A solution of hydrazine hydrate (8.0 g) in methanol (16 ml) was added to a suspension of benzyl 2-phthalimidoxyacetate (46.0 g) in tetrahydrofuran (150 ml), and the mixture was stirred at ambient temperature for 30 minutes. To the reaction mixture was added 20% hydrochloric acid under ice-cooling, followed by stirring at the same temperature for 10 minutes. The insoluble substance was filtered off to give a solution containing benzyl 2-aminooxyacetate. To this solution were added (2-formamidothiazol-4-yl)glyoxylic acid (24.7 g) and pyridine (24.8 ml), and the mixture was stirred at ambient temperature for 3 hours. The reaction mixture was adjusted to pH 7.5 with 10% aqueous sodium hydroxide and then washed with ethyl acetate. The resultant aqueous solution was acidified to pH 2.0 with 10% hydrochloric acid, followed by extraction with ethyl acetate. The extract was washed with an aqueous sodium chloride ad then dried over magnesium sulfate. The solution was evaporated and the residue was pulverized with diisopropyl ether to give 2-benzyloxycarbonylmethoxyimino-2-(2-formamidothiazol-4-yl)acetic acid (syn isomer) 37 g), mp 152° C. (dec.).
