Research On Secondary Metabolites And Their Activities From Two Mangrove Fungi

Secondary metabolites have played an important role for drug discovery as lead compounds.Microorganisms have been widely studied for their abundant secondary metabolites and convenience for large-scale production.Since the specific living environment,such as high salt level,high temperatures,low oxygen,tide and Strong light,mangrove fungi have unique metabolite pathways,and synthesize some distinct antibiotics in structures and activities.In this study,the OSMAC strategy was used to optimize the fermentation conditions,and the rice solid fermentation products of the mangrove fungi Aspergillus sp.（03-44）and Penicillium sp.（LA11）was chemically investigated.As a result,thirty-four compounds including six new ones were isolated and indentified.These compounds were evaluated for their antimicrobial activities.The mangrove fungus Aspergillus sp.（03-44）was screened out for investigations.As a result,Twenty compounds including four new alkaloids,asperkaloids A-D（1–4）and two new terpenoids,asperrpenoid A（5）and asperrpenoid B（6）were isolated from the culture extract.The planar structures of the new compounds were elucidated by comprehensive spectroscopic analyses of NMR and HRESIMS.The absolute configuration of 1–4 were deduced by electronic circular dichroism calculations（ECD）.All compounds were evaluated for their antimicrobial activities.Compounds 5,14,15and 17 showed antibacterial activity against Staphylococcus aureus,Compounds 14 and17 showed antibacterial activity against Bacillus subtilis and compounds 14-18 also showed antibacterial activity against Ralstonia solanacarum While compound 8 inhibited the production of pigment of Chromobacterium violaceum ATCC1247.Fourteen known compounds（21-34）were isolated from the fermentation of the fungus Penicillium sp.（LA11）.The structures of compounds 21–34 were determined by¹H NMR and ¹³C NMR.It includes three esters（21,22 and 25）,one fatty acid（23）,one coumarin（24）,four indole alkaloids（26–29）,one cyclodepsipeptide（30）,two dicoumarins（31 and 32）,one cytochalasin（33）and five-membered lactone（34）;Compound 33 showed antibacterial activity against Ralstonia solanacarum.In conclusion,the chemical investigation and bioactivity evalution on two mangrove fungi led to the discovery of a series of structurally diverse and biologically active compounds.This study not only enriches the structural types of secondary metabolites from the mangrove fungi,but also lays the foundation for the discovery of drug lead-compounds.