Studies On Secondary Metabolites Of Marine-derived Fungi From Different Environment: Structures And Bioactivities

Special environment may create specific chemical diversity and biodiversity ofmarine-derived fungi, which made prominent contribution to new lead compounds. Inorder to look for new lead compounds with novel skeletons and potent bioactivities, astudy was carried out to investigate the bioactive compounds derived frommarine-derived fungi. Studies include isolation and screening of bioactive fungalstrains, purification and structural elucidation of the secondary metabolites, exploringthe biosynthetic pathways of the novel compounds, preliminary evaluation forbioactivities of pure compounds and the targets of the active compounds.300fungal strains were isolated from20samples, including marine sediment andsediment around the mangrove roots (Jiaozhou Bay of Shandong Province and HainanProvince). Using cytotoxicity assay and P388cell line as bioactive screen model,together with applying the TLC and HPLC chemical screen assays,10fungal strainswere detected the cytotoxic activity. Among the bioactive strains, a Jiaozhou Baymarine sediment derived fungus Penicillium sp. GHQ-18and a Haikou mangroveroots sediment derived fungus Penicillium sp. GHQ-208, were picked out as theaimed strains. Two Guangdong mangrove roots sediment derived fungi Aspergillusterreus GWQ-48and Cladosporium sp. TZP-29, a Fujian mangrove roots sedimentderived fungus Aspergillus effuses H1-1, a Yellow Sea marine sediment derivedfungus Aspergillus versicolor ZLN-60, a Xisha sponge derived fungus Penicilliumcitrinum MXH-28and a South China Sea marine sediment derived fungusEmericella sp.XJW-9from other sources were also chosen. In all,88compounds were isolated and purified, from the bioactive extracts ofthe8aimed strains, by using solvent extraction, silica gel column, ODS, SephadexLH20, PHPLC and etc. From fungus Aspergillus effuses H1-1,3compounds (1-3)were isolated; from fungus Aspergillus versicolor ZLN-60,25compounds (4-28)were isolated; from fungus Penicillium sp. GHQ-18,8compounds (29-36) wereisolated; from fungus Aspergillus terreus GWQ-48,8compounds (37-44) wereisolated; from fungus Penicillium sp. GHQ-208,12compounds (45-56) were isolated;from fungus Cladosporium sp. TZP-29,6compounds (57-62) were isolated; fromfungus Penicillium citrinum MXH-28,18compounds (63-80) were isolated; fromfungus Emericella sp.XJW-9,8compounds (63-80) were isolated.Basing on their physicochemical properties and spectral data (IR, UV, MS, NMR,CD, and X-ray), combined with quantum chemical CD calculation and marfey’smothod, structures of the88pure compounds were respectively determined. Amongthem there are33alkaloids (1-21,32,45-49,56,87-88),44polyketides (22,25-28,31,33-36,40-44,50,57-83,86),7diterpenes (23-24,51-55),2glycosides (84-85) and2other structural type compounds (29-30). Thirty-four compounds are new, including7new prenylated indole diketopiperazines (4-11),6new cyclic peptides (15-20)，5new fatty acids (26,28,57-59),2new xanthones (31,63),3new benzoic derivates(29,81-82),2new α-pyrones (33,34),1new butyrolactone analog (37),2newmeroterpenoids (51,52) and3other kind alkaloids(32,45,49). In the study, weestablished the relative and absolute configurations of prenylated indolediketopiperazine alkaloids (4-11) by the combination of NOESY, X-Ray, CD, andtheir possible biogenetic deduction. We determined the relative or absoluteconfigurations of the6new cyclic peptides (15-20) by NOESY, Marfy’s method andtheir possible biogenetic deduction. We also determined the absolute configurations ofother7new compounds (31,34,35,37,49,81,82) by NOESY, coupling constantsand optical rotations. Compounds1-3are racemic mixtures, their two enantiomerswere resolved by HPLC on a chiral phase respectively and their absoluteconfigurations were assigned online, right from the peaks in the chromatogram, by acombination of HPLC-CD and quantum chemical CD calculations. With the purpose of exploring the potential therapeutical effect of the compoundsisolated, the assays of antitumor and anti-influenza virus activities were applied. Severalcompounds were evaluated for their cytotoxicities against several cancer cell linessuch as HepG2, HL-60, K562, A-549, P-388and etc., by the MTT or SRB method.Among them,7compouds showed different levels of cytotoxicities. The IC50valuesof compound1against P388, HL-60and A-549were1.83,4.70and17.1μM,respectively. The inhibition ration of compound4against HL-60and K-562on50μMwere88.61%and88.38%, respectively. The IC50values of compounds29,30,46and47against HepG2were9.9,9.7,11.3and13.2μM, respectively. The IC50values ofcompound32against HL-60and P388were2.5and3.1, respectively. The moleculartargets of compound1,2and their enantiomers (1a,1b,2a,2b) were further explored,and2a showed moderate activity against topoisomerase I.Summarily,88compounds were isolated and identified from8aimed fungalstrains, including34new compounds and3new natural products. Furthermore, weestablished their absolute configurations of the isolated compounds and possiblebiosynthetic pathways of the spiro-polyketide-diketopiperazine hybrids (1-3) andprenylated indole diketopiperazine alkaloids (4-11). We also evaluated thebioactivities of pure compounds, and ten of which showed significant activity. Basedon the results of this research, we could do further more.