Diterpenes and Sesquiterpenes from the Marine Algicolous Fungus Trichoderma harzianum X-5

Ether-Diol Ambiguity: An Inconspicuous Issue in the Structure Elucidation of Oxygenated Natural Products

Tertiary and allylic hydroxyl groups readily eliminate water during positive ion mode mass spectrometry and may show similar NMR spectra to their corresponding ethers. In a routine structure elucidation workflow, these factors can cause researchers to incorrectly assign diol moieties as ethers or vice versa, leading to inaccurate chemical structures. After facing this problem during our work on oxygenated sesquiterpenoids from a Fusarium sp. fungal strain, we became aware of this challenging issue. We examined the literature for oxygenated natural products bearing these functional groups, and with the aid of density functional calculations of NMR chemical shifts, we now report the structures of 15 natural products that should be revised. We further establish that derivatizing sub-micromolar amounts of alcohols to their sulfates can be used to distinguish these from their corresponding ethers using liquid chromatography negative ion mode mass spectrometry. Finally, we isolated lignoren/cyclonerodiol from the Fusarium sp. culture extract and supported its revised identity as cyclonerodiol using this sulfation approach. Our results suggest that ether-diol ambiguity could be a prevalent issue affecting the structure elucidation of oxygenated natural products and highlight the importance of using complementary techniques, such as sulfation with LC-(-)-ESI-MS or density functional calculations of NMR chemical shifts.

Diterpenoids with Antibacterial Activities from the Fungus Trichoderma harzianum

A new fusicoccane diterpenoid, harziaderma A (1), two novel harziane diterpenoids, harzianones G and H (2 and 3), one revised harziane diterpenoid (4), and two known diterpenoids (5 and 6) were isolated from the fungus Trichoderma harzianum and established via NMR, HRESIMS, Mo2(OAc)4-induced circular dichroism (ICD) and electronic circular dichroism (ECD) calculations. It is worth noting that compound 1 represents the first instance of a fusicoccane-type diterpenoid derived from T. harzianum. The structure of furanharzianone B was revised to 4 via careful spectroscopic analyses. Additionally, compounds 2 and 5 could suppress the overall growth of the foodborne bacterial pathogen Bacillus cereus. Compound 4 showed a moderate suppressive impact on NO generation in lipopolysaccharide (LPS)-treated RAW 264.7 cells. The discoveries from the current study not only expanded the structural variety of diterpenoids isolated from T. harzianum but also laid a robust foundation for the development of harziane diterpenoids as anti-foodborne pathogen agents.

Research Progress on Sesquiterpene Compounds from Artabotrys Plants of Annonaceae

Artabotrys, a pivotal genus within the Annonaceae family, is renowned for its extensive biological significance and medicinal potential. The genus's sesquiterpene compounds have attracted considerable interest from the scientific community due to their structural complexity and diverse biological activities. These compounds exhibit a range of biological activities, including antimalarial, antibacterial, anti-inflammatory analgesic, and anti-tumor properties, positioning them as promising candidates for medical applications. This review aims to summarize the current knowledge on the variety, species, and structural characteristics of sesquiterpene compounds isolated from Artabotrys plants. Furthermore, it delves into their pharmacological activities and underlying mechanisms, offering a comprehensive foundation for future research.

Chemistry and biology of marine-derived Trichoderma metabolites

Marine-derived fungi of the genus Trichoderma have been surveyed for pharmaceuticals and agrochemicals since 1993, with various new secondary metabolites being characterized from the strains of marine animal, plant, sediment, and water origin. Chemical structures and biological activities of these metabolites are comprehensively reviewed herein up to the end of 2022 (covering 30 years). More than 70 strains that belong to at least 18 known Trichoderma species have been chemically investigated during this period. As a result, 445 new metabolites, including terpenes, steroids, polyketides, peptides, alkaloids, and others, have been identified, with over a half possessing antimicroalgal, zooplankton-toxic, antibacterial, antifungal, cytotoxic, anti-inflammatory, and other activities. The research is highlighted by the molecular diversity and antimicroalgal potency of terpenes and steroids. In addition, metabolic relevance along with co-culture induction in the production of new compounds is also concluded. Trichoderma strains of marine origin can transform and degrade heterogeneous molecules, but these functions need further exploration.

