Study On The Secondary Metabolites Of Two Marine Endophytic Fungi And Their Biological Activities

Marine microorganism is one of the hot research of natural products,many novel compounds were found in them.It is of great significance to study the innovative drugs and lead compounds.The secondary metabolites of fungi include terpenoids,steroids,alkaloids and so on.A large number of compounds have been shown to have significant antibacterial,antioxidant and antitumor activities.Marine microorganisms are involved in the metabolism of host plants,they have diversity in structure and activity.In this study,we study the secondary metabolites of marine endophytic fungi and screen their secondary metabolites.1.Isolation and identification of marine endophytic fungiIn this paper,marine algae were collected from the intertidal zone in Weihai,and a total of 35 strains were isolated.Batch fermentation in three different culture medium was conducted in small scale,ethyl acetate was used to extract the secondary metabolites.The biological activity of these 35 strains was screened by DPPH method.The chemical composition of 35 actinomycetes were determined by high performance liquid chromatography,thin layer chromatography and its content.1403-08 PDP was selected as the active strain for further study.2.Isolation,identification and antibacterial activity of secondary metabolites of Aspergillus versicolor PT-20Modified PDP medium was used to ferment Aspergillus versicolor PT-20 strain,and its secondary metabolites were extracted by ethyl acetate.Using thin layer chromatography,silica gel column chromatography,reversed-phase silica gel column chromatography and Sephadex LH-20 gel column chromatography and recrystallization method,the secondary metabolites were isolated and purified.14 compounds were identified by nuclear magnetic resonance,infrared spectrum,mass spectrometry.These compounds are anthraquinone,xanthone,diketopiperazine,sulfur-containing benzofurans and steroidal compounds.The antibacterial activity of isolated compounds detected by filter paper method against Bacillus subtilis,Escherichia coli and Staphylococcus aureus.The minimum inhibitory concentrationby the broth dilution method was used to determine the activity of compound 3.The antioxidant activity of the compounds was determined by DPPH method.The results showed that compounds 8,9,and 10 had higher antioxidant activity.The scavenging rate of DPPH was about 89.95%,73.75%and 88.89%.3.Isolation,identification and antibacterial activity of secondary metabolites of Aspergillus versicolor 1403-08The 1403-08 strain were fermented by modified PDP medium.Ethyl acetate was used to extract of mycelium and fermentation liquid.Sephadex LH-20 gel column chromatography,silica column chromatography,reversed-phase silica column chromatography,thin layer chromatography were used to separate the secondary metabolites.6 were identified by spectroscopic methods as anthraquinone and ketone compounds.The antibacterial activity of these compounds against Bacillus subtilis,Staphylococcus aureus and Escherichia coli were assayed by filter paper method.DPPH method was used to determine the antioxidant activity and none of them showed this kind of activity.This paper screened the marine fungi,isolated the secondary metabolites and identified the structure of the compounds.A series of anthraquinone,xanthone,diketopiperazine and steroid compounds were found.The above studies provide support for the discovery of active species and lead compounds in marine natural product.