Acetylcholinesterase inhibitors and antioxidants mining from marine fungi: bioassays, bioactivity coupled LC–MS/MS analyses and molecular networking

Marine fungi are potentially important resources for bioactive lead compounds for discovering new drugs for diseases such as Alzheimer's disease. In this paper, the combined bioassay model of acetylcholinesterase (AChE) inhibition, 1, 1-diphenyl-2-picrylhydrazyl (DPPH) free radical scavenging, and Artemia larval lethality was used to evaluate the activity and toxicity of 35 marine fungal strains from seas around China. Their bioactive constituents were revealed by thin layer chromatography (TLC) autography, bioactivity coupled LC–MS/MS and Global Natural Products Social Molecular Networking (GNPS). The results show that the extracts of five strains exhibited higher AChE inhibition ratios than the positive control compound, 'tacrine', for which the ratio was 89.8% at 200 μg/ml. Six strains displayed both AChE inhibition (inhibition ratios>20% at 200 μg/ml) and DPPH scavenging activity (scavenging ratios>30% at 200 μg/ml) together with low Artemia larval toxicity (lethal rates<12%). TLC autography showed that the fractioned extracts of four strains contained highly diverse and different bioactive constituents, including strains Talaromyces sp. C21-1, Aspergillus terreus C23-3, Trichoderma harzianum DLEN2008005, and Penicillium corylophilum TBG1-17. From the most potent sample F-11-1-b (derived from Aspergillus terreus C23-3), five AChE inhibitors and seven antioxidants were recognized as bioactive molecules by AChE coupled ultrafiltration followed by LC–MS/MS, and LC–MS/MS coupled with DPPH incubation. Furthermore, with the aid of GNPS, the AChE inhibitors were plausibly annotated as territrem analogues including territrems A–C/D, arisugacin A and an unknown compound 4, and the seven antioxidants were assigned as butyrolactone Ι, aspernolide E, a phenolic derivative and possibly unknown compounds 8–10 and 12.