The Secondary Metabolites And Antibacterial Activities Of Three Marine-derived Fungi And Four Soft Corals Sinularia Sp.

Since terrestrial environment is deteriorating, terrestrial resources areincreasingly scarce, and the incurable diseases, a serious threat to human life andhealth, occur frequently. The demand for new drugs is increasing. Therefore, the hopeof seeking new drugs was put on the marine ecology environment. Marine ecologyenvironment which have a high pressure, high salt, hypothermia, hypoxia and otherspecial environmental characteristics may create abundant biodiversity which can beendowed with unique chemical diversity and distinct bioactivities. Among them, avariety of marine natural products exhibited antibacterial activities. Marineinvertebrates and microorganisms from coral reef ecosystem, rich in antibacterialsecondary metabolites, have become important bioresources for screening anddiscovery of lead compounds and marine drugs. In this study, the chemical diversityand antibacterial activity of secondary metabolites of three marine-derived fungi andfour soft corals Sinularia sp. have been investigated. These researches providedfoundations for the screening and discovery of bioactive marine natural products andlead compounds of marine drugs.In this study, under the guidance of the chemical and bioactive screening, threemarine-derived fungi including Penicillium sp., Phoma sp., Talaromyces sp. and foursoft corals Sinularia sp. collected from the same area at the same time wereinvestigated for their bioactive secondary metabolites. The compounds were isolatedby column chromatography on silica gel, Sephadex LH-20and preparative reversedphase HPLC, and identified by spectroscopy of NMR, MS, IR, UV, CD as well aschemical methods. From these organisms,110compounds were obtained, including 21new compounds (1–3,6–8,11–14,36–38,40,50,66,80,81and91). More than9structural types were found, including21isocoumarins and benzofurans,10chromones,6diphenyl ethers,40steroids,11terpenoids,7aromatic compounds,12nitrogen compounds,2quinone derivatives and1lactone. Compounds1,1A-1and1A-2were isolated from the sponge-derived fungus, Penicillium sp., which representa rare naturally occurring isocoumarin derivative with4-substitution, but nosubstituent at the3-position. The relative and absolute configurations of1weredetermined by quantum chemical calculation of its ECD spectrum combined with themodified Mosher’s method. The isocoumarins (2–5) with side chain at C-3, were alsoobtained from the Penicillium sp. fungus. The absolute configurations of compounds2–5were assigned by the modified Mosher’s method together with comparison of CDspectra. The new aromatic amphilectane-type diterpenes (80and81) were isolatedfrom Sinularia sp. for the first time.The isolated compounds were evaluated their antibacterial activity and otheractivities by various of screening modles including antifouling, ichthyotoxic, lethalityand so on. A variety of bioactive compounds had been found, including25antibacterial and cytotoxic activity compounds and24antifouling, lethality activity,and ichthyotoxic activity compounds. Amphilectane-type diterpenes showed stronginhibitory activity against Escherichia coli, Staphylococcus albus and Vibrioanguillarum. Compound80displayed strong inhibitory activity against S. albus withan MIC value of0.156μM, which was stronger than that of the positive controlciprofloxacin (MIC0.312μM). Steroids15,18,21and22exhibited inhibitory activityagainst Vibrio anguillarum with MIC values of0.39,0.78,0.78and0.39μM,respectively, which were stronger than or equivalent to that of the positive controlciprofloxacin. The results of antibacterial activity suggested that the ketone carbonylgroups, epoxy rings and peroxy groups in steroids played apparent role on theantibacterial activity. The diphenyl ethers exhibited antibacterial activity. Compound39displayed better potent antibacterial activity than compounds36and38, with thesubstituted methoxy and hexose residue. These results indicated that the antibacterialactivity might be weakened due to the substituent of methoxy and hexose residue. And the isocoumarins2,4,5and7displayed24h coagulated eggs of zebrafish at theconcentrate of6.42,5.68,8.87and7.13μg/mL,72h death of zebrafish at theconcentrate of4.07,3.95,6.48and4.15μg/mL, respectively. The study ofstructure-activity relationships about isocoumarins showed that the presence of3-substituted side chain and the acetylation of hydroxymethyl at C-4increased thezebrafish toxicity. The substituted hydroxyl at C-7probably weakened thezebrafish toxicity. The bioactive results indicated that isocoumarins, benzofurans,9,11-secosterols,13(14â†'8)abeo-8-ergostane and diphenyl ethers exhibited a varietyof biological activities.The secondary metabolites of four soft corals Sinularia sp.1(GX-WZ-27-49),Sinularia sp.2(GX-WZ-32-47), Sinularia sp.3(GX-WZ-28-33), Sinularia sp.4(GX-WZ-46) collected from the same area at the same time were compared andanalyzed. It indicated that the different species in Sinularia genus collected from thesame area at the same time shared similarities and differences. The secondarymetabolites included many structural types, such as9,11-secosterols,amphilectane-type diterpenes, pregnane, cyclic sesquiterpene peroxides, and so on. Itsupplied foundation for further investigation for the chemotaxonomic significance ofthe Sinularia genus.In conclusion, in present study under the guidance of the chemical and bioactivescreening, bioassay-guided fractionation of three marine-derived fungi and four softcorals Sinularia sp. led to the isolation of a variety of bioactive natural products. Theabsolute configurations of isocoumarins were assigned by the modified Mosher’smethod and TDDFT ECD calculation together with comparison of CD spectra. Theresults of antibacterial activity suggested that the ketone carbonyl groups, epoxy ringsand peroxy groups in steroids played apparent role on the antibacterial activity. Thearomatization of amphilectane-type diterpenes increased the antibacterial activity. Theresults of bioactive evaluation indicated that the isolated compounds exhibited avariety of biological activities, and some compounds have been found to possessecological activity and pharmacological activities at the same time. The studyindicated that the secondary metabolites of marine-derived fungi and soft corals display chemical diversity and pronounced antibacterial activity. It providedfoundations for the discovery and exploration of antibacterial marine natural products.