Pyridone alkaloids from an Antarctic endolichenic Tolypocladium sp.

Three new pyridone alkaloids, tolypyrone A (1), tolypyrosides A (2) and B (3), and a new tetramic acid 2'-epitolypoalbin (4), along with ten known compounds, were obtained from Tolypocladium sp. CPCC 401485 isolated from an unidentified Antarctic lichen specimen. Structural elucidation of new compounds was achieved by analyses of HRESIMS and NMR spectroscopic data combined with X-ray crystallography, advanced Marfey's method, and ECD calculation. Tolypyrone A (1) was the first 4-pyridone alkaloid with an unusual octahydro-1H-isochromeno[3,4-b]pyridin-4-one triheterocyclic ring system. Compounds 1, 4 and 6 exhibited antimicrobial activities with the minimum inhibition concentration of 16-64 μg/mL.