Design and synthesis of novel baicalein-isoxazoles based scaffolds and their anti-microbial potential: in vitro and...

Baicalein, a naturally occurring flavonoid known for its diverse pharmacological properties, was chosen as the core scaffold for the synthesis of a novel series of isoxazole derivatives. The synthetic pathway involved three key steps: protection of baicalein's hydroxyl groups, introduction of a dipolarophile, and a 1,3-dipolar cycloaddition to yield isoxazole-based flavonoid hybrids. The resulting compounds were thoroughly characterized using modern spectroscopic techniques, including LC-MS, ¹H NMR, ¹³C NMR, DEPT-135, and 2D NMR analyses. The antimicrobial activity of all synthesized compounds was evaluated against a panel of Gram-negative and Gram- positive pathogens. Among these derivatives, compound 4p showed remarkable antibacterial activity, with MIC values of 0.88 μM (Staphylococcus aureus), 0.15 μM (Klebsiella pneumoniae), 0.76 μM (Acinetobacter baumannii), and 0.02 μM (Escherichia coli), and corresponding MBC values of 1.56 μM, 0.19 μM, 1.56 μM, and 0.04 μM, confirming its potent biocidal effect. Further, the time-kill kinetics study revealed that the potent hit (4p) exhibited bactericidal activity against the tested pathogens. Additionally, cytotoxicity and hemolysis studies demonstrated a favourable safety profile of a potent hit (4p) against a panel of mammalian cell lines and red blood cells (RBCs), respectively. Highlighting the potential of baicalein-derived isoxazoles as promising scaffolds for the development of novel antimicrobial agents. Molecular docking analysis further indicated satisfactory interaction of the 4p molecule with the target proteins compared to the parent molecule (Baicalein), supporting its potential relevance for further advanced antibacterial studies against ESKAPE pathogens.