CC[O:3][C:4]([C:6]1([CH3:17])[N:10]([C:11](=[O:13])[CH3:12])[CH:9]([C:14]([OH:16])=[O:15])[CH2:8][S:7]1)=[O:5].[OH-].[Na+]>C(O)C>[C:11]([N:10]1[CH:9]([C:14]([OH:16])=[O:15])[CH2:8][S:7][C:6]1([CH3:17])[C:4]([OH:5])=[O:3])(=[O:13])[CH3:12]The crude product (10.19 g) of N-acetyl-2-methylthiazolidine-2,4-dicarboxylic acid 2-ethyl ester, which was obtained by a method similar to that in Synthetic Example 13, was dissolved in ethanol (20 ml), and 4N NaOH was added thereto. The mixture was stirred under an argon atmosphere, and ethanol was added thereto to give a pale-yellow solid. The obtained solid was collected by filtration to give N-acetyl-2-methylthiazolidine-2,4-dicarboxylic acid 2Na salt (trans form) as crystals (9.09 g, about 72%).
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