Structures and Biological Activities of Secondary Metabolites from the Trichoderma genus (Covering 2018-2022)

Trichoderma, a genus with more than 400 species, has a long history of use as an industrial bioreactor, biofertilizer, and biocontrol agent. It is considered a significant source of secondary metabolites (SMs) that possess unique structural features and a wide range of bioactivities. In recent years, numerous secondary metabolites of Trichoderma, including terpenoids, polyketides, peptides, alkaloids, and steroids, have been identified. Most of these SMs displayed antimicrobial, cytotoxic, and antifungal effects. This review focuses on the structural diversity, biological activities, and structure-activity relationships (SARs) of the SMs isolated from Trichoderma covered from 2018 to 2022. This study provides insights into the exploration and utilization of bioactive compounds from Trichoderma species in the agriculture or pharmaceutical industry.

Isolation and characterization of three pairs of verrucosidin epimers from the marine sediment-derived fungus Penicillium cyclopium and configuration revision of penicyrone A and related analogues

Verrucosidins, a methylated α-pyrone class of polyketides rarely reported upon, have been implicated in one or more neurological diseases. Despite the significance of verrucosidins as neurotoxins, the absolute configurations of most of the derivatives have not been accurately characterized yet. In this study, three pairs of C-9 epimeric verrucosidin derivatives, including the known compounds penicyrones A and B (1a/1b) and 9-O-methylpenicyrones A and B (2a/2b), the new compounds 9-O-ethylpenicyrones A and B (3a/3b), together with the related known derivative verrucosidin (4), were isolated and identified from the culture extract of Penicillium cyclopium SD-413, which was obtained from the marine sediment collected from the East China sea. Their structures were established based on an in-depth analysis of nuclear magnetic resonances (NMR) and mass spectroscopic data. Determination of the absolute configurations of these compounds was accomplished by Mosher's method and time-dependent density functional theory (TDDFT) calculations of electronic circular dichroism (ECD) and optical rotation (OR). The configurational assignment of penicyrone A demonstrated that the previously reported C-6 absolute configuration of verrucosidin derivatives needs to be revised from (6S) to (6R). The 9R/9S epimers of compounds 1-3 were found to exhibit growth inhibition against some pathogenic bacteria, indicating that they have potential as lead compounds for the creation of antimicrobial agents.

Supplementary Information

The online version contains supplementary material available at 10.1007/s42995-023-00173-2.

Strain improvement of Trichoderma harzianum for enhanced biocontrol capacity: Strategies and prospects

In the control of plant diseases, biocontrol has the advantages of being efficient and safe for human health and the environment. The filamentous fungus Trichoderma harzianum and its closely related species can inhibit the growth of many phytopathogenic fungi, and have been developed as commercial biocontrol agents for decades. In this review, we summarize studies on T. harzianum species complex from the perspective of strain improvement. To elevate the biocontrol ability, the production of extracellular proteins and compounds with antimicrobial or plant immunity-eliciting activities need to be enhanced. In addition, resistance to various environmental stressors should be strengthened. Engineering the gene regulatory system has the potential to modulate a variety of biological processes related to biocontrol. With the rapidly developing technologies for fungal genetic engineering, T. harzianum strains with increased biocontrol activities are expected to be constructed to promote the sustainable development of agriculture.

From Genes to Molecules, Secondary Metabolism in Botrytis cinerea: New Insights into Anamorphic and Teleomorphic Stages

The ascomycete Botrytis cinerea Pers. Fr., classified within the family Sclerotiniaceae, is the agent that causes grey mould disease which infects at least 1400 plant species, including crops of economic importance such as grapes and strawberries. The life cycle of B. cinerea consists of two phases: asexual (anamorph, Botrytis cinerea Pers. Fr.) and sexual (teleomorph, Botryotinia fuckeliana (de Bary) Wetzel). During the XVI International Symposium dedicated to the Botrytis fungus, which was held in Bari in June 2013, the scientific community unanimously decided to assign the most widely used name of the asexual form, Botrytis, to this genus of fungi. However, in the literature, we continue to find articles referring to both morphic stages. In this review, we take stock of the genes and metabolites reported for both morphic forms of B. cinerea between January 2015 and October 2022.

