Alkylated Salicylaldehydes and Prenylated Indole Alkaloids from the Endolichenic Fungus Aspergillus chevalieri and Their Bioactivities

Endophytic microorganisms in lichen: rising stars in the biomedicine field deserving broader recognition

Lichens are renowned for their ability to thrive in extreme environments and for producing unique metabolites with considerable bioactive potential. However, their medicinal value remains largely underexplored, primarily due to slow growth rates and habitat specificity. Notably, endolichenic microorganisms, particularly fungi, are the predominant producers of these bioactive compounds, which exhibit antimicrobial, antiviral, and anticancer properties. Investigating these microorganisms and their metabolites presents promising biomedical opportunities, underscoring the importance of sustainably utilizing lichen resources and discovering novel compounds. This paper reviews the diversity and bioactive potential of endophytic microorganisms in lichens, providing valuable insights for the exploration of natural resources.

Extraction, isolation, identification and bioactivity of anthraquinones from Aspergillus cristatus derived from Fuzhaun brick tea

Aspergillus cristatus, a probiotic fungus isolated from Fuzhuan brick tea (FBT), produces various valuable but uncharacterized secondary metabolites. We hypothesized that diverse anthraquinones metabolized by A. cristatus possess promising bioactivities and influence fermentation process of FBT. In this study, five benzaldehyde derivatives, three indolediketopiperazine alkaloids and twelve anthraquinones were profiled from A. cristatus, and the methods for extracting and purifying anthraquinones were established. Twelve anthraquinones were identified as (+)-variecolorquinone A, fallacinol, (+)1-O-demethylvariecolorquinone A, dermolutein, citreorosein, endocrocin, questin, rubrocristin, emodin, catenarin, physcion and erythroglaucin, providing clues for deducing their biosynthetic pathways. Functionally, these compounds demonstrated antioxidant, anti-inflammatory and antibacterial effects. Notably, emodin, catenarin, citreorosein and erythroglaucin exhibited remarkable anti-inflammatory activity. Furthermore, the antibacterial metabolites, especially emodin and catenarin, demonstrated potent antibacterial properties against Escherichia coli and Staphylococcus aureus, elucidating that A. cristatus antagonized pathogens during FBT production. Collectively, these anthraquinones hold promise as stable colorants and effective preservatives in food industry.

Comparative Antagonistic Activities of Endolichenic Fungi Isolated from the Fruticose Lichens Ramalina and Usnea

Persistent fungal pathogens remain a threat to global food security as these pathogens continue to infect crops despite different mitigating strategies. Traditionally, synthetic fungicides are used to combat these threats, but their environmental and health impacts have spurred interest in a more sustainable, eco-friendly approach. Endolichenic fungi (ELF) are a relatively underexplored group of microorganisms found thriving inside the lichen thalli. They are seen as promising alternatives for developing sustainable plant disease management strategies. Hence, in this study, a total of forty ELF isolates from two fruticose lichen hosts-Ramalina and Usnea, were tested and compared for their antagonistic activities against three economically important filamentous fungal pathogens-Colletotrichum gloeosporioides, Cladosporium cladosporioides, and Fusarium oxysporum. The results of the dual culture assay showed that all ELF isolates successfully reduced the growth of the three filamentous fungal pathogens with varying degrees, and with direct contact inhibition as the predominant trait among the endolichenic fungi. Comparing the antagonistic activities between the different endolichenic fungi from the two lichen hosts, ELF isolates from Ramalina generally demonstrated a higher percentage inhibition of growth of the test fungi as compared to ELF isolates from Usnea. This study underscores the importance of endolichenic fungi as an efficient biocontrol agent.

