Induction of new metabolites from sponge-associated fungus Aspergillus carneus by OSMAC approach.

A comparative study on the metabolic profile of the sponge-associated fungus Aspergillus carneus using the OSMAC approach was conducted. The fungal strain was fermented on three different media including solid rice medium with or without sea salt and modified Czapek medium. Three new natural products, isopropylchaetominine (1), isoterrelumamide A (2) and 5'-epi-averufanin (3), together with fourteen known compounds (4-17) were isolated. The structures of the new compounds were established by 1D and 2D NMR spectroscopic analysis as well as by HRESIMS. Compound 2 was only found when the fungus was cultivated on modified Czapek medium, whereas compounds 4, 7, 11, 12, and 14 were only detected in fungal extracts from solid rice media lacking sea salt. Compounds 8 and 13 on the other hand were only found when A. carneus was cultured on solid rice with sea salt. The cytotoxic and antimicrobial activities of all isolated compounds were evaluated. Compounds 1, 9 and 17 showed strong cytotoxicity against the mouse lymphoma cell line L5178Y with IC50 values of 0.4, 0.3 and 0.2 μM, respectively. In addition, compounds 3, 5 and 6 showed inhibitory activity against different Gram-positive bacterial strains with MIC values ranging from 2.3 to 18.4 μg/mL.