[CH2:1]([O:8][C@H:9]([CH3:15])[C@@H:10]([C:12]([OH:14])=[O:13])[NH2:11])[C:2]1[CH:7]=[CH:6][CH:5]=[CH:4][CH:3]=1.C([O-])([O-])=O.[Na+].[Na+].[C:22](Cl)(=[O:29])[C:23]1[CH:28]=[CH:27][CH:26]=[CH:25][CH:24]=1>O.O1CCCC1>[C:22]([NH:11][C@H:10]([C:12]([OH:14])=[O:13])[C@@H:9]([CH3:15])[O:8][CH2:1][C:2]1[CH:7]=[CH:6][CH:5]=[CH:4][CH:3]=1)(=[O:29])[C:23]1[CH:28]=[CH:27][CH:26]=[CH:25][CH:24]=1A mixture containing 10 mmoles of O-benzyl-threonine, 10 mmoles of Na2CO3 in water and tetrahydrofuran (THF) is stirred at room temperature. Benzoyl chloride (10 mmoles), dissolved in anhydrous THF, is added gradually with continued stirring at room temperature. The reaction mixture is stirred until the reaction is completed as judged by thin layer chromatography (TLC). The solvent is removed by a rotary evaporator at 30° C. An excess of water is added and the reaction mixture extracted several times with ethyl acetate. The aqueous phase is adjusted to pH 2 with 1N HCl. The precipitate is recovered by filtration and washed with dilute HCl and then with cold water. The precipitate is dried over P2O5 in a vacuum desiccator. The precipitate is homogeneous as judged by TLC. In this reaction sequence, the racemate is obtained.
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