Crystal Structure of Autophagy-Associated Protein 8 at 1.36 Å Resolution and Its Inhibitory Interactions with Indole Analogs

Autophagy-associated protein 8 (ATG8) is essential for autophagy and organismal growth and development. In this study, we successfully resolved the crystal structure of Drosophila melanogaster (D. melanogaster) ATG8a (DmATG8a) at 1.36 Å resolution. Being distinct from previously characterized ATG8 homologues, DmATG8a (121 residues) adopts a unique fold comprising five α-helices and four β-folding strands, in contrast to the canonical four α-helices and four β-folding strands observed in other ATG8 proteins. DmATG8a features two active cavities: hydrophobic pocket 1 (HP1) and hydrophobic pocket 2 (HP2), which are essential for the normal physiological function of ATG8. Indole and its analogs can bind specifically with HP1. Microscale thermophoresis results demonstrated a strong affinity of 6-fluoroindole with DmATG8a (3.54 μmol/L), but no affinity with the DmATG8aK48A mutant, suggesting that Lys48 is critical in binding 6-fluoroindole probably via a hydrogen bond interaction. The half-maximum lethal concentration (LC50) of 6-fluoroindole against D. melanogaster adult flies was 169 μg/mL. Our findings establish DmATG8a as a promising target for developing indole-based insecticides.

Cytochalasins and orsellinic acid derivatives with cytotoxicity from the soil-derived fungus Trichocladium asperum

Four undescribed cytochalasins (1-4), three undescribed orsellinic acid derivatives (5-7) and two known metabolites including methyl lecanorate (8) and methyl orsellinate (9) were isolated from the solid-state cultivation of a soil-derived fungus Trichocladium asperum SQ2-3 collected in Qinghai-Tibet Plateau. Their structures were elucidated by analysis of NMR (1D and 2D) and mass spectrometry data. The absolute configurations of 1-7 were assigned by a combination of the modified Mosher's method, microscale derivatization and Mo2(OAc)4-induced circular dichroism experiment. Compounds 1, 2, 3 and 6 showed significant cytotoxicity against HL-60, A3494, SMMC-7721, MDA-MB-231 and SW480 cell lines with IC50 values ranging from 4.74 to 15.84 μM, respectively. Meanwhile, compound 1 could obviously damage mitochondrial membrane potential and induce G2/M cell cycle arrest in A549 cells.

Chevalierlin: A spirocyclic alkaloid from a hydrothermal vent associated fungus Aspergillus chevalieri TW132-65

A previously undescribed spirodiketopiperazine-indole alkaloid, chevalierlin (1), two pairs of previously undescribed dihydroisocoumarin enantiomers eurotiumides H-I (2-3), as well as six related known compounds (4-9) were isolated from the culture of a hydrothermal vent associated fungus Aspergillus chevalieri TW132-65. Their structures were unambiguously determined by NMR, mass spectrometry, and ECD calculations. Chevalierlin (1) exhibits moderate cytotoxic activities with IC50 values of 6.20 ± 0.05 μM and 7.68 ± 0.01 μM against Namalwa and Raji cell lines.

Endophytic fungi: nature's solution for antimicrobial resistance and sustainable agriculture

The growing threat of antimicrobial resistance (AMR) has underlined the need for a sustained supply of novel antimicrobial agents. Endophyte microorganism that reside within plant tissues as symbionts have been the source of potential antimicrobial substances. However, many novel and potent antimicrobials are yet to be discovered from these endophytes. The present study investigates the potential of endophytic fungi as a source of novel bioactive chemicals with antibacterial capabilities. These fungi synthesize secondary metabolites such as polyketides and peptides via polyketide synthase (PKS) and nonribosomal peptide synthetase (NRPS) pathways. Notable substances, like prenylated indole alkaloids and fumaric acid, have shown promising antibacterial and antifungal properties against multidrug-resistant infectious agents. This review also emphasizes the symbiotic link between endophytes and their host plants, which is critical for secondary metabolite production. The study focuses on the significance of isolation methods for endophytes and proposes their use in for sustainable agriculture, bioremediation, and medicine. Future research combining endophytic biodiversity analysis with next-generation sequencing (NGS) and nanotechnology could provide novel techniques for combating AMR and contributing to sustainability across multiple industries.

