Stereochemical determination of new cytochalasans from the plant endophytic fungus Trichoderma gamsii

The cytochalasans: potent fungal natural products with application from bench to bedside

Covering: 2000-2023Cytochalasans are a fascinating class of natural products that possess an intricate chemical structure with a diverse range of biological activities. They are known for their complex chemical architectures and are often isolated from various fungi. These compounds have attracted attention due to their potential pharmacological properties, including antimicrobial, antiviral, and anticancer effects. For decades, researchers have studied these molecules to better understand their mechanisms of action and to explore their potential applications in medicine and other fields. This review article aims to shed light over the period 2000-2023 on the structural diversities of 424 fungal derived cytochalasans, insights into their biosynthetic origins, pharmacokinetics and their promising therapeutic potential in drug discovery and development.

Marcytoglobosins A and B, Cytochalasans From a Marine Sponge Associated Chaetomium globosum 162105 Fungus

Two new cytochalasans, marcytoglobosins A (1) and B (2) were isolated from the marine sponge associated fungus Chaetomium globosum 162105, along with six known compounds (3-8). The complete structures of two new compounds were determined based on 1D/2D NMR and HR-MS spectroscopic analyses coupled with ECD calculations. All eight isolates were evaluated for their antibacterial activity. Among them, compounds 3-8 displayed antibacterial effects against Staphylococcus epidermidis, Bacillus thuringiensis, Pseudomonas syringae pv. Actinidiae, Vibrio alginolyticus, and Edwardsiella piscicida with minimum inhibitory concentration (MIC) values ranging from 10 to 25 μg/mL.

Antitumor aspochalasin and antiviral benzofuran derivatives from a marine-derived fungus Aspergillus sp. SCSIO41032

Chemical investigation of the EtOAc extract of a deep-sea derived fungus Aspergillus sp. SCSIO41032 resulted in the isolation of ten known compounds, including eight aspochalasins. Their structures were elucidated by using extensive NMR spectroscopic, mass spectrometric and single crystal X-ray diffraction analysis. The detailed crystallographic data for structures 1, 2, and 4, along with the relative configurations of aspochalasin E (3) determined by its acetonide derivative were reported for the first time. The results of antitumor and antiviral activities showed that 3 displayed moderate antitumor activities against 22Rv1, PC-3, A549, and HCT-15 cell lines with IC50 values ranged from 5.9 ± 0.8 to 19.0 ± 7.7 μM, and 9 exhibited moderate antiviral activities against HSV-1/2 with EC50 values of 9.5 ± 0.5 and 5.4 ± 0.6 μM, respectively. Plate clone formation assays results indicated that 3 inhibited the 22Rv1, PC-3 cells growth in a dose-dependent manner.

Evolution-Based Discovery of Polyketide Acylated Valine from a Cytochalasin-Like Gene Cluster in Simplicillium lamelliciola HDN13430

Utilizing a gene evolution-oriented approach for gene cluster mining, a cryptic cytochalasin-like gene cluster (sla) in Antarctic-derived Simplicillium lamelliciola HDN13430 was identified. Compared with the canonical cytochalasin biosynthetic gene clusters (BGCs), the sla gene cluster lacks the key α,β-hydrolase gene. Heterologous expression of the sla gene cluster led to the discovery of a new compound, slamysin (1), characterized by an N-acylated amino acid structure and demonstrating weak anti-Bacillus cereus activity. These findings underscore the potential of genetic evolution in uncovering novel compounds and indicating specific adaptive evolution within specialized habitats.

New insight into the production improvement and resource generation of chaetoglobosin A in Chaetomium globosum

