Ethyl Acetate → 7beta-[2-(5-Amino-1,2,4-thiadiazol-3-yl)-2-methoxyiminoacetamido]-3-(3-carboxymethylamino-2-methyl-1-pyrazolio)methyl-3-cephem-4-carboxylate

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To a solution of 7β-amino-3-[2-methyl-3-methoxycarbonylmethylamino-1-pyrazolio]methyl-3-cephem-4-carboxylate trihydrochloride (0.7 g) and N-(trimethylsilyl)acetamide (1.87 g) in tetrahydrofuran (14 ml) was added (Z)-2-(5-amino-1,2,4-thiadiazol-3-yl)-2-methoxyiminoacetyl chloride hydrochloride (0.37 g) under ice-cooling and the mixture was stirred at room temperature for 2 hours. The reaction mixture was poured into ethyl acetate (140 ml) and the resultant powder was collected by filtration. The powder was dissolved in ice-water and adjusted to pH 13 with 1N aqueous sodium hydroxide. After stirring for 20 minutes under ice-cooling, the solution was adjusted to pH 2 with 3N hydrochloric acid and subjected to column chromatography on "Diaion HP-20" using 5% aqueous isopropyl alcohol as an eluent. Fractions containing the object compound were combined, evaporated in vacuo to remove isopropyl alcohol and lyophilized to give 7β-[2-(5-amino-1,2,4-thiadiazol-3-yl)-2-methoxyiminoacetamido]-3-(3-carboxymethylamino-2-methyl-1-pyrazolio)methyl-3-cephem-4-carboxylate (syn isomer) (0.24 g).

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