1.17 ml of isobutyl chloroformate was added dropwise under an inert atmosphere to a mixture of 4.1 g of the product of Step C, 36 ml of tetrahydrofuran, 27 ml of methylene chloride and 0.99 ml of N-methyl-morpholine cooled to -20° C. and after standing at -20° C. for 3 minutes, the mixture was cooled to -35° C. and a solution of 2.45 g of 7-aminocephalosporanic acid in 45 ml of methylene chloride and 252 ml of triethylamine were added thereto. The mixture stood for 21/2 hours with spontaneous heating and was then evaporated to dryness. The residue was taken up in a mixture of methylene chloride, water and N hydrochloric acid with a pH of 1-2 and the mixture was extracted with methylene chloride. The organic extracts were washed with water, dried and vacuum filtered. The filtrate was evaporated to dryness and the residue was taken up in ethyl acetate. The solution was diluted with isopropyl ether and was stirred and vacuum filtered The recovered product was rinsed with isopropyl ether and dri to obtain 4.87 g of the anti isomer of 3-acetoxymethyl-7-[2-(2-tritylamino-4-thiazolyl)-2-ethoxyiminoacetamido]-ceph-3-em-4-carboxylic acid. The said product was dissolved in 10 ml of hot ethyl acetate and the solution was slowly diluted with isopropyl ether. The mixture was stirred and was vacuum filtered and the recevered product was rinsed with isopropyl ether and dried to obtain 4.53 g of purified product.
