Polyoxygenated Cyclohexenoids with Promising α-Glycosidase Inhibitory Activity Produced by Phomopsis sp. YE3250, an Endophytic Fungus Derived from Paeonia delavayi

Novel Polyketides with Agricultural Bioactivity Produced by Phomopsis sp. HDSJ-28, an Endophytic Fungus Derived from Taxus yunnanensis

Phomopsisols A and B (1 and 2), possessing an unprecedented highly oxygenated isobenzofuran dimer core, along with one new tenellone derivative (3), and two new polyketides (13 and 14), as well as 11 known compounds, were isolated from the endophytic Phomopsis sp. associated with Taxus yunnanensis. The structures were determined mainly by the NMR, MS, ECD, and optical rotation calculations and single-crystal X-ray diffraction analyses. Most compounds demonstrated selective antifungal activity against the phytopathogens Colletotrichum karsti and Colletotrichum gloeosporioides, rather than against the biocontrol fungus Clonostachys rosea. Compounds 1-6 and 9-12 exhibited attractive feeding activities toward silkworms with attraction rates of 33-65%. Compounds 1, 9, 10, 15, and 16 promoted the growth of Oryza sativa seedlings. In contrast, compounds 3-6 completely inhibited both shoot and root growths of rice at a concentration of 20 μg/mL. Notably, compound 3 demonstrated significant multiple agricultural activities, including antifungal activity, feeding attraction, and phytotoxicity.

Endophytic Fungi: A Treasure Trove of Antifungal Metabolites

Emerging and reemerging fungal infections are very common in nosocomial and non-nosocomial settings in people having poor immunogenic profiles either due to hematopoietic stem cell transplants or are using immunomodulators to treat chronic inflammatory disease or autoimmune disorders, undergoing cancer therapy or suffering from an immune weakening disease like HIV. The refractory behavior of opportunistic fungi has necessitated the discovery of unconventional antifungals. The emergence of black fungus infection during COVID-19 also triggered the antifungal discovery program. Natural products are one of the alternative sources of antifungals. Endophytic fungi reside and co-evolve within their host plants and, therefore, offer a unique bioresource of novel chemical scaffolds with an array of bioactivities. Hence, immense possibilities exist that these unique chemical scaffolds expressed by the endophytic fungi may play a crucial role in overcoming the burgeoning antimicrobial resistance. These chemical scaffolds so expressed by these endophytic fungi comprise an array of chemical classes beginning from cyclic peptides, sesquiterpenoids, phenols, anthraquinones, coumarins, etc. In this study, endophytic fungi reported in the last six years (2018-2023) have been explored to document the antifungal entities they produce. Approximately 244 antifungal metabolites have been documented in this period by different groups of fungi existing as endophytes. Various aspects of these antifungal metabolites, such as antifungal potential and their chemical structures, have been presented. Yet another unique aspect of this review is the exploration of volatile antifungal compounds produced by these endophytic fungi. Further strategies like epigenetic modifications by chemical as well as biological methods and OSMAC to induce the silent gene clusters have also been presented to generate unprecedented bioactive compounds from these endophytic fungi.

The limitless endophytes: their role as antifungal agents against top priority pathogens

Multi resistant fungi are on the rise, and our arsenal compounds are limited to few choices in the market such as polyenes, pyrimidine analogs, azoles, allylamines, and echinocandins. Although each of these drugs featured a unique mechanism, antifungal resistant strains did emerge and continued to arise against them worldwide. Moreover, the genetic variation between fungi and their host humans is small, which leads to significant challenges in new antifungal drug discovery. Endophytes are still an underexplored source of bioactive secondary metabolites. Many studies were conducted to isolate and screen endophytic pure compounds with efficacy against resistant yeasts and fungi; especially, Candida albicans, C. auris, Cryptococcus neoformans and Aspergillus fumigatus, which encouraged writing this review to critically analyze the chemical nature, potency, and fungal source of the isolated endophytic compounds as well as their novelty features and SAR when possible. Herein, we report a comprehensive list of around 320 assayed antifungal compounds against Candida albicans, C. auris, Cryptococcus neoformans and Aspergillus fumigatus in the period 1980-2024, the majority of which were isolated from fungi of orders Eurotiales and Hypocreales associated with terrestrial plants, probably due to the ease of laboratory cultivation of these strains. 46% of the reviewed compounds were active against C. albicans, 23% against C. neoformans, 29% against A. fumigatus and only 2% against C. auris. Coculturing was proved to be an effective technique to induce cryptic metabolites absent in other axenic cultures or host extract cultures, with Irperide as the most promising compounds MIC value 1 μg/mL. C. auris was susceptible to only persephacin and rubiginosin C. The latter showed potent inhibition against this recalcitrant strain in a non-fungicide way, which unveils the potential of fungal biofilm inhibition. Further development of culturing techniques and activation of silent metabolic pathways would be favorable to inspire the search for novel bioactive antifungals.

