Crystallographic Study, Biological Evaluation and Docking/MD/POM Analyses of Isoxazole-Linked Sulfonate Ester Conjugates

In the present study, a series of isoxazole derivatives were severally evaluated for their antifungal activity against the yeast Candida albicans and molds such as Aspergillus niger, Aspergillus flavus, and Fusarium oxysporum. The results demonstrate that the isoxazole derivatives exhibit considerable antifungal potential, particularly isoxazole-sulfonate ester 4b (Ar= 4-(Cl)C6H4, Ar′= 4-(CH3)C6H4), which was found to be active with significant inhibition zones; the diameters of the C. albicans and F. oxysporum samples were measured at 17.00 ± 0.00 mm and 14.00 ± 0.00 mm, respectively. Furthermore, compounds 4a (Ar= 4-(CH3)C6H4, Ar′= 4-(CH3)C6H4), 4c (Ar: 4-(Cl)C6H4, Ar′: 4-(NO2)C6H4) and 4d (Ar: 4-(Cl)C6H4, Ar′: 3-(Cl)-2-(OCH3)C6H3) demonstrated MIC and MFC values of 20 µg/mL against C. albicans. In addition, the anti-hemolytic activity of these derivatives was evaluated. Compounds 4a, 4e (Ar: 4-(Cl)C6H4, Ar′: 3,4-(OCH3)2C6H3) and aroylisoxazole 3a (Ar: 4-(CH3)C6H4) demonstrated a high degree of anti-hemolytic activity (>99%) at all concentrations evaluated (10, 15, and 20 mg/mL). Molecular docking and molecular dynamics studies over 200 ns revealed protein–ligand complexes to have high affinity and stability, which agrees with the experimental results. The compounds 4d, 4e, and 3a have shown significant interaction with the target proteins of C. albicans, A. flavus, and F. oxysporum, respectively. The results have revealed that the major interaction sites are hydrogen bonding, hydrophobic interactions, and the presence of a water molecule, especially with key residues like TYR_84, ASP_120, SER_90, and THR_89. The crystal structure of compound 4a was also obtained.