Chemical investigation of the fruits of Garcinia schomburgkiana collected in Vietnam led to the isolation of eight new schomburgkianones, A-H (1-8), four known (9-12) polyprenylated benzoylphloroglucinols, and four known biflavonoids. The structures of these compounds were elucidated by spectroscopic and chemical means. The absolute configuration at C-40 of 1 and 2 was determined by (1)H NMR analyses of their MPA esters. The configuration of the bicyclo[3.3.1]nonane core of the polyprenylated benzoylphloroglucinols was assigned by comparison of their experimental ECD spectra with those of related compounds. The polyprenylated benzoylphloroglucinols exhibited inhibitory activities against mammalian DNA polymerases α and λ, with IC50 values ranging from 5.0 to 8.8 μM. Compounds 1, 2, 4, 5, and 9-11 showed cytotoxic effects against HeLa human cervical cancer cells with median lethal dose values lower than 10 μM.

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A spore-derived mycobiont of a crustose Pyrenula sp. lichen collected in Vietnam was cultivated on a malt-yeast extract medium supplemented with 10% sucrose. Chemical investigation of the cultivated colonies led to the isolation of eight new alkylated decalin-type polyketides (1-8) along with three known compounds. The structures of these compounds were elucidated by spectroscopic and chemical means. This is the first instance of this type of polyketide being isolated from a cultured lichen mycobiont. The isolated polyketides 1 and 7 exhibited inhibitory activities against mammalian DNA polymerases α and β with IC50 values ranging from 8.1 to 19.5 μM. Compound 1 showed cytotoxic effects against the HCT116 human colon carcinoma cultured cell line with an IC50 value of 6.4 ± 0.7 μM.

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Spore-derived mycobionts of the crustose lichen Graphis vestitoides collected in Vietnam were cultivated on a malt-yeast extract medium supplemented with 10% sucrose. The investigation of their metabolites resulted in isolation of a novel 14-membered macrolide and a new isocoumarin, together with five known isocoumarin derivatives. Their structures were determined by spectroscopic and chemical means. This is the first instance of isolation of a 14-membered macrolide from a lichen mycobiont.Key words Graphis vestitoides; lichen; mycobiont; 14-membered macrolide; isocoumarin Lichens, symbiotic associations between fungi (mycobionts) and photoautotrophic algae or cyanobacteria (photobionts), produce a wide range of characteristic secondary metabolites, namely, lichen substances, some of which are potentially useful and biologically active compounds.1-3) Most of these metabolites are produced by the fungus, in symbiosis or in the aposymbiotic state. However, previous studies demonstrated that the secondary metabolites in cultured mycobionts are often structurally unique and similar to fungal metabolites. [4][5][6] These findings suggested that laboratory cultures of lichen mycobionts could provide a potential source of novel secondary metabolites to be produced for pharmaceutical purposes. In continuing our chemical studies on the cultured mycobionts of lichens, 7) we cultivated the spore-derived mycobionts of Graphis vestitoides collected in Vietnam and isolated a novel 14-membered macrolide and a new isocoumarin as well as five known isocoumarin derivatives from their cultures. In this paper, the isolation and characterization of these new metabolites are described. Results and DiscussionSpecimens of Graphis vestitoides (Fink) Staiger were collected from the bark of trees in Dong Nai Province, Vietnam, in 2008. The polyspore-derived mycobionts were cultivated on a malt-yeast extract medium supplemented with 10% sucrose at 18°C in the dark. After three months, the cultures were harvested and extracted with Et 2 O, acetone and then with MeOH. Subsequent purification of the extracts by a combination of column chromatography, preparative TLC and HPLC gave new compounds 1 and 2, together with five known compounds: 6,8-dihydroxy-3-(hydroxymethyl) isocoumarin (3), 8) 4, 6-dihydroxy-3,9-dehydromellein, 9) cis-4,6-dihydroxymellein, 10,11) trans-5,7-dihydroxy-3-(1-hydroxyethyl) phthalide 12) and cis -5,7-dihydroxy-3-(1-hydroxyethyl) phthalide.