New azaphilones and chlorinated phenolic glycosides from Chaetomium elatum with caspase-3 inhibitory activity

Chemical diversity and biological activities of specialized metabolites from the genus Chaetomium: 2013-2022

Chaetomium (Chaetomiaceae), a large fungal genus consisting of at least 400 species, has been acknowledged as a promising resource for the exploration of novel compounds with potential bioactivities. Over the past decades, emerging chemical and biological investigations have suggested the structural diversity and extensive potent bioactivity of the specialized metabolites in the Chaetomium species. To date, over 500 compounds with diverse chemical types have been isolated and identified from this genus, including azaphilones, cytochalasans, pyrones, alkaloids, diketopiperazines, anthraquinones, polyketides, and steroids. Biological research has indicated that these compounds possess a broad range of bioactivities, including antitumor, anti-inflammatory, antimicrobial, antioxidant, enzyme inhibitory, phytotoxic, and plant growth inhibitory activities. This paper summarizes current knowledge referring to the chemical structure, biological activity, and pharmacologic potency of the specialized metabolites in the Chaetomium species from 2013 to 2022, which might provide insights for the exploration and utilization of bioactive compounds in this genus both in the scientific field and pharmaceutical industry.

Naturally Occurring Organohalogen Compounds-A Comprehensive Review

The present volume is the third in a trilogy that documents naturally occurring organohalogen compounds, bringing the total number-from fewer than 25 in 1968-to approximately 8000 compounds to date. Nearly all of these natural products contain chlorine or bromine, with a few containing iodine and, fewer still, fluorine. Produced by ubiquitous marine (algae, sponges, corals, bryozoa, nudibranchs, fungi, bacteria) and terrestrial organisms (plants, fungi, bacteria, insects, higher animals) and universal abiotic processes (volcanos, forest fires, geothermal events), organohalogens pervade the global ecosystem. Newly identified extraterrestrial sources are also documented. In addition to chemical structures, biological activity, biohalogenation, biodegradation, natural function, and future outlook are presented.

Key insights into secondary metabolites from various Chaetomium species

Endophytic fungi have proved to be a major source of secondary metabolites, wherein the genus Chaetomium has emerged as a source of multifarious bioactive natural compounds belonging to diverse classes such as chaetoglobosins, epipolythiodioxopiperazines, azaphilones, xanthones, anthraquinone, chromones, depsidones, terpenoids, and steroids. The objective of this review is to encapsulate recent findings on various Chaetomium strains, such as C. globosum, C. cupreum, C. elatum, C. subspirale, C. olivaceum, C. indicum, and C. nigricolor known for production of beneficial secondary metabolites, with an insight into their origin and function. A thorough literature survey was conducted for obtaining Chaetomium-derived secondary metabolites, with a scope of future application into drug development efforts. More than 100 secondary metabolites, with various beneficial properties such as antitumor, cytotoxic, antimalarial, and enzyme inhibitory activities, were enlisted. We believe this review will enhance the understanding of beneficial effects conferred by various Chaetomium-derived secondary metabolites and emphasize their potential in serving novel drug development efforts. KEY POINTS: • Identified Chaetomium-derived metabolites with potential for drug development. • More than 100 beneficial metabolites are enlisted. • Benefits include anti-cancerous, antimalarial, and anti-enzymatic properties.

Chaetomugilins and Chaetoviridins—Promising Natural Metabolites: Structures, Separation, Characterization, Biosynthesis, Bioactivities, Molecular Docking and Molecular Dynamics

Fungi are recognized as luxuriant metabolic artists that generate propitious biometabolites. Historically, fungal metabolites have largely been investigated as leads for various therapeutic agents. Chaetomugilins and the closely related chaetoviridins are fungal metabolites, and each has an oxygenated bicyclic pyranoquinone core. They are mainly produced by various Chaetomaceae species. These metabolites display unique chemical features and diversified bioactivities. The current review gives an overview of research about fungal chaetomugilins and chaetoviridins regarding their structures, separation, characterization, biosynthesis, and bioactivities. Additionally, their antiviral potential towards the SARS-CoV-2 protease was evaluated using docking studies and molecular dynamics (MD) simulations. We report on the docking and predictive binding energy estimations using reported crystal structures of the main protease (PDB ID: 6M2N, 6W81, and 7K0f) at variable resolutions—i.e., 2.20, 1.55, and 1.65 Å, respectively. Chaetovirdin D (43) exhibited highly negative docking scores of −7.944, −8.141, and −6.615 kcal/mol, when complexed with 6M2N, 6W81, and 7K0f, respectively. The reference inhibitors exhibited the following scores: −5.377, −6.995, and −8.159 kcal/mol, when complexed with 6M2N, 6W81, and 7K0f, respectively. By using molecular dynamics simulations, chaetovirdin D’s stability in complexes with the viral protease was analyzed, and it was found to be stable over the course of 100 ns.

