Synthesis and antibacterial activities of quercetagetin derivatives

The global rise of bacterial drug resistance has prompted growing attention towards the development of novel antibacterial lead compounds. This work reports the synthesis and characterisation of a series of quercetagetin derivatives (2-15) using comprehensive spectroscopic techniques (1H/1³C NMR, HRMS). Antimicrobial screening against four bacterial strains (Escherichia coli, Staphylococcus aureus, Salmonella enteritidis and Pseudomonas aeruginosa) identified compound 14 as the most potent agent, exhibiting an MIC of 16 µg/mL against S. aureus. Further pharmacological evaluation demonstrated its rapid bactericidal effect (complete eradication within 8 h) and biofilm inhibition capability. SAR analysis revealed that pentenyl modification significantly enhances antibacterial activity, suggesting new directions for developing quercetagetin-based antimicrobials.