| Because of the special living environment, mangrove endophytic fungi possess distinct and complex metabolic capabilities, resulting in wide diversity of their secondary metabolites in chemical structure and biological activity. Thus, mangrove endophytic fungi become one of the important resources of active lead compounds. This thesis describes the screening of cytotoxic mangrove endophytic fungi and the secondary metabolites produced by two selected endophytic fungi. Studies include isolation of endophytic fungi from mangrove samples and screening of cytotoxic strains, selecting talented strains, fermentation studies, bioassay-guided fractionation, structural elucidation and cytotoxicity evaluation of pure compounds.173 fungal strains are isolated from 33 mangrove samples inclouding roots and stalks collected from Wenchang, Shankou, Haikou, China, from which 44 strains are found to have a wide diversity of secondary metabolites and 35 strains exhibited cytotoxicity against P388 cell lines. 7 talented strains are obtained by integrated cytotoxic and chemical screening methods from the mangrove plant, and two of them were selected as working strains for further study of secondary metabolites. The fermentation broth of Cladosporium sp. WC13-1 showed a series peaks with similar UV absorption in HPLC profile, and HK13-8 showed a main peak. Monitoring by bioassay-guided isolation, the active fractions was subjected to chromatography over silica gel, Sephadex LH-20 and prepared TLC, and preparative HPLC to afford 9 new compounds and 16 known compounds from Cladosporium sp. WC13-1. By the same procedure, 5 compounds were isolated and identified from HK 13-8. By means of spectroscopic and chemical methods, their structures were elucidated as trans-2,3- dihydro-2-methyl-4-methoxybenzopyran-5-ol (1), (2r,3cis,4trans)-2,3-dihydro-2- methylbenzopyran-3,4,5-triol (2), (2R+2S)-7-O-α-D-ribofuranosyl-2,3-dihydro-5- hydroxy-2-methylbenzopyran-4-one (3+4), 7-O-α-D-ribofuranosyl-5-hydroxy-2- propylbenzopyran-4-one (5), methyl 3S-(2,3-dihydroxy phenyloxy)butyrate (6), 3S- (2,3-dihydroxy phenyloxy)butanoic acid (7), (E, threo)-hepta-4,6-dien-2,3-diol (8), (3E,8E,6S)-undeca-3,8,10-trien-1,6-diol (9), trans-2,3-dihydro-2-methylbenzopyran- 4,5-diol (10), (±)-2,3-dihydro-5-hydroxy-2-methyl-4H-1-benzopyran-4-one (11), (±)- 5,7-dihydroxy-2-methylchroman-4-one (12), 1-(2,6-dihydroxyphenyl)butan-1-one (13), 1-(2,6-dihydroxylphenyl)propan-1-one (14), 1-(2,6-dihydroxyphenyl)ethan-1- one (15), N-(4-hydroxylphenethyl)acetamide (16), 4-(2-hydroxyethyl)benzaldehyde (17), cyclo- (Pro-Leu) (18), cyclo-(Val-Pro) (19), cyclo-(Pro-Ile) (20), cyclo-(Tyr-Pro) (21), cyclo-(Pro-Phe) (22), 1-(3-indolyl)-2,3-dihydroxypropan-1-one (23), butyrolactone I (24), 2-butyryl-3,5-dihydroxycyclohex-2-en-l-one (25), thymine (26), uracil (27), (22E,24R)-3β,5α,9α-trihydroxyergosta-7,22-dien-6-one (28), ergosterol (29) and S-curvularin (30), respectively. Among them, compounds 1-9 are new compounds.The cytotoxicity of these compounds against several cancer cell lines was evaluated by SRB and MTT method. New compound 1 exhibited weak cytotoxicity against HL-60 and BEL-7402 cells with the IC50 values of 47.9 and 77.0μM, respectively. S-curvularin (30) showed moderate inhibitory effects on HL-60 cells with an IC50 value of 2.56μM. The radical scavenging activity against DPPH experiment showed that the new compounds 1, 6-7, and the known compound 10 exhibited strong radical scavenging activity against DPPH, with the IC50 values of 1.1, 0.6, 0.05 and 1.2μg/ml, respectively, and the known compounds 12-15, and 23 exhibited weak radical scavenging activity against DPPH, with IC50 values from 20.7 to 71μg/ml.In a word, nine new compunds together with twenty-one known ones were obtained from the two endophytic fungal strains. Studies mentioned above provide novel structures for searching new leading compounds and microbial resources for further study and it proves the method we used is effective in finding new active compounds. |
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