Rare Chlorinated Fungal Metabolite and Alpha-Pyrones from an Endophytic Fungus Nigrospora sp.

Endophytic microorganisms have been recognized as potential sources of new chemical entities with applications in the pharmaceutical, biotechnology, agricultural, and other industries. This study investigated the secondary metabolites produced by an endophytic Nigrospora sp. isolated from the Nigerian plant, <i>Gongronema latifolium</i>. Standard procedures were followed for fungal isolation, taxonomic identification, fermentation, and extraction of secondary metabolites. The antioxidant and antimicrobial properties of the fungal extract were assessed using the 1,1-diphenyl-2-picrylhydrazyl (DPPH) antioxidant assay and the agar-well diffusion assay, respectively. Various chromatographic and spectroscopic techniques were used to isolate, purify, and characterize compounds from the fungal extract. At 500 μg/mL, the fungal crude extract showed average antioxidant activity with a 48% inhibition. The extract also demonstrated moderate antimicrobial activity at 1 mg/mL against <i>Bacillus subtilis</i> and <i>Salmonella typhi</i>, with an inhibition zone diameter of 2 mm produced against both test strains. The fungal extract yielded six compounds, including the rare, chlorinated metabolite, acrodontiolamide (<b>1</b>), and five α-pyrone derivatives: hydroxypestalopyrone (<b>2</b>), pestalopyrone (<b>3</b>), pestalotiopyrone D (<b>4</b>), <i>cis</i>-4-hydroxymellein (<b>5</b>), and its <i>trans</i>-isomer (<b>6</b>). Interestingly, this is the second report of acrodontiolamide (<b>1</b>) in nature, after its first report in 1993. These compounds possess a wide range of known biological activities, including antimicrobial, antitumor, and cytotoxic effects, valorizing their potential in drug development.