Macrocyclic Trichothecenes from Myrothecium roridum Strain M10 with Motility Inhibitory and Zoosporicidal Activities against Phytophthora nicotianae

Triterpenoid and trichothecenes from a rhizospheric soil-derived Paramyrothecium sp. KMU22107

A new phthalide derivative named paramlyktone (1) and a new arborinane-type triterpenoid named paramyrpenoid (2), together with ten previously described trichothecenes derivatives (3-12) were isolated and identified from a rhizospheric soil-derived Paramyrothecium sp. KMU22107 associated with Delphinium yunnanense. Their structural elucidation was achieved by the comprehensive analysis of spectroscopic data and comparison with literature values. Notably, paramyrpenoid (2) was the first example of an arborinane-type triterpenoid with a double bond at Δ12(13) and an additional methyl motif at C-8. This was the first report of arborinane-type triterpenoids from a fungus belonging to Paramyrothecium genus. In pharmacological studies, paramyrpenoid (2) demonstrated significant cytotoxic activity against the HL-60, SW480, A-549, MDA-MB-231 and SMMC-7721 cell lines, with IC50 values from 2.0 to 16.1 μM. Compounds 1 and 2 were also evaluated for anti-inflammatory, anti-acetylcholinesterase (AChE), and protein tyrosine phosphatase 1B (PTP1B) inhibitory activities in vitro.

Pararorine A, isoindolinone alkaloid from the endophytic fungus Paramyrothecium roridum and its anti-tumor activity

Pararorine A, a new isoindolinone alkaloid was isolated from Paramyrothecium roridum, an endophytic fungus from the medicinal plant Gynochthodes officinalis (F.C. How) Razafim. & B. Bremer. The structure of this compound was elucidated by extensive spectroscopic (UV, IR, MS, and NMR) analyses. In addition, the antitumor activity of pararorine A was evaluated against SF-268, MCF-7, HepG2, and A549 tumor cell lines. The results revealed that pararorine A exhibited potent antitumor activities with the IC50 values ranging from 1.69 to 8.95 μM. Moreover, the tumor cell inhibitory activity of pararorine A was evidenced by promoting cytochrome C release and cell cycle arrest as well as the induction of apoptosis by the up-regulation of the protein expressions of JNK and Bax through PARP-cleavage and caspase 3-cleavage.

Myrochromanol analogues and trichothecene derivatives from the shellfish-derived fungus Albifimbriaverrucaria

Eight myrochromanol analogues, including three pairs of epimers at C-2 with the myrochromanol scaffold and two examples of myrochromanol with sugar moiety linked at C-4, together with twelve trichothecene derivatives were isolated from the cultures of a shellfish-derived fungus Albifimbria verrucaria CD1-4. Among them, eight compounds named 2-epi-myrochromanol, ent-myrochromanol B, 4-epi-myrochromanol B, 2-epi-myrochromanol A, myrochromanosides A and B, 6',7'-erythro-(2'E,4'Z)-trichoverrol B, 3R,8S-dihyroxyroridin H were previously undescribed fungal metabolites. Their planar structures and relative configurations were established by 1D and 2D NMR, and HR-MS data analysis, and their absolute configurations were determined using the modified Mosher's method and electronic circular dichrosim calculations. Almost all isolates were evaluated for growth rate inhibition of three marine harmful microalgae Chattonella marina, Heterosigma akashiwo, and Prorocentrum donghaiense, and lethal activity to one marine zooplankton, Artemia salina. Myrochromanosides A and B exhibited obvious inhibitory against three tested microalgae with IC₅₀ values in the range of 9.2-108.9 μM. 8α-Hydroxyroridin H, roridin A and verrucarin A exhibited significant inhibition against P. donghaiense with IC₅₀ values of 6.1, 5.8, and 6.0 μM and toxicity against brine shrimp larvae with LC₅₀ values of 1.4, 2.8, and 0.26 μM, respectively.

Fatal attraction: How Phytophthora zoospores find their host

Oomycete plant pathogens, such as Phytophthora and Pythium species produce motile dispersal agents called zoospores that actively target host plants. Zoospores are exceptional in their ability to display taxis to chemical, electrical and physical cues to navigate the phyllosphere and reach stomata, wound sites and roots. Many components of root exudates have been shown attractive or repulsive to zoospores. Although some components possess very strong attractiveness, it seems that especially the mix of components exuded by the primary host is most attractive to zoospores. Zoospores actively approach attractants with swimming behaviour reminiscent of other microswimmers. To achieve a unified description of zoospore behaviour when sensing an attractant, we propose the following terms for the successive stages of the homing response: reorientation, approaching, retention and settling. How zoospores sense and process attractants is poorly understood but likely involves signal perception via cell surface receptors. Since zoospores are important for infection, undermining their activity by luring attractants or blocking receptors seem promising strategies for disease control.

