Bioactive secondary metabolites from Trichoderma viride MM21: structure elucidation, molecular docking and biological activity

Four bioactive metabolites; ergosterol (1), peroxy ergosterol (2), α-cyclopiazonic acid (3) and kojic acid (4), were isolated from the fungal sp. Trichoderma viride MM21. Their structures were assigned by cumulative analysis of NMR and mass spectra, and comparison with literature. The antimicrobial activity of the fungus supernatant, mycelial cake, cumulative crude extract and compounds 1-4 was broadly studied against 11 diverse pathogens, revealing auspicious activity results. Based on the molecular docking, ergosterol (1) and peroxy ergosterol (2) were picked up to be computationally tested against topoisomerase IV of Staphylococcus aureus. The nominated enzyme is a possible target for the antibacterial activity of triterpenoidal/steroidal compounds. Compounds 1, 2 showed a deep inserting inside the enzyme groove recording a good binding affinity of -8.1 and -8.4 kcal/mol, respectively. Noteworthy that the antibacterial activity of ergosterol was higher (14-17 mm) than peroxy ergosterol (11-14 mm), although ergosterol formed only one hydrogen bond with the target, while peroxy ergosterol formed three hydrogen bonds. Such higher antibacterial activity of ergosterol may be attributed to its interference with other proteins included in this inhibition. The cytotoxic activity was tested against brine shrimp, revealing 100% mortality for the supernatant, crude extract and whole isolated compounds. Such strong cytotoxicity is attributed most likely to the abundant productivity/concentration of α-cyclopiazonic acid and kojic acid.