Development of Membrane-Targeting Fluorescent 2-Phenyl-1H-phenanthro[9,10-d]imidazole-Antimicrobial Peptide Mimic Conjugates against Methicillin-Resistant Staphylococcus aureus

The escalation of multidrug-resistant bacterial infections, especially infections caused by methicillin-resistant Staphylococcus aureus (MRSA), underscores the urgent need for novel antimicrobial drugs. Here, we synthesized a series of amphiphilic 2-phenyl-1H-phenanthro[9,10-d]imidazole-antimicrobial peptide (AMP) mimic conjugates (III1–30). Among them, compound III13 exhibited excellent antibacterial activity against G+ bacteria and clinical MRSA isolates (MIC = 0.5–2 μg/mL), high membrane selectivity, and low toxicity. Additionally, compared with traditional clinical antibiotics, III13 demonstrated rapid bactericidal efficacy and was less susceptible to causing bacterial resistance. Mechanistic studies revealed that III13 targets phosphatidylglycerol (PG) on bacterial membranes to disrupt membrane integrity, leading to an increase in intracellular ROS and leakage of proteins and DNA, ultimately causing bacterial cell death. Furthermore, III13 possessed good fluorescence properties with potential for further dynamic monitoring of the antimicrobial process. Notably, III13 showed better in vivo efficacy against MRSA compared to vancomycin, suggesting its potential as a promising candidate for anti-MRSA medication.