2-(2-Formamidothiazol-4-yl)-2-propoxyiminoacetic acid (syn isomer, 0.515 g.), N,N-dimethylformamide (0.161 g.), phosphoryl chloride (0.337 g.) and ethyl acetate (7.9 ml.) were treated in a similar manner to that of Example 15-(1) to give the activated acid solution. On the other hand, trimethylsilylacetamide (1.85 g.) and bis(trimethylsilyl)acetamide (1.60 g.) were added to a suspension of 4-nitrobenzyl 7-amino-3-hydroxy-3-cephem-4-carboxylate (0.703 g.) in ethyl acetate (10 ml.), and stirred at room temperature for an hour. To the solution was added the activated acid solution obtained above at -10° C. all at once, and stirred at the same temperature for an hour. To the resultant solution were added water (20 ml.) and ethyl acetate (20 ml.). The organic layer was separated, washed with a saturated aqueous solution of sodium bicarbonate (8 ml.) and water (14 ml.) and dried over magnesium sulfate. After the solution was concentrated in vacuo, the residue was pulverized with diethyl ether, and the precipitates were collected by filtration to give 4-nitrobenzyl 7-[2-(2-formamidothiazol-4-yl)-2-propoxyiminoacetamido]-3-hydroxy-3-cephem-4-carboxylate (syn isomer, 0.75 g.).