Cytochalasans and azaphilones: suitable chemotaxonomic markers for the Chaetomium species

The accurate taxonomic concept of the fungal Chaetomium species has been a hard work due to morphological similarity. Chemotaxonomy based on secondary metabolites is a powerful tool for taxonomical purposes, which could be used as an auxiliary reference to solve the problems encountered in the classification of Chaetomium. Among secondary metabolites produced by Chaetomium, cytochalasans and azaphilones exhibited a pattern of distribution and frequency of occurrence that establish them as chemotaxonomic markers for the Chaetomium species. This review attempted to elucidate the composition of the Chaetomium species and its relationship with classical taxonomy by summarizing the pattern of cytochalasans and azaphilones distribution and biosynthesis in the Chaetomium species. KEY POINTS: • Secondary metabolites from the genus Chaetomium are summarized. • Cytochalasans and azaphilones could be characteristic metabolites of the Chaetomium species. • Cytochalasans and azaphilones could be used to analyze for taxonomical purposes.

Genetic and Histopathological Alterations in Caco-2 and HuH-7 Cells Treated with Secondary Metabolites of Marine fungi

The present work aimed to study the activity of naturally derived fungal secondary metabolites as anticancer agents concerning their cytotoxicity, apoptotic, genetic, and histopathological profile. It was noticed that Aspergillus terreus, Aspergillus flavus, and Aspergillus fumigatus induced variable toxic potential that was cell type, secondary metabolite type, and concentration dependent. Human colonic adenocarcinoma cells (Caco-2) showed less sensitivity than hepatocyte-derived cellular carcinoma cells (HuH-7), and in turn, the half-maximal inhibitory concentration (IC₅₀) was variable. Also, the apoptotic potential of Aspergillus species-derived fungal secondary metabolites was proven via detection of up-regulated pro-apoptotic genes and down-regulation of anti-apoptotic genes. The expression level was cell type dependent. Concurrently, apoptotic profile was accompanied with cellular DNA accumulation at the G2/M phase, as well as an elevation in Pre-G1 phase but not during G0/G1 and S phases. Also, there were characteristic apoptotic features of treated cells presented as abnormal intra-nuclear eosinophilic structures, dead cells with mixed euchromatin and heterochromatin, ruptured cell membranes, apoptotic cells with irregular cellular and nuclear membranes, as well as peripheral chromatin condensation. It can be concluded that Aspergillus secondary metabolites are promising agents that can be used as supplementary agents to the currently applied anti-cancer drug regimen.

Bioactive metabolites from the desert plant-associated endophytic fungus Chaetomium globosum (Chaetomiaceae)

Globosumin, an undescribed chromene-4,7(4aH)-dione-tetramic acid PKS-PKS-NRPS hybrid, and globosumone, an undescribed azaphilone, together with ten known metabolites, were isolated from the desert plant-associated endophytic fungus Chaetomium globosum (Chaetomiaceae). The planar structures and relative configurations of globosumin and globosumone were determined by high-resolution ESI-MS and NMR data, and the absolute configurations of these two metabolites were determined by electronic circular dichroism (ECD) and circular dichroism (CD) combined with time-dependent density functional theory (TDDFT)-based quantum-chemical calculations. Chaetoglobosin A displayed biological effects against the seedling growth of Arabidopsis thaliana (Brassicaceae) in a dose-dependent manner, and this compound also exhibited biological activity against two cancer cell lines, A549 and HepG2, with IC₅₀ values of 6.82 ± 2.34 and 38.62 ± 7.44 μM, respectively.