Chemical Investigation of Endophytic Diaporthe unshiuensis YSP3 Reveals New Antibacterial and Cytotoxic Agents

Chemical investigation of the plant-derived endophytic fungus Diaporthe unshiuensis YSP3 led to the isolation of four new compounds (1-4), including two new xanthones (phomopthane A and B, 1 and 2), one new alternariol methyl ether derivative (3) and one α-pyrone derivative (phomopyrone B, 4), together with eight known compounds (5-12). The structures of new compounds were interpreted on the basis of spectroscopic data and single-crystal X-ray diffraction analysis. All new compounds were assessed for their antimicrobial and cytotoxic potential. Compound 1 showed cytotoxic activity against HeLa and MCF-7 cells with IC₅₀ values of 5.92 µM and 7.50 µM, respectively, while compound 3 has an antibacterial effect on Bacillus subtilis (MIC value 16 μg/mL).

Sesquiterpenoids Specially Produced by Fungi: Structures, Biological Activities, Chemical and Biosynthesis (2015-2020)

Fungi are widely distributed in the terrestrial environment, freshwater, and marine habitat. Only approximately 100,000 of these have been classified although there are about 5.1 million characteristic fungi all over the world. These eukaryotic microbes produce specialized metabolites and participate in a variety of ecological functions, such as quorum detection, chemical defense, allelopathy, and maintenance of symbiosis. Fungi therefore remain an important resource for the screening and discovery of biologically active natural products. Sesquiterpenoids are arguably the richest natural products from plants and micro-organisms. The rearrangement of the 15 high-ductility carbons gave rise to a large number of different skeletons. At the same time, abundant structural variations lead to a diversification of biological activity. This review examines the isolation, structural determination, bioactivities, and synthesis of sesquiterpenoids that were specially produced by fungi over the past five years (2015-2020).

Recent Advances on Macrocyclic Trichothecenes, Their Bioactivities and Biosynthetic Pathway

Macrocyclic trichothecenes are an important group of trichothecenes bearing a large ring. Despite the fact that many of trichothecenes are of concern in agriculture, food contamination, health care and building protection, the macrocyclic ones are becoming the research hotspot because of their diversity in structure and biologic activity. Several researchers have declared that macrocyclic trichothecenes have great potential to be developed as antitumor agents, due to the plenty of their compounds and bioactivities. In this review we summarize the newly discovered macrocyclic trichothecenes and their bioactivities over the last decade, as well as identifications of genes tri17 and tri18 involved in the trichothecene biosynthesis and putative biosynthetic pathway. According to the search results in database and phylogenetic trees generated in the review, the species of the genera Podostroma and Monosporascus would probably be great sources for producing macrocyclic trichothecenes. Moreover, we propose that the macrocyclic trichothecene roridin E could be formed via acylation or esterification of the long side chain linked with C-4 to the hydroxyl group at C-15, and vice versa. More assays and evidences are needed to support this hypothesis, which would promote the verification of the proposed pathway.

Genetic bases for variation in structure and biological activity of trichothecene toxins produced by diverse fungi

Trichothecenes are sesquiterpene toxins produced by diverse but relatively few fungal species in at least three classes of Ascomycetes: Dothideomycetes, Eurotiomycetes, and Sordariomycetes. Approximately 200 structurally distinct trichothecene analogs have been described, but a given fungal species typically produces only a small subset of analogs. All trichothecenes share a core structure consisting of a four-ring nucleus known as 12,13-epoxytrichothec-9-ene. This structure can be substituted at various positions with hydroxyl, acyl, or keto groups to give rise to the diversity of trichothecene structures that has been described. Over the last 30 years, the genetic and biochemical pathways required for trichothecene biosynthesis in several species of the fungi Fusarium and Trichoderma have been elucidated. In addition, phylogenetic and functional analyses of trichothecene biosynthetic (TRI) genes from fungi in multiple genera have provided insights into how acquisition, loss, and changes in functions of TRI genes have given rise to the diversity of trichothecene structures. These analyses also suggest both divergence and convergence of TRI gene function during the evolutionary history of trichothecene biosynthesis. What has driven trichothecene structural diversification remains an unanswered question. However, insight into the role of trichothecenes in plant pathogenesis of Fusarium species and into plant glucosyltransferases that detoxify the toxins by glycosylating them point to a possible driver. Because the glucosyltransferases can have substrate specificity, changes in trichothecene structures produced by a fungus could allow it to evade detoxification by the plant enzymes. Thus, it is possible that advantages conferred by evading detoxification have contributed to trichothecene structural diversification. KEY POINTS : • TRI genes have evolved by diverse processes: loss, acquisition and changes in function. • Some TRI genes have acquired the same function by convergent evolution. • Some other TRI genes have evolved divergently to have different functions. • Some TRI genes were acquired or resulted from diversification in function of other genes. • Substrate specificity of plant glucosyltransferases could drive trichothecene diversity.