Chaetoglobosin A is a complex macrocyclic alkaloid with potent antimycotic, antiparasitic and antitumor properties. However, the low output and high cost of chaetoglobosin A biosynthesis have hampered the application and commercialization of chaetoglobosin A in agriculture and biomedicine. Here, the CgMfs1 gene, which encodes the major facilitator superfamily secondary transporter, was identified based on bioinformatics analysis, and an intensive study of its effects on chaetoglobosin A biosynthesis and secretion was performed using CgMfs1‐silencing and CgMfs1‐overexpression strategies. Inactivation of CgMfs1 caused a notable decrease in chaetoglobosin A yield from 58.66 mg/L to 19.95 mg/L (MFS1–3) and 17.13 mg/L (MFS1–4). The use of an efficient expression plasmid in Chaetomium globosum W7 to generate the overexpression mutant OEX13 resulted in the highest chaetoglobosin A increase to 298.77 mg/L. Interestingly, the transcription level of the polyketide synthase gene significantly fluctuated with the change in CgMfs1, confirming that the predicted efflux gene CgMfs1 could play a crucial role in chaetoglobosin A transportation. Effective efflux of chaetoglobosin A could possibly alleviate feedback inhibition, resulting in notable increase in the expression of the polyketide synthase gene. Furthermore, we utilized cornstalk as the fermentation substrate to produce chaetoglobosin A, and scanning electron microscopy and Fourier transform‐infrared spectroscopy revealed that the strain OEX13 could well degrade cornstalk, presenting significant increases in the chaetoglobosin A yield, when compared with that produced by the wild‐type strain (from 40.32 to 191.90 mg/L). Thus, this research provides a novel analogous engineering strategy for the construction of high‐yielding strain and offers new insight into large‐scale chaetoglobosin A production.

Insights into the Chemical Diversity of Selected Fungi from the Tza Itzá Cenote of the Yucatan Peninsula

Cenotes are habitats with unique physical, chemical, and biological features. Unexplored microorganisms from these sinkholes represent a potential source of bioactive molecules. Thus, a series of cultivable fungi (Aspergillus spp. NCA257, NCA264, and NCA276, Stachybotrys sp. NCA252, and Cladosporium sp. NCA273) isolated from the cenote Tza Itzá were subjected to chemical, coculture, and metabolomic analyses. Nineteen compounds were obtained and tested for their antimicrobial potential against ESKAPE pathogens, Mycobacterium tuberculosis, and nontuberculous mycobacteria. In particular, phenylspirodrimanes from Stachybotrys sp. NCA252 showed significant activity against MRSA, MSSA, and mycobacterial strains. On the other hand, the absolute configuration of the new compound 17-deoxy-aspergillin PZ (1) isolated from Aspergillus sp. NCA276 was established via single-crystal X-ray crystallography. Also, the chemical analysis of the cocultures between Aspergillus and Cladosporium strains revealed the production of metabolites that were not present or were barely detected in the monocultures. Finally, molecular networking analysis of the LC-MS-MS/MS data for each fungus was used as a tool for the annotation of additional compounds, increasing the chemical knowledge on the corresponding fungal strains. Overall, this is the first systematic chemical study on fungi isolated from a sinkhole in Mexico.

Bioinspired Network Analysis Enabled Divergent Syntheses and Structure Revision of Pentacyclic Cytochalasans

We accomplished the divergent total syntheses of ten pentacyclic cytochalasans (aspergillin PZ, trichodermone, trichoderones, flavipesines, and flavichalasines) from a common precursor aspochalasin D and revised the structures of trichoderone B, spicochalasin A, flavichalasine C, aspergilluchalasin based on structure network analysis of the cytochalasans biosynthetic pathways and DFT calculations. The key steps of the syntheses include transannular alkene/epoxyalkene and carbonyl-ene cyclizations to establish the C/D ring of pentacyclic aspochalasans. Our bioinspired approach to these pentacyclic cytochalasans validate the proposed biosynthetic speculation from a chemical view and provide a platform for the synthesis of more than 400 valuable cytochalasans bearing different macrocycles and amino-acid residues.

Progress in the Chemistry of Cytochalasans

Cytochalasans are a group of fungal-derived natural products characterized by a perhydro-isoindolone core fused with a macrocyclic ring, and they exhibit a high structural diversity and a broad spectrum of bioactivities. Cytochalasans have attracted significant attention from the chemical and pharmacological communities and have been reviewed previously from various perspectives in recent years. However, continued interest in the cytochalasans and the number of laboratory investigations on these compounds are both growing rapidly. This contribution provides a general overview of the isolation, structural determination, biological activities, biosynthesis, and total synthesis of cytochalasans. In total, 477 cytochalasans are covered, including "merocytochalasans" that arise by the dimerization or polymerization of one or more cytochalasan molecules with one or more other natural product units. This contribution provides a comprehensive treatment of the cytochalasans, and it is hoped that it may stimulate further work on these interesting natural products.