Phomopamide A, a cyclic pentadepsipeptide with α-glucosidase inhibition activity from the endophytic fungus Diaporthe sp

An undescribed cytotoxic cyclopeptide named phomopamide A (1) was isolated from Diaporthe sp., which is an endophytic fungus from Artemisia argyi. Phomopamide A (1) featured an pentadepsipeptide skeleton and composed of two Phe, one Val, one Leu, and one 2-hydroxyoctanoic acid units. The structure of this new compound was fully characterised on the basis of extensive spectroscopic analysis. Moreover, phomopamide A was evaluated for in vitro cyctotoxic and α-glucosidase inhibitory activity. As a result, phomopaminde A exhibited no cytotoxic activity against four tumour cell lines, while it showed a potent α-glucosidase inhibition effect with IC50 value of 62.35 µM.

Natural epoxyquinoids: isolation, biological activity and synthesis. An update

Epoxyquinoids are of continuing interest due to their wide natural distribution and diverse biological activities, including, but not limited to, antibacterial, antifungal, anticancer, enzyme inhibitory, and others. The last review on their total synthesis was published in 2017. Since then, almost 100 articles have been published on their isolation from nature and their biological profile. In addition, the review specifically considers synthesis, including total and enantioselective, as well as the development of shorter approaches for the construction of epoxyquinoids with complex chemical architecture. Thus, this review focuses on progress in this area in order to stimulate further research.

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.

Polyhydroxylated sesquiterpenes and ergostane glycosides produced by the endophytic fungus Xylaria sp. from Azadirachta indica

The investigation of the metabolites from the endophytic fungus Xylaria sp. YM 311647 in solid fermentation resulted in the isolation of six undescribed compounds, namely xylarioxides A-F, respectively. These included one eremophilane sesquiterpene, three guaiane sesquiterpene glycosides, and two ergostane glycosides. The structures of the compounds were determined by extensive analyses of spectroscopic data, including 1D and 2D NMR, as well as HRESIMS data. The stereochemistry of xylarioxide A was confirmed by X-ray crystallographic analysis. All of the isolated compounds were assayed for their antifungal activities against seven phytopathogenic fungi and two human pathogenic fungi. Among them, xylarioxides A, E and F showed potent activities against the tested phytopathogens. Particularly, xylarioxide E exhibited the highest activity against Gibberella saubinetii, Curvularia lunata, and Colletotrichum gloeosporioides with MIC values of 4, 4, and 8 μg/mL, respectively, which were comparable to the positive control of nystatin. Interestingly, guaiane sesquiterpene glycosides have been rarely reported from fungal sources. Additionally, xylarioxide E represented an unusual naturally occurring 3,4-seco-steroidal glycoside with a seven-membered lactone in ring A.

Polyketides with Anti-neuroinflammatory Activity from Theissenia cinerea

Theissenia cinerea 89091602 is a previously reported plant-derived bioactive fungal strain, and the active principles separated from the extracts of its submerged culture were shown to exhibit potent anti-neuroinflammatory activities in both cellular study and animal testing. In a continuation of our previous investigation on the bioactive entities from this fungus, solid state fermentation was performed in an attempt to diversify the bioactive secondary metabolites. In the present study, five previously unreported polyketides, theissenophenol (1), theissenepoxide (2), theissenolactone D (3), theissenone (4), and theissenisochromanone (5), together with the known theissenolactone B (6), theissenolactone C (7), and arthrinone (8), were isolated and characterized through spectroscopic analysis and comparison with the literature data. The configurations of theissenepoxide (2) and theissenisochromanone (5) were further corroborated by single-crystal X-ray diffraction data analysis. Theissenone (4), theissenolactone B (6), theissenolactone C (7), and arthrinone (8) exhibited potent nitric oxide production inhibitory activities in murine brain microglial BV-2 cells with IC₅₀ values of 5.0 ± 1.0, 4.5 ± 0.6, 1.1 ± 0.1, and 3.2 ± 0.3 μM, respectively, without any significant cytotoxic effects.

