Development of the semi-synthetic penicillins and cephalosporins.

Semi-synthetic penicillins and cephalosporins both derive from their respective chemical nuclei, 6-aminopenicillanic acid (6-APA) and 7-aminocephalosporanic acid (7-ACA). Work leading to their isolation was being carried out in parallel, but following very different pathways, during the last half of the 1950s. The development of 6-APA was reviewed recently in this journal, and in the present article I take a closer look at early work on 'penicillin amidase' and revisit the steps that led to 7-ACA.