The inhibition of metallo-β-lactamase by thioxo-cephalosporin derivatives

The 8-thioxocephalosporins are poor substrates for the B. cereus metallo β-lactamase (kcat/Km=61.4 M−1 s−1) and act as weak competitive inhibitors (Ki 700 μM). The hydrolysis product of thioxocephalosporin, a thioacid, also inhibits the enzyme competitively with a Ki=96 μM, whereas the cyclic thioxo-piperazinedione, formed by intramolecular aminolysis of thioxocephalexin has a Ki of 29 μM.