The discovery, made in Oxford, that crude penicillin could cure systemic and life-threatening bacterial infections was followed by attempts to purify penicillin, to determine its structure and then to produce it by total chemical synthesis. The plactam structure of the molecule, first proposed in October 1943, was a source of controversy until 1945. However, no useful chemical synthesis was achieved and fermentation became the commercial source of the antibiotic.
In 1953, one of the products of a Cephalosporium sp. from Sardinia was shown to be a new and hydrophilic penicillin (penicillin N). This was contaminated with a substance having the same side-chain but a characteristic absorption spectrum. The latter, cephalosporin C, showed antibacterial activity but was not inactivated by a penicillinase. The determination of its plactam structure and isolation of its nucleus enabled pharmaceutical companies to produce many semisynthetic cephalosporins.
A new tripeptide was later found to be an intermediate in the biosynthesis of both penicillin N and cephalosporin C, and this was followed by the complete elucidation of the biosynthetic pathways leading to these compounds and to benzylpenicillin.