NMR screening approach for discovery of new 6-methylpyridinone derivatives from the marine-derived fungus Leptosphaerulina sp.

By the method of 1H NMR prescreening and tracing the diagnostic signals, 6-methylpyridinone derivatives, (8R,9S)-dihydroisoflavipucine (1), (8S,9S)-dihydroisoflavipucine (2), 3-(1-hydroxy-4-methyl-2-oxopentylidene)-6-methylpyridine-2,4(1H,3H)-dione (3), 4-hydroxy-3-(2-hydroxy-4-methylpentanoyl)-6-methylpyridin-2(1H)-one (4), 4-hydroxy-3-[(4-hydroxy-6-methyl-2-oxo-2H-pyran-3-yl)methyl]-6-methylpyridin-2(1H)-one (5) and a known 6-methylpyranone derivative 3,3′-methylenebis(4-hydroxy-6-methyl-2H-pyran-2-one) (6) were isolated from the marine fungus Leptosphaerulina sp., which was collected from the starfish Acanthaster planci from the South China Sea. Compounds 2 and 3 are new compounds. Their structures were elucidated on the basis of MS, 1D and 2D NMR, and X-ray single crystal diffraction data. The absolute configurations of compounds 1 and 2 were determined by analysis on the experimental circular-dichroism spectra.