A Selective Bis-Catecholate Siderophore-Ampicillin Conjugate Expands Activity against Multidrug-Resistant Pseudomonas aeruginosa.

Antimicrobial resistance is a global public health crisis, with multidrug-resistant P. aeruginosa among the most critical threats. The high cost and slow pace of novel antibiotic development, coupled with rapid resistance evolution, demand innovative strategies. Here, we present a Trojan horse approach using siderophore-antibiotic conjugates (SACs) to hijack bacterial iron uptake systems and deliver β-lactam payloads across the Gram-negative outer membrane. We designed a series of ampicillin conjugates with mono-catecholate, bis-catecholate, and catecholate-hydroxamate siderophores. These conjugates demonstrate potent antimicrobial activity. Notably, the lead compound, BC-2-Amp, shows broad-spectrum and highly selective activity against a panel of 105 clinical isolates of P. aeruginosa. Mechanistic studies demonstrated that BC-2-Amp utilizes PiuA as a critical receptor for targeted delivery. Complementary in vivo experiments further confirmed its promising therapeutic efficacy. Collectively, these findings establish SACs as a potent strategy for broadening the spectrum of β-lactam antibiotics and provide a robust platform for high-potency drug delivery.