Development of Phloroglucinol-Linked Tris-Quaternary Ammonium Salt Antimicrobial Peptide Mimics with Low Cytotoxicity and Broad-Spectrum Antibacterial Activity

Encouraged by the significantly different toxicities and antibacterial activities of diverse linkers, such as alkyl and aromatic nuclei linkers, and the unique structure of phloroglucinol, we synthesized a series of tris-quaternary ammonium salt (tris-QAS) antibacterial peptide mimics based on the marketed drug phloroglucinol. Among them, 2f displayed excellent activity against Staphylococcus aureus (MIC = 0.5 μg/mL) and high selectivity (SI > 2560). Surprisingly, the cytotoxicity of 2f (CC₅₀ = 152.7 μg/mL) was dramatically better than those of alkyl QAS I and hydroquinone QAS II. Additionally, 2f possessed rapid bactericidal capability, was not prone to inducing bacterial resistance, and also exhibited excellent activity against S. aureus biofilms and persistent bacteria. Mechanistic research and transcriptome analysis revealed that 2f can interfere with the normal metabolism of bacterial cells, and it can specifically bind with phosphatidylglycerol to destroy the cell membrane. Importantly, 2f exhibited potent in vivo antibacterial activity in a mouse subcutaneous methicillin-resistant S. aureus (MRSA) infection model.