Asteltoxins from the Entomopathogenic Fungus Pochonia bulbillosa 8-H-28

Isolation and Structure Elucidation of New Metabolites from the Mariana-Trench-Associated Fungus Aspergillus sp. SY2601

Fungi are important resource for the discovery of novel bioactive natural products. This study investigated the metabolites produced by Mariana-Trench-associated fungus Aspergillus sp. SY2601 in EY liquid and rice solid media, resulting in the isolation and structure determination of 28 metabolites, including five new compounds, asperindopiperazines A-C (1-3), 5-methoxy-8,9-dihydroxy-8,9-deoxyaspyrone (21), and 12S-aspertetranone D (26). Structures of the new compounds were elucidated based on extensive NMR spectral analyses, HRESIMS data, optical rotation, ECD, and 13C NMR calculations. The new compound 12S-aspertetranone D (26) exhibited antibacterial activity against both methicillin-resistant Staphylococcus aureus and Escherichia coli with MIC values of 3.75 and 5 μg/mL, respectively.

Two new α-pyrone-containing polyketides isolated from the fungus Aspergillus aureoterreus

Two undescribed α-pyrone-containing polyketide derivatives designated aurovertins V (1) and W (2), and a known analogue (3), were isolated from the fungus Aspergillus aureoterreus. Their structures including the absolute configuration were elucidated on the basis of extensive spectroscopic methods and theoretical ECD calculation. Compound 1 is the first example of aurovertins with a 7R configuration, whereas 2 comprises a S configuration for C-6 and a Z geometry of the double bond Δ8. Both 1 and 2 showed no cytotoxicity against human cancer cell lines HL-60, SU-DHL-2 and U266) at the concentration of 20.0 μM.

Study of Pathogenesis Using Fluorescent Strain of Cordyceps farinosa Revealed Infection of Thitarodes armoricanus Larvae via Digestive Tract

Cordyceps farinosa is often utilized as a biocontrol agent because of its wide host range, strong lethality, and safety for mammals. Artificial rearing of Thitarodes armoricanus larvae is a prerequisite for the artificial cultivation of Chinese cordyceps, and C. farinosa is the most lethal pathogenic fungus during the rearing process. However, the infection process of C. farinosa is still unclear. In this study, we cloned the promoter of the C. farinosa glyceraldehyde 3-phosphate dehydrogenase gene, constructed the EGFP expression cassette, and integrated it into the C. farinosa genome via Agrobacterium transformation. We obtained a fluorescent strain for better observation of the infection process. Using two different inoculation methods of the fluorescent strain, we observed the traditional infection process through the body surface as well as through the digestive tract via feeding. Both infection modes can lead to larval death and mummification. Our findings demonstrated that during the artificial rearing of T. armoricanus, preventing C. farinosa pollution should be an important part of the disinfection of the rearing environment.

Polyketides with quorum sensing inhibitory activity from the marine-derived fungus Aspergillus sp. ZF-79

Seven compounds were isolated from a marine-derived fungus Aspergillus sp. ZF-79, including three new polyketides (1-3), named asperochrins D-F, along with four known compounds 4-7. Their structures were determined on the basis of spectroscopic methods. All the compounds were tested for quorum sensing inhibitory (QSI) activity. Compounds 1, 3, 4, 5, and 6 exhibited QSI activity against Chromobacterium violaceum CV026 with MIC values of 50, 100, 50, 50, and 6.25 μM, respectively.

Screening Fungal Endophytes Derived from Under-Explored Egyptian Marine Habitats for Antimicrobial and Antioxidant Properties in Factionalised Textiles

Marine endophytic fungi from under-explored locations are a promising source for the discovery of new bioactivities. Different endophytic fungi were isolated from plants and marine organisms collected from Wadi El-Natrun saline lakes and the Red Sea near Hurghada, Egypt. The isolated strains were grown on three different media, and their ethyl acetate crude extracts were evaluated for their antimicrobial activity against a panel of pathogenic bacteria and fungi as well as their antioxidant properties. Results showed that most of the 32 fungal isolates initially obtained possessed antimicrobial and antioxidant activities. The most potent antimicrobial extracts were applied to three different cellulose containing fabrics to add new multifunctional properties such as ultraviolet protection and antimicrobial functionality. For textile safety, the toxicity profile of the selected fungal extract was evaluated on human fibroblasts. The 21 strains displaying bioactivity were identified on molecular basis and selected for chemical screening and dereplication, which was carried out by analysis of the MS/MS data using the Global Natural Products Social Molecular Networking (GNPS) platform. The obtained molecular network revealed molecular families of compounds commonly produced by fungal strains, and in combination with manual dereplication, further previously reported metabolites were identified as well as potentially new derivatives.

