Synthesis and biological evaluation of tris(4-methoxyphenyl)phosphonium-hydrazone derivatives against clinical methicillin-resistant Staphylococcus aureus (MRSA) isolates: antibacterial, antibiofilm, and gene expression analyses.

In this study, four novel tris(4-methoxyphenyl)phosphonium-hydrazone derivatives were synthesized and structurally characterized by FT-IR and NMR spectroscopy. Their antioxidant activities were evaluated using DPPH and ABTS radical scavenging assays. The antibacterial and antibiofilm activities of the synthesized compounds were investigated against eight clinical MRSA isolates. Furthermore, the effects of the most active compound on the expression of the icaA, dltB, and mepA genes were determined by quantitative real-time PCR (qRT-PCR). Among the synthesized compounds, compound 1d exhibited the strongest antioxidant activity, with IC₅₀ values of 37.1 ± 0.62 and 23.1 ± 0.70 µg/mL against DPPH and ABTS radicals, respectively. In the disk diffusion assay, all synthesized compounds produced larger inhibition zones than the cefoxitin (FOX, 30 µg) control. Compound 1c demonstrated superior antibacterial activity with MIC values ranging from 0.5 to 1 µg/mL against the tested clinical MRSA isolates. At the MIC level, compound 1c maintained considerable antibiofilm activity, reducing biofilm formation by 30.2-48.4%. Moreover, compound 1c significantly downregulated the expression of the biofilm- and resistance-associated genes icaA, dltB, and mepA. These findings indicate that tris(4-methoxyphenyl)phosphonium-hydrazone derivatives, particularly compound 1c, are promising candidates for the development of new therapeutic agents against biofilm-associated MRSA infections.