Azacoccones F-H, new flavipin-derived alkaloids from an endophytic fungus Epicoccum nigrum MK214079.

Three new flavipin-derived alkaloids, azacoccones F-H (1-3), along with six known compounds (4-9) were isolated from the endophytic fungus Epicoccum nigrum MK214079 associated with leaves of Salix sp. The structures of the new compounds were established by analysis of their 1D/2D nuclear magnetic resonance (NMR) and high-resolution electrospray ionization mass spectroscopy (HRESIMS) data. The absolute configuration of azacoccones F-H (1-3) was determined by comparison of experimental electronic circular dichroism (ECD) data with reported ones and biogenetic considerations. Epicocconigrone A (4), epipyrone A (5), and epicoccolide B (6) exhibited moderate antibacterial activity against Staphylococcus aureus ATCC 29213 with minimal inhibitory concentration (MIC) values ranging from 25 to 50 μM. Furthermore, epipyrone A (5) and epicoccamide A (7) displayed mild antifungal activity against Ustilago maydis AB33 with MIC values of 1.6 and 1.8 mM, respectively. Epicorazine A (8) showed pronounced cytotoxicity against the L5178Y mouse lymphoma cell line with an IC50 value of 1.3 μM.