The general procedure for the synthesis of (6R,7R)-7-amino-8-oxo-3-vinyl-5-thia-1-azabicyclo[4.2.0]oct-2-ene-2-carboxylic acid from cefixime impurity is as follows: 25.5 g (0.05 mol) of GVNA was placed in a 1,000 mL three-necked flask fitted with a thermometer and a mechanical stirrer, and 300 g of phenol and 2.8 g of acetic acid and the reaction was held at 35°C. After the reaction was complete (about 6 hours), the reaction mixture was slowly poured into a mixed solution consisting of sodium bicarbonate, purified water, and butyl acetate (5 g of purified water, 200 mL of purified water, and 200 mL of butyl acetate). The aqueous phase was extracted twice with 50 mL of butyl acetate and the aqueous phases were combined. The aqueous phase was transferred to a 500 mL reaction flask and stirred at room temperature for 2 hours. 4 g of immobilized acyltransferase PGA-450 was added, followed by dropwise addition of 15% aqueous sodium carbonate solution, maintaining the pH between 8.0-8.2 until the HPLC assay showed less than 0.5% GVNA. The enzyme was recovered by filtration. The filtrate was collected and the pH was adjusted with 10% hydrochloric acid to 3.4. The filter cake was washed with 50 mL of acetone and dried to give 10.7 g of AVNA (93.8% yield as GVNA).
