[CH:1]([NH:3][C:4]1[S:5][CH:6]=[C:7]([C:9](=O)[C:10]([OH:12])=[O:11])[N:8]=1)=[O:2].[NH2:14][O:15][CH2:16][CH2:17][NH:18][C:19](=[O:25])[O:20][C:21]([CH3:24])([CH3:23])[CH3:22]>CO>[CH:1]([NH:3][C:4]1[S:5][CH:6]=[C:7]([C:9](=[N:14][O:15][CH2:16][CH2:17][NH:18][C:19]([O:20][C:21]([CH3:24])([CH3:23])[CH3:22])=[O:25])[C:10]([OH:12])=[O:11])[N:8]=1)=[O:2]A mixture of 2-(2-formamidothiazol-4-yl)-glyoxylic acid (1.59 g.), tert-butyl N-aminooxyethylcarbamate (1.40 g.) and methanol (25 ml.) was stirred at room temperature for 6 hours. After removal of methanol from the resultant solution under reduced pressure, the residue was pulverized with diethyl ether. The precipitates were collected by filtration to give 2-(2-formamidothiazol-4-yl)-2-(2-tert-butoxycarbonylaminoethoxyimino)acetic acid (syn isomer, 2.2 g.).
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