In dimethylformamide (20 ml) is dissolved sodium 7β-(t-butoxycarbonyl)amino-3-hydroxymethyl-3-cephem-4-carboxylate (3.20 g), followed by the addition of N-carboethoxysaccharin (3.20 g) and triethylamine (2.0 ml). The solution is stirred for one hour at room temperature and, after the addition of triethylamine (2.0 ml), stirred further for one hour. The solution is poured into toleune (1 L) and the resultant precipitate is collected by filtration, washed with toleune and dried. The powder thus obtained is dissolved in water (30 ml). After the addition of ethyl acetate (200 ml), the solution is adjusted to pH 4.0 with diluted phosphoric acid. After separation, the ethyl acetate solution is washed with water, dried over anhydrous sodium sulfate and concentrated. To the concentrate (30 ml), ether (200 ml) is added under stirring and the resultant precipitate is filtered off. The filtrate is concentrated under reduced pressure and to the concentrate (30 ml) is added carbon tetrachloride (100 ml). The resultant precipitate is collected by filtration, washed with carbon tetrachloride and dried over phosphorus pentoxide. The procedure provides 7β-(t-butoxycarbonyl)amino-3-[2-(N-carboethoxysulfamoyl)benzoyloxy]methyl-3-cephem-4-carboxylic acid (2.50 g).