Antioxidative and Neuroprotective Effects of the Cytochalasans From Endophytes

Six 10-indolyl-cytochalasans, chaetoglobosin F (1), chaetoglobosin Fex (2), chaetoglobosin E (3), cytoglobosin A (4), penochalasin C (5), and isochaetoglobosin D (6), and 2 10-phenyl-cytochalasans, cytochalasin H (7) and 18-methoxycytochalasin J (8) were isolated from 2 plant endophytes, Chaetomiun globosum WQ and Phomopsis sp. IFB-E060, respectively. These cytochalasans were investigated with radical-scavenging activity assay and hydrogen peroxide (H2O2)/ N-methyl-4-phenylpyridinium iodide (MPP+)-induced pheochromocytoma cell line 12 (PC12) cell models, respectively. Results showed that 7 compounds had antioxidative effects except 5, with scavenging 2,2-diphenyl-1-picrylhydrazyl radical effect 1 = 6= 7 > 2> 4 = 3 > 8 and scavenging 2,2-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt radical effect 1 = 6 = 7 > 2 > 3 > 8 > 4. They could also inhibit H2O2/MPP+-induced damage in PC12 cells by increasing cell viability and decreasing lactate dehydrogenase release. Compounds 1, 6, and 7 exhibited the strongest antioxidative potencies, which are more potent than vitamin E. Additionally, antioxidative and neuroprotective effects of 1∼8 showed some structure–activity relationship. These findings would be useful for looking for cytochalasin-related new lead compounds or drugs to prevent and treat Parkinson’s disease.

Mining the Metabolome and the Agricultural and Pharmaceutical Potential of Sea Foam-Derived Fungi

Sea foam harbors a diverse range of fungal spores with biological and ecological relevance in marine environments. Fungi are known as the producers of secondary metabolites that are used in health and agricultural sectors, however the potentials of sea foam-derived fungi have remained unexplored. In this study, organic extracts of six foam-derived fungal isolates belonging to the genera Penicillium, Cladosporium, Emericellopsis and Plectosphaerella were investigated for their antimicrobial activity against plant and human pathogens and anticancer activity. In parallel, an untargeted metabolomics study using UPLC-QToF–MS/MS-based molecular networking (MN) was performed to unlock their chemical inventory. Penicillium strains were identified as the most prolific producers of compounds with an average of 165 parent ions per strain. In total, 49 known mycotoxins and functional metabolites were annotated to specific and ubiquitous parent ions, revealing considerable chemical diversity. This allowed the identification of putative new derivatives, such as a new analog of the antimicrobial tetrapeptide, fungisporin. Regarding bioactivity, the Penicillium sp. isolate 31.68F1B showed a strong and broad-spectrum activity against seven plant and human pathogens, with the phytopathogen Magnaporthe oryzae and the human pathogen Candida albicans being the most susceptible (IC₅₀ values 2.2 and 6.3 µg/mL, respectively). This is the first study mining the metabolome of the sea foam-derived fungi by MS/MS-based molecular networking, and assessing their biological activities against phytopathogens.

Pycnidiophorones A–D, four new cytochalasans from the wetland derived fungus Pycnidiophora dispersa

Pycnidiophorones A–D (1–4), four new cytochalasans with a rare 5/6/6/5/6 pentacyclic skeleton incorporating the unique 12-oxatricyclo[6.3.1.0^2,7]dodecane core, and six known depsidones (5–10) were isolated from cultures of the wetland-soil-derived fungus Pycnidiophora dispersa. Their chemical structures were unambiguously determined using NMR spectroscopic data. The absolute configurations of 1 and 3 were assigned by electronic circular dichroism (ECD) calculations. Compounds 1–10 showed moderate cytotoxicity against a panel of five human tumor cell lines.

Four new 5/6/6/5/6 pentacyclic cytochalasan pycnidiophorones A–D (1–4) and six known depsidones were identified from the wetland-soil-derived fungus Pycnidiophora dispersa.

