C[O:2][C:3]([CH:5]1[CH2:9][C:8](=[O:10])[N:7]([C:11]2[CH:16]=[CH:15][C:14]([O:17][CH2:18][C:19]3[CH:24]=[CH:23][C:22]([F:25])=[CH:21][CH:20]=3)=[CH:13][CH:12]=2)[CH2:6]1)=[O:4].[OH-].[Na+].O1CCCC1>O>[F:25][C:22]1[CH:21]=[CH:20][C:19]([CH2:18][O:17][C:14]2[CH:13]=[CH:12][C:11]([N:7]3[C:8](=[O:10])[CH2:9][CH:5]([C:3]([OH:4])=[O:2])[CH2:6]3)=[CH:16][CH:15]=2)=[CH:24][CH:23]=1A suspension of 7.12 g (20.7 mmol) of (RS)-1-[4-(4-fluoro-benzyloxy)-phenyl]-5-oxo-pyrrolidine-3-carboxylic acid methyl ester in 10.3 ml of a solution of sodium hydroxide (1N) is prepared and tetrahydrofurane is added until a clear solution is obtained. The mixture is heated to 50° C. for 1 hour. For the working-up, the tetrahydrofurane is evaporated under reduced pressure. The white suspension obtained is diluted with water, then filtered. The white product is treated with toluene and evaporated under reduced pressure to remove most of the water. The azetropic distillation is repeated three times. There are obtained 5.78 g (85% of theory) of (RS)-1-[4-(4-fluoro-benzyloxy)-phenyl]-5-oxo-pyrrolidine-3-carboxylic acid as a white solid.
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