6-Acetylmethylenepenicillanic acid (Ro 15-1903), a potent beta-lactamase inhibitor. I. Inhibition of chromosomally and R-factor-mediated beta-lactamases.

6-Acetylmethylenepenicillanic acid (Ro 15-1903) was seen to be a powerful inhibitor of various beta-lactamases. Nearly all of the chromosomally and R-factor-mediated beta-lactamases which were studied were inhibited at much lower concentrations than required with clavulanic acid or sulbactam. Ro 15-1903 protected beta-lactamase-labile penicillins and cephalosporins from hydrolysis. The compound itself was stable against hydrolysis and inhibition of beta-lactamase was irreversible.