Secondary metabolites of Hypoxylon investiens, an endophytic fungus derived from Ilex formosana

Hypoxylon investiens (Xylariaceae) is an endophytic fungus, which was isolated from the root of Ilex formosana (Aquifoliaceae), an endemic plant in Taiwan. The chemical constituents of 32 species of Hypoxylon genus were studied previously. The isolated secondary metabolites including of azaphilones, benzenoids, chromones, cytochalasins, diterpenoids, fatty acids, isocoumarins, macrocyclic polyesters, and tetralones, and showed antimicrobial, antifungal, superoxide anion radical inhibitory, antitumor, anti-HIV-I, cytotoxicity, and antibacterial activities. This H. investiens was processed through liquid fermentation, and the fermentate was partitioned with ethyl acetate and water. The ethyl acetate layer potentially inhibited the production of proinflammatory mediators in RAW264.7 mouse macrophage cells in a dose dependent manner. A subfraction suppressed the lipopolysaccharide-induced interleukin-6 (IL-6) and the nitric oxide (NO) production with IC₅₀ values of 14.03 µg/mL and 14.62 µg/mL, respectively. Bioassay-guided fractionation of the active ethyl acetate layer of H. investiens led to the isolation of one new benzenoid, hypoxyphenone (1), one new azaphilone derivative, hypoillexidiol (2), and one alkaloid, firstly isolated from nature, 1-hydroxy-isoindolinone (3), along with 11 known compounds, including three isocoumarins, (R)-(–)-5-methylmellein (4), (R)-(–)-5-formylmellein (5), (R)-5-hydroxymellein (6), three sesquiterpenoids, hypoxylonol A (7), xylaranol A (8), xylaranol B (9), two benzenoids, 4-methoxybenzoic acid (10), tyrosol (11), one alkaloid, cyclo (L-Lue-L-Pro) (12), one lignan, syringaresinol (13), and one steroid, ergosta-4,6,8(14),22-tetraen-3-one (14). The structures of these compounds were elucidated by spectroscopic methods, mainly 1D and 2D NMR spectroscopy together with HRESIMS analysis.

Keywords: Hypoxylon investiens, Xylariaceae, Endophytic fungus, Ilex formosana, Aquifoliaceae