Phomoeuphorbins A-D, azaphilones from the fungus Phomopsis euphorbiae

Five new secondary metabolites from an endophytic fungus Phomopsis sp. SZSJ-7B

Two previously undescribed lactones, phomolides A and B (1 and 2), and three new sesquiterpenoids, phomenes A-C (3-5), together with one known compound, colletotricholide A (6), were isolated from the endophytic fungus Phomopsis sp. SZSJ-7B. Their chemical structures, including the absolute configurations, were comprehensively established by extensive analyses of NMR, high-resolution electrospray ionization mass spectrometry, electronic circular dichroism powered by theoretical calculations, and X-ray diffractions. Moreover, the cytotoxic and antibacterial activities of compounds 1-6 were also evaluated, and the results demonstrated that compound 2 showed significant antibacterial effects towards methicillin-resistant Staphylococcus aureus and S. aureus strains with minimum inhibitory concentration as low as 6.25 μg/ml, which was comparable to that of the clinical drug vancomycin. Moreover, all compounds showed no cytotoxic activity.

Isolation and screening of stress-resistant endophytic fungus strains from wild and cultivated soybeans in cold region of China

In this study, we firstly reported the large-scale screening and isolation of endophytic fungi from nine wild and six cultivated soybeans in the cold regions of China. We totally isolated 302 endophytic fungal strains, of which 215 strains are isolated from the wild soybeans and 87 are identified from cultivated soybeans. Among these endophytic fungal strains, in the roots, stems, and leaves, 24.17% were isolated from roots, 28.8% were isolated from stems, and 47.01% were isolated from leaves, respectively. Most endophytic fungal strains isolated from the wild soybean roots were the species of Fusarium genus, and the fungal strains in the stems were the species of ascomycetes and Fusarium fungi, whereas most strains in the leaves were Alternaria fungi. To analyze the taxonomy of the obtained samples, we sequenced and compared their rDNA internal transcribed spacer (ITS) sequences. The data showed that 6 strains are putatively novel strains exhibiting ≤ 97% homology with the known strains. We next measured the secondary metabolites produced by the different strains and we found 11 strains exhibited high-performance synthesis of triterpenoids, phenols, and polysaccharides. Furthermore, we characterized their tolerance to abiotic stresses. The results indicated that 4 strains exhibited high tolerance to cadmium, and some strains exhibited resistance to acid, and alkali. The results of the study could facilitate the further exploration of the diversity of plant endophytic fungi and the potential applications of the fungi to practical agriculture and medicine industries. KEY POINTS: • 302 endophytic fungal strains isolated from wild soybean and cultivated soybean • 11 strains had high contents of triterpenoids, phenols, and polysaccharides • 4 strains exhibited high Cd tolerance, and a few strains with strong tolerance to acid and alkali solution.

Three novel chromanones with biological activities from the endophytic fungus Phomopsis CGMCC No. 5416

Three undescribed chromanones (1-3) and two known chromanones (4 and 5) were isolated from the culture of endophytic fungus Phomopsis CGMCC No. 5416 from the stems of Achyranthes bidentata. Their structures were determined by spectroscopic analysis. Compounds 1 and 2 showed inhibitory activities against HIV-1 with IC₅₀ values of 20.4 and 32.5 μg ml^-1, respectively. Compounds 1-3 displayed moderate cytotoxicity with CC₅₀ values of 36.5-79.3 μg ml^-1 against A549, MDA-MB-231, and PANC-1 cell lines. Moreover, compound 3 can induce the early apoptosis of PANC-1 cancer cells with the apoptosis rate of 10.52%.

