[C:1]([CH2:6][O:7][C:8]1[CH:21]=[CH:20][C:11]([CH2:12][CH:13]2[S:17][C:16](=[O:18])[NH:15][C:14]2=[O:19])=[CH:10][CH:9]=1)([O:3]CC)=[O:2].[OH-].[Na+].Cl>O>[C:1]([CH2:6][O:7][C:8]1[CH:21]=[CH:20][C:11]([CH2:12][CH:13]2[S:17][C:16](=[O:18])[NH:15][C:14]2=[O:19])=[CH:10][CH:9]=1)([OH:3])=[O:2]A suspension of the 5-[4-[(carboethoxy)methoxy]benzyl]thiazolidine-2,4-dione obtained by following a procedure described in any of Examples 16-22 (135 g, 0.44 M) and water (540 ml, 4 times w/v) was taken in a round bottom flask fitted with a mechanical stirrer. Aq. sodium hydroxide solution (37 g of NaOH in 135 ml of water) was added slowly over a period of 5-10 minutes at 20-25° C. Stirring was continued at ambient temperature for a further period of 2-3 h, while monitoring the reaction by TLC. After the completion of reaction, the pH of the reaction mixture was adjusted to 2 using conc. HCl (temp. raises to ˜40-45° C.) and allowed to attain room temperature. The mass was cooled to ˜10-15° C. and the solid thus obtained was filtered and dried at 60-70° C. under 1-2 mm Hg of vacuum to afford 5-[4-[(carboxy)methoxy]benzyl]thiazolidine-2,4-dione (121 g, Y=99% P=99.2%).
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