Metabolites of Marine Fungus Aspergillus sp. Collected from Soft Coral Sarcophyton tortuosum

Fungus Aspergillus sp., which was isolated from soft coral Sarcophyton tortuosum, was cultured in the GPY medium containing glucose 10 g/L, peptone 5 g/L, yeast extract 2 g/L, sea water 1 L, at pH=7.5. Four com- pounds, 3,6-diisobutyl-2(1H)-pyrazinone(1), 3-isobutyl-6-(1-hydroxy-2-methylpropyl)-2(1H)-pyrazinone(2), 3-meth- oxy-4-methyl-2,4-dien-pentanoic acid(3) and penicillic acid(4) were obtained from the AcOEt extract of the culture broth. Their structures were elucidated mainly based on the NMR, HR-EI-MS and X-ray single crystal diffraction experimental data. Compound 3 is a new compound. Compound 1 was previously proposed to be the tautomer of flavacol(3,6-diisobutylpyrazin-2-ol, 5). However, the evaluation of the NMR and X-ray single crystal diffraction experimental data permitted us to propose that compound 1 existed as amide form instead of tautomers. Compound 1 is stable both in solution and crystal due to strong intermolecular hydrogen bonds. Incidentally supplying anthracenone to the GPY medium with a dose of 100 mg/L, the yield of penicillic acid(4) in the culture broth of the strain Aspergillus sp. was increased dramatically from 6 mg/L to 57 mg/L.