A new asteltoxin analog with insecticidal activity from Pochonia suchlasporia TAMA 87

A new asteltoxin analog, named asteltoxin H (1), was isolated by the solid-state fermentation of the fungus Pochonia suchlasporia var. suchlasporia TAMA 87. The chemical structure of 1 was deduced by spectroscopic methods, including 1D and 2D NMR, HRESIMS, and UV-Vis analyses. Compound 1 showed insecticidal activity against prepupae of the blowfly, Lucilia sericata, with an LD₅₀ value of 0.94 µg/mg prepupal body weight.

Functional expression of a highly-reducing polyketide synthase of Emericella variecolor IFM42010, an asteltoxin-producing strain, resulted in production of two polyenoic β-ketolactones with opposite stereochemistry

The asteltoxin-producing fungus Emericella variecolor IFM42010 possesses 22 highly-reducing polyketide synthase (HR-PKS) genes. Of these, an HR-PKS with a methyltransferase domain but lacking an enoylreductase domain could be involved in the biosynthesis of asteltoxin and related compounds. From six such candidate HR-PKS genes, Ev460pks was analyzed by gene disruption in E. variecolor and heterologous expression in Aspergillus oryzae. The Ev460pks-disrupted strain retained asteltoxin production ability, indicating that Ev460pks is not involved in asteltoxin biosynthesis. The A. oryzae transformant harboring the Ev460pks gene produced compounds 1 and 2, along with several unidentified products possibly decomposed from 2. Spectroscopic analyses revealed that 1 was a 4-methyl-β-ketolactone with a methylheptatriene side-chain at the C-5 position, and 2 was also a 4-methyl-β-ketolactone, bearing a dimethyltetradecahexaene side-chain at the same position. The relative configuration at C-4 in compounds 1 and 2 was opposite.

Trienic α-pyrone and ochratoxin derivatives from a sponge-derived fungus Aspergillus ochraceopetaliformis

A new trienic α-pyrone derivative asteltoxin G (1) bearing a tetrahydrofuran ring and a new ochratoxin derivative named ochratoxin A₁ (5), along with seven known compounds, were isolated from a sponge-derived fungus Aspergillus ochraceopetaliformis. The compounds (1-9) were evaluated on the basis of spectroscopic analyses and comparison with those of the reported data. The new compound ochratoxin A₁ (5) exhibited anti-inflammatory activity against IL-6 and TNF-α expression of the LPS-induced THP-1 cells with inhibitory rates of 74.4 and 67.7% at concentration of 10 μM, respectively.

Coordinated and Iterative Enzyme Catalysis in Fungal Polyketide Biosynthesis

Fungal polyketides are natural products with great chemical diversity that exhibit a wide range of biological activity. This chemical diversity stems from specialized enzymes encoded in the biosynthetic gene cluster responsible for the natural product biosynthesis. Fungal polyketide synthases (PKS) are the megasynthases that produce the carbon scaffolds for the molecules. Subsequent downstream tailoring enzymes such as oxygenases will then further modify the organic framework. In fungi, many of these enzymes have been found to work iteratively-catalyzing multiple reactions on different sites of the substrate. This perspective will analyze several examples of fungal polyketides that are assembled from a scaffold-building iterative PKS and an accompanying iterative tailoring oxygenase. In these examples, the PKS product is designed for downstream iterative oxygenations to generate additional complexity. Together, these iterative enzymes orchestrate the efficient biosynthesis of elaborate natural products such as lovastatin, chaetoglobosin A, cytochalasin E, and aurovertin E.

