[NH:1]1[CH2:8][CH2:7][CH2:6][C@H:2]1[C:3]([OH:5])=[O:4].Br[CH:10]([C:14]([F:17])([F:16])[F:15])[C:11](Cl)=[O:12].[S:18]1C=C[CH:20]=[C:19]1CC(O)=O.C(=O)([O-])[O-].[K+].[K+].[OH-:33].[Na+]>O>[C:19]([S:18][CH:10]([C:14]([F:17])([F:16])[F:15])[C:11]([N:1]1[CH2:8][CH2:7][CH2:6][C@H:2]1[C:3]([OH:5])=[O:4])=[O:12])(=[O:33])[CH3:20]To a solution of L-proline (5.75 g.) in 1 N sodium hydroxide (50 ml.), chilled in an ice-water bath, 2-bromo-3,3,3-trifluoropropanoic acid chloride (12 g.) is added and the mixture is vigorously stirred at room temperature for three hours. A solution of thiolacetic acid (4 ml.) and potassium carbonate (4.8 g.) in water (50 ml.) is added and the mixture is stirred at room temperature for sixteen hours. After extraction with ethyl acetate, the aqueous layer is acidified with concentrated hydrochloric acid and extracted again with ethyl acetate. This last organic phase is dried over magnesium sulfate and concentrated to dryness in vacuo. The residue is chromatographed on a silica gel column with a mixture of benzene-acetic acid (7:2) to yield 1-(2-acetylthio-3,3,3-trifluoropropanoyl)-L-proline.
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