Cyclopentenone and wickerol derivatives from the marine algicolous fungus Trichoderma atroviride A-YMD-9-4

A new cyclopentenone derivative, 4-hydroxyhypocrenone A, and a new naturally-occurring wickerol derivative, 8-acetoxywickerol A, as well as two known compounds, hypocrenone A and wickerol B, were purified from Trichoderma atroviride A-YMD-9-4, an endophytic fungus isolated from the marine red alga Gracilaria verrucosa. The structures and relative configurations of two new isolates were established by a combination of 1 D/2D NMR, IR, and mass spectroscopic methods, and the absolute configuration of 1 was assigned on the basis of ECD data analyzed by quantum chemical calculations. Compounds 1 and 2 exhibited weak inhibition of one or two marine phytoplankton species.

Novel Sesquiterpene and Diterpene Aminoglycosides from the Deep-Sea-Sediment Fungus Trichoderma sp. SCSIOW21

Six new sesquiterpene aminoglycosides, trichaspside F (2) and cyclonerosides A-E (5-9), two new diterpene aminoglycosides, harzianosides A and B (10, 11), and three known sesquiterpenes, trichodermoside (1), cycloneran-3,7,10,11-tetraol (3), and cyclonerodiol (4), have been isolated from the n-butanol extract of Trichoderma sp. SCSIOW21 (Hypocreaceae), a deep-sea-sediment-derived fungus. The structures and relative configurations of the new compounds were determined using spectroscopic techniques and comparisons with those reported in the literature. The absolute configurations of the aglycone part of cyclonerosides A-E (5-9) were tentatively proposed based on optical rotation and biogenic considerations. Cyclonerosides A-E (5-9) represent the first glycosides of cyclonelane-type sesquiterpenes generated from Trichoderma. The NO-production-inhibitory activities were evaluated using macrophage RAW264.7 cells. Among the isolated compounds, trichaspside F (2) and cyclonerosides B-E (6-9) exhibited the strongest NO-production-inhibitory activities with IC₅₀ values of 54.8, 50.7, 57.1, 42.0, and 48.0 µM, respectively, compared to the IC₅₀ value of 30.8 µM for the positive control (quercetin). When tested for anti-fungal activities against several pathogenic fungi, none of the compounds exhibited significant activities at a concentration of 100 µM.

A Review of Diterpenes from Marine-Derived Fungi: 2009-2021

Marine-derived fungi are important sources of novel compounds and pharmacologically active metabolites. As an important class of natural products, diterpenes show various biological activities, such as antiviral, antibacterial, anti-inflammatory, antimalarial, and cytotoxic activities. Developments of equipment for the deep-sea sample collection allow discoveries of more marine-derived fungi with increasing diversity, and much progress has been made in the identification of diterpenes with novel structures and bioactivities from marine fungi in the past decade. The present review article summarized the chemical structures, producing organisms and biological activities of 237 diterpenes which were isolated from various marine-derived fungi over the period from 2009 to 2021. This review is beneficial for the exploration of marine-derived fungi as promising sources of bioactive diterpenes.

Structures and Biological Activities of Secondary Metabolites from Trichoderma harzianum

The biocontrol fungus Trichoderma harzianum, from both marine and terrestrial environments, has attracted considerable attention. T. harzianum has a tremendous potential to produce a variety of bioactive secondary metabolites (SMs), which are an important source of new herbicides and antibiotics. This review prioritizes the SMs of T. harzianum from 1988 to June 2022, and their relevant biological activities. Marine-derived SMs, especially terpenoids, polyketides, and macrolides compounds, occupy a significant proportion of natural products from T. harzianum, deserving more of our attention.

Trichoderma species from plant and soil: An excellent resource for biosynthesis of terpenoids with versatile bioactivities

BACKGROUND

Trichoderma species are rich source of bioactive secondary metabolites. In the past decades, a series of secondary metabolites were reported from different Trichoderma fungi, among which terpenoids possessing versatile structural diversities and extensive pharmacological activities are one of the particularly important categories.

