Design and Synthesis of Novel 1,2,4-Triazole Tethered 4-(1,5-Diphenyl-4,5-dihydro-1H-pyrazol-3-yl) phenol Hybrids: Molecular Docking and In Vitro Antifungal Studies

With the rise of invasive fungal infections and the increasing amount of clinical resistance to azole antifungals, developing new classes of antifungal agents that exhibit better binding to molecular target sites has become critical. In this paper, we describe the synthesis, characterization, molecular docking and antifungal testing of ten new antifungal hybrids (12a-j), which have been produced by linking two pharmacophores, a 1,2,4-triazole-3-thiol and a 4-(1,5-diphenyl-4,5-dihydro-1H-pyrazol-3-yl)phenol, through a methylene linker. The hybrids were prepared via a convergent synthetic scheme involving: thiocarbohydrazide production, triazole cyclization, Claisen-Schmidt stoichiometric coupling, pyrazolines formation and finally, etherification of the products using KOH in alcohol and DMF. The hybrids were successfully synthesized in yields between 71% and 81% on average. All compounds were fully characterized by IR, ¹H NMR, Mass spectroscopy and elemental analysis, and each compound exhibited spectroscopic data consistent with proposed structures. The binding of the intermediate compound with CYP51 lanosterol 14α-demethylase (PDB ID: 5TZ1) was confirmed after molecular docking where all compounds had a higher binding value compared to fluconazole (-7.38 kcal/mol), with the compound 12c having the highest at -11.8 kcal/mol. In vitro antifungal screening using the agar disc diffusion method showed the compound had a better result than fluconazole for testing against Aspergillus niger, Candida albicans, Candida glabrata and Candida tropicalis, and found that the greatest inhibition zone (17.5 mm and 16.2 mm versus a control of 14 mm) against A. niger resulted from the use of compounds 12e and 12c, and the greatest inhibition zones (20.2 mm and 19.1 mm versus a control of 18 mm) against C. albicans were from use of the compounds 12e and 12b. A clear structure activity trend was evident in that the presence of halogen substituents on an electron withdrawing basis increased CYP51 binding to the compounds, while compounds containing an electron-donating group scored lower in biological activity. Therefore, the compounds identified as the best for further preclinical development were compounds 12c, 12b, 12e and 12f.