Exploration Novel of Pyrazole and Isoxazole Derivatives as Potential Antimicrobial Agents: Design, Synthesis,...

Developing new antimicrobial drugs is crucial for combating global drug resistance caused by microbial infections. Here, a new series of pyrazole and isoxazole derivatives were synthesized using a multicomponent reaction based on ethylvanillin and active methylene group as well as binucleophile reagents under basic conditions. The designed derivatives were confirmed using FT-IR, ¹H NMR, ¹³C NMR, Mass spectrum, and elemental analysis. Subsequently, all the designed derivatives were evaluated against four bacterial and one fungal strain. The synthesized derivatives demonstrated significant to good antimicrobial activity with low MIC values against the tested strains, especially against Bacillus subtilis, Staphylococcus aureus, and Candida albicans. Notably, four compounds 14, 17, 20, and 24 showed promising MIC values ranging from 7.8 to 62.5 µg/mL) against gram-positive strains and for gram-negative strains (MIC = 31.25-125 µg/mL), compared to gentamycin (15.62 and 31.25 µg/mL), respectively. In addition, these derivatives revealed MIC values from 15.62 to 31.25 µg/mL compared to fluconazole (MIC = 15.62 µg/mL) against C. albicans. Additionally, the structure activity relationships (SAR) were discussed. Moreover, the MBC and MFC values were evaluated and the results exhibited bactericidal and fungicidal properties, except for 5-hydroxy-1H-pyrazole-1-carbothioamide derivative 14 that demonstrated bacteriostatic activity against B. subtilis. Moreover, the biofilm inhibitory activity of the most promising derivatives demonstrated a dose-dependent effect and inhibit biofilm formation from 96.17 ± 0.004% to 66.04 ± 0.004%. Among these compounds, the 5-hydroxy-1H-pyrazole-1-carbothioamide derivative 14 emerged as the most active, exhibiting a biofilm inhibitory percentage (BIP) of 96.17 ± 0.004% compared to gentamicin's BIP of 96.44 ± 0.004% at 75% MIC. Finally, a docking simulation of the most promising derivatives was conducted within the active site of Las R, suggesting a potential mode of action, where these derivatives displayed different binding interaction with low binding affinity. Moreover, in-silico oral bioavailability and toxicity profile was predicted for the most promising derivatives and exhibited promising physicochemical properties with a safe toxicity profile, opening up the possibility of the discovery of new antibiotics.