Secondary Metabolites From Three Marine-Derived Fungi And Their Bioactivities

The sea covers more than two-thirds of the earth’s surface,and nearly four-fifths of all lives on earth thrive in the oceans.So,the sea is an enormous treasure trove of resources.The harsh ecological environment of the ocean makes marine organisms more tolerant to salt,hunger,and pressure.Therefore,the metabolic pathways of marine fungi are quite different from those of terrestrial fungi.The secondary metabolites produced by marine-derived fungi have more special and diverse structures and stronger biological activity and pharmacological properties.Hence,more and more researchers pin their hope for new drug development on the discovery of secondary metabolites.In this paper,three marine-derived fungi from different sources were selected as objects.Trichoderma longibrachiatum A-WH-20-2 was isolated from the marine alga Laurencia okamurai collected from the coasts of Weihai.T.longibrachiatum RR-DL5-4 was isolated from the marine alga Rhodomela confervoides collected from the coasts of Dalian.Aspergillus amstelodami 3-7 was isolated from the marine sediments collected from Yantai coasts.Totally,forty-nine secondary metabolites,including steroids,phenols,terpenes,piperazines,and lactones,were isolated from the three fungal strains,and their bioactivities against bacteria,fungi,microalgae,and brine shrimp were evaluated.The compounds in the sample were repeatedly extracted by organic solvents.Pure compounds were obtained by column chromatography(silica gel column chromatography,RP-18 reversed-phase silica gel,Sephadex LH-20 gel column chromatography),thin-layer chromatography(TLC),and high performance liquid chromatography(HPLC).A total of 26 compounds,including a new compound A1 and a new naturally occurring compond A2,were obtained from T.longibrachiatum A-WH-20-2.18 compounds were isolated from T.longibrachiatum RR-DL5-4.The metabolites of the two strains were very similar.Additionally,5 compounds were isolated from A.amstelodami.All the compounds were tested for antibacterial,antifungal,and antimicroalgal activities as well as brine shrimp lethality.The results showed that compounds A5,A6,and B3 showed significant inhibitory activity against Glomerella cingulata,and the activities were better than that of amphotericin B.Compound A19 has good inhibitory activity against Bacillus subtilis.The inhibition rates of compounds A1–A8,A13,A17,A19–A21,A23,A26,B3,C2,C3,and C5 on Heterosigma akashiwo,Chattonella marina,Prorocentrum donghaiense,and Karlodinium veneficum reached 100% at the final concentration of 100 μg/mL.In this paper,the secondary metabolites of three marine-derived fungi and their biological activities were systematically studied.This not only enriched the research content of secondary metabolites of marine-derived fungi,but also found some active compounds.This study contributes to the further development and utilization of marine-derived fungi.