AIM OF REVIEW

The review aims to summarize the terpenoids isolated from Trichoderma species regarding their structural diversities, biological activities, and promising biosynthetic potentials.

KEY SCIENTIFIC CONCEPTS OF REVIEW

So far, a total of 253 terpenoids, including 202 sesquiterpenes, 48 diterpenes, 2 monoterpenes and 1 meroterpenoid, were isolated and identified from Trichoderma species between 1948 and 2022. Pharmacological investigations of Trichoderma terpenoids mainly focused on their antibacterial activities, antifungal activities, inhibitory activities on marine plankton species and cytotoxic activities, indicating that Trichoderma species are important microbial agents for drug discovery and environmentally friendly agrochemicals development. Intriguing chemistry and enzymology involved in the biosynthesis of Trichoderma terpenoids were also presented to facilitate further precise genome mining-guided novel structure discovery. Taken together, the abundance of novel skeletons, bioactivities and biosynthetic potentials presents new opportunities for drug and agrochemicals discovery, genome mining and enzymology exploration from Trichoderma species. The work will provide references for the profound study of terpenoids derived from Trichoderma, and facilitate further studies on Trichoderma species in the areas of chemistry, medicine, agriculture and microbiology.

Diterpenes Specially Produced by Fungi: Structures, Biological Activities, and Biosynthesis (2010–2020)

Fungi have traditionally been a very rewarding source of biologically active natural products, while diterpenoids from fungi, such as the cyathane-type diterpenoids from Cyathus and Hericium sp., the fusicoccane-type diterpenoids from Fusicoccum and Alternaria sp., the guanacastane-type diterpenoids from Coprinus and Cercospora sp., and the harziene-type diterpenoids from Trichoderma sp., often represent unique carbon skeletons as well as diverse biological functions. The abundances of novel skeletons, biological activities, and biosynthetic pathways present new opportunities for drug discovery, genome mining, and enzymology. In addition, diterpenoids peculiar to fungi also reveal the possibility of differing biological evolution, although they have similar biosynthetic pathways. In this review, we provide an overview about the structures, biological activities, evolution, organic synthesis, and biosynthesis of diterpenoids that have been specially produced by fungi from 2010 to 2020. We hope this review provides timely illumination and beneficial guidance for future research works of scholars who are interested in this area.

Endophytic Fungal Terpenoids: Natural Role and Bioactivities

Endophytic fungi are a highly diverse group of fungi that intermittently colonize all plants without causing symptoms of the disease. They sense and respond to physiological and environmental changes of their host plant and microbiome. The inter-organism interactions are largely driven by chemical networks mediated by specialized metabolites. The balance of these complex interactions leads to healthy and strong host plants. Endophytic strains have particular machinery to produce a plethora of secondary metabolites with a variety of bioactivities and unknown functions in an ecological niche. Terpenoids play a key role in endophytism and represent an important source of bioactive molecules for human health and agriculture. In this review, we describe the role of endophytic fungi in plant health, fungal terpenoids in multiple interactions, and bioactive fungal terpenoids recently reported from endophytes, mainly from plants used in traditional medicine, as well as from algae and mangroves. Additionally, we highlight endophytic fungi as producers of important chemotherapeutic terpenoids, initially discovered in plants. Despite advances in understanding endophytism, we still have much to learn in this field. The study of the role, the evolution of interactions of endophytic fungi and their terpenoids provide an opportunity for better applications in human health and agriculture.

α-Pyrone and decalin derivatives from the marine-derived fungus Trichoderma harzianum PSU-MF79

Two new compounds, one α-pyrone (trichoharzianone) and one decalin (trichoharzianin), along with eight known compounds including three decalins, two δ-lactones, two carboxylic acids and one isochroman were isolated from the marine-derived fungus Trichoderma harzianum PSU-MF79. The structures were determined by spectroscopic methods. The relative configuration of trichoharzianin was assigned based on NOEDIFF data and coupling constants whereas the absolute configurations were established by comparison of electronic circular dichroism data with those of the co-metabolites. Known (-)-massoia lactone exhibited mild antifungal activity against Cryptococcus neoformans ATCC90113 flucytosine-resistant, Candida albicans ATCC90028 and C. albicans NCPF3153 with MIC values of 128, 200 and 200 µg/mL, respectively, and weak cytotoxic activity against HCT-116 and MCF-7 cell lines with the respective IC₅₀ values of 17 and 32 µM. In addition, it was noncytotoxic against noncancerous Vero cells with an IC₅₀ value of >100 µM.