Cytotoxic Nitrogenated Azaphilones from the Deep-Sea-Derived Fungus Chaetomium globosum MP4-S01-7

Eight new nitrogenated azaphilones (1-8) and two known compounds (chaetoviridin A and chaetoviridin E, 9, 10) were isolated from the culture of the deep-sea-derived fungus Chaetomium globosum MP4-S01-7. The absolute configurations of new compounds were elucidated by HSQC-HECADE NMR data, J-based configuration analysis, and modified Mosher's method and finally verified by comparison of recorded and computed NMR chemical shifts from quantum chemical calculations coupled with a statistical procedure (DP4+). All of the compounds were evaluated for their in vitro cytotoxicities against the gastric cancer cell lines MGC803 and AGS, and most of them showed significant inhibition on cancer cell viability at 10 μM. Among them, compounds 1, 2, and 5 exerted the most potent cytotoxic activities, with IC₅₀ values less than 1 μM. Further studies showed that compound 2 inhibited cell cycle progression, and both compounds 1 and 2 induced apoptosis of gastric cancer cells in a concentration-dependent manner.

Potentially harmful secondary metabolites produced by indoor Chaetomium species on artificially and naturally contaminated building materials

The presence of the fungal genus Chaetomium and its secondary metabolites in indoor environments is suspected to have a negative impact on human health and well-being. About 200 metabolites have been currently described from Chaetomium spp., but only the bioactive compound group, chaetoglobosins, have been screened for and thus detected in buildings. In this study, we used a liquid chromatography high-resolution mass spectrometry approach to screen both artificially and naturally infected building materials for all the Chaetomium metabolites described in the literature. Pure agar cultures were also investigated to establish differences between metabolite production in vitro and on building materials as well as in comparison with non-indoor reference strains. On building materials, six different chaetoglobosins were detected in total concentrations of up to 950 mg/m² from Chaetomium globosum along with three different chaetoviridins/chaetomugilins in concentrations up to 200 mg/m² . Indoor Chaetomium spp. preferred wood-based materials over gypsum, both in terms of growth rate and metabolite production. Cochliodones were detected for the first time on all building materials infected by both C. globosum and Chaetomium elatum and are thus candidates as Chaetomium biomarkers. No sterigmatocystin was produced by Chaetomium spp. from indoor environment.

A New Xanthone Glycoside from the Endolichenic Fungus Sporormiella irregularis

A new xanthone glycoside, sporormielloside (1), was isolated from an EtOAc extract of an endolichenic fungal strain Sporormiella irregularis (No. 71-11-4-1), along with two known xanthones (2, 3). Their structures were determined by detailed spectroscopic analysis (IR, MS, and 1D- and 2D-NMR), a chemical method, and a comparison of NMR data with closely related compounds previously reported. According to the structures of isolated compounds, their plausible biosynthetic pathway was deduced.

Structures and biological activities of azaphilones produced by Penicillium sp. KCB11A109 from a ginseng field

Twelve metabolites, including five highly oxygenated azaphilones, geumsanols A-E, along with seven known analogues were isolated from Penicillium sp. KCB11A109, a fungus derived from a ginseng field. Their structures were assigned by spectroscopic means (NMR and MS), and stereochemistries were determined by extensive spectroscopic analyses ((1)H-(1)H coupling constants, NOESY, and HETLOC) and chemical derivatizations (modified Mosher's method and acetonide formation). The isolates were evaluated for their anticancer, antimicrobial, antimalarial activities, and phenotypic effects in zebrafish development. Of these compounds possessing no pyranoquinone core, only geumsanol E exhibited cytotoxic activities and toxic effects on zebrafish embryos, suggesting that a double bond at C-11 and C-12 is important for biological activity.

Sporormiellin A, the first tetrahydrofuran-fused furochromone with an unprecedented tetracyclic skeleton from Sporormiella minima

Sporormiellin A (1), the first tetrahydrofuran-fused furochromone with an unprecedented tetracyclic skeleton, has been obtained from the fungal strain Sporormiella minima.

Xylariterpenoids A–D, four new sesquiterpenoids from the Xylariaceae fungus

Four new sesquiterpenoids, sesquiterpenoids A–D (1–4), were isolated from solid cultures of the Xylariaceae fungus (no. 63-19-7-3).