Antiviral Merosesquiterpenoids Produced by the Antarctic Fungus Aspergillus ochraceopetaliformis SCSIO 05702

Five new highly oxygenated α-pyrone merosesquiterpenoids, ochraceopones A-E (1-5), together with one new double bond isomer of asteltoxin, isoasteltoxin (6), and two known asteltoxin derivatives, asteltoxin (7) and asteltoxin B (8), were isolated from an Antarctic soil-derived fungus, Aspergillus ochraceopetaliformis SCSIO 05702. Their structures were determined through extensive spectroscopic analysis, CD spectra, quantum mechanical calculations, and X-ray single-crystal diffraction. Ochraceopones A-D (1-4) are the first examples of α-pyrone merosesquiterpenoids possessing a linear tetracyclic carbon skeleton, which has not been previously described. All the isolated compounds were tested for their antiviral, cytotoxic, antibacterial, and antitubercular activities. Among these compounds, ochraceopone A (1), isoasteltoxin (6), and asteltoxin (7) exhibited antiviral activities against the H1N1 and H3N2 influenza viruses with IC50 values of >20.0/12.2 ± 4.10, 0.23 ± 0.05/0.66 ± 0.09, and 0.54 ± 0.06/0.84 ± 0.02 μM, respectively. A possible biosynthetic pathway for ochraceopones A-E (1-5) was proposed.

Asteltoxins with Antiviral Activities from the Marine Sponge-Derived Fungus Aspergillus sp. SCSIO XWS02F40

Two new asteltoxins named asteltoxin E (2) and F (3), and a new chromone (4), together with four known compounds were isolated from a marine sponge–derived fungus, Aspergillus sp. SCSIO XWS02F40. The structures of the compounds (1–7) were determined by the extensive 1D- and 2D-NMR spectra, and HRESIMS spectrometry. All the compounds were tested for their antiviral (H1N1 and H3N2) activity. Compounds 2 and 3 showed significant activity against H3N2 with the prominent IC₅₀ values of 6.2 ± 0.08 and 8.9 ± 0.3 μM, respectively. In addition, compound 2 also exhibited inhibitory activity against H1N1 with an IC₅₀ value of 3.5 ± 1.3 μM.

Avertoxins A-D, Prenyl Asteltoxin Derivatives from Aspergillus versicolor Y10, an Endophytic Fungus of Huperzia serrata

Aspergillus versicolor Y10 is an endophytic fungus isolated from Huperzia serrata, which showed inhibitory activity against acetylcholinesterase. An investigation of the chemical constituents of Y10 led to the isolation of four new prenylated asteltoxin derivatives, named avertoxins A-D (2-5), together with the known mycotoxin asteltoxin (1). In the present study, we report structure elucidation for 2-5 and the revised NMR assignments for asteltoxin and demonstrated that avertoxin B (3) is an active inhibitor against human acetylcholinesterase with the IC50 value of 14.9 μM (huperzine A as the positive control had an IC50 of 0.6 μM). In addition, the cytotoxicity of asteltoxin (1) and avertoxins A-D (2-5) against MDA-MB-231, HCT116, and HeLa cell lines was evaluated.

Efficient Biosynthesis of Fungal Polyketides Containing the Dioxabicyclo-octane Ring System

Aurovertins are fungal polyketides that exhibit potent inhibition of adenosine triphosphate synthase. Aurovertins contain a 2,6-dioxabicyclo[3.2.1]octane ring that is proposed to be derived from a polyene precursor through regioselective oxidations and epoxide openings. In this study, we identified only four enzymes required to produce aurovertin E. The core polyketide synthase produces a polyene α-pyrone. Following pyrone O-methylation by a methyltransferase, a flavin-dependent mono-oxygenase and an epoxide hydrolase can iteratively transform the terminal triene portion of the precursor into the dioxabicyclo[3.2.1]octane scaffold. We demonstrate that a tetrahydrofuranyl polyene is the first stable intermediate in the transformation, which can undergo epoxidation and anti-Baldwin 6-endo-tet ring opening to yield the cyclic ether product. Our results further demonstrate the highly concise and efficient ways in which fungal biosynthetic pathways can generate complex natural product scaffolds.