Scytalols A, B, C, and D and other modulators of melanin biosynthesis from Scytalidium sp. 36-93

Antibacterial Polyketides Isolated from the Marine-Derived Fungus Fusarium solani 8388

Seven new polyketides named fusarisolins F-K (1-6) and fusarin I (7) were isolated from the marine-derived fungus Fusarium solani 8388, together with the known anhydrojavanicin (8), 5-deoxybostry coidin (9), and scytalol A (10). Their structures were established by comprehensive spectroscopic data analyses, and by comparison of the 1H and 13C NMR data with those reported in literature. Fusarisolin F (1) contained both a dichlorobenzene group and an ethylene oxide unit, which was rare in nature. In the bioassays, fusarisolin I (4), fusarisolin J (5), and 5-deoxybostry coidin (9) exhibited obvious antibacterial activities against methicillin-resistant Staphylococcus aureus n315 with MIC values of 3, 3, and 6 μg/mL, respectively. Fusarisolin H (3) and fusarisolin J (5) showed inhibitory effects against methicillin-resistant Staphylococcus aureus NCTC 10442 with the same MIC value of 6 μg/mL. With the exception of 5, all other compounds did not show or showed weak cytotoxicities against HeLa, A549, and KB cells; while fusarisolin J (5) demonstrated moderate cytotoxicities against the three human cancer cell lines with CC50 values between 9.21 and 14.02 μM.

Asymmetric synthesis of (+)-teratosphaerone B, its non-natural analogue and (+)-xylarenone using an ene- and naphthol reductase cascade

Herein, a one-pot bienzymatic cascade containing an ene and a naphthol reductase is developed. It is applied for the synthesis of (+)-(3R,4R)-teratosphaerone B, its non-natural regioisomer in both cis- and trans-forms and (+)-xylarenone by the reduction of chemically synthesized naphthoquinone precursors in high yields (76-92%) and excellent ee (>99%). This work implies similar biosynthetic steps in the formation of the synthesized natural products.

Fungal Naphthalenones; Promising Metabolites for Drug Discovery: Structures, Biosynthesis, Sources, and Pharmacological Potential

Fungi are well-known for their abundant supply of metabolites with unrivaled structure and promising bioactivities. Naphthalenones are among these fungal metabolites, that are biosynthesized through the 1,8-dihydroxy-naphthalene polyketide pathway. They revealed a wide spectrum of bioactivities, including phytotoxic, neuro-protective, cytotoxic, antiviral, nematocidal, antimycobacterial, antimalarial, antimicrobial, and anti-inflammatory. The current review emphasizes the reported naphthalenone derivatives produced by various fungal species, including their sources, structures, biosynthesis, and bioactivities in the period from 1972 to 2021. Overall, more than 167 references with 159 metabolites are listed.

Biosynthesis and biological function of secondary metabolites of the rice blast fungus Pyricularia oryzae

Filamentous fungi have many secondary metabolism genes and produce a wide variety of secondary metabolites with complex and unique structures. However, the role of most secondary metabolites remains unclear. Moreover, most fungal secondary metabolism genes are silent or poorly expressed under laboratory conditions and are difficult to utilize. Pyricularia oryzae, the causal pathogen of rice blast disease, is a well-characterized plant pathogenic fungus. P. oryzae also has a large number of secondary metabolism genes and appears to be a suitable organism for analyzing secondary metabolites. However, in case of this fungus, biosynthetic genes for only four groups of secondary metabolites have been well characterized. Among two of the four groups of secondary metabolites, biosynthetic genes were identified by activating secondary metabolism. These secondary metabolites include melanin, a polyketide compound required for rice infection; tenuazonic acid, a well-known mycotoxin produced by various plant pathogenic fungi and biosynthesized by a unique nonribosomal peptide synthetase-polyketide synthase hybrid enzyme; nectriapyrones, antibacterial polyketide compounds produced mainly by symbiotic fungi, including plant pathogens and endophytes, and pyriculols, phytotoxic polyketide compounds. This review mainly focuses on the biosynthesis and biological functions of the four groups of P. oryzae secondary metabolites.

