][NH:24][CH2:23][CH2:22]1To a suspension of 5-oxo-pyrrolidine-3-carboxylic acid pentafluorophenyl ester 17 (40.1 mg, 0.0578 mmol) in 2 mL THF extra dry was added piperazine (19.9 mg, 0.231 mmol) at room temperature. The reaction mixture was stirred for 10 hours at room temperature. Afterwards, 20 mL methylene chloride were added. The resulting organic layer was washed with 20 mL of a saturated aqueous solution of sodium hydrogenocarbonate, dried over magnesium sulfate and the solvent was removed in vacuo. Finally, the crude product was purified by chromatography on silica gel (ethyl acetate:methanol 9:1→1:1) to afford the desired 4-(piperazine-1-carbonyl)-pyrrolidin-2-one 18 as a white solid (12.2 mg, 45.91%).
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