Cyclobutanone Analogues of β-Lactams Revisited: Insights into Conformational Requirements for Inhibition of Serine- and Metallo-β-Lactamases

Abstract

The most important mode of bacterial resistance to beta-lactam antibiotics is the expression of beta-lactamases. New cyclobutanone analogues of penams and penems have been prepared and evaluated for inhibition of class A, B, C, and D beta-lactamases. Inhibitors which favor conformations in which the C4 carboxylate is equatorial were found to be more potent than those in which the carboxylate is axial, and molecular modeling studies with enzyme-inhibitor complexes indicate that an equatorial orientation of the carboxylate is required for binding to beta-lactamases. An X-ray structure of OXA-10 complexed with a cyclobutanone confirms that a serine hemiketal is formed in the active site and that the inhibitor adopts the exo envelope. An unsaturated penem analogue was also found to enhance the potency of meropenem against carbapenem-resistant MBL-producing strains of Chryseobacterium meningosepticum and Stenotrophomonas maltophilia. These cyclobutanones represent the first type of reversible inhibitors to show moderate (low micromolar) inhibition of both serine- and metallo-beta-lactamases and should be considered for further development into practical inhibitors.

Large Scale Structural Rearrangement of a Serine Hydrolase from Francisella tularensis Facilitates Catalysis

“…Cyclobutanones have previously been explored as reversible ␤-lactamase inhibitors with modest, but broad-spectrum ␤-lactamase inhibition. Cyclobutanones also exhibit covalent binding as the hemiketal to the active-site serine of serine hydrolases as seen crystallographically (56). The three different isomers of a mechanistic cyclobutanone ligand (Scheme 1) were screened for relative activity against FTT258 before attempting co-crystallization.…”

Targeting clinically-relevant metallo-β-lactamases: from high-throughput docking to broad-spectrum inhibitors

“…General formula for compounds [6][7][8] 3e displayed notable inhibitory activity on VIM-2 isoform (K i of 15 and 6 mM, respectively). Conversely, aldehyde 2e was characterized by a comparable inhibitory profile toward both VIM-2 and NDM-1 (K i ¼ 10 mM).…”

“…Therefore, facing the mounting threat of antimicrobial resistance today represents a great challenge for clinicians and medicinal chemists. One important mechanism of resistance to b-lactams 5 is the production of one or more b-lactamase(s), which efficiently inactivate these antibiotics 6,7 . The global spread of extended-spectrum b-lactamases (ESBLs) led to increased use of carbapenems, broad-spectrum antibiotics which are stable to ESBLs.…”

Cyclobutanone Mimics of Intermediates in Metallo‐β‐Lactamase Catalysis

“…Recently, we have found that cyclobutanone analogues of the penems and penams inhibit both SBLs and MBLs 8a. We identified the cyclobutanone penem analogue 1 (Figure 1) to be the most potent compound tested against class A and C SBLs, and to have modest inhibition of the IMP‐1 MBL 8a. However, although we obtained crystallographic evidence for SBL inhibition, involving binding of the cyclobutanone by a hemiketal to the nucleophilic serine,8a no information has been available on how cyclobutanones inhibit MBLs.…”

“…Our results, however, show that the SPM‐1 active site can bind with reasonable affinity to a species (i.e., a hydrated cyclobutanone) whose tetrahedral carbon (C6) atoms render it closely (though not perfectly) analogous to the oxyanion intermediate. Taking into consideration the activity of cyclobutanones and boronates against all classes of SBLs,8a, 17 these results indicate that structures mimicking the tetrahedral oxyanion merit investigation as starting points for potent inhibitors that are hydrolytically stable and effective against both SBLs and MBLs.…”