Potential of small-molecule fungal metabolites in antiviral chemotherapy

Various viral diseases, such as acquired immunodeficiency syndrome, influenza, and hepatitis, have emerged as leading causes of human death worldwide. Scientific endeavor since invention of DNA-dependent RNA polymerase of pox virus in 1967 resulted in better understanding of virus replication and development of various novel therapeutic strategies. Despite considerable advancement in every facet of drug discovery process, development of commercially viable, safe, and effective drugs for these viruses still remains a big challenge. Decades of intense research yielded a handful of natural and synthetic therapeutic options. But emergence of new viruses and drug-resistant viral strains had made new drug development process a never-ending battle. Small-molecule fungal metabolites due to their vast diversity, stereochemical complexity, and preapproved biocompatibility always remain an attractive source for new drug discovery. Though, exploration of therapeutic importance of fungal metabolites has started early with discovery of penicillin, recent prediction asserted that only a small percentage (5-10%) of fungal species have been identified and much less have been scientifically investigated. Therefore, exploration of new fungal metabolites, their bioassay, and subsequent mechanistic study bears huge importance in new drug discovery endeavors. Though no fungal metabolites so far approved for antiviral treatment, many of these exhibited high potential against various viral diseases. This review comprehensively discussed about antiviral activities of fungal metabolites of diverse origin against some important viral diseases. This also highlighted the mechanistic details of inhibition of viral replication along with structure-activity relationship of some common and important classes of fungal metabolites.

The diversity and antimicrobial activity of endophytic fungi associated with medicinal plant Baccharis trimera (Asteraceae) from the Brazilian savannah

The fungal endophyte community associated with Baccharis trimera, a Brazilian medicinal plant, was characterized and screened for its ability to present antimicrobial activity. By using molecular methods, we identified and classified the endophytic fungi obtained into 25 different taxa from the phyla Ascomycota and Basidiomycota. The most abundant species were closely related to Diaporthe phaseolorum, Pestalotiopsis sp. 1, and Preussia pseudominima. The differences observed in endophytic assemblages from different B. trimera specimens might be associated with their crude extract activities. Plants that had higher α-biodiversity were also those that contributed more to the regional (γ) diversity. All fungal isolates were cultured and their crude extracts screened to examine the antimicrobial activities. Twenty-three extracts (12.8%) displayed antimicrobial activities against at least one target microorganism. Among these extracts, those obtained from Epicoccum sp., Pestalotiopsis sp. 1, Cochliobolus lunatus, and Nigrospora sp. presented the best minimum inhibitory concentration values. Our results show that the endophytic fungal community associated with the medicinal plant B. trimera included few dominant bioactive taxa, which may represent sources of compounds with antifungal activity. Additionally, the discovery of these bioactive fungi in association with B. trimera suggests that Brazilian plants used as folk medicine may shelter a rich fungal diversity as well as taxa able to produce bioactive metabolites with antimicrobial activities.

Inhibition of HIV-1 Replication by Secondary Metabolites From Endophytic Fungi of Desert Plants

Most antiretroviral drugs currently in use to treat an HIV-1 infection are chemically synthesized and lead to the development of viral resistance, as well as cause severe toxicities. However, a largely unexplored source for HIV-1 drug discovery is endophytic fungi that live in a symbiotic relationship with plants. These fungi produce biologically active secondary metabolites, which are natural products that are beneficial to the host. We prepared several hundred extracts from endophytic fungi of desert plants and evaluated the inhibitory effects on HIV-1 replication of those extracts that showed less than 30% cytotoxicity in T-lymphocytes. Those extracts that inhibited viral replication were fractionated in order to isolate the compounds responsible for activity. Multiple rounds of fractionation and antiviral evaluation lead to the identification of four compounds, which almost completely impede HIV-1 replication. These studies demonstrate that metabolites from endophytic fungi of desert plants can serve as a viable source for identifying potent inhibitors of HIV-1 replication.

A novel phytotoxic nonenolide from Phomopsis sp. HCCB03520

A novel phytotoxic nonenolide, (6S,7R,9R)-6,7-dihydroxy-9-propylnon-4-eno-9-lactone (1), was isolated from solid cultures of the endophytic fungus Phomopsis sp. HCCB03520, together with three known compounds, cytochalasin H (2), cytochalasin N (3), and epoxycytochalasin H (4). The structures of these compounds were elucidated through spectroscopic analysis, and the absolute configurations were determined by CD spectroscopy. Phytotoxic activities of compounds 1-4 were also investigated. Compound 1 showed phytotoxic activity on germination and radicle growth of Medicago sativa, Trifolium hybridum, and Buchloe dactyloides.