Antifungal Secondary Metabolites Produced by the Fungal Endophytes: Chemical Diversity and Potential Use in the Development of Biopesticides

Plant diseases caused by phytopathogenic fungi can lead to huge losses in the agricultural fields and therefore remain a continuous threat to the global food security. Chemical-based fungicides contributed significantly in securing crop production. However, indiscriminate application of fungicides has led to increased chemical resistance and potential risks to human health and environment. Thus, there is an urgent need for searching for new bioactive natural products and developing them into new biopesticides. Fungal endophytes, microorganisms that reside in the fresh tissues of living plants, are regarded as untapped sources of novel natural products for exploitation in agriculture and/or medicine. Chemical examination of endophytic fungi has yielded enormous antifungal natural products with potential use in the development of biopesticides. This review summarizes a total of 132 antifungal metabolites isolated from fungal endophytes in the past two decades. The emphasis is on the unique chemical diversity of these metabolic products, together with their relevant antifungal properties. Moreover, some "star molecules," such as griseofulvin and trichothecene, as well as their synthetic derivatives that possess high potential as candidates of new natural fungicides, are also presented herein.

Bioactive Secondary Metabolites of the Genus Diaporthe and Anamorph Phomopsis from Terrestrial and Marine Habitats and Endophytes: 2010-2019

The genus Diaporthe and its anamorph Phomopsis are distributed worldwide in many ecosystems. They are regarded as potential sources for producing diverse bioactive metabolites. Most species are attributed to plant pathogens, non-pathogenic endophytes, or saprobes in terrestrial host plants. They colonize in the early parasitic tissue of plants, provide a variety of nutrients in the cycle of parasitism and saprophytism, and participate in the basic metabolic process of plants. In the past ten years, many studies have been focused on the discovery of new species and biological secondary metabolites from this genus. In this review, we summarize a total of 335 bioactive secondary metabolites isolated from 26 known species and various unidentified species of Diaporthe and Phomopsis during 2010-2019. Overall, there are 106 bioactive compounds derived from Diaporthe and 246 from Phomopsis, while 17 compounds are found in both of them. They are classified into polyketides, terpenoids, steroids, macrolides, ten-membered lactones, alkaloids, flavonoids, and fatty acids. Polyketides constitute the main chemical population, accounting for 64%. Meanwhile, their bioactivities mainly involve cytotoxic, antifungal, antibacterial, antiviral, antioxidant, anti-inflammatory, anti-algae, phytotoxic, and enzyme inhibitory activities. Diaporthe and Phomopsis exhibit their potent talents in the discovery of small molecules for drug candidates.

Bioactive cyclohexene derivatives from a mangrove-derived fungus Cladosporium sp. JJM22

Four new cyclohexene derivatives cladoscyclitols A-D (1-4) and one new ribofuranose phenol derivative 4-O-α-D-ribofuranose-2-pentyl-3-phemethylol (5) were obtained from the EtOAC extract of the mangrove-derived endophytic fungus Cladosporium sp. JJM22. The structures were elucidated by extensive NMR and MS analysis, while the absolute configurations of the stereogenic carbons were established based on quantum-chemical electronic circular dichroism calculations or comparison of the optical rotations with those of related compounds. Compounds 2 and 5 displayed potent inhibitory activity against α-glucosidase with the IC₅₀ values of 2.95 and 2.05 μM, respectively.

Isolation and Characterization of Antifungal Metabolites from the Melia azedarach-Associated Fungus Diaporthe eucalyptorum

Two biosynthetically related new metabolites, eucalyptacid A (1) and eucalactam B (2), along with six known compounds (3-8), eugenitol (3), cytosporone C (4), 4-hydroxyphenethyl alcohol (5), 1-(4-hydroxyphenyl)ethane-1,2-diol (6), N-(2-hydroxy-2-phenylethyl)acetamide (7), and phomopene (8), were isolated from the solid rice cultures of the endophytic fungus Diaporthe eucalyptorum KY-9 that had been isolated from Melia azedarach. Also, two further new derivatives (2a, 2b) were prepared from 2. The structures were elucidated by exhaustive analysis of NMR and ESIMS data and chemical methods such as Marfey's protocol. Compound 1 was identified as a rare polyketide fatty acid, (8E)-3,5,11-trihydroxy-2,10,12-trimethyltetradecenoic acid, and 2 was determined to be the first cyclic depsipeptide containing the same fatty acid unit as 1 and a Gly-Gly-Thr tripeptide chain. Its N-terminal end is N-acylated by an 11-hydroxy fatty acid with a branch alkyl chain of 14:1. The 11-hydroxyl group connects to the carboxylic group of the C-terminal amino acid to form a 22-membered lactone ring. A hypothetical biosynthetic pathway for the new polyketides is proposed. The isolated compounds were assayed for their inhibition against four plant pathogenic fungi, Alternaria solani, Botrytis cinerea, Fusarium solani, and Gibberella saubinettii. Compounds 1, 4, 6, and 7 exhibited antifungal activities against Alternaria solani, with minimal inhibitory concentration (MIC) values from 6.25 to 50 μM. Thus, strain KY-9 represents an untapped source for the development of biological control agents to prevent the infection of pathogenic fungus A. solani.