Diketopiperazines and 2H-pyran-2-ones with antioxidant activity from the rice fermented with Aspergillus luchuensis.

Aspergillus luchuensis is widely used as a starter of saccharification in the koji industry, but no secondary metabolites have been reported from this fungus. Herein, we report the isolation and identification of four new diketopiperazine derivatives (1-4), one new methyl 4-(3-acetyl-2, 6-dihydroxyphenyl)-2-methoxybutanoate (5), and six known compounds (6-11) from the rice koji of A. luchuensis. The structures of 1-5 were determined by extensive spectral analysis including 1D and 2D NMR, HRESIMS, and CD, and ECD calculation. In antioxidant assays, compound 10 displayed moderate DPPH scavenging activity with an EC50 value of 60.8μM; compounds 1-4, 10 and 11 showed reducing ability with EC50 values ranging from 8.73 to 176.39μM. Compounds 1-11 showed no cytotoxicity against cell lines A549, K562, ASPC, and H460 at 200μM. Our current reports support the safety of A. luchuensis in food chemistry and confirm this fungus to be a new source of natural antioxidants.