Isolation, structure elucidation and biological activity of metabolites from Sch-642305-producing endophytic fungus Phomopsis sp. CMU-LMA

Eight polyketide compounds were isolated from the cultivation broth of Phomopsis sp. CMU-LMA. We have recently described LMA-P1, a bicyclic 10-membered macrolide, obtained as a bioconversion derivative of Sch-642305, the major compound isolated in this study. Benquinol is the ethyl ester derivative of the 13-dihydroxytetradeca-2,4,8-trienoic acid produced by Valsa ambiens. This compound is concomitantly produced with the 6,13-dihydroxytetradeca-2,4,8-trienoic acid (DHTTA) previously isolated from Mycosphaerellarubella. The absolute configuration of the new compound, (2R,3R,4S,5R)-3-hydroxy-2,4-dimethyl-5-[(S,Z)-3-methylpentenyl]-tetrahydro-pyranone LMA-P2 was confirmed by X-ray crystallography. The δ-lactone 2,3-dihydroxytetradecan-5-olide (DHTO) was previously isolated from Seiridium unicorne. This compound may form through the cyclization of the methyl-2,3,5-trihydroxytridecanoate LMA-P3, a new linear polyketide isolated in this study. Benquoine, a new 14-membered lactone generated from the cyclization of benquinol, is proposed as the key precursor for the biosynthesis of Sch-642305. Antimicrobial activity and cancer cell viability inhibition by the new compounds were investigated. Benquoine exhibits antimicrobial activity against Gram positive bacteria, and cytotoxicity against HCT-116 cancer cell line.

Chemical and molecular characterization of Phomopsis and Cytospora-like endophytes from different host plants in Brazil

Phomopsis and related taxa comprise important endophytic and plant pathogenic species, and are known for the production of a diverse array of secondary metabolites. Species concepts within this group based on morphological characters and assumed host specificity do not reflect phylogenetic affinities. Additional phenotypic characters, such as profiles of secondary metabolites, are needed for practical species recognition. We investigated 36 strains of Phomopsis spp. and Cytospora-like fungi, obtained as endophytes of different host plants in Brazil, using metabolite profiling based on HPLC-UV/liquid chromatography -mass spectrometry (LC-MS) combined with cluster analysis of the results. Strains were also subjected to phylogenetic analyses based on internal transcribed spacer (ITS) rDNA. Six chemotypes were identified. Chemotypes 1-5 contained Phomopsis strains, while Cytospora-like strains formed the chemotype 6. Strains of chemotype 1 typically produced alternariols, altenusin, altenuene, cytosporones, and dothiorelones. Alternariol and seven unknown compounds were consistently produced by strains of chemotype 2. Members of chemotypes 3-5 produced poor metabolite profiles containing few chemical markers. Cytospora-like endophytes (chemotype 6) produced a characteristic set of metabolites including cytosporones and dothiorelones. Bayesian and Maximum Parsimony (MP) trees classified strains of each chemotype into single phylogenetic lineages or closely related groups. Strains of chemotypes 1 and 2 formed a monophyletic group along with Diaporthe neotheicola. The remaining Phomopsis strains formed monophyletic (chemotype 4) or polyphyletic (chemotypes 3 and 5) lineages inside a large and well supported clade. Cytospora-like strains formed a monophyletic lineage located at an intermediary position between Diaporthe/Phomopsis and Valsa/Cytospora clades. The combined results show that the production of secondary metabolites by Phomopsis and related Diaporthales may be species-specific, giving support to the use of metabolite profiling and chemical classification for phenotypic recognition and delimitation of species.

Cytotoxic pentacyclic and tetracyclic aromatic sesquiterpenes from Phomopsis archeri

Three new sesquiterpenes, named phomoarcherins A-C (1-3), and four known compounds, kampanol A (4), R-mevalonolactone, ergosterol, and ergosterol peroxide, were isolated from the endophytic fungus Phomopsis archeri. These structures were established on the basis of spectroscopic evidence. The structure and absolute configuration of 1 were confirmed by X-ray crystallographic analysis of its p-bromobenzoate derivative (1a). Compounds 1-4 showed cytotoxicity against five cholangiocarcinoma cell lines (0.1-19.6 μg/mL), while 1 and 2 exhibited weak cytotoxicity against the KB cell line with IC(50) values of 42.1 and 9.4 μg/mL, respectively. In addition, compound 2 showed antimalarial activity against Plasmodium falciparum with an IC(50) value of 0.79 μg/mL.