[CH:1]([NH:3][C:4]1[S:5][C:6]([Br:18])=[C:7]([C:9](=[N:15][O:16][CH3:17])[C:10]([O:12]CC)=[O:11])[N:8]=1)=[O:2]>[OH-].[Na+]>[CH:1]([NH:3][C:4]1[S:5][C:6]([Br:18])=[C:7]([C:9](=[N:15][O:16][CH3:17])[C:10]([OH:12])=[O:11])[N:8]=1)=[O:2]1N-Aqueous sodium hydroxide (290 ml.) was added dropwise to an aqueous suspension (325 ml.) of ethyl 2-(2-formamido-5-bromothiazol-4-yl)-2-methoxyiminoacetate (syn isomer, 32.5 g.) under ice-cooling, and the mixture was treated in a similar manner to that of Preparation 2-(2) to give 2-(2-formamido-5-bromothiazol-4-yl)-2-methoxyiminoacetic acid (syn isomer, 21.9 g.), m.p. 165° to 167° C.
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