Investigation of Antimicrobial Compounds Produced by Endolichenic Fungi in Different Culture Media

Continuous use of synthetic fungicides has led to explosive emergence of fungicide-resistant microbes. Therefore, there are urgent needs for environmentally friendly antimicrobial agents with novel modes of action. This study investigated endolichenic fungi (ELF) as a source of antimicrobial compounds against various plant pathogens. We utilized an One Strain MAny Compounds (OSMAC) approach to enhance the chemical diversity of fourteen ELF. This involved cultivation of ELF in four growth media and subsequently assessing antimicrobial activities of culture extracts. Nearly half of the culture extracts exhibited antimicrobial activity against a Gram-positive bacterium, but showed minimal activity against Gram-negative bacteria tested. Notably, culture extracts from two ELF, Chaetomium globosum and Nodulisporium sp., demonstrated significant inhibitory effects against plant pathogenic fungi. LC-MS/MS-based metabolome profiling confirmed the presence of known bioactive compounds like cyclic dipeptides and chaetoglobosins. These findings highlight the effectiveness of combining OSMAC and metabolomics for identifying antimicrobial agents for agricultural use.

In Vitro Antiproliferative Activity of Echinulin Derivatives from Endolichenic Fungus Aspergillus sp. against Colorectal Cancer

The endolichenic fungus Aspergillus sp. was isolated from the lichen Xanthoparmelia conspersa harvested in France. Aspergillus sp. was grown on a solid culture medium to ensure the large-scale production of the fungus with a sufficient mass of secondary metabolites. The molecular network analysis of extracts and subfractions enabled the annotation of 22 molecules, guiding the purification process. The EtOAc extract displayed an antiproliferative activity of 3.2 ± 0.4 µg/mL at 48 h against human colorectal cancer cells (HT-29) and no toxicity at 30 µg/mL against human triple-negative breast cancer (TNBC) cells (MDA-MB-231) and human embryonic kidney (HEK293) non-cancerous cells. Among the five prenylated compounds isolated, of which four are echinulin derivatives, compounds 1 and 2 showed the most important activity, with IC50 values of 1.73 µM and 8.8 µM, respectively, against HT-29 cells.

New butanolide derivatives from the marine derived fungus Aspergillus terreus GZU-31-1 by chemical epigenetic manipulation

Chemical epigenetic manipulation of Aspergillus terreus GZU-31-1 led to the discovery of five butanolide derivatives (1-5), including two new ones (1 and 2), and four known diphenyl ether derivatives (6-9). Compound 1 featured a Z-configuration double bond in the isoprenyl group was a potential anti-inflammatory bioactive group. Compound 2 was a new natural product. Moreover, compound 3 with a deacetylated group at C-4 was rarely reported as a butanolide analogue, which was isolated from the liquid culture treated with polyketide pathway inhibitor sodium citrate dihydrate. All of the isolates (1-9) were tested for their anti-inflammatory effects on the production of nitric oxide in lipopolysaccharide-induced microglial cells (RAW 264.7 cells). Compounds 1, 7, 8 and 9 exhibited more potent anti-inflammatory activity with IC50 values of 16.31, 20.16, 9.53 and 21.64 μM than the positive control (indomethacin, IC50, 24.0 μM).

Antimicrobial Action Mechanisms of Natural Compounds Isolated from Endophytic Microorganisms

Infectious diseases are a significant challenge to global healthcare, especially in the face of increasing antibiotic resistance. This urgent issue requires the continuous exploration and development of new antimicrobial drugs. In this regard, the secondary metabolites derived from endophytic microorganisms stand out as promising sources for finding antimicrobials. Endophytic microorganisms, residing within the internal tissues of plants, have demonstrated the capacity to produce diverse bioactive compounds with substantial pharmacological potential. Therefore, numerous new antimicrobial compounds have been isolated from endophytes, particularly from endophytic fungi and actinomycetes. However, only a limited number of these compounds have been subjected to comprehensive studies regarding their mechanisms of action against bacterial cells. Furthermore, the investigation of their effects on antibiotic-resistant bacteria and the identification of biosynthetic gene clusters responsible for synthesizing these secondary metabolites have been conducted for only a subset of these promising compounds. Through a comprehensive analysis of current research findings, this review describes the mechanisms of action of antimicrobial drugs and secondary metabolites isolated from endophytes, antibacterial activities of the natural compounds derived from endophytes against antibiotic-resistant bacteria, and biosynthetic gene clusters of endophytic fungi responsible for the synthesis of bioactive secondary metabolites.

