The ability of the endophytic fungus Umbelopsis dimorpha SWUKD3.1410 to transform the triterpene nigranoic acid (3, 4-secocycloarta-4(28), 24-(Z)-diene-3, 26-dioic acid; 1) was investigated. Co-culture of nigranoic acid with U. dimorpha SWUKD3.1410 yielded six major products, including a new triterpene (2) and 5 known compounds (3-7). Their structures were identified by the extensive 1D, 2D NMR and HR-ESI-MS Data analysis, and by comparison with those reported data. Among them, 2-4 were transformed from nigranoic acid (1), while 5-7 were derived from the culture medium stimulated by the substrate. On the basis of the structures of 2-4, it was proposed that the transformative process probably involved isomerase and hydroxylase, in which the former was rare in fungi. Additionally, all the compounds (1-7) were evaluated for their cytotoxic activity. As a result, compounds 1, 3-5 exhibited weak cytotoxicity against the tested cell lines, while others showed no cytotoxicity.
Keywords: Endophytic fungus; Umbelopsis dimorpha; cytotoxicity; microbial transformation; nigranoic acid; structural identification.