Highly efficient synthesis of ampicillin in an "aqueous solution-precipitate" system: Repetitive addition of substrates in a semicontinuous process

The synthesis of ampicillin catalyzed by Escherichia coli penicillin acylase was optimized in an aqueous system with partially dissolved antibiotic nucleus 6‐aminopenicillanic acid (6‐APA). The yields of both 6‐APA and acyl donor could be improved by repetitively adding substrates to the reaction, allowing the concentration of 6‐APA to remain saturated throughout. In this reaction concept, with four subsequent additions of substrates, 97% conversion of 6‐APA and 72% of D‐(−)‐phenylglycine methyl ester (D‐PGM) to ampicillin was achieved. The synthetic potential of this concept was estimated using a mathematical model which showed that by increasing the amount of added substrates a nearly quantitative conversion of 6‐APA and 85% conversion of acyl donor into ampicillin could be achieved . © 2001 John Wiley & Sons, Inc. Biotechnol Bioeng 73: 426–430, 2001.