N-BOC-o-phenylglycine (753 mg, 3 mmol) was dissolved in a mixture of tetrahydrofuran (THF) (15 ml), Et3N 0.42 ml (3 mmol), and 3 drops of N-methylmorpholine, and stirred for 10 min at -15 C. Isobutyl chloroformate (0.41 ml, 3 mmol) in 2 ml of THF was added dropwise. After stirring at -15C for 20 min, 1.1 g (3 mmol) of cefadroxil was dissolved in 10 ml of THF-H2O (1:l) containing 0.42in1 (3 mmol) of Et,N. Add. The mixture was stirred at 0C for 3 hours. THF was removed by evaporation.H2O (10 ml) was added and the pH was adjusted to 2 with 2NHCl.The solution was then extracted with EtOAc (3 20 ml). Combined tissues. The aqueous layer was washed with H2O (20 ml), dried with anhydrous MgSO4, filtered and evaporated. The residue was dissolved in about 2 ml of fluoroacetic acid and stored at room temperature. It lasted for 16 hours. The solution was evaporated and the residue dissolved in water was placed on an anion exchange column (Bio-RadAG-3, 200-400 mesh, acetate, 13 x 2 cm) and eluted with water to remove trifluoroacetic acid. The eluate was evaporated and the residue was crystallized from acetone-water and dried under vacuum. Cefadroxil EP impurity C yielded 900 mg (63%).
