To a solution of 7β-amino-3-(5-oxo-4,5,6,7-tetrahydro-1-pyrazolo[1,5-a]pyrimidinio)methyl-3-cephem-4-carboxylate bis(trifluoroacetate) (1.5 g) in a mixture of tetrahydrofuran (40 ml) and water (20 ml) was added N,N-dimethylformamide solvate (1.02 g) of 1-[2-(2-aminothiazol-4-yl)-2-methoxyiminoacetyl]-1H-benzotriazol-3-oxide at ambient temperature. The mixture was stirred for 4 hours at pH 7. The solution was adjusted to pH 2 with 1N hydrochloric acid, washed with ethyl acetate five times and evaporated in vacuo to remove ethyl acetate. The solution was subjected to column chromatography on HP-20 and the elution was carried out with 5% aqueous isopropyl alcohol. The objective fraction was collected and lyophilized to give 7β-[2-(2-aminothiazol-4-yl)-2-methoxyiminoacetamido]-3-(5-oxo-4,5,6,7-tetrahydro-1-pyrazolo[1,5-a]pyrimidinio)methyl-3-cephem-4-carboxylate (syn isomer) (261 mg).
