Antibiotic Modulation and Efflux Pump Inhibition by Piperine-Derived Esters and Thiazole Analogs in Multidrug-Resistant Staphylococcus aureus

This article presents the design, synthesis, and biological evaluation of two series of piperinebased derivatives: benzyl piperate esters (12a-12d) and thiazole-acetamide hybrids (17a-17d). Scalable, low-cost synthetic routes afforded the target compounds in moderate to good yields (31-70%). Structural characterization was achieved by infrared spectroscopy (IR), one-dimensional nuclear magnetic resonance (NMR) and high-resolution mass spectrometry (HRMS). In silico absorption, distribution, metabolism, excretion, and pharmacokinetics (ADME) analysis indicated that the compounds are largely consistent with Lipinski’s and Veber’s criteria. Antibacterial activity was evaluated against clinically relevant Gram-positive and Gram-negative bacteria, including Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa. When analyzed on a molar basis, the compounds exhibited moderate intrinsic antibacterial activity, with minimum inhibitory concentrations typically in the hundreds to low thousands of micromolar range. In particular, para‑bromo derivatives and the meta-nitro thiazole displayed the lowest against S. aureus and selected E. coli strains. Mechanistic studies performed in multidrug-resistant S. aureus strains overexpressing NorA (nonoperating room anesthesia) or MsrA (methionine sulfoxide reductase A) efflux pumps demonstrated that the bromo- and nitro-thiazole derivatives significantly reduced the minimum inhibitory concentration (MIC) of norfloxacin in NorA-expressing strains and in MsrA-expressing strains, consistent with the possibility of inhibiting the efflux pump.