[CH2:1]([O:3][C@@H:4]([CH2:8][C:9]1[CH:14]=[CH:13][C:12]([C:15]2[S:19][C:18]([NH:20][CH3:21])=[N:17][CH:16]=2)=[CH:11][CH:10]=1)[C:5]([OH:7])=[O:6])[CH3:2].[OH-].[Na+].[CH3:24]O>S(=O)(=O)(O)O.O>[CH2:1]([O:3][C@@H:4]([CH2:8][C:9]1[CH:10]=[CH:11][C:12]([C:15]2[S:19][C:18]([NH:20][CH3:21])=[N:17][CH:16]=2)=[CH:13][CH:14]=1)[C:5]([O:7][CH3:24])=[O:6])[CH3:2]0.5 g (1.6 mmol) of 2(S)-ethoxy-3-[4-(2-methylaminothiazol-5-yl)phenyl]propanoic acid in 10 ml of methanol and a few drops of sulfuric acid is heated at 60° C. for 2 hours. The reaction medium is cooled, diluted with water, neutralized to pH 7 with aqueous 1M sodium hydroxide solution and then extracted with ethyl acetate. The organic phase is washed with saturated sodium chloride solution, dried over magnesium sulfate, filtered and evaporated. The residue obtained is purified by chromatography on a column of silica eluted with a 50/50 heptane/ethyl acetate mixture. 0.34 g (67%) of methyl 2(S)-ethoxy-3-[4-(2-methylaminothiazol-5-yl)phenyl]propanoate is obtained in the form of a yellow solid.
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