Endolichenic Fungi: A Promising Medicinal Microbial Resource to Discover Bioactive Natural Molecules-An Update

Lichens are some of the most unique fungi and are naturally encountered as symbiotic biological organisms that usually consist of fungal partners (mycobionts) and photosynthetic organisms (green algae and cyanobacteria). Due to their distinctive growth environments, including hot deserts, rocky coasts, Arctic tundra, toxic slag piles, etc., they produce a variety of biologically meaningful and structurally novel secondary metabolites to resist external environmental stresses. The endofungi that live in and coevolve with lichens can also generate abundant secondary metabolites with novel structures, diverse skeletons, and intriguing bioactivities due to their mutualistic symbiosis with hosts, and they have been considered as strategically significant medicinal microresources for the discovery of pharmaceutical lead compounds in the medicinal industry. They are also of great importance in the fundamental research field of natural product chemistry. In this work, we conducted a comprehensive review and systematic evaluation of the secondary metabolites of endolichenic fungi regarding their origin, distribution, structural characteristics, and biological activity, as well as recent advances in their medicinal applications, by summarizing research achievements since 2015. Moreover, the current research status and future research trends regarding their chemical components are discussed and predicted. A systematic review covering the fundamental chemical research advances and pharmaceutical potential of the secondary metabolites from endolichenic fungi is urgently required to facilitate our better understanding, and this review could also serve as a critical reference to provide valuable insights for the future research and promotion of natural products from endolichenic fungi.

Secondary Metabolites from the Genus Eurotium and Their Biological Activities

Eurotium is the teleomorph genus associated with the section Aspergillus. Eurotium comprises approximately 20 species, which are widely distributed in nature and human environments. Eurotium is usually the key microorganism for the fermentation of traditional food, such as Fuzhuan brick tea, Liupao tea, Meju, and Karebushi; thus, Eurotium is an important fungus in the food industry. Eurotium has been extensively studied because it contains a series of interesting, structurally diverse, and biologically important secondary metabolites, including anthraquinones, benzaldehyde derivatives, and indol diketopiperazine alkaloids. These secondary metabolites have shown multiple biological activities, including antioxidative, antimicrobial, cytotoxic, antitumor, insecticidal, antimalarial, and anti-inflammatory activities. This study presents an up-to-date review of the phytochemistry and biological activities of all Eurotium species. This review will provide recent advances on the secondary metabolites and their bioactivities in the genus Eurotium for the first time and serve as a database for future research and drug development from the genus Eurotium.

Structural identification of pyridinopyrone compounds with anti-neuroinflammatory activity from streptomyces sulphureus DSM 40104

This study investigated the chemical composition and biosynthesis pathway of compounds produced by Streptomyces sulphureus DSM 40104. With the guild of molecular networking analysis, we isolated and identified six uncommon structural characteristics of compounds, including four newly discovered pyridinopyrones. Based on genomic analysis, we proposed a possible hybrid NRPS-PKS biosynthesis pathway for pyridinopyrones. Notably, this pathway starts with the use of nicotinic acid as the starting unit, which is a unique feature. Compounds 1-3 exhibited moderate anti-neuroinflammatory activity against LPS-induced BV-2 cell inflammation. Our study demonstrates the diversity of polyene pyrone compounds regarding their chemical structure and bioactivity while providing new insights into their biosynthesis pathway. These findings may lead to the development of new treatments for inflammation-related diseases.

