Discovery of novel xanthotoxin-pyridine quaternary ammonium derivatives with membrane-targeting mode of action as potential antimicrobials against methicillin-resistant Staphylococcus aureus.

Methicillin-resistant Staphylococcus aureus (MRSA) is a major global health threat owing to its multi-drug resistance, creating an urgent need for novel antibiotics. This study focused on developing anti-MRSA agents by designing and synthesizing 30 xanthotoxin-pyridine quaternary ammonium derivatives, followed by evaluating their antibacterial activity and dissecting their mechanism of action against MRSA. Among all derivatives, III13 demonstrated as the most promising candidate: it exhibited potent anti-MRSA activity (MIC = 1 μg/mL), low cytotoxicity, minimal hemolysis, rapid bactericidal effects, and the ability to disrupt biofilms. Mechanistically, transcriptomics analyses showed III13 inhibited DNA replication-related genes and impaired cell membrane function; further studies confirmed it targeted phosphatidylglycerol (PG) in bacterial membranes, which compromised membrane integrity and induced DNA leakage and oxidative stress. Moreover, III13 displayed excellent efficacy and safety in MRSA-infected mouse models (skin abscesses and sepsis), with performance comparable to vancomycin. Collectively, these results highlight III13 as a promising lead compound for the clinical treatment of MRSA infections.