New tricks for old dogs: Two new macrocyclic trichothecene epimers and absolute configuration of 16-hydroxyverrucarin B

Two new compounds, 3'-epi-16-hydroxyverrucarin A and 3'-epiverrucarin X, have been isolated and identified, and the characterization data of a series of known trichothecenes have been refined. The interesting structure and potent biological activities of macrocyclic trichothecenes have been of interest to the scientific community for several decades. However, some of the characterization data for the older analogues of this class are not well documented, either because of a lack of absolute configuration or a lack of clarity in the NMR data, largely due to technological limitations at the time they were discovered. NMR techniques, application of Mosher's esters analysis, and electronic circular dichroism were used here both to refine the characterization of known trichothecenes, as well as to uncover new structures. These studies demonstrate strategies that can be used to interrogate the characterization data of well-known secondary metabolites, thereby gaining greater insight into methods that can be used to refine previous literature.

Antifungal Macrocyclic Trichothecenes from the Insect-Associated Fungus Myrothecium roridum

Three new macrocyclic trichothecenes possessing rare 6'-ketal moieties, roridoxins A-C (1-3), and five known compounds (4-8) were isolated from the insect-associated fungus Myrothecium roridum. Their structures were confirmed by a combination of NMR and HRESIMS data, while their absolute configurations were unambiguously determined by single-crystal X-ray analysis and electronic circular dichroism experiments. Trichothecenes 1 and 3 showed potent antifungal activities against four strains of phytopathogenic fungi. In addition, 1, 3, 5, and 6 were found to significantly inhibit the cell growth of Candida albicans with minimal inhibitory concentration values from 8.8 to 18.5 μg/mL. Moreover, they were able to inhibit the biofilm formation of C. albicans better than the positive control.

New Alkylitaconic Acid Derivatives from Nodulisporium sp. A21 and Their Auxin Herbicidal Activities on Weed Seeds

Five alkylitaconic acid (AA) derivatives, including two novel compounds, epideoxysporothric acid (2) and sporochartine F (5), and three known compounds, deoxysporothric acid (1), deoxyisosporothric acid (3), and 1-undecen-2,3-dicarboxylic acid (4), were obtained from the fermentation culture of the endophytic fungus Nodulisporium sp. A21. The auxin herbicidal activities of compounds 1-4 against weed seeds were investigated under laboratory conditions. In general, the tested compounds displayed radicle growth promoting activity at low doses and inhibitory activity at higher doses. Compounds 1 and 2 could significantly inhibit the radicle growth of dicotyledon weeds, Eclipta prostrata and Veronica persica, at a concentration range from 50 to 200 μg mL^-1, while 3 notably stimulated radicle growth at the same concentration range. The results suggested that these AA derivatives have the potential to be used as the lead scaffold for novel auxin herbicide development. In addition, the biosynthetic pathways of 1-4 were deduced based on ¹³C labeling experiment.

Macrocyclic Trichothecene Mycotoxins from a Deadly Poisonous Mushroom, Podostroma cornu-damae

Three new macrocyclic trichothecenes (1-3) and five known related compounds (4-8) were isolated from the MeOH extract of a plate culture of the fungus Podostroma cornu-damae, a deadly poisonous mushroom. Miophytocen D (1) is a rearranged macrocyclic type D trichothecene, featuring a bicyclo-[6.5]dodecahydrocyclopenta[ b]chromene scaffold, and the structures of new compounds (1-3) were delineated by the combination of 1D and 2D NMR spectroscopic experiments and HRESIMS, modified Mosher's esterification, and quantum chemical ECD calculations. The isolated compounds (1-8) were evaluated for cytotoxicity against four human breast cancer cell lines (Bt549, HCC70, MDA-MB-231, and MDA-MB-468). Compounds 4, 6, and 8 exhibited significant cytotoxic effects against the breast cancer cell lines, with IC₅₀ values in the range of 0.02-80 nM, which is stronger than doxorubicin, the positive control, and a structure-activity relationship was suggested.

