2,2,2-Trichloroethyl 2-methyl-7-amino-3-cephem-4-carboxylate hydrochloride (3.82 g) was suspended in dried dichloromethane (80 ml) and dissolved by adding under stirring and ice-cooling a solution of triethylamine (0.9 g) and dimethylaniline (0.15 g) in dichloromethane (20 ml). To the solution were added (1,3,4-thiadiazol-2-ylthio)acetic acid (1.8 g) and dicyclohexylcarbodiimide (2.25 g) under stirring and ice-cooling, and the mixture was stirred for 1 hour under ice-cooling. To the reaction mixture, was added 5% hydrochloric acid (50 ml), and the mixture was stirred for 30 minutes, after which the organic layer was separated, washed in turn with 5% hydrochloric acid, a saturated sodium bicarbonate aqueous solution and a saturated sodium chloride aqueous solution, and then dried over magnesium sulfate. The solvent was distilled off to give pale brown powder of 2,2,2-trichloroethyl 2-methyl-7-[2-(1,3,4-thiadiazol-2-ylthio)acetamido]-3-cephem-4-carboxylate (4.5 g), mp 130° to 140° C. (dec.).
