title: Design, synthesis, and crystal structures of 6-alkylidene-2'-substituted penicillanic acid sulfones as potent inhibitors of Acinetobacter baumannii OXA-24 carbapenemase.
abstract: Class D β-lactamases represent a growing and diverse class of penicillin-inactivating enzymes that are usually resistant to commercial β-lactamase inhibitors. As many such enzymes are found in multi-drug resistant (MDR) Acinetobacter baumannii and Pseudomonas aeruginosa, novel β-lactamase inhibitors are urgently needed. Five unique 6-alkylidene-2'-substituted penicillanic acid sulfones (1-5) were synthesized and tested against OXA-24, a clinically important β-lactamase that inactivates carbapenems and is found in A. baumannii. Based upon the roles Tyr112 and Met223 play in the OXA-24 β-lactamase, we also engineered two variants (Tyr112Ala and Tyr112Ala,Met223Ala) to test the hypothesis that the hydrophobic tunnel formed by these residues influences inhibitor recognition. IC(50) values against OXA-24 and two OXA-24 β-lactamase variants ranged from 10 ± 1 (4 vs WT) to 338 ± 20 nM (5 vs Tyr112Ala, Met223Ala). Compound 4 possessed the lowest K(i) (500 ± 80 nM vs WT), and 1 possessed the highest inactivation efficiency (k(inact)/K(i) = 0.21 ± 0.02 μM(-1)  s(-1)). Electrospray ionization mass spectrometry revealed a single covalent adduct, suggesting the formation of an acyl-enzyme intermediate. X-ray structures of OXA-24 complexed to four inhibitors (2.0-2.6 Å) reveal the formation of stable bicyclic aromatic intermediates with their carbonyl oxygen in the oxyanion hole. These data provide the first structural evidence that 6-alkylidene-2'-substituted penicillin sulfones are effective mechanism-based inactivators of class D β-lactamases. Their unique chemistry makes them developmental candidates. Mechanisms for class D hydrolysis and inhibition are discussed, and a pathway for the evolution of the BlaR1 sensor of Staphylococcus aureus to the class D β-lactamases is proposed.
authors.affiliation: Instituto de Investigación Biomédica de A Coruña (INIBIC), Complejo Hospitalario Universitario A Coruña, 15006-A Coruña, Spain.
authors.forename: German
authors.initials: G
authors.lastname: Bou
authors.forename: Elena
authors.initials: E
authors.lastname: Santillana
authors.forename: Anjaneyulu
authors.initials: A
authors.lastname: Sheri
authors.forename: Alejandro
authors.initials: A
authors.lastname: Beceiro
authors.forename: Jared M
authors.initials: JM
authors.lastname: Sampson
authors.forename: Matthew
authors.initials: M
authors.lastname: Kalp
authors.forename: Christopher R
authors.initials: CR
authors.lastname: Bethel
authors.forename: Anne M
authors.initials: AM
authors.lastname: Distler
authors.forename: Sarah M
authors.initials: SM
authors.lastname: Drawz
authors.forename: Sundar Ram Reddy
authors.initials: SR
authors.lastname: Pagadala
authors.forename: Focco
authors.initials: F
authors.lastname: van den Akker
authors.forename: Robert A
authors.initials: RA
authors.lastname: Bonomo
authors.forename: Antonio
authors.initials: A
authors.lastname: Romero
authors.forename: John D
authors.initials: JD
authors.lastname: Buynak
mesh_terms: D040981:Acinetobacter baumannii / Q000187:drug effects / Q000201:enzymology*; D001426:Bacterial Proteins / Q000037:antagonists & inhibitors*; D018360:Crystallography, X-Ray; D004791:Enzyme Inhibitors / Q000138:chemical synthesis / Q000737:chemistry* / Q000494:pharmacology; D008826:Microbial Sensitivity Tests; D015394:Molecular Structure; D010397:Penicillanic Acid / Q000737:chemistry*; D021241:Spectrometry, Mass, Electrospray Ionization; D013450:Sulfones / Q000138:chemical synthesis / Q000737:chemistry* / Q000494:pharmacology; D065093:beta-Lactamase Inhibitors; D001618:beta-Lactamases
chemical_list: D001426:Bacterial Proteins; D004791:Enzyme Inhibitors; D013450:Sulfones; D065093:beta-Lactamase Inhibitors; D010397:Penicillanic Acid; D001618:beta-Lactamases; C063912:carbapenemase
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