Secondary Metabolites of the Rice Blast Fungus Pyricularia oryzae: Biosynthesis and Biological Function

Plant pathogenic fungi produce a wide variety of secondary metabolites with unique and complex structures. However, most fungal secondary metabolism genes are poorly expressed under laboratory conditions. Moreover, the relationship between pathogenicity and secondary metabolites remains unclear. To activate silent gene clusters in fungi, successful approaches such as epigenetic control, promoter exchange, and heterologous expression have been reported. Pyricularia oryzae, a well-characterized plant pathogenic fungus, is the causal pathogen of rice blast disease. P. oryzae is also rich in secondary metabolism genes. However, biosynthetic genes for only four groups of secondary metabolites have been well characterized in this fungus. Biosynthetic genes for two of the four groups of secondary metabolites have been identified by activating secondary metabolism. This review focuses on the biosynthesis and roles of the four groups of secondary metabolites produced by P. oryzae. These secondary metabolites include melanin, a polyketide compound required for rice infection; pyriculols, phytotoxic polyketide compounds; nectriapyrones, antibacterial polyketide compounds produced mainly by symbiotic fungi including endophytes and plant pathogens; and tenuazonic acid, a well-known mycotoxin produced by various plant pathogenic fungi and biosynthesized by a unique NRPS-PKS enzyme.

Cytotoxic Heptaketides from the Endolichenic Fungus Ulospora bilgramii

Eleven new metabolites including nine heptaketides, ulosporin A-G (1a-7b), one diphenyl compound, ulophenol (8), and one spirobisnaphthalene, palmarumycin P5 (9), were isolated from the endolichenic fungus Ulospora bilgramii, which inhabits the lichen Umbilicaria sp. The structures of these compounds were elucidated based on comprehensive analysis of their spectroscopic, electronic circular dichroism (ECD), and single-crystal X-ray diffraction data. Ulosporin G (7) inhibited the growth of the human cancer cell lines A549, MCF-7, and KB with IC₅₀ values of 1.3, 1.3, and 3.0 μM, respectively. Additionally, it induced A549 cell apoptosis through G0/G1 cell cycle arrest caused by DNA damage.

Cytotoxic and Noncytotoxic Metabolites from Teratosphaeria sp. FL2137, a Fungus Associated with Pinus clausa

A new naphthoquinone, teratosphaerone A (1), four new naphthalenones, namely, teratosphaerone B (2), structurally related to 1, iso-balticol B (3), iso-balticol B-4,9-acetonide (4), and (+)-balticol C (5), a new furanonaphthalenone, (3a S,9 R,9a S)-1(9a),3(3a),9-hexahydromonosporascone (6), and the known metabolite monosporascone (7) were isolated from Teratosphaeria sp. FL2137, a fungal strain inhabiting the internal tissue of recently dead but undecomposed foliage of Pinus clausa. The structures of 1-6 were elucidated on the basis of their spectroscopic data including 2D NMR, and absolute configurations of 2, 3, and 6 were determined by the modified Mosher's ester method. When evaluated in a panel of five tumor cell lines, metabolites 1 and 7 isolated from a cytotoxic fraction of the extract exhibited moderate selectivity for metastatic breast adenocarcinoma cell line MDA-MB-231. Of these, 1 showed cytotoxicity to this cell line with an IC₅₀ of 1.2 ± 0.1 μM.

Heptaketides from an Endolichenic Fungus Biatriospora sp. and Their Antifungal Activity

Twelve new heptaketides, biatriosporins A-L (1-12), biatriosporin M (13) (a ramulosin derivative), and 19 known compounds (14-32) were isolated from the endolichenic fungus Biatriospora sp. (8331C). The structures of these compounds were determined by analyzing MS and NMR data. The absolute configurations of compounds 1, 2, 7, and 9 were determined by single-crystal X-ray diffraction analysis, whereas compound 10 was deduced with Mosher's method. Four of the compounds were active in an antifungal assay. The most potent compound, compound 4, also sensitized clinically derived azole-resistant Candida albicans strains to fluconazole (FLC). A mechanistic investigation revealed that 4 inhibited the function of efflux pumps and reduced the transcriptional expression of the efflux-pump-related genes CDR1 and CDR2.

Maximizing chemical diversity of fungal metabolites: biogenetically related Heptaketides of the endolichenic fungus Corynespora sp. (1)

In an attempt to explore the biosynthetic potential of the endolichenic fungus Corynespora sp. BA-10763, its metabolite profiles under several culture conditions were investigated. When cultured in potato dextrose agar, it produced three new heptaketides, 9-O-methylscytalol A (1), 7-desmethylherbarin (2), and 8-hydroxyherbarin (3), together with biogenetically related metabolites scytalol A (4), 8-O-methylfusarubin (5), scorpinone (6), and 8-O-methylbostrycoidin (7), which are new to this organism, and herbarin (8), a metabolite previously encountered in this fungal strain. The use of malt extract agar as the culture medium led to the isolation of 6, 8, 1-hydroxydehydroherbarin (9), and 1-methoxydehydroherbarin (10), which was found to be an artifact formed during the extraction of the culture medium with methanol. The structures of all new compounds were determined by interpretation of their spectroscopic data and chemical interconversions.

