Bioactive secondary metabolites from the endophytic fungi Alternaria sp.

Shifting the drug discovery from plants to microorganisms due to minimizing the ecological effects has led to the increasing work on finding bioactive metabolites from endophytic fungi, especially those isolated from medicinal plants growing in arid and semi-arid land. An endophytic fungi Alternaria sp. isolated from dry land was cultivated on solid rice media and then extracted with ethyl acetate. From the fungal ethyl acetate crude extract of Alternaria sp., compounds altertoxin I (1) and II (2), and stemphyltoxin III (3), were isolated based on the bioactivity assay. The structures of compounds 1-3 were identified using UV, NMR, and mass spectral data and compared to those spectral data reported in the literature. The absolute configuration was determined to be the same as the previous report based on the comparison with the optical rotation value. The three compounds showed strong cytotoxic activity, with altertoxin II being the most active ones having the inhibition of growth observed at 94.4% against murine lymphoma L5178Y cell line at 10 µg/mL. The activity of altertoxin II (2) was probably contributed by the epoxytetralone moiety. The finding of this study still confirms the importance of endophytic fungi as sources of bioactive molecules.