Bioactive nonanolide derivatives isolated from the endophytic fungus Cytospora sp

Cytospolides F-Q (6-17) and decytospolides A and B (18 and 19), 14 unusual nonanolide derivatives, were isolated from Cytospora sp., an endophytic fungus from Ilex canariensis. The structures were elucidated by means of detailed spectroscopic analysis, chemical interconversion, and X-ray single crystal diffraction. The solution- and solid-state conformers were compared by the combination of experimental methods (X-ray, NMR) supported by DFT calculations of the conformers. Absolute configurations were assigned using the modified Mosher's method and solution- and solid-state TDDFT ECD calculations. In an in vitro cytotoxicity assay toward the tumor cell lines of A549, HCT116, QGY, A375, and U973, the γ-lactone 17 demonstrated a potent growth inhibitory activity toward the cell line A-549, while nonanolide 16 with (2S) configuration showed the strongest activity against cell lines A-549, QGY, and U973. A cell cycle analysis indicated that compound 16 can significantly mediate G1 arrest in A549 tumor cells, confirming the important role of the C-2 methyl in the growth inhibition toward the tumor line. The discovery of an array of new nonanolides demonstrates the productivity of the fungus, and it is an example of chemical diversity, extending the nonanolide family by derivatives formed by ring cleavage, oxidation, esterification, and Michael addition.     

Xyloketal H from the mangrove endophytic fungus Xylaria sp. 2508

(3R*,3aR*,9aR*)-3,9a-Dimethyl-2,3,3a,9a-tetrahydro-4H-furo[2,3-b]chromene-5,7-diol (xyloketal H), a representative of a new family of xyloketals, was isolated from the marine-derived mangrove fungus Xylaria sp. 2508. Its structure was elucidated by spectroscopic data and single-crystal X-ray diffraction analysis. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1051–1052, June, 2006.     

Eremophilane sesquiterpenes from the endophytic fungus Xylaria sp. GDG-102

A new eremophilane sesquiterpene, xylareremophil (1), together with five known eremophilanes, 1α,10α-epoxy-3α-hydroxyeremophil-7(11)-en-12,8β-olide (2), 1,10α,13-trihydroxyeremophil-7(11)-en-12,8-olide (3), 1α,10α-epoxy-13-hydroxyeremophil-7(11)-en-12,8β-olide (4), mairetolides B (5) and G (6) were isolated from the endophytic fungus Xylaria sp. GDG-102 cultured from Sophora tonkinensis. Their structures were elucidated on the basis of spectroscopic data analysis. The absolute configurations of 1 was determined by comparing computed electronic circular dichroism (ECD) and optical rotation (OR) with experimental results. Compounds 1, 5 and 6 showed antibacterial activities against Proteus vulgaris, Micrococcus luteus, Micrococcus lysodeikticus and Bacillus subtilis with MIC values of 25–100 μg/mL.     

Secondary metabolites of Xylaria sp., an endophytic fungus from Taxus mairei

One new metabolite 3,7-dimethyl-9-(-2,2,5,5-tetramethyl-1,3-dioxolan-4-yl)nona-1,6-dien-3-ol, together with nine known compounds, were isolated from the strain Xylaria sp., an endophytic fungus of Taxus mairei. Their structures were deduced from 1D and 2D NMR data. In vitro cytotoxicity and antibacterial activity of these compounds were evaluated. Some of them exhibited substantial activity.     

A new phthalide from the endophytic fungus Xylaria sp. GDG-102

A new phthalide derivative, xylarphthalide A (1), along with two known compounds (-)-5-carboxylmellein (2) and (-)-5-methylmellein (3), were isolated from the endophytic fungus Xylaria sp. GDG-102 cultured from the Chinese medicinal plant Sophora tonkinensis. Their structures were identified by MS and NMR experiments, and the absolute configuration of 1 was further confirmed by single-crystal X-ray diffraction analysis. Compound 1–3 showed antibacterial activities against Bacillus megaterium, Bacillus subtilis, Staphylococcus aureus, Escherichia coli and Shigella dysenteriae with MIC values of 12.5–25 μg/mL.     

