6‑Halopyridylmethylidene Penicillin-Based Sulfones Efficiently Inactivate the Natural Resistance of Pseudomonas aeruginosa to β‑Lactam Antibiotics

Pseudomonas aeruginosa, a major cause of nosocomial infections, is considered a paradigm of antimicrobial resistance, largely due to hyperproduction of chromosomal cephalosporinase AmpC. Here, we explore the ability of 6-pyridylmethylidene penicillin-based sulfones 1–3 to inactivate the AmpC β-lactamase and thus rescue the activity of the antipseudomonal ceftazidime. These compounds increased the susceptibility to ceftazidime in a collection of clinical isolates and PAO1 mutant strains with different ampC expression levels and also improved the inhibition kinetics relative to avibactam, displaying a slow deacylation rate and involving the formation of an indolizine adduct. Bromide 2 was the inhibitor with the lowest K I (15.6 nM) and the highest inhibitory efficiency ( k inact / K I ). Computational studies using diverse AmpC enzymes revealed that the aromatic moiety in 1–3 targets a tunnel-like site adjacent to the catalytic serine and induces the folding of the H10 helix, indicating the potential value of this not-always-evident pocket in drug design.