Novel Harziane Diterpenes from Deep-Sea Sediment Fungus Trichoderma sp. SCSIOW21 and Their Potential Anti-Inflammatory Effects

Five undescribed harziane-type diterpene derivatives, namely harzianol K (1), harzianol L (4), harzianol M (5), harzianol N (6), harzianol O (7), along with two known compounds, hazianol J (2) and harzianol A (3) were isolated from the deep-sea sediment-derived fungus Trichoderma sp. SCSIOW21. The relative configurations were determined by meticulous spectroscopic methods including 1D, 2D NMR spectroscopy, and HR-ESI-MS. The absolute configurations were established by the ECD curve calculations and the X-ray crystallographic analysis. These compounds (1, and 4–7) contributed to increasing the diversity of the caged harziane type diterpenes with highly congested skeleton characteristics. Harzianol J (2) exhibited a weak anti-inflammatory effect with 81.8% NO inhibition at 100 µM.

Sesquiterpenoids Specially Produced by Fungi: Structures, Biological Activities, Chemical and Biosynthesis (2015-2020)

Fungi are widely distributed in the terrestrial environment, freshwater, and marine habitat. Only approximately 100,000 of these have been classified although there are about 5.1 million characteristic fungi all over the world. These eukaryotic microbes produce specialized metabolites and participate in a variety of ecological functions, such as quorum detection, chemical defense, allelopathy, and maintenance of symbiosis. Fungi therefore remain an important resource for the screening and discovery of biologically active natural products. Sesquiterpenoids are arguably the richest natural products from plants and micro-organisms. The rearrangement of the 15 high-ductility carbons gave rise to a large number of different skeletons. At the same time, abundant structural variations lead to a diversification of biological activity. This review examines the isolation, structural determination, bioactivities, and synthesis of sesquiterpenoids that were specially produced by fungi over the past five years (2015-2020).

Identification of Antagonistic Compounds between the Palm Tree Xylariale Endophytic Fungi and the Phytopathogen Fusarium oxysporum

To discover microorganisms that naturally possess chemical weapons against the phytopathogen Fusarium oxysporum, the biological and chemical diversity of plant leaf endophytes was investigated. Endophytes were isolated from the palm tree Astrocaryum sciophyllum collected in pristine forests of French Guiana. Several Xylariaceae inhibited the growth of F. oxysporum and were further explored. Antifungal specialized metabolites were isolated from the Xylariaceae BSNB-0294 strain in confrontation with the phytopathogen and led to the identification of undescribed compounds, i.e., two depsipeptides named xylariaceins, two metabolites containing a 3-imidazolinone moiety, and four new compounds including a nitro-phenylpropanamide and three phenylalanine analogues named xylariains A-D. In parallel, the chemical investigation of the phytopathogen during the coculture led to the identification of an unknown compound, which we named focicin. The production of focicin was exacerbated during the competition. Matrix-assisted laser desorption/ionization coupled to time-of-flight mass spectometry (MALDI-TOF MS) imaging of the competition between BSNB-0294 (endophytic strain) and F. oxysporum f.sp. ciceris (phytopathogen) highlighted time-dependent chemical interactions between the two microorganisms.

Bisabolane, cadinane, and cyclonerane sesquiterpenes from an algicolous strain of Trichoderma asperelloides

Ten new bisabolane derivatives, trichobisabolins Q-Z (1-10), one new cadinane derivative, cadin-4-en-11-ol (11), and three new cyclonerane derivatives, cycloner-3-en-7,11-diol (12), isoepicyclonerodiol oxide (13), and norepicyclonerodiol oxide (14), were isolated from the endophytic fungal strain RR-dl-6-11 of Trichoderma asperelloides that was obtained from a marine alga. Their structures along with relative configurations were established mainly by NMR and IR as well as MS techniques, and the absolute configurations of 10 and 11 were assigned by ECD and X-ray diffraction data, respectively. Sesquiterpenes from the fungus T. asperelloides are reported for the first time. It is interesting that half of the bisabolane derivatives are demethylated. Compound 12 represents the first the occurrence of cyclopentenyl-bearing cycloneranes, and 14 seems a cyclopentyl-degrading cyclonerane derivative. Several isolates feature potent inhibition of marine phytoplankton species.

