β-Lactamase Inhibition by 7-Alkylidenecephalosporin Sulfones: Allylic Transposition and Formation of an Unprecedented Stabilized Acyl-Enzyme

Journal of the American Chemical Society (Impact Factor: 12.11). 11/2013; 135(49). DOI: 10.1021/ja403598g
Source: PubMed


The inhibition of the class A SHV-1 β-lactamase by 7-(tert-butoxycarbonyl)methylidenecephalosporin sulfone was examined kinetically, spectroscopically, and crystallographically. An 1.14Å X-ray crystal structure shows that the stable acyl-enzyme, which incorporates an eight-membered ring, is a covalent derivative of Ser70 linked to the 7-carboxy group of 2-H-5,8-dihydro-1,1-dioxo-1,5-thiazocine-4,7-dicarboxylic acid. A cephalosporin-derived enzyme complex of this type is unprecedented and the rearrangement leading to its formation may offer new possibilities for inhibitor design. The observed acyl-enzyme derives its stability from the resonance stabilization conveyed by the -aminoacrylate (i.e. vinylogous urethane) functionality as there is relatively little interaction of the eight-membered ring with active site residues. Two mechanistic schemes are proposed, differing in whether, subsequent to acylation of the active site serine and opening of the β-lactam, the resultant dihydrothiazine fragments on its own, or is assisted by an adjacent nucleophilic atom, in the form of the carbonyl oxygen of the C7 tert-butyloxycarbonyl group. This compound was also found to be a submicromolar inhibitor of the class C ADC-7 and PDC-3 β-lactamases.

15 Reads
  • [Show abstract] [Hide abstract]
    ABSTRACT: A simple, efficient and catalyst-free procedure has been developed for the construction of sulfonated oxindoles via the direct arylsulfonylation of N-arylacrylamides with sulfinic acids. The present protocol, which simply utilizes cheap oxidants, readily-available starting materials, and catalyst-free conditions, provides an alternative and highly attractive approach to a series of sulfonated oxindoles with high atom efficiency and excellent functional group tolerance.
    Green Chemistry 05/2014; 16(6). DOI:10.1039/C4GC00231H · 8.02 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: A novel iron-catalyzed direct difunctionalization of alkenes with sulfinic acids and dioxygen for the synthesis of β-ketosulfones has been developed under mild conditions. The present protocol, which utilizes inexpensive iron salt as the catalyst, readily available benzenesulfinic acids as the sulfonylating reagents, and dioxygen as the oxidant and oxygen source, provides a cost-effective and environmentally benign approach to access various β-ketosulfones.
    Organic & Biomolecular Chemistry 08/2014; 46(11). DOI:10.1039/C4OB01369G · 3.56 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Class C cephalosporinases are a growing threat and inhibitors of these enzymes are currently unavailable. Studies exploring the YXN loop asparagine in the Escherichia coli AmpC, P99 and CMY-2 enzymes have suggested that interactions between C6' or C7' substituents on penicillins or cephalosporins and this Asn are important in determining substrate specificity and enzymatic stability. We sought to characterize the YXN loop asparagine in the clinically important ADC-7 Class C β-lactamase of Acinetobacter baumannii. Mutagenesis at the N148 position in ADC-7 yields functional mutants (N152G, -S, -T, Q, A, C) that retain cephalosporinase activity. Using standard assays, we show that N148G, -S and -T variants possess good catalytic activity towards cefoxitin and ceftaroline, but cefepime is a poor substrate. Because N152 variants of CMY-2, another Class C β-lactamase, are more readily inhibited by tazobactam due to more rapid rates of inactivation, we also tested if the N148 substitutions in ADC-7 would affect inactivation by sulfone inhibitors, sulbactam and tazobactam, Class A β-lactamase and A. baumannii PBP inhibitors with in vitro activity against ADC-7. The IC50s for tazobactam and sulbactam improve, with 7-fold and 2-fold reductions respectively for the N148S variant. A homology model of the N148S ADC-7 enzyme in a Michaelis-Menten complex with tazobactam shows loss of interaction between N148 and the sulfone moiety of the inhibitor. We postulate that this may result in more rapid secondary ring opening of the inhibitor as the unbound sulfone is an excellent leaving group, leading to more rapid formation of the stable linearized inhibitor. Copyright © 2014, American Society for Microbiology. All Rights Reserved.
    Antimicrobial Agents and Chemotherapy 12/2014; 59(3). DOI:10.1128/AAC.03537-14 · 4.48 Impact Factor