Lipophilic Trimethoprim Analogues and Their Potent Antibacterial Activity Against Trimethoprim‐Resistant MRSA

Abstract The alarming emergence of methicillin‐resistant Staphylococcus aureus ( S. aureus ) or MRSA has posed a severe threat worldwide. In addition to β‐lactam antibiotics, MRSA has also been reported resistance towards other antibiotics, including trimethoprim. The rise of multi‐drug resistance has called for new antibacterial strategies. In this study, we revisited trimethoprim and its binding to dihydrofolate reductase (DHFR) in trimethoprim‐resistant strains. S. aureus DHFR has a shallow surface cavity that is electron‐rich. Therefore, incorporating lipophilic groups into trimethoprim could improve its binding to S. aureus DHFR and potentially enhance antibacterial activity. We synthesized lipophilic trimethoprim derivatives and subjected to susceptibility testing against methicillin‐susceptible S. aureus , global predominant MRSA USA300 strain, and trimethoprim‐resistant MRSA strain COL. ( E )‐5‐(3,4‐dimethoxy‐5‐(4‐methoxystyryl)benzyl) pyrimidine‐2,4‐diamine or TMP‐sytrene‐OMe ( 6 ) was the most potent growth inhibitory activity with minimum inhibitory concentration (MIC) of 4 µg/mL and minimum bactericidal concentration (MBC) of 8 µg/mL against trimethoprim‐resistant strain COL. The modification led to a significant improvement over TMP. DHFR kinetic assay indicated that compound 6 inhibited DHFR‐catalyzed reaction in concentration‐dependent manner. Molecular docking studies suggested the increase of binding interactions to S. aureus DHFR and trimethoprim‐resistant S1DHFR when compared to trimethoprim. These findings underscore the promise of lipophilic‐incorporated trimethoprim derivatives as effective antibiotics against MRSA infections.