Ergostane-type sterols and sesquiterpenes with anti-neuroinflammatory activity from a Nigrograna species associated with Clematis shensiensis

Nigrograna sp. LY66, an endophytic fungus associated with the herbal medicinal plant Clematis shensiensis, produced four undescribed steroids, nigergostanes A-D (1-4), including an unusual ketal-containing nigergostane (1), and four undescribed sesquiterpenoids decorated with cyclohexanone motifs, nigbisabolanes A-D (7-10), along with three known compounds, 23R-hydroxy-(20Z,24R)-ergosta-4,6,8(14),20(22)-tetraen-3-one (5), ergosta-5,7,22-trien-3β-ol (6), and curculonone A (11). The structures and absolute configurations of these undescribed compounds were confirmed using spectroscopic data (NMR and HRESIMS), modified Mosher's method, and ECD experiments. Additionally, compounds 5 and 8 displayed significant inhibition of nitric oxide generation in lipopolysaccharide-induced BV-2 microglial cells with IC₅₀ values of 2.8 and 2.7 μM, respectively, and is thus more potent than that of the positive control, quercetin (IC₅₀ = 8.77 μM). A molecular docking study revealed that 23-OH of 5 binds to the Y347 residue of inducible nitric oxide synthase (iNOS), whereas the 2-OH and 9,10-diol moieties of 8 bind to R381 and W463 and haeme residues of iNOS, respectively, which has rarely been reported in previous studies. These findings provide a set of undescribed lead compounds that can be developed into anti-neuroinflammatory agents.

Marine Aspergillus: A Treasure Trove of Antimicrobial Compounds

Secondary metabolites from marine organisms are diverse in structure and function. Marine Aspergillus is an important source of bioactive natural products. We reviewed the structures and antimicrobial activities of compounds isolated from different marine Aspergillus over the past two years (January 2021-March 2023). Ninety-eight compounds derived from Aspergillus species were described. The chemical diversity and antimicrobial activities of these metabolites will provide a large number of promising lead compounds for the development of antimicrobial agents.

Secondary Metabolites Produced by the Blue-Cheese Ripening Mold Penicillium roqueforti; Biosynthesis and Regulation Mechanisms

Filamentous fungi are an important source of natural products. The mold Penicillium roqueforti, which is well-known for being responsible for the characteristic texture, blue-green spots, and aroma of the so-called blue-veined cheeses (French Bleu, Roquefort, Gorgonzola, Stilton, Cabrales, and Valdeón, among others), is able to synthesize different secondary metabolites, including andrastins and mycophenolic acid, as well as several mycotoxins, such as Roquefortines C and D, PR-toxin and eremofortins, Isofumigaclavines A and B, festuclavine, and Annullatins D and F. This review provides a detailed description of the biosynthetic gene clusters and pathways of the main secondary metabolites produced by P. roqueforti, as well as an overview of the regulatory mechanisms controlling secondary metabolism in this filamentous fungus.

Chemical synthesis and mechanism of a natural product from endolichenic fungus with a broad-spectrum anti microorganism activity

Background

The antibiotic resistance in various bacteria is consistently increasing and is posing a serious threat to human health, prompting the need for the discovery of novel structurally featured natural products with promising biological activities in drug research and development. Endolichenic microbes have been proven to be a fertile source to produce various chemical components, and therefore these microbes have been on a prime focus for exploring natural products. In this study, to explore potential biological resources and antibacterial natural products, the secondary metabolites of an endolichenic fungus have been investigated.

Methods

The antimicrobial products were isolated from the endolichenic fungus using various chromatographic methods, and the antibacterial and antifungal activities of the compounds were evaluated by the broth microdilution method under in vitro conditions. The antimicrobial mechanism has been discussed with measuring the dissolution of nucleic acid and protein, as well as the activity of alkaline phosphatase (AKP) in preliminary manner. Chemical synthesis of the active product compound 5 was also performed, starting from commercially available 2,6-dihydroxybenzaldehyde through a sequence of transformations that included methylation, the addition of propylmagnesium bromide on formyl group, the oxidation of secondary alcohol, and the deprotection of methyl ether motif.

Results

Among the 19 secondary metabolites of the endolichenic fungus, Daldinia childiae (compound 5) showed attractive antimicrobial activities on 10 of the 15 tested pathogenic strains, including Gram-positive bacteria, Gram-negative bacteria, and fungus. The Minimum Inhibitory Concentration (MIC) of compound 5 for Candida albicans 10213, Micrococcus luteus 261, Proteus vulgaris Z12, Shigella sonnet, and Staphylococcus aureus 6538 was identified as 16 μg/ml, whereas the Minimum Bactericidal Concentration (MBC) of other strains was identified as 64 μg/ml. Compound 5 could dramatically inhibit the growth of S. aureus 6538, P. vulgaris Z12, and C. albicans 10213 at the MBC, likely affecting the permeability of the cell wall and cell membrane. These results enriched the library of active strains and metabolites resources of endolichenic microorganisms. The chemical synthesis of the active compound was also performed in four steps, providing an alternative pathway to explore antimicrobial agents.

