Novel Rationally Designed Lipopeptides Derived from Bacitracin: Combating Multidrug Resistance and Evading Bacitracin Resistance via Potentiated Cell Wall and Membrane Inhibitions.

The escalating threat posed by multidrug-resistant bacteria underscores the urgent need for novel antibiotics. Bacitracin, with its unique undecaprenyl pyrophosphate-targeting mechanism, serves as an ideal template for structural optimization. Herein, we developed a site-selective modification strategy targeting the 7-ornithine amino group, a critical yet underexplored residue in bacitracin. This approach revitalized bacitracin's therapeutic potential against multidrug-resistant pathogens, achieving even up to 256-fold improved activity against methicillin-, vancomycin-, and daptomycin-resistant strains while systematically establishing previously unreported SAR at this locus. The lead compound, Bac-51, incorporating an optimized trifluoromethyl biphenyl moiety, demonstrated superior in vitro potency, favorable safety/pharmacokinetic profiles, and single-dose efficacy in a lethal MRSA sepsis murine model. Mechanistic studies revealed it has a dual mode of action: enhanced peptidoglycan biosynthesis inhibition and membrane-disrupting activity, which minimized resistance development and exhibited continuous efficacy against acquired bacitracin-resistant strains. Collectively, Bac-51 represents a next-generation bacitracin analog as a promising candidate for combating multidrug-resistant Gram-positive infections.