Bioactive metabolites from Guignardia sp., an endophytic fungus residing in Undaria pinnatifida

To isolate new and/or bioactive constituents from EtOAc extract of liquid culture of endophyte Guignardia sp. from the leaves of Undaria pinnatifida (Harv.) Sur.

Isolation and purification were performed through silica gel column chromatograph, Sephadex LH-20 and reversed-phase ODS column and the structures of the compounds obtained were identified through a combination of spectral and chemical methods (IR, MS, (1)H and (13)C NMR). In vitro bioactive assays including antifungal activity against three human pathogenic fungi Microsporum canis, Tricophyton rubrum and Epidermophyton floccosom and cytotoxic activity against the human nasopharyngeal epidermoid tumor KB cell line were evaluated.

Seven compounds have been obtained from the liquid culture of the title endophyte: ergosterol peroxide (6, 22-diene-5, 8-epidioxyergosta-3-ol) (1), ergosterol (2), cyclo-(Tyr-Leu) (3), cyclo-(Phe-Phe) (4), cyclo-(Val-Leu) (5), cyclo-(Phe-Pro) (6) and cyclo-(Leu-Ile) (7). Compounds 1-3 and 6 inhibited the growth of M. canis with MICs of 10.0, 20.0, 50.0 and 5.0 μg·mL(-1), respectively and compounds 1, 2 and 6 against T. rubrum with MICs of 15.0, 20.0 and 10.0 μg·mL(-1), respectively and 1 and 6 against E. floccosom with MICs of 20.0 and 50.0 μg·mL(-1), respectively. In addition, compounds 1, 3 and 6 exhibited cytotoxic activity against KB cell line with IC(50) of 20.0, 10.0, 10.0 μg·mL(-1), respectively.

Compounds 1-7 were obtained from Guignardia sp. of U. pinnatifida for the first time, and compounds 1 and 6 had potent cytotoxic and antifungal activity.