Mechanism of β-lactam ring opening in cephalosporins

Article abstract of DOI:10.1021/ja00325a019

The mechanism of the aminolysis of cephalosporins is a stepwise process. A tetrahedral intermediate is formed by the reversible addition of the amine to the beta -lactam carbonyl carbon. Expulsion of the attacking amine from the tetrahedral intermediate occurs faster than fission of the beta -lactam C-N bond. The reaction proceeds by trapping the intermediate with base. Expulsion of a leaving group at C-3 prime in cephalosporins is not concerted with nucleophilic attack of the amine on the beta -lactam carbonyl carbon and makes little difference to the rate of beta -lactam C-N bond fission.