Cinchona alkaloids are also produced by an endophytic filamentous fungus living in cinchona plant

We report that the endophytic filamentous fungus Diaporthe sp., isolated from Cinchona ledgeriana and cultivated in a synthetic liquid medium, produces Cinchona alkaloids (quinine, quinidine, cinchonidine, and cinchonine). This shows that Cinchona alkaloids are produced not only in Cinchona plant cells, but also in endophytic microbe cells.     

Bioactive aromatic derivatives from endophytic fungus, Cytospora sp

Two new benzyl gamma-butyrolactone analogues, (R)-5-((S)-hydroxy(phenyl)-methyl)dihydrofuran-2(3H)-one (1) and its 6-acetate (2), and a new naphthalenone derivative (8), together with eight additional known aromatic derivatives, (S)-5-((S)-hydroxy(phenyl)-methyl)dihydrofuran-2(3H)-one (3), (S)-5-benzyl-dihydrofuran-2(3H)-one (4), 5-phenyl-4-oxopentanoic acid (5), gamma-oxo-benzenepentanoic acid methyl ester (6), 3-(2,5-dihydro-4-hydroxy-5-oxo-3-phenyl-2-furyl)propionic acid (7), (3R)-5-methylmellein (9), integracins A (10) and B (11) were isolated from Cytospora sp., an endophytic fungus isolated from Ilex canariensis from Gomera. The structures of these compounds were elucidated by detailed spectroscopic analysis, comparison with reported data, and chemical interconversion. The absolute configurations of the new compounds (1, 2, 8) were established on the basis of optical rotation or CD spectra analysis. Preliminary studies showed antimicrobial activity of these compounds against the fungi Microbotryum violaceum, Botrytis cinerea and Septoria tritici, the alga Chlorella fusca, and the bacterium Bacillus megaterium.     

Biooxidation of (+)-catechin and (-)-epicatechin into 3,4-dihydroxyflavan derivatives by the endophytic fungus Diaporthe sp. isolated from a tea plant

The microbial transformation of (+)-catechin (1) and (-)-epicatechin (2) by endophytic fungi isolated from a tea plant was investigated. It was found that the endophytic filamentous fungus Diaporthe sp. transformed them (1, 2) into the 3,4-cis-dihydroxyflavan derivatives, (+)-(2R,3S,4S)-3,4,5,7,3',4'-hexahydroxyflavan (3) and (-)-(2R,3R,4R)-3,4,5,7,3',4'-hexahydroxyflavan (7), respectively, whereas (-)-catechin (ent-1) and (+)-epicatechin (ent-2) with a 2S-phenyl group resisted the biooxidation.     

1H and 13C NMR assignments for two new xanthones from the endophytic fungus Xylaria sp. FRR 5657

The complete 1H and 13C NMR assignments are reported for the new natural products, 7-hydroxy-3-(hydroxymethyl)-1-methoxy-9H-xanthen-9-one (1) and 2,5-dihydroxy-8-methoxy-6-methyl-9-oxo-9H-xanthene -1-carboxylic acid (2). Both of these secondary metabolites were isolated from the fermentation culture of the endophytic fungus Xylaria sp. FRR 5657. 1D and 2D NMR experiments that included 1H, gCOSY, gHSQC and gHMBC were used for the determination of the structure and assignment of these xanthones.     

New borrelidin derivatives from an endophytic Streptomyces sp.

Three new borrelidin-type macrolactones, designated as borrelidins J?L (4–6), together with borrelidin A (1), borrelidin E (2), and 12-desnitrile-12-carboxyl-borrelidin (3) were isolated from a plant endophytic Streptomyces sp. NA06554. Their structures were determined by extensive spectroscopic analysis including HRESIMS, 1D and 2D NMR data. The antibacterial activities for compounds 1–6 were examined. Borrelidins A (1) and L (6) showed potent and moderate antibacterial activity against Micrococcus luteus, respectively, whereas other derivatives (2–5) are almost inactive, which allows us to propose a plausible structure-activity relationship.     