Indole Diketopiperazine Alkaloids Isolated From the Marine-Derived Fungus Aspergillus chevalieri MCCC M23426

Two new indole diketopiperazines (1-2) obtained from the fermentation culture of a deep-sea-derived fungus Aspergillus chevalieri MCCC M23426, were characterized, together with nine biogenetic related compounds (3-11). The structures of 1-2 were assigned based on NMR, MS, NMR calculation, DP4+ analysis, and ECD calculation. The bioactive assay showed that compounds 1, 5-7 significantly inhibited the growth of Staphylococcus aureus. Meanwhile, compound 8 potently reduced the cell viability of gastric cancer cell MKN1 with an IC50 value of 4.6 μM.

2-Arylindoles: Concise Syntheses and a Privileged Scaffold for Fungicide Discovery

Indole is a popular and functional scaffold existing widely in the fields of medicine, pesticides, spices, food and feed additives, dyes, and many others. Among indoles, 2-arylindole represents a particular and interesting subset but has attracted less attention for drug discovery. In this study, we report a general, practical one-pot assembly of a variety of 2-arylindole derivatives. To develop novel fungicide scaffolds, their fungicide activity was also evaluated. The bioassay results showed that many of the synthesized 2-arylindoles exhibited considerable fungicidal activities especially toward Rhizoctonia cerealis, and several demonstrated an inhibition rate of more than 90%. Notably, 4-fluoro-2-phenyl-1H-indole 6e was obtained with a broad spectrum of fungicidal activities, which showed excellent growth inhibition activities against R. cerealis, Rhizoctonia solani, Botrytis cinerea, Magnaporthe oryza, and Sclerotinia sclerotiorum with EC₅₀ values of 2.31, 4.98, 6.78, 10.57, and 17.80 μg/mL, respectively. Preliminary fungicidal mode of action of 6e showed a significant inhibition effect on mycelial growth and spore germination. These results indicated that 2-arylindoles as privileged scaffolds exhibited potential fungicidal activities that deserve further study.

Two New Sulfate-Modified Dibenzopyrones With Anti-foodborne Bacteria Activity From Sponge-Derived Fungus Alternaria sp. SCSIOS02F49

At present, foodborne diseases (FBDs) caused by bacteria are gradually increasing every year, and the development of new antibiotics is an urgent necessity for human beings. To find novel antibacterial compounds, three sponge-derived fungal strains (SCSIOS02F40, F46, and F49) were investigated. As a result, Alternaria sp. SCSIOS02F49 was selected for investigation on its secondary metabolites because its ethyl acetate (EtOAc) extract of potato dextrose broth (PDB) culture showed rich metabolites and strong antibacterial activity. Two new dibenzopyrones with rare sulfate group (1–2), together with 10 known compounds (3–12), were isolated from the Alternaria sp. SCSIOS02F49. Their structures were confirmed by nuclear magnetic resonance (NMR), mass spectrometry (MS) data, and comparison with data from the relevant literature. Almost all compounds showed moderate inhibitory activity against eight foodborne bacteria (FBB) with minimum inhibitory concentration (MIC) values in the range of 15.6–250 μg/ml, and minimum bactericidal concentration (MBC) values in the range of 31.3–250 μg/ml. The antibacterial mechanism of compound 1 was preliminarily investigated using growth curves, scanning electron microscopy (SEM), and flow cytometry (FCM), which revealed that compound 1 altered the external structure of Staphylococcus aureus and caused the rupture or deformation of the cell membranes. This research provides lead compounds for the development of new antibiotics or microbial preservatives.

