Chemical Diversity And Biological Evaluation Of Secondary Metabolites From Four Strains Of Deep Sea-Derived Fungi

Structurally unique and biologically active natural products have historically served as a rich source for drug discovery.The special environmental characteristics in deep-sea(>1000 m),such as high pressure,darkness,and extreme living conditions like cold seep and hydrothermal area,has played a major role in the evolution of microbial diversity.Strikingly,deep-sea-derived microorganisms survive under extreme environment,leading to prolific metabolisms and special biological diversity.In this paper,137 strains of fungi were isolated from the deep-sea sediments and benthos samples obtained in different sea areas and water depths.After screening and optimization of culture conditions,in conjunction with chemical and biological indicators,as well as pre-literature searching,four potential strains(Epicoccum nigrum SD-388,Aspergillus insuetus SD-512,A.penicillioides SD-311,and Trichoderma longibrachiatum SD-529)were finally selected for further chemical investigations.As a result,91 compounds were isolated and identified,containing 21 new compounds and one new natural product.Besides,their antimicrobial,antiviral and cytotoxic activities were evaluated.32 compounds(EN 1–EN 32),including eleven new compounds(EN 1*–EN 10*)and one new natural product(EN 11^#),were isolated and identified from the deep-sea-derived fungus E.nigrum SD-388.The relative and absolute configurations of new compounds were determined by RDC and RCSA,chiral HPLC,ECD calculation,as well as X-ray crystallography.Bioactivity assays showed that compounds EN 5*and EN 28 exhibited potent cytotoxic activity against Huh7.5 liver tumor cells with IC₅₀values of 9.5 and 4.9?M,respectively,which were comparable to that of the positive control.Besides,EN 5*and EN 28 showed moderate inhibitory effect against nine strains of pathogenic bacteria.Moreover,(-)-EN 6*inhibited eight strains of pathogenic bacteria,indicating 2R configuration may be essential for the activity.Meanwhile,EN8*and EN 9*displayed moderate antimicrobial activity.34 compounds(AI 1–AI 34),containing nine new compounds(AI 1*–AI 3*,AI 9*–AI 13*,AI 34*),were isolated and elucidated from the cold-seep-derived fungus A.insuetus SD-512.The absolute configurations of new compounds were determined by ECD calculation,acid hydrolysis and derivation and X-ray crystallography.Antibacterial assays showed that AI 3*inhibited eight pathogenic bacteria,implying 6S configuration may be important for the activity.Furthermore,caused by the substituents,AI 9*–AI 11*displayed differences in anti-microbial activity,while the decreasing trend of the activity should be deduced as acetyl substitution>double bond>hydroxy-substitution.In addition,AI12*and AI 34*exhibited moderate antibacterial activity.Nineteen compounds(AP 1–AP 19),covering one new compound(AP 1*),were isolated and clarified from the deep-sea-derived fungus A.penicillioides SD-311.The absolute configuration of AP 1*was established by X-ray crystallography.Bioactivity assays showed that AP 1*displayed weak antibacterial activity.Meanwhile,AP 8 inhibited H1N1 influenza virus at the concentration of 30?M,with the inhibition ratio of 61.7%.Six compounds(TL1–TL 6)were isolated and identified from the cold-seep-derived fungus T.longibrachiatum SD-529.In summary,this study provided the cultural condition optimization,systematical isolation and identification of the secondary metabolites,and bioactivity assays for the metabolites of four deep-sea-derived fungal strains,which enriched the structural types of natural products from the deep-sea-derived fungi and offered foundation for further exploitation and utilization of deep-sea microbial resources.