Three pairs of variecolortide enantiomers from Eurotium sp. with caspase-3 inhibitory activity

7-O-methylvariecolortide A (1), variecolortide B (2), and variecolortide C (3), the rare variecolortides existing in racemic manner, were isolated from an endolichenic fungal strain Eurotium sp. (No. 17-11-8-1). With the chiral HPLC technology, (-)-(S)-7-O-methylvariecolortide A (1a), (+)-(R)-7-O-methylvariecolortide A (1b), (-)-(S)-variecolortide B (2a), (+)-(R)-variecolortide B (2b), (-)-(S)-variecolortide C (3a), and (+)-(R)-variecolortide C (3b) were successfully separated and obtained. Their absolute configurations were firstly assigned by ECD experiment and ECD calculation. According to the relation of isolated compounds, a plausible biosynthetic pathway for variecolortides was proposed. In caspase-3 enzymatic assay, compounds 1-3 showed inhibitory activity, with IC50 values of 1.7, 0.8 and 15.7 μM, respectively.

Anticancer and antifungal compounds from Aspergillus, Penicillium and other filamentous fungi

This review covers important anticancer and antifungal compounds reported from filamentous fungi and in particular from Aspergillus, Penicillium and Talaromyces. The taxonomy of these fungi is not trivial, so a focus of this review has been to report the correct identity of the producing organisms based on substantial previous in-house chemotaxonomic studies.

Nodulisporisteriods A and B, the first 3,4-seco-4-methyl-progesteroids from Nodulisporium sp

Two new 4-methyl-progesteroids, nodulisporisteriod A (1) and nodulisporisteriod B (2), were isolated from the extract of an endolichenic fungal strain Nodulisporium sp. (No. 65-17-2-1), along with two related metabolites, demethoxyviridin (3) and inoterpene B (4). Their structures were determined by detailed spectroscopic analyses, X-ray crystallographic analysis and comparison of the NMR data with those of the closely related compounds previously reported. Nodulisporisteriod A (1) and nodulisporisteriod B (2) possess new carbon skeletons, which are the first cases of fission at C-3,4 in 4-methyl-progesteroids. A hypothetical biosynthetic pathway for 1 and 2 was proposed. Moreover, the Aβ42 aggregation inhibitory activities of 1-4 were evaluated using standard thioflavin T (ThT) fluorescence assay with epigallocatechin gallate (EGCG) as positive control. Demethoxyviridin (3) displayed anti-Aβ42 aggregation activity with IC50 value of 13.4μM.

Three new glucosides from a cold-adapted fungal strain Mucor sp

Two new naphthaline glucosides, 2-hydroxy-3-methoxy-8-methyl-1-O-β-d-glucopyranosylnaphthaline (1) and 1-hydroxy-3-methoxy-8-methyl-2-O-β-d-glucopyranosylnaphthaline (2), together with one new isocoumarin glucoside, 3-(3,3-dichloro-2-hydroxylpropyl)-6-methoxy-8-O-β-d-glucopyranosyl-1H-isochromen-1-one (3), were isolated from a cold-adapted fungal strain Mucor sp. (No. XJ07027-5). Their structures were characterized by detailed analyses of IR, MS, 1D- and 2D-NMR spectra. Among them, 2 showed moderate cytotoxic activity against five tumor cells (A-549, HL-60, MCF-7, SMMC-7721, and SW480).

Angular tricyclic benzofurans and related natural products of fungal origin. Isolation, biological activity and synthesis

Naturally-occurring angular tricyclic benzofuran/isobenzofuran derivatives of fungal origin and related compounds, in which two heterocyclic rings are fused to a central benzenoid moiety, are covered. Emphasis is placed on the structure of the compounds, together with their relevant biological activities, source microorganisms, country or region of origin and environmental conditions. In addition, proposed biosynthetic pathways, as well as the total syntheses of some of the compounds, including those that lead to structural revision or to correct stereochemical assignments, and related synthetic efforts, are discussed in detail.

Xanthoquinodins from the endolichenic fungal strain Chaetomium elatum

Five new xanthoquinodins, A4-A6 (1-3), B4 (4), and B5 (5), were isolated from the crude extract of the endolichenic fungal strain Chaetomium elatum (No. 63-10-3-1), along with three known xanthoquinodins, A1-A3 (6-8). Their structures were determined by detailed spectroscopic analysis and comparison of the NMR data with those of the closely related compounds previously reported. The absolute configuration of 1 was established by X-ray crystallographic analysis and ECD calculation. The cytotoxic activity of all compounds was tested against HL-60, SMMC-7721, A-549, MCF-7, and SW480 human cancer cell lines.