1.50 ml of triethylamine, 1.6 ml of N,N-dimethylaniline and 2,3 ml of trimethylchlorosilane are added to a stirred suspension of 2.13 g of 7β-amino-3-[(6-methyl-1-oxido-pyridazin-3-ylthio)-methyl]-ceph-3-em-4-carboxylic acid in 20 ml of methylene chloride at 20°-25° C. The mixture is warmed to 40° C over the course of 20 minutes, whilst stirring, and is then cooled to +5° C. At the same time, 1.95 g of 2-(5-tert.-butoxycarbonylaminomethyl-2-thienyl)-acetic acid are dissolved in 20 ml of methylene chloride, 0.05 ml of dimethylformamide and 5 ml of oxalyl chloride. The mixture is stirred for 30 minutes at the reflux temperature under a slight stream of nitrogen, the readily volatile constituents are distilled off in vacuo and the oily residue is dissolved in 10 ml of methylene chloride. This solution is added, at 5°-10° C, to the solution which contains the amine component which has now been silylated. This mixture is stirred for 2 hours at 10°-25° C and poured into water, the pH is adjusted to approx. 7 with sodium bicarbonate, the whole is extracted with methylene chloride and carefully acidified to approx. pH 2 with concentrated hydrochloric acid, and the precipitate formed is filtered off. It is repeatedly washed with water and after subsequent drying of the filter residue in a high vacuum over potassium hydroxide, 7β-[2-(5-tert.-butoxycarbonylaminomethyl-2-thienyl)-acetylamino]-3-[(6-methyl-1-oxido-pyridazin-3-yl-thio)-methyl]-ceph-3-em-4-carboxylic acid is obtained; thin layer chromatogram (silica gel; glacial acetic acid/water/butanol, 45:10:45): Rf = 0.58; infrared absorption spectrum (in mineral oil): bands at 5.63μ and 5.96μ.
