Dicyclohexylcarbodiimide → N,N'-Dicyclohexylurea

In 20 ml of tetrahydrofuran were dissolved 430 mg of 3-hydroxy-2-(2-tritylaminothiazol-4-yl)propionic acid and 270 mg of 7β-aminodesacetoxycephalosporanic acid tert-butyl ester and after adding thereto 206 mg of N,N'-dicyclohexylcarbodiimide, the mixture was stirred for 2 hours at room temperature. The solvent was distilled off from the reaction mixture under reduced pressure and 60 ml of ethyl acetate was added to the residue. Insoluble N,N'-dicyclohexylurea thus formed was filtered off and the filtrate was washed with an aqueous hydrochloric acid solution, an aqueous solution of sodium hydrogencarbonate, and then water followed by drying with anhydrous magnesium sulfate. The solvent was distilled off under reduced pressure and the residue was dissolved in 2 ml of dichloromethane. After adding 4 ml of trifluoroacetic acid and 0.5 ml of anisole to the solution followed by stirring the mixture for 10 minutes at room temperature, 0.5 ml of water was added and the mixture was stirred vigorously. The solvent was distilled off from the reaction mixture under reduced pressure and ether was added to the residue to facilitate the formation of a powder, which was recovered by filtration. The powder was dissolved in 20 ml of ethanol, the insoluble materials which had formed were filtered off, the filtrate was adjusted to pH 4 by pyridine, the solvent was distilled off under reduced pressure, and isopropyl alcohol was added to the residue to form precipitates, which were recovered by filtration. The product was purified by a column chromatography using Diaion HP 20 (trade name) to provide 7β-[2-(2-aminothiazol-4-yl)-3-hydroxypropionamido]-3-methyl-Δ3 -cephem-4-carboxylic acid.