C(OC([N:8]1[CH2:13][CH2:12][N:11]([C:14](=[O:24])[C@H:15]([CH2:20][CH2:21][S:22][CH3:23])[NH:16][C:17](=[O:19])[CH3:18])[CH2:10][CH2:9]1)=O)(C)(C)C.FC(F)(F)C(O)=O>ClCCl>[C:17]([NH:16][C@H:15]([C:14]([N:11]1[CH2:12][CH2:13][NH:8][CH2:9][CH2:10]1)=[O:24])[CH2:20][CH2:21][S:22][CH3:23])(=[O:19])[CH3:18]To a solution of 8.6 g (0.024 mol) of 1-(t-butoxycarbonyl)-4-(N-acetyl-L-methionyl)piperazine in 60 ml of dichloromethane was added 10 ml of trifluoroacetic acid and the mixture was stirred at room temperature overnight. The solution was extracted with water and the resulting aqueous solution was made basic with sodium hydroxide. The product was extracted with dichloromethane, dried over sodium sulfate, and filtered. Evaporation of the solvent gave 2.1 g of 1-(N-acetyl-L-methionyl)piperazine, as an oil: IR (film) 3304, 3051, 2917, 2861, 1645, 1546, 1448, 1377 cm−1; NMR (CDCl3) δ 1.95 m, 2 H), 2.02 (s, 3 H), 2.10 (s, 3 H), 2.54 (m, 2 H), 2.98 (m, 4 H), 3.74 (m, 4 H), 5.10 (m, 1 H), 6.40 (b, 0.5 H), 6.48 (b, 0.5 H).
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