Rational N-Terminal Tuning of Bacitracin A: Repurposing a Classic Antibiotic to Combat Multidrug-Resistant Gram-Positive Pathogens.

The increasing threat of infections caused by multidrug-resistant Gram-positive pathogens such as MRSA and VRE has driven the structural remodeling and repurposing of traditional antibiotics as a key strategy to combat bacterial resistance. Herein, using bacitracin A as a lead template, we established a site-selective semisynthetic modification strategy via reductive amination of its N-terminal primary amine. 32 derivatives were designed and synthesized, and their structure-activity relationships were systematically evaluated. Optimized derivatives exhibited potent activity against MRSA and VRE, with 4-32-fold enhanced antibacterial potency compared with bacitracin A, together with improved bactericidal properties, safety profiles, and pharmacokinetic characteristics. Mechanistically, hydrophobic N-terminal modification endows bacitracin A with multiple antibacterial modes, including enhanced inhibition of cell wall peptidoglycan biosynthesis, obvious membrane depolarization, and disruption of the purine metabolic pathway. These findings provide a rational strategy for bacitracin optimization and highlight the potential of N-terminal modification for developing improved antibacterial agents.