Identification and characterization of a T-2 toxin-producingFusarium poaestrain and the anti-tumor effect of the T-2 toxin on human hepatoma cell line SMMC-7721

T-2 toxin, produced by Fusarium moulds, is a type A trichothecene mycotoxin which is known to inhibit protein synthesis and also reported to induce DNA lesions, potentially causing DNA fragmentation. T-2 toxin is a very potent cytotoxic toxin, which displays anti-tumor properties. Nevertheless, more studies are still needed to explore its antitumor mechanisms as well as its clinical application in cancer treatment. Here, we report the identification and characterization of a T-2 toxin produced by a Fusarium poae isolated from Jilin, Northeast China. 17 strains of Fusarium poae were screened for T-2 toxin-production and one strain with the highest yield was selected further studies. T-2 toxin produced by the selected Fusarium poae was isolated and purified by HPLC. Anticancer properties of the purified T-2 toxin were evaluated with human hepatoma cell SMMC-7721. The purified T-2 toxin inhibits the proliferation of SMMC-7721 cells and induces cell apoptosis. The mitochondrial membrane potential decreased and the intracellular ROS was up-regulated after T-2 treatment of the cells. Further studies revealed that T-2 treatment activates the intrinsic mitochondrial and MAPKs pathway. Our data provide insight into the promising application of the T-2 toxin in cancer treatment.

T-2 toxin produced by Fusarium poae strain can induces apoptosis in SMMC-7721 cells.

Evolution of structural diversity of trichothecenes, a family of toxins produced by plant pathogenic and entomopathogenic fungi

Trichothecenes are a family of terpenoid toxins produced by multiple genera of fungi, including plant and insect pathogens. Some trichothecenes produced by the fungus Fusarium are among the mycotoxins of greatest concern to food and feed safety because of their toxicity and frequent occurrence in cereal crops, and trichothecene production contributes to pathogenesis of some Fusarium species on plants. Collectively, fungi produce over 150 trichothecene analogs: i.e., molecules that share the same core structure but differ in patterns of substituents attached to the core structure. Here, we carried out genomic, phylogenetic, gene-function, and analytical chemistry studies of strains from nine fungal genera to identify genetic variation responsible for trichothecene structural diversity and to gain insight into evolutionary processes that have contributed to the variation. The results indicate that structural diversity has resulted from gain, loss, and functional changes of trichothecene biosynthetic (TRI) genes. The results also indicate that the presence of some substituents has arisen independently in different fungi by gain of different genes with the same function. Variation in TRI gene duplication and number of TRI loci was also observed among the fungi examined, but there was no evidence that such genetic differences have contributed to trichothecene structural variation. We also inferred ancestral states of the TRI cluster and trichothecene biosynthetic pathway, and proposed scenarios for changes in trichothecene structures during divergence of TRI cluster homologs. Together, our findings provide insight into evolutionary processes responsible for structural diversification of toxins produced by pathogenic fungi.

Toxins produced by pathogens can contribute to infection and/or colonization of hosts. Some toxins consist of a family of metabolites with similar but distinct chemical structures. This structural variation can affect biological activity, which in turn likely contributes to adaptation to different environments, including to different hosts. Trichothecene toxins consist of over 150 structurally distinct molecules produced by certain fungi, including some plant and insect pathogens. In multiple systems that have been examined, trichothecenes contribute to pathogenesis on plants. To elucidate the evolutionary processes that have given rise to trichothecene structural variation, we conducted comparative analyses of nine fungal genera, most of which produce different trichothecene structures. Using genomic, molecular biology, phylogenetic, and analytical chemistry approaches, we obtained evidence that trichothecene structural variation has arisen primarily from gain, loss, and functional changes of trichothecene biosynthetic genes. Our results also indicate that some structural changes have arisen independently in different fungi. Our findings provide insight into genetic and biochemical changes that can occur in toxin biosynthetic pathways as fungi with the pathways adapt to different environmental conditions.

Metabolites from the Endophytic Fungus Curvularia sp. M12 Act as Motility Inhibitors against Phytophthora capsici Zoospores

The endophytic fungus Curvularia sp., strain M12, was isolated from a leaf of the medicinal plant Murraya koenigii and cultured on rice medium followed by chemical screening of the culture extract. Chromatographic analysis led to the isolation of four new compounds, murranofuran A (1), murranolide A (2), murranopyrone (3a), and murranoic acid A (4a), along with six known metabolites, N-(2-hydroxy-6-methoxyphenyl)acetamide (5), curvularin (6), (S)-dehydrocurvularin (7), pyrenolide A (8), modiolide A (9), and 8-hydroxy-6-methoxy-3-methylisocoumarin (10). The structures of the known compounds were confirmed by comparing ESI HR mass spectra, ¹H and ¹³C NMR, and optical rotation data with values reported in the literature. The planar structures of the new compounds were elucidated by extensive analysis of 1D and 2D NMR and mass data. The absolute configurations of the new compounds were established by coupling constant analysis, modified Mosher's method, and CD data. Compound 8 showed a strong motility impairing activity against Phytophthora capsici zoospores at a low concentration (100% at 0.5 μg/mL) in a short time (30 min). Compounds 2, 3a, 6, 7, 9, and 10 exhibited zoospore motility impairment activity at higher concentrations (IC₅₀: 50-100 μg/mL).