Gallium(iii) and iron(iii) complexes of quinolone antimicrobials

Abstract

Iron is an essential nutrient for many microbes. According to the “Trojan Horse Hypothesis”, biological systems have difficulties distinguishing between Fe³⁺ and Ga³⁺, which constitutes the antimicrobial efficacy of the gallium(III) ion. Nine novel tris(quinolono)gallium(III) complexes and their corresponding iron(III) analogs have been synthesized and fully characterized. Quinolone antimicrobial agents from three drug generations were used in this study: ciprofloxacin, enoxacin, fleroxacin, levofloxacin, lomefloxacin, nalidixic acid, norfloxacin, oxolinic acid, and pipemidic acid. The antimicrobial efficacy of the tris(quinolono)gallium(III) complexes was studied against E. faecalis and S. aureus (both Gram-positive), as well as E. coli, K. pneumonia, and P. aeruginosa (all Gram-negative) in direct comparison to the tris(quinolono)iron(III) complexes and the corresponding free quinolone ligands at various concentrations. For the tris(quinolono)gallium(III) complexes, no combinational antimicrobial effects between Ga³⁺ and the quinolone antimicrobial agents were observed.