Cytochalasins D1 and C1, unique cytochalasans from endophytic fungus Xylaria cf. curta

Cytochalasins D1 (1) and C1 (2) were isolated from the liquid fermentation of fungus Xylaria cf. curta. Their structures and absolute configurations were determined by comprehensive experimental spectroscopic methods as well as ECD and GIAO ¹³C NMR calculation. They possess a unique eleven-membered macrocycle with an oxygen bridge. Cytochalasins D1 and C1 showed moderate cytotoxicity against human leukemia cell lines HL-60 with IC₅₀ value of 12.7 and 22.3 μM, respectively.     

Chemical investigation of metabolites produced by an endophytic Aspergillus sp. isolated from Limonia acidissima

Endophytic fungi are considered as a good source to produce important secondary metabolites with interesting bioactivities. In a continuation of our studies towards the search for environmentally friendly bioactive compounds from Sri Lankan flora, we investigated the secondary metabolites produced by the endophytic fungi Aspergillus sp. isolated from the seeds of the popular edible fruit Limonia acidissima L. of the family Rutaceae. The pure culture of the Aspergillus sp. was grown on potato dextrose broth media. After 4 weeks fermentation, fungal media were extracted with organic solvents. Chromatographic separation of the fungal extracts over silica gel, Sephadex LH-20 and RP-HPLC furnished flavasperone (1), rubrofusarin B (2), aurasperone A (3), fonsecinone D (4) and aurasperone B (5). Compounds 1–4 showed moderate activities in brine shrimp toxicity assay. This is the first report of the ¹³C NMR data of compounds 4 and 5.     

The newly isolated endophytic fungus Paraconiothyrium sp. LK1 produces ascotoxin

We have isolated five endophytic fungi from the roots of Capsicum annuum, Cucumis sativus and Glycine max. The culture filtrates (CF) of these endophytes were screened on dwarf mutant rice (Waito-C) and normal rice (Dongjin-byeo). Endophyte CAC-1A significantly inhibited the growth of Waito-C and Dongjin-byeo. Endophyte CAC-1A was identified as Paraconiothyrium sp. by sequencing the ITS rDNA region and phylogenetic analysis. The ethyl acetate fraction of Paraconiothyrium sp. suppressed the germination of Lactuca sativa and Echinochloa crus-galli seeds. The ethyl acetate fraction of the endophyte was subjected to bioassay-guided isolation and we obtained the phytotoxic compound ascotoxin (1) which was characterized through NMR and GC/MS techniques. Ascotoxin revealed 100% inhibitory effects on seed germination of Echinochloa crus-galli. Compound (1) was isolated for the first time from Paraconiothyrium sp.     

Polyketide derivatives of endophytic fungus Pestalotiopsis sp. isolated from the Chinese mangrove plant Rhizophora mucronata

A detailed chemical investigation of the minor metabolites produced by the endophytic fungus Pestalotiopsis sp. isolated from the Chinese mangrove Rhizophora mucronata afforded sixteen new compounds of polyketide origin, including pestalotiopyrones A-H (1-8), pestalotiopisorin A (10), pestalotiollides A-B (11-12), pestalotiopin A (13), and four amides pestalotiopamides A-D (14-17), along with three known compounds, nigrosporapyrone D (9), 2-anhydromevalonic acid (18), and p-hydroxy benzaldehyde (19). The structures of all compounds were unambiguously established from their spectroscopic data that included HR-ESIMS and 1- and 2-dimensional NMR spectroscopy, and by comparison with the literature.     

