A Novel Natural Siderophore Antibiotic Conjugate Reveals a Chemical Approach to Macromolecule Coupling

Abstract

Inspired by natural sideromycins, the conjugation of antibiotics to siderophores is an attractive strategy to facilitate "Trojan horse" delivery of antibiotics into bacteria. Genome analysis of a soil bacterium, Dactylosporangium f ulvum, found a "hybrid" biosynthetic gene cluster responsible for the production of both an antibiotic, pyridomycin, and a novel chlorocatecholcontaining siderophore named chlorodactyloferrin. While both of these natural products were synthesized independently, analysis of the culture supernatant also identified a conjugate of both molecules. We then found that the addition of ferric iron to purified chlorodactyloferrin and pyridomycin instigated their conjugation, leading to the formation of a covalent bond between the siderophore-catechol and the pyridomycin-pyridine groups. Using model reactants, this iron-based reaction was found to proceed through a Michael-type addition reaction, where ferric iron oxidizes the siderophore-catechol group into its quinone form, which is then attacked by the antibiotic pyridyl-nitrogen to form the catechol−pyridinium linkage. These findings prompted us to explore if other "cargo" molecules could be attached to chlorodactyloferrin in a similar manner, and this was indeed confirmed with a pyridine-substituted TAMRA fluorophore as well as with pyridine-substituted penicillin, rifampicin, and norfloxacin antibiotic analogues. The resultant biomimetic conjugates were demonstrated to effectively enter a number of bacteria, with TAMRA−chlorodactyloferrin conjugates causing fluorescent labeling of the bacteria, and with penicillin and rifampicin conjugates eliciting antibiotic activity. These findings open up new opportunities for the design and facile synthesis of a novel class of biomimetic siderophore conjugates with antibiotic activity.

Production of the siderophore lysochelin in rich media through maltose-promoted high-density growth of Lysobacter sp. 3655

“…Due to the high affinity for iron, siderophores exhibit great potential for applications in agriculture, pharmaceutics, and environmental protection. The siderophore-antibiotic conjugation is an attractive strategy to enhance uptake and antibacterial potency against multi-drug resistant pathogens (Caradec et al, 2023 ). Siderophore-producing microbes have the potential to be developed into eco-friendly and sustainable agents to mitigate plant stresses in degraded lands (Singh et al, 2022 ).…”

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“…Due to the high affinity for iron, siderophores exhibit great potential for applications in agriculture, pharmaceutics, and environmental protection. The siderophore-antibiotic conjugation is an attractive strategy to enhance uptake and antibacterial potency against multi-drug resistant pathogens (Caradec et al, 2023). Siderophore-producing microbes have the potential to be developed into eco-friendly and sustainable agents to mitigate plant stresses in degraded lands (Singh et al, 2022).…”