Design, Synthesis, and Insecticidal Activity of Novel Pyrido[1, 2-a]pyrimidinone Mesoionic Compounds Containing an Indole Moiety as Potential Acetylcholine Receptor Insecticides

In this study, a series of novel mesoionic pyrido[1,2-a]pyrimidinone compounds containing a natural skeleton indole were designed and synthesized, and the insecticidal activities of the target compounds were tested. The results showed that the target compounds had good to excellent insecticidal activities against white-backed planthoppers (Sogatella furcifera) and bean aphids (Aphis craccivora). Among them, compound 7 showed outstanding insecticidal activities against both S. furcifera and A. craccivora, with LC₅₀ values of 0.86 and 0.85 μg/mL, respectively. The insecticidal activity against bean aphids (A. craccivora) was superior to that of triflumezopyrim (LC₅₀ = 3.67 μg/mL). Proteomics and quantitative real-time polymerase chain reaction (qRT-PCR) results revealed that compound 7 may interact with α1 and α7 nAChR subunits of S. furcifera. The results of enzyme activities indicated that compound 7 was an inhibitor of AChE in S. furcifera. This study provides new ideas for the discovery of new mesoionic pyrido[1,2-a]pyrimidinone insecticides.

Bioactive Monomer and Polymer Polyketides from Edible Mushroom Cortinarius caerulescens as Glutamate Dehydrogenase Inhibitors and Antioxidants

Two new polyketides named rufoolivacin E and viocristin B, a new natural product named 1-hydroxy-3,6,8-trimethoxyanthraquinone, and 13 known compounds were isolated from edible mushroom Cortinarius purpurascens in this work. Their structures were assigned on the basis of high-resolution electrospray ionization mass spectrometry, 1D and 2D nuclear magnetic resonance, and electronic circular dichroism data. Notably, the enzyme activity test on glutamate dehydrogenase indicated that 1, 3, 4, 5, 6, 10, 11, and 15 displayed an excellent inhibition effect. Further kinetic studies showed that the most potent compounds, 4 and 10, possess great potential as competitive inhibitors of glutamate dehydrogenase. Molecular docking and computational chemistry were applied to illustrate the binding mechanism in detail. 2,2-Diphenyl-1-picrylhydrazyl and reactive oxygen species assay results showed that compounds 1, 2, 3, and 8 exhibited significant antioxidant activities with IC₅₀ values of 7.0 ± 0.3, 8.6 ± 0.1, 7.5 ± 0.1, and 2.8 ± 0.2 μg mL^-1, respectively. Thus, Cortinarius caerulescens represents a novel resource of these polyketides to be utilized in food selection and drug discovery.

Eremophilane Sesquiterpenoids with Antibacterial and Anti-inflammatory Activities from the Endophytic Fungus Septoria rudbeckiae

Fourteen eremophilane sesquiterpenoids (1-14), including nine new congeners, septoreremophilanes A-I (1-9), together with three known sesquiterpenes (15-17), two known tetralone derivatives (18, 19), and two known cholesterol analogues (20, 21), were isolated from the endophytic fungus Septoria rudbeckiae. Compounds 1-6 and 7a belong to the family of the highly oxygenated eremophilane sesquiterpenoids with a 6/6/5 tricyclic system and bearing a hemiacetal moiety. The inhibitions of all metabolites against eight bacteria were estimated in vitro, and nine new metabolites (1-9) were tested for antineuroinflammatory activity. Notably, the effects of 4 against Pseudomonas syringae pv. actinidae and 20 against Bacillus cereus displayed potent inhibitory, with the MIC values of 6.25 and 6.25 μM, respectively. Further, scanning electron microscopy analyses indicated that 4 and 20 were to change the outer configuration of bacterial cells, respectively, and the investigations demonstrated that 4 and 20 may act as potential structure templates for the development of the agrochemical bactericides. Additionally, compound 6 displayed potent inhibition of NO generation in lipopolysaccharide-induced BV-2 microglial cells (IC₅₀ = 12.0 ± 0.32 μM), and the conceivable anti-inflammatory mechanisms implicated were also investigated by molecular docking. Thus, the bioactive metabolites of the strain S. rudbeckiae may serve as a novel resource to be developed.