Conversion of cloxacillin into a progressive inhibitor of beta-lactamases by sulfonation and its activity against various types of these enzymes.

On the assumption of the theory that the sulfone of a penam derivative should effectively act as a suicide substrate against beta-lactamases to which the parent compound is a poor substrate, the action of cloxacillin sulfone on four different types of beta-lactamases was studied. As we expected, cloxacillin sulfone showed strong mechanism-based irreversible inactivation against type Ib penicillinase and Proteus vulgaris cephalosporinase whereas it showed no progressive inactivation against cloxacillin-hydrolyzing type II penicillinase. However, an unexpected result was that cloxacillin sulfone could not inactivate Citrobacter freundii cephalosporinase which itself could hardly hydrolyze the parent cloxacillin. The number of hydrolytic events which occurred before inactivation of type Ib penicillinase, and P. vulgaris cephalosporinase, by the inactivator was 190 and 13, respectively. These values indicate that cloxacillin sulfone is far more effective as a suicide substrate against the two types of beta-lactamases than penam sulfones so far reported. The inactivation proceeded via the formation of an irreversible enzyme-inhibitor complex which could be detected by isoelectric focusing.