Three new polyketides from fruiting bodies of the endophytic ascomycete Xylaria polymorpha

The isolation of three new secondary metabolites from the fruiting body of Xylaria polymorpha is described. The new compounds are of mixed biosynthetic origin consisting of a polyketide starter, extended with a methyl orsellinate unit and terminated hydrolytically or with an amine-containing terminal unit.     

New diketopiperazine derivatives isolated from sea urchin-derived bacillus sp

Two new diketopiperazine derivatives, bacillusamides A (1) and B (2), have been isolated from the EtOAc extract of the sea urchin-derived Bacillus sp. along with the known cyclo(-L-pro-L-val-) (3), cyclo(-L-pro-L-tyr-) (4), cyclo(-L-pro-L-phe-) (5). These structures were elucidated by extensive spectroscopic methods. Furthermore, the absolute configurations of the amino acid residues were determined using Marfey's method. Compound 1 displayed weak antifungal activity against Aspergillus niger.     

Mass spectrometry characterization of endophytic bacterium Curtobacterium sp. strain ER1/6 isolated from Citrus sinensis

The bacteria of the genus Curtobacterium are usually seen as plant pathogen, but some species have been identified as endophytes of different crops and could as such present a potential for disease control and plant growth promotion. We have therefore applied the desorption electrospray ionization mass spectrometry imaging (DESI‐MSI) in the direct analysis of living Curtobacterium sp. strain ER1/6 colonies to map the surface metabolites, and electrospray ionization tandem mass spectrometry (ESI‐MS/MS) for characterization of these compounds. Several colony‐associated metabolites were detected. The ESI‐MS/MS showed characteristic fragmentations for phospholipids including the classes of glycerophosphocholine, glycerophosphoglycerol, and glycerophosphoinositol as well as several fatty acids. Although a secure identification was not obtained, many other metabolites were also detected for this bacteria species. Principal component analysis showed that fatty acids were discriminatory for Curtobacterium sp. ER1/6 during inoculation on periwinkle wilt (PW) medium, whereas phospholipids characterize the bacterium when grown on the tryptic soy agar (TSA) medium.     

Transformation of indole alkaloids—I : Conversion of oxindole alkaloids into indole alkaloids

Chemical conversion of some natural oxindoles (pteropodine, isopteropodine and isorhynchophylline) into the corresponding indole alkaloids has been made by way of a sequence of reactions which include formation of iminoethers of the natural oxindoles with Meerwein's reagent, reduction of the iminoethers to 2,3-seco-indoles and cyclization of 2,3-seco-indoles to the desired natural indole alkaloids. Sodium borohydride in acetic acid was found to be a specific reagent for the reduction of oxindole-iminoethers to 2,3-seco-indoles which were the key intermediates in these transformations. Yohimbine-oxindole iminoether was similarly converted to yohimbine and pseudoyohimbine. A number of by-products were obtained and their structures were elucidated.     

Fusaroside, a unique glycolipid from Fusarium sp., an endophytic fungus isolated from Melia azedarach

Fusaroside (1), a unique trehalose-containing glycolipid composed of the 4-hydroxyl group of a trehalose unit attached to the carboxylic carbon of a long-chain fatty acid, was isolated from the organic extract of fermentation broths of an endophytic fungus, Fusarium sp. LN-11 isolated from the leaves of Melia azedarach. Six known compounds, phalluside (2), (9R*,10R*,7E)-6, 9,10-trihydroxyoctadec-7-enoic acid (3), porrigenic acid (4), (9Z)-2,3-dihydroxypropyl octadeca-9-enoate (5), cerevisterol (6) and ergokonin B (7), were also isolated from this fungus. The glycolipid contains a rare branched long-chain fatty acid (C(20:4)) with a conjugated diene moiety and a conjugated ketone moiety. The structure of the new compound 1 was elucidated by spectroscopic methods (1D and 2D NMR experiments, MS) and chemical degradations. The metabolites 1-5 were shown to have moderate to weak active against the brine shrimp larvae. To our knowledge, this is the first report of isolation of the first representative of a new family of glycolipids from natural sources.