Chaetomadrasins A and B, Two New Cytotoxic Cytochalasans from Desert Soil-Derived Fungus Chaetomium madrasense 375

Two new cytochalasans, Chaetomadrasins A (1) and B (2), along with six known analogues (3-8), were isolated from the solid-state fermented culture of desert soil-derived Chaetomium madrasense 375. Their structures were clarified by comprehensive spectroscopic analyses, and the absolute configurations of Compounds 1 and 2 were confirmed by electronic circular dichroism (ECD) and calculated ECD. For the first time, Chaetomadrasins A (1), which belongs to the chaetoglobosin family, is characterized by the presence of all oxygen atoms in the form of Carbonyl. Chaetomadrasin B (2) represents the first example of chaetoglobosin type cytochalasan characterized by a hydroxy unit and carbonyl group fused to the indole ring. Compounds 1 and 2 displayed moderate cytotoxicity against HepG2 human hepatocellular carcinoma cells.

Genetic dereplication of Trichoderma hypoxylon reveals two novel polycyclic lactones

Previous study demonstrated large scale production of trichochecenes which limited the discovery of novel metabolites in Trichoderma hypoxylon. By genetic deletion of trichothecene synthase encoding gene thtri5, we created the dereplication mutant which eliminated the production of trichothecenes. Through chemical isolation, we characterized a couple of rare new polycyclic lactones tricholactones A and B from the thtri5 deletion strain. The structures of these two compounds were well determined by NMR, HR-ESI-MS and IECD analysis.

Amiaspochalasins A-H, Undescribed Aspochalasins with a C-21 Ester Carbonyl from Aspergillus micronesiensis

Amiaspochalasins A-H (1-8), eight undescribed aspochalasins, and trichalasin D (9), a known analogue, were isolated from the solid culture of Aspergillus micronesiensis. Compounds 1-9 are aspochalasins with a C-21 ester carbonyl, and their structures were determined by spectroscopic data, X-ray crystallographic analyses, electronic circular dichroism calculations, and chemical methods. The CH₃-25 in compound 1 is located at C-16 rather than C-14 in the previously reported aspochalasins, endowing 1 with an unexpected carbon skeleton. Compounds 2 and 3 are the first examples of aspochalasins with an unprecedented 5/6/6/8 tetracyclic ring system. Compounds 4 and 5 are diastereomers of aspochalasins I and J, respectively. Compounds 6 and 7 are the first aspochalasins featuring a long open-chain system, and their absolute configurations were discussed by comparing the NMR data of the hydrolysis and methyl esterification products of 4 and 5. Compound 8 is an isomeride of 9. The cytotoxic and antimicrobial effects of 1-9 were tested.

Biomimetic Synthesis of (+)-Aspergillin PZ

The cytochalasans are a large family of polyketide natural products with potent bioactivities. Amongst them, the aspochalasins show particularly intricate and fascinating structures. To gain insight into their structural diversity and innate reactivity, we have developed a rapid synthesis of aspochalasin D, the central member of the family. It proceeded in 13 steps starting from divinyl carbinol and utilized a high pressure Diels-Alder reaction that features high regio- and stereoselectivity. So far, our work has culminated in a biomimetic synthesis of aspergillin PZ, an intricate pentacyclic aspochalasan.

Molecular Networking-Based Metabolome and Bioactivity Analyses of Marine-Adapted Fungi Co-cultivated With Phytopathogens

Fungi represent a rich source of bioactive metabolites and some are marketed as alternatives to synthetic agrochemicals against plant pathogens. However, the culturability of fungal strains in artificial laboratory conditions is still limited and the standard mono-cultures do not reflect their full spectrum chemical diversity. Phytopathogenic fungi and bacteria have successfully been used in the activation of cryptic biosynthetic pathways to promote the production of new secondary metabolites in co-culture experiments. The aim of this study was to map the fungal diversity of Windebyer Noor, a brackish lake connected to Baltic Sea (Germany), to induce the chemical space of the isolated marine-adapted fungi by co-culturing with phytopathogens, and to assess their inhibitory potential against six commercially important phytopathogens. Out of 123 marine-adapted fungal isolates obtained, 21 were selected based on their phylogenetic and metabolite diversity. They were challenged with two phytopathogenic bacteria (Pseudomonas syringae and Ralstonia solanacearum) and two phytopathogenic fungi (Magnaporthe oryzae and Botrytis cinerea) on solid agar. An in-depth untargeted metabolomics approach incorporating UPLC-QToF-HRMS/MS-based molecular networking (MN), in silico MS/MS databases, and manual dereplication was employed for comparative analysis of the extracts belonging to nine most bioactive co-cultures and their respective mono-cultures. The phytopathogens triggered interspecies chemical communications with marine-adapted fungi, leading to the production of new compounds and enhanced expression of known metabolites in co-cultures. MN successfully generated a detailed map of the chemical inventory of both mono- and co-cultures. We annotated overall 18 molecular clusters (belonging to terpenes, alkaloids, peptides, and polyketides), 9 of which were exclusively produced in co-cultures. Several clusters contained compounds, which could not be annotated to any known compounds, suggesting that they are putatively new metabolites. Direct antagonistic effects of the marine-adapted fungi on the phytopathogens were observed and anti-phytopathogenic activity was demonstrated.The untargeted metabolomics approach combined with bioactivity testing allowed prioritization of two co-cultures for purification and characterization of marine fungal metabolites with crop-protective activity. To our knowledge, this is the first study employing plant pathogens to challenge marine-adapted fungi.

New 19-Residue Peptaibols from Trichoderma Clade Viride

Trichoderma koningiopsis and T. gamsii belong to clade Viride of Trichoderma, the largest and most diverse group of this genus. They produce a wide range of bioactive secondary metabolites, including peptaibols with antibacterial, antifungal, and antiviral properties. The unusual amino acid residues of peptaibols, i.e., α-aminoisobutyric acid (Aib), isovaline (Iva), and the C-terminal 1,2-amino alcohol make them unique among peptides. In this study, the peptaibiomes of T. koningiopsis and T. gamsii were investigated by HPLC-ESI-MS. The examined strains appeared to produce 19-residue peptaibols, most of which are unknown from literature, but their amino acid sequences are similar to those of trikoningins, tricholongins, trichostrigocins, trichorzianins, and trichorzins. A new group of peptaibols detected in T. koningiopsis are described here under the name “Koningiopsin”. Trikoningin KA V, the closest peptaibol compound to the peptaibols produced by these two strains, was selected for structural investigation by short MD simulation, which revealed that many residues show high preference for left handed helix formation. The bioactivity of the peptaibol mixtures produced by T. koningiopsis and T. gamsii was tested on agar plates against bacteria, yeasts, and filamentous fungi. The results revealed characteristic differences in bioactivities towards the different groups of target microorganisms, which can be explained with the differences in their cell wall structures.

Flavichalasines A-M, cytochalasan alkaloids from Aspergillus flavipes

Two new tetracyclic cytochalasans, flavichalasines A and B (1 and 2), three new pentacyclic cytochalasans, flavichalasines C-E (3-5), and eight new tricyclic cytochalasans, flavichalasines F-M (6-13), together with eight known analogues (14-21), were isolated from the solid culture of Aspergillus flavipes. Structures of these new compounds were elucidated on the basis of extensive spectroscopic analyses including 1D, 2D NMR and HRESIMS data. Their absolute configurations were determined by comparison of their experimental ECD with either computed ECD or experimental ECD spectrum of known compound. The structure and absolute configuration of 2 were further determined by X-ray crystallographic diffraction. Flavichalasine A (1) represents the first example of cytochalasan with a terminal double bond at the macrocyclic ring and flavichalasine E (5) is the only cytochalasan with an α-oriented oxygen-bridge in D ring. These new compounds were evaluated for their cytotoxic activities against seven human cancer cell lines, of which, 6 and 14 displayed moderate inhibitory activities against tested cell lines. In addition, compounds 6 and 14 induced apoptosis of HL60 cells by activation of caspase-3 and degradation of PARP.

Koninginins N-Q, Polyketides from the Endophytic Fungus Trichoderma koningiopsis Harbored in Panax notoginseng

Four new fungal polyketides named koninginins N-Q (1-4), together with four known analogues (5-8), were isolated from the endophytic fungus Trichoderma koningiopsis YIM PH30002 harbored in Panax notoginseng. Their structures were determined on the basis of spectral data interpretation. These compounds were evaluated for their antifungal activity, nitric oxide inhibition, and anticoagulant activity.