Mechanism of Antibacterial and Degradation Behavior of a Chlorinated Isoxazolylnaphthoquinone

The chemical stability of 3-chloro-2-hydroxy-(3,4-dimethyl-5-isoxazolyl)-1,4-naphthoquinon-4-imine (ClQ1), a new potential antimicrobial agent was analyzed at different pH values by first-derivative spectroscopy. The degradation of ClQ1 followed a pseudo-first-order kinetics in aqueous media at different pH values. The interaction of antibiotics with respiratory chain of Staphylococcus aureus generates superoxide anion, an oxygen radical capable of producing damage to the bacteria. The performed assays have demonstrated that ClQ1 presents higher activity and toxic oxidant generation at pH 5.0 than at pH 7.5. In addition, the antibacterial activity of other halogenated isoxazolylnaphthoquinones was also studied in different collection and clinical strains which presented the following decreasing activity, ClQ1 > BrQ1 > DClQ1 whereas DBrQ1 did not show inhibition properties. The antibacterial and stability properties evidenced by ClQ1 are so important that must be taken into account when new alternative treatments against β-lactamase-positive S. aureus strains are investigated.