Trichoderma: A Treasure House of Structurally Diverse Secondary Metabolites With Medicinal Importance

Fungi play an irreplaceable role in drug discovery in the course of human history, as they possess unique abilities to synthesize diverse specialized metabolites with significant medicinal potential. Trichoderma are well-studied filamentous fungi generally observed in nature, which are widely marketed as biocontrol agents. The secondary metabolites produced by Trichoderma have gained extensive attention since they possess attractive chemical structures with remarkable biological activities. A large number of metabolites have been isolated from Trichoderma species in recent years. A previous review by Reino et al. summarized 186 compounds isolated from Trichoderma as well as their biological activities up to 2008. To update the relevant list of reviews of secondary metabolites produced from Trichoderma sp., we provide a comprehensive overview in regard to the newly described metabolites of Trichoderma from the beginning of 2009 to the end of 2020, with emphasis on their chemistry and various bioactivities. A total of 203 compounds with considerable bioactivities are included in this review, which is worth expecting for the discovery of new drug leads and agrochemicals in the foreseeable future. Moreover, new strategies for discovering secondary metabolites of Trichoderma in recent years are also discussed herein.

The chemical diversity, the attractant, anti-acetylcholinesterase, and antifungal activities of metabolites from biocontrol Trichoderma harzianum uncovered by OSMAC strategy

Eight new compounds (1-8) were discovered from Trichoderma harzianum associated with edible mushroom by the one strain many compounds (OSMAC) strategy. Triharzianin A (1) is the first naturally scaffold characterized by a C₁₃-prostaglandin skeleton. The configurations of 1-3, and 5 were determined by the Mosher's method, experimental and calculated ECD spectra, and plausible biosynthesis of stereospecific epoxidation. Most compounds indicated obvious feeding attractant activities to silkworm with attraction rates at 30-90%. Compound 7 showed anti-acetylcholinesterase (anti-AChE) activity with a ratio of 29% at a concentration of 50 μM for insecticidal potential. So 2,​3-​dialkylchromone (7) had potential of chemical entrapment and killing of insects. Compounds 2, 3 and 7-11 showed antifungal activities against Aspergillus fumigates, and Trichoderma sp. from mushroom with MICs ≤ 300 μM. The four fermentation extracts also indicated obvious feeding attractant activities to silkworm for the activities brought by active metabolites from T. harzianum. The material base of biocontrol induced by the interaction of host-fungal symbiont can be investigated by the antifungal metabolites against pathogen fungi.

Sesquiterpenoids and a steroid from the algicolous Trichoderma brevicompactum

Six new sesquiterpenoids including three bisabolane derivatives, trichobisabolins O₁, O₂, and P (1-3), two nerolidol derivatives, trichonerolins A and B (4 and 5), one acorane, trichoacorin A (6), along with one new steroid, isoergokonin B (7), were isolated from the culture of Trichoderma brevicompactum A-DL-9-2 obtained from the inner tissue of the red alga Chondria tenuissima. Their structures and relative configurations were assigned by interpretation of 1D/2D NMR and MS data. As acyclic sesquiterpenoids, compounds 4 and 5 were discovered from Trichoderma for the first time. Compounds 1-7 were evaluated for the inhibition of some marine-derived organisms, in which, 3 and 4/5 exhibited potent inhibition against Amphidinium carterae and Chattonella marina with IC₅₀ of 1.8 μg/mL and 1.2 μg/mL, respectively. In addition, compound 7 could inhibit the growth of Pseudoalteromonas citrea with an MIC value of 64 μg/mL.

