6-beta-bromopenicillanic acid, a potent beta-lactamase inhibitor

6-beta-Bromopenicillanic acid, which arises from the epimerization of 6-alpha-bromopenicillanic acid in aqueous solution or from hydrogenation of 6,6-dibromopenicillanic acid, is a powerful, irreversible, active-site-directed inhibitor of several typical beta-lactamases (penicillinase; penicillin amido-beta-lactamhydrolase, EC 3.5.2.6); 6-alpha-bromopenicillanic acid, being completely inhibited at less than micromolar concentrations through what is probably a 1:1 interaction. The B. licheniformis exoenzyme is similarly susceptible, while the Staphylococcus aureus enzyme and the Escherichia coli (R factor) enzyme are less so; the B. cereus beta-lactamase II is not inhibited. Very high concentrations (greater than or equal to 0.1 M) of benzylpenicillin, a good substrate, are required to significantly reduce the rate of inhibition of B. cereus beta-lactamase I by 6-beta-bromopenicillanic acid.