Balticols A-F, new naphthalenone derivatives with antiviral activity, from an ascomycetous fungus

Six new naphthalenone derivatives, balticols A-F and the known metabolite altechromone A were isolated from the AcOEt extract of the culture broth of fungal strain 222 belonging to the Ascomycota, which was found on driftwood collected at the coast of the Greifswalder Bodden, Baltic Sea, Germany. All structures were elucidated on the basis of NMR spectroscopic data and mass spectrometric analyses. The balticols were found to exhibit inhibitory activity against influenza virus A and herpes simplex virus. The most potent antiviral activity was observed for balticol E with an IC(50) value of 0.01 microg/ml against Herpes simplex virus type I.

Heptaketides from Corynespora sp. inhabiting the cavern beard lichen, Usnea cavernosa: first report of metabolites of an endolichenic fungus

Two new heptaketides, corynesporol (1) and 1-hydroxydehydroherbarin (2), along with herbarin (3) were isolated from an endolichenic fungal strain, Corynespora sp. BA-10763, occurring in the cavern beard lichen Usnea cavernosa. The structures of 1-3 were elucidated from their spectroscopic data. Aerial oxidation of corynesporol (1) yielded herbarin (3). Acetylation of 1 afforded the naphthalene derivative 4, whereas acetylation of 3 gave the corresponding naphthoquinone 6 and dehydroherbarin (5). All compounds were evaluated for their cytotoxicity and ability to inhibit migration of human metastatic breast and prostate cancer cell lines MDA-MB-231 and PC-3M, respectively. Dehydroherbarin (5) inhibited migration of both cell lines at concentrations not toxic to these cell lines. This is the first report of metabolites from an endolichenic fungus.

Scytalidium dimidiatum causing recalcitrant subcutaneous lesions produces melanin

Scytalidium dimidiatum is a pigmented dematiaceous coelomycete that typically causes chronic superficial skin diseases and onychomycosis, as well as deeper infections, such as subcutaneous abscesses, mycetoma, and even fungemia in immunocompromised patients. A second species, Scytalidium hyalinum, has hyaline hyphae and arthroconidia and is considered by some authors to be an albino mutant of S. dimidiatum. This study aimed to confirm the presence of melanin or melanin-like compounds (which have been previously implicated in the virulence of other fungal pathogens) in S. dimidiatum from a patient with multiple subcutaneous nodules. Treatment of the hyphae and arthroconidia with proteolytic enzymes, denaturant, and concentrated hot acid yielded dark particles, which were stable free radicals, consistent with their identification as melanins. Extracted melanin particles from S. dimidiatum cultures were labeled by melanin-binding monoclonal antibodies (MAbs) from Sporothrix schenckii, Aspergillus fumigatus, and Cryptococcus neoformans. Lesional skin from the patient infected with S. dimidiatum contained fungal cells that were labeled by melanin-binding MAbs, and digestion of the tissue yielded dark particles that were also reactive. S. hyalinum was also subjected to the melanin extraction protocol, but no dark particles were yielded.

Fungal secondary metabolites as inhibitors of infection-related morphogenesis in phytopathogenic fungi

The life-cycle of many plant-pathogenic fungi, especially those infecting aerial plant organs, contains several specific developmental stages. If these are sufficiently distinct in their physiology from vegetative hyphal growth, they present potential targets for non-fungitoxic plant protectants. The present review identifies such targets especially in the pre-penetration stages of the infection cycle of Magnaporthe grisea and other fungi infecting from air-borne spores. Examples of non-toxic natural products with activity against spore germination, attachment, appressorium formation, appressorium maturation and penetration of the host surface are given. In contrast, no substances selectively active against in planta growth or sporulation appear to be known. The selective activity of numerous secondary metabolites against specific infection stages without accompanying toxicity against vegetatively growing hyphae indicates a direction for the development of future natural product-derived fungicides which are more easily degraded in the environment and possess fewer non-target effects. Such substances are produced by many saprotrophic and endophytic fungi in pure culture. The paucity of data on the production of biologically active substances in natural situations limits the interpretation of their ecophysiological significance for the producer.