Binding of β-Lactam Antibiotics to a Bioinspired Dizinc Complex Reminiscent of the Active Site of Metallo-β-lactamases

Metallo-beta-lactamases (m beta ls) cause bacterial resistance toward a broad spectrum of beta-lactam antibiotics by catalyzing the hydrolytic cleavage of the four-membered beta-lactam ring, thus inactivating the drug. Minutiae of the mechanism of these enzymes are still not well understood, and reports about binding studies of the substrates to the enzymes as well as to synthetic model systems are rare. Here we report a new pyrazolate-based bioinspired dizinc complex (1) reminiscent of the active site of binuclear m beta ls. Since 1 does not mediate hydrolytic degradation of beta-lactams, the binding of a series of common beta-lactam antibiotics (benzylpenicillin, cephalotin, 6-aminopenicillanic acid, ampicillin) as well as the inhibitor sulbactam and the simplest beta-lactam, 2-azetidinone, to the dizinc core of 1 could now be studied in detail by NMR and IR spectroscopy as well as mass spectrometry. X-ray crystallographic information was obtained for 1 and its complexes with 2-azetidinone (2) and sulbactam (3); the latter represents the first structurally characterized dizinc complex with a bound beta-lactam drug. While 2-azetidinone was found deprotonated and bridging in the clamp of the two zinc ions in 2, in 3 and all other cases the substrates preferentially bind via their carboxylate group within the bimetallic pocket. The relevance of this binding mode for m beta ls and consequences for the design of functional model systems are discussed.