Terpenoids from the Marine-Derived Fungus Aspergillus sp. RR-YLW-12, Associated with the Red Alga Rhodomela confervoides

Two new meroterpenoids, aspermeroterpenes D and E (1 and 2), two new ophiobolin-type sesterterpenoids, the C-18 epimers of 18,19-dihydro-18-methoxy-19-hydroxyophiobolin P (6 and 7), and two new drimane-type sesquiterpenoids, 3S-hydroxystrobilactone A (8) and 6-epi-strobilactone A (9), along with 11 known terpenoids (3-5 and 10-17) were isolated from the cultures of the algicolous fungus Aspergillus sp. RR-YLW-12, derived from the red alga Rhodomela confervoides. The structures and relative configurations of new compounds were established by detailed spectroscopic analysis of NMR and HRMS experiments, and the absolute configurations were assigned by X-ray diffraction experiments and comparison of their experimental and calculated ECD spectra. Compound 1 features a rare 6/6/6/6/5 pentacyclic system with a meroterpenoid skeleton, and the structure of terretonin E (3) was revised in this study. Compound 4 showed significant inhibitory activities against three microalgae, Prorocentrum donghaiense, Heterosigma akashiwo, and Chattonella marina, with IC₅₀ values of 10.5, 5.2, and 3.1 μg/mL, respectively.

Synthetic Strategy for Construction of Highly Congested Tetracyclic Core (6-5-7-4) of Harziane Diterpenoids

The structurally intriguing tetracyclic core of complex harziane diterpenoid was constructed in 14 steps from commercially available 3-ethoxycyclohex-2-en-1-one. The key steps were a Mn/Cu-mediated oxidative 1,3-dicarbonyl radical cascade cyclization reaction, which diastereoselectively formed the core of dimethylbicyclo[3.2.1]octane structure, and a Au-catalyzed diastereoselective formal [2 + 2] cycloaddition for construction of the harziane diterpenoid tetracyclic framework. The developed method paves the way for achieving total synthesis of this type of complex natural product.

Proharziane and Harziane Derivatives from the Marine Algicolous Fungus Trichoderma asperelloides RR-dl-6-11

One new proharziane and three new harziane derivatives (1-4) together with six known ones (5-10) were isolated from the marine-alga-derived ascomycete Trichoderma asperelloides RR-dl-6-11. Their structures and relative configurations were determined via spectroscopic techniques, and the absolute configurations were ascertained by analysis of ECD curves. This is the first report on the secondary metabolites of T. asperelloides, and the new isolates (1-4), especially seco-harziane 4, greatly add to the structural diversity of harziane diterpenes as well as their precursors and catabolites. Compounds 1-5 inhibited four marine phytoplankton species, and the structure-activity relationship of harziane derivatives is analyzed.

Marine natural products

This review covers the literature published between January and December in 2018 for marine natural products (MNPs), with 717 citations (706 for the period January to December 2018) referring to compounds isolated from marine microorganisms and phytoplankton, green, brown and red algae, sponges, cnidarians, bryozoans, molluscs, tunicates, echinoderms, mangroves and other intertidal plants and microorganisms. The emphasis is on new compounds (1554 in 469 papers for 2018), together with the relevant biological activities, source organisms and country of origin. Reviews, biosynthetic studies, first syntheses, and syntheses that led to the revision of structures or stereochemistries, have been included. The proportion of MNPs assigned absolute configuration over the last decade is also surveyed.

Molecular methods unravel the biosynthetic potential of Trichoderma species

Members of the genus Trichoderma are a well-established and studied group of fungi, mainly due to their efficient protein production capabilities and their biocontrol activities. Despite the immense interest in the use of different members of this species as biopesticides and biofertilizers, the study of their active metabolites and their biosynthetic gene clusters has not gained significant attention until recently. Here we review the challenges and opportunities in exploiting the full potential of Trichoderma spp. for the production of natural products and new metabolic engineering strategies used to overcome some of these challenges.

Combined Comparative Genomics and Gene Expression Analyses Provide Insights into the Terpene Synthases Inventory in Trichoderma

Trichoderma is a fungal genus comprising species used as biocontrol agents in crop plant protection and with high value for industry. The beneficial effects of these species are supported by the secondary metabolites they produce. Terpenoid compounds are key players in the interaction of Trichoderma spp. with the environment and with their fungal and plant hosts; however, most of the terpene synthase (TS) genes involved in their biosynthesis have yet not been characterized. Here, we combined comparative genomics of TSs of 21 strains belonging to 17 Trichoderma spp., and gene expression studies on TSs using T. gamsii T6085 as a model. An overview of the diversity within the TS-gene family and the regulation of TS genes is provided. We identified 15 groups of TSs, and the presence of clade-specific enzymes revealed a variety of terpenoid chemotypes evolved to cover different ecological demands. We propose that functional differentiation of gene family members is the driver for the high number of TS genes found in the genomes of Trichoderma. Expression studies provide a picture in which different TS genes are regulated in many ways, which is a strong indication of different biological functions.

A Review of Terpenes from Marine-Derived Fungi: 2015-2019

Marine-derived fungi are a significant source of pharmacologically active metabolites with interesting structural properties, especially terpenoids with biological and chemical diversity. In the past five years, there has been a tremendous increase in the rate of new terpenoids from marine-derived fungi being discovered. In this updated review, we examine the chemical structures and bioactive properties of new terpenes from marine-derived fungi, and the biodiversity of these fungi from 2015 to 2019. A total of 140 research papers describing 471 new terpenoids of six groups (monoterpenes, sesquiterpenes, diterpenes, sesterterpenes, triterpenes, and meroterpenes) from 133 marine fungal strains belonging to 34 genera were included. Among them, sesquiterpenes, meroterpenes, and diterpenes comprise the largest proportions of terpenes, and the fungi genera of Penicillium, Aspergillus, and Trichoderma are the dominant producers of terpenoids. The majority of the marine-derived fungi are isolated from live marine matter: marine animals and aquatic plants (including mangrove plants and algae). Moreover, many terpenoids display various bioactivities, including cytotoxicity, antibacterial activity, lethal toxicity, anti-inflammatory activity, enzyme inhibitor activity, etc. In our opinion, the chemical diversity and biological activities of these novel terpenoids will provide medical and chemical researchers with a plenty variety of promising lead compounds for the development of marine drugs.

Terpenoids From the Coral-Derived Fungus Trichoderma harzianum (XS-20090075) Induced by Chemical Epigenetic Manipulation

The soft coral-derived fungus Trichoderma harzianum (XS-20090075) was found to be a potential strain to produce substantial new compounds in our previous study. In order to explore its potential to produce more metabolites, chemical epigenetic manipulation was used on this fungus to wake its sleeping genes, leading to the significant changes of its secondary metabolites by using a histone deacetylase (HDAC) inhibitor. The most obvious difference was the original main products harziane diterpenoids were changed into cyclonerane sesquiterpenoids. Three new terpenoids were isolated from the fungal culture treated with 10 μM sodium butyrate, including cleistanthane diterpenoid, harzianolic acid A (1), harziane diterpenoid, harzianone E (2), and cyclonerane sesquiterpenoid, 3,7,11-trihydroxy-cycloneran (3), together with 11 known sesquiterpenoids (4-14). The absolute configurations of 1-3 were determined by single-crystal X-ray diffraction, ECD and OR calculations, and biogenetic considerations. This was the first time to obtain cleistanthane diterpenoid and africane sesquiterpenoid from genus Trichoderma, and this was the first chlorinated cleistanthane diterpenoid. These results demonstrated that the chemical epigenetic manipulation should be an efficient technique for the discovery of new secondary metabolites from marine-derived fungi.

Sesquiterpenes and Cyclodepsipeptides from Marine-Derived Fungus Trichoderma longibrachiatum and Their Antagonistic Activities against Soil-borne Pathogens

Soil-borne pathogens, including phytopathogenic fungi and root-knot nematodes, could synergistically invade vegetable roots and result in serious economic losses. The genus of Trichoderma has been proven to be a promising reservoir of biocontrol agents in agriculture. In this study, the search for antagonistic metabolites from a marine-derived fungus, Trichoderma longibrachiatum, obtained two structural series of sesquiterpenes 1-6 and cyclodepsipeptides 7-9. Notably, the novel 1 was a rare