Secondary Metabolites And Their Bioactivities Of A Hibiscus Tiliaceus-Derived Endophytic Fungus Eurotium Rubrum And A Mangrove Plant Rhizophora Stylosa Griff.

Mangrove plants are distributed in most tropical and subtropical coastal regions of the world. Some of them have been proven to be a rich source of structural interesting and biological active secondary metabolites. Furthermore, because of their ecosystems that straddled the land and the sea, from freshwater to seawater, mangrove plants are found to be resources of abundant distinct microorganism species including mutualistic fungal endophytes. Mangrove-derived fungi have drawn the interest of more and more natural product chemists as a rich source of structurally unique natural products with a wide range of biological activities.In this dissertation, the static fermentation extracts of 9 endophytic fungal strains derived from mangrove plants on 4 different kinds of liquid cultural mediums, were comprehensively evaluated on the basis of mycelia'biomass, weight of fermentation extracts, antimicrobial activities, and the results of TLC and HPLC analysis. As a result, a strain G2 Eurotium rubrum (isolated from the inner tissue of the semi-mangrove plant Hibiscus tiliaceus) was selected as aimed strain to be inoculated into 30 L of PDB medium for further investigation of its secondary metabolites. Some of the isolated compounds were evaluated for their bioactivities.Additionally, this dissertation also describes the isolation, structure elucidation of chemical constituents from the mangrove plant Rhizophora stylosa Griff., as well as the DPPH radical scavenging activity of some isolated compounds.The compounds were isolated by repeated column chromatography (CC) on silica gel, RP-18, and Sephadex LH-20, as well as by preparative thin layer chromatography (pTLC) and recrystallization. The structures of these compounds were elucidated by means of spectroscopic methods including IR, UV, MS, 1D-NMR and 2D-NMR, as well as compared with reference materials or literatures. Totally, 45 compounds were isolated and structurally elucidated from the extract of Eurotium rubrum G2. Among them, 13 were found to be new structures, including 6 new benzaldehyde derivatives (ER1*~ER6*), 4 new anthraquinone derivatives (ER15*~ER18*), and 3 new dioxopiperazine alkaloids (ER27*~ER29*).Some of the isolated pure compounds were evaluated for their DPPH radical scavenging activity, insecticidal activity, antibacterial and cytotoxic activity. In DPPH radical scavenging assay, ER15*, ER20, ER39, and ER40 showed strong activity. In insecticidal assay, ER15* exhibited moderate insecticidal activity towards neonate larvae of the pest insect Spodoptera littoralis, while ER5* and ER18* did not show any insecticidal activity but seemed to have ability to promote the larvae's growth. It was revealed that the new compounds ER15* and ER18* exhibited weak inhibitory activity against Staphylococcus aureus. None of the tested compounds showed remarkable activity in the in vitro cytotoxic assay against tumor cell lines A-549, HL-60, and P-388.Chemical investigation of the stems and twigs of R. stylosa afforded 29 compounds. Among them, 2 were found to be new structures, including 1 pentacyclic triterpenoid ester (RS1*) and 1 flavanol derivative (RS12*). Additionally, 1 pentacyclic triterpenoid ester (RS5) and 1 flavanol derivative (RS11) were isolated and elucidated as natural substance for the first time.The DPPH radical scavenging activity of some isolated compounds from EtOAc-soluble fraction and n-BuOH-soluble fraction of R. stylosa was studied. Flavanol derivatives RS16 and RS17 showed strongest activity. Moreover, the results revealed that the DPPH radical scavenging activity of flavanol derivatives seemed to be related to the number of phenol groups. Further data analysis revealed that compounds having adjacent hydroxyl groups on the ring-B possessed higher activity.