Targeting fungal biofilms: design, synthesis, biological and in silico studies of novel N-(5-undecyl-1,3,4-oxadiazol-2-yl)benzamide derivatives against Candida albicans

The inhibition of fungal biofilm formation has garnered significant attention as a promising therapeutic strategy against fungal infections. In this study, a series of N-(5-undecyl-1,3,4-oxadiazol-2-yl)benzamide derivatives 5(a–o) were synthesized as novel biofilm inhibitors targeting Candida albicans, utilizing the well-known biological activities linked with the oxadiazole nucleus. The in vitro antifungal activity of all derivatives was evaluated using the broth microdilution method, with fluconazole serving as the reference drug. Notably, compound 5e exhibited potent activity, with a minimum inhibitory concentration (MIC) of 7 μg/mL and a minimum fungicidal concentration (MFC) of 32 μg/mL, outperforming the standard drug (MIC: 8 μg/mL; MFC: 64 μg/mL). Biofilm and hyphal filament inhibition assays further revealed that compound 5e achieved 86.29 % inhibition of biofilm formation and 72.30 % inhibition of fungal filamentation. Additionally, RT-PCR analysis demonstrated that treatment with compound 5e significantly downregulated the expression of key biofilm genes, including ALS1, ALS3, and HWP1. Scanning electron microscopy (SEM) of C. albicans treated with 5e confirmed substantial inhibition of biofilm formation compared to both untreated controls and the fluconazole-treated group. Screening of compound 5e for blood compatibility by hemolytic assay revealed 4.83 % cell lysis at 1125 μg/mL, and cytotoxicity assay on human HEK293 cell line demonstrated that compound 5e was non-toxic to normal cells at the tested concentrations. Furthermore, molecular docking studies to investigate the potential binding interactions of the lead compound, along with ADMET analysis, were performed to assess pharmacokinetic and bioavailability profiles. The enhanced bioactivity of compound 5e is associated with the presence of an ortho-substituted hydroxy group, a 1,3,4-oxadiazole core, and a long hydrophobic alkyl chain, which collectively improve target binding, membrane interaction, and antifungal effectiveness. These findings suggest that compound 5e is a promising candidate for the development of next-generation antifungal agents to combat drug-resistant Candida albicans infections.