Synthesis and Estimation of the Antibacterial Potency of a Series of Azithromycin-Siderophore Conjugates

The increasing threat of antimicrobial resistance (AMR) has driven the need for novel antibacterial agents. Conjugating antibiotics with siderophores may expand their spectrum of activity or enhance their efficacy against AMR strains. In this study, we developed a synthetic route for azithromycin derivatives bound with siderophore moieties containing one or two 2,3-dihydroxybenzamide residues, yielding two series of hybrid molecules (5a-b, 6a-b, 7a-b, and 8a-b, 9a-b, 10a-b). Derivatives 5a, 6a-b, and 7a-b, which bear a single siderophore fragment, exhibited MIC values comparable to those of azithromycin against the majority of tested pathogens. Notably, compounds 7a-b demonstrated increased activity under iron-deficient conditions against Gram-negative Pseudomonas aeruginosa and Escherichia coli strains. In contrast, azotochelin-containing conjugates (9ab and 10a-b) were found to be completely inactive. Although the introduction of a siderophore did not significantly enhance the potency of macrolides in this study, further optimization of the conjugation strategy, linker structure, or chelating moieties may lead to more effective siderophore-macrolide antibiotics.