Secondary Metabolites From Three Endophytic Fungi Isolated From The Medicinal Plant Mahonia Fortunei

An endophyte is a bacterial（including actinomycete）or fungal microorganism,which spends the whole or part of its life cycle colonizing in the healthy tissues of the host plant harmoniously without causing any apparent negative effect.There are long-term,stable and complex interactions between endophytes and host plants or environment.These interactions promote endophytic fungi with strong biosynthesis ability,and can produce structurally interesting and biologically active secondary metabolites.Endophytic secondary metabolites,a major source of lead compounds,are widely considered to be one of the best reservoirs for drug discovery from natural sources.Recently,whole genome sequencing of microbes has revealed the existence of silent pathways,which are not always expressed under standard culture conditions.These pathways allow researchers to explore the chemical diversity of microbes by physically or chemically triggering these silent gene clusters,such as OSMAC（one strain–many compounds）.In this paper,on the base of pre-screening activity,three endophytic fungi（including Colletotrichum fioriniae F18,Clonostachys rosea F6 and Chaetomium nigricolor F5）,harbored in the medicinal plant Mahonia fortunei,were selected for large scale fermentation,led to the isolation of 22 compounds including one cytochalasans,chamiside A（1）,seven illudalane sesquiterpene compounds,granulolactone B（2）,echinolactone A（3）,radulactone（4）,deoxypterolactone（5）,calomelanolactone（6）,granulolactone（7）and granulolactone C（10）,five alkaloid compounds,glioperazine C（13）,N-acetyltryptamine（14）,makomotindoline B（15）,3-indoleacetic acid methyl ester（16）and N-phenethylacetamide（22）,seven aromatic compounds,isochaetochromin A₁（9）,dibutyl phthalate（12）,2-（4-hydroxyphenyl）acetic acid（17）,4-（2-hydroxyethyl）phenol（18）,2-（4-methoxyphenyl）acetic acid（19）,4-hydroxyphenethyl 2-（4-hydroxyphenyl）acetate（20）and regiolone（21）,and other compounds 4-Methyl-5,6-dihydro-2H-pyran-2-one（8）and ergosterol（11）.Their structures were elucidated by extensive spectroscopic analyses,ECD calculation,and single-crystal X-ray diffraction analysis.compounds 1,2,10 and 14 were new.Compound 1 represents a new family of cytochalasans featuring an unprecedented6/6/5-fused tricyclic core skeleton.A rare seven-membered lactone and a benzene ring were further linked to the tricyclic skeleton.The unprecedented skeleton of 1 enriches the structural diversity of cytochalasans.Notably,combination with whole genome sequencing of Chaetomium nigricolor F5,the biosynthetic pathway for the unique core structure of 1has been proposed.Compound 2-7 belong to illudalane sesquiterpene,which is currently derived from fungi,and only 15 such compounds have been found.Additional,OSMAC method used in Chaetomium nigricolor F5 afforded a new compound 10.Antibacterial activity assay indicated that compounds 13-22 had no antibacterial activities against Bacillus subtilis,Staphylococcus aureus,Escherichia coli,and Pseudomonas aeruginosa,as well as no quorum sensing inhibitory（QSI）activity for Chromobacterium violaceum.Chamiside A（1）was evaluated for antibacterial activities showed moderate efficacy against the bacterium S.aureus with an MIC of 25μg/mL,and weak cytotoxic activities(against human lung cancer cell line A549,the human breast adenocarcinoma cell lines MCF-7 and mouse colon cancer cell CT-26,showed IC₅₀ 27,32,38μM,respectively).