Design, Synthesis, and Evaluation of Pyrazole-Isoxazole Hybrids as Dual-Action Agents Against Biofilm-Forming Drug-Resistant Bacteria

The increasing rates of multidrug-resistant (MDR) bacterial infections with the complication of biofilm formation can pose a significant threat to global public health. The present work has involved rational design, synthesis and overall antimicrobial assessment of new pyrazole-isoxazole hybrid scaffolds which target non-adherent as well as adherent bacterial groups. compounds, N’-[(1-(4-chlorophenyl)-1H-pyrazol-4-yl)methylidene]-3-phenylisoxazole-5-carbohydrazide (H1) and N’-[(1-(4-methoxyphenyl)-1H-pyrazol-4-yl)methylidene]-3-phenylisoxazole-5-carbohydrazide (H2), were synthesized via acid-catalyzed condensation of substituted pyrazole-4-carbaldehydes with 3-phenylisoxazole-5-carbohydrazide, achieving yields of 82-85%. The structural elucidation was done using the 1H-NMR, FT-IR, ESI-MS. In vitro antimicrobial evaluation against clinically relevant drug-resistant strains of methicillin-resistant Staphylococcus aureus (MRSA ATCC-43300) and multidrug-resistant Pseudomonas aeruginosa (MDR-PA ATCC-27853) showed promising activity: MIC values were 6.25 to 25.0-μg/ml. It is worth highlighting that H2 with 4-methoxyphenyl substituent was more potent (MIC=6.25 μg/ml against MRSA) compared to the standard ciprofloxacin (MIC=16 μg/ml). Assays of crystal violet biofilm inhibition showed concentration-dependent effectiveness of antibiofilm; H2 exhibited 76.4% biofilm reduction at a half of MIC with MRSA. Time-kill kinetics proved the bactericidal effect, and > 4Log10 reduction of CFU at 2X MIC. These results set pyrazole-isoxazole hybrids as privileged scaffolds on the formation of subsequent-generation antimicrobials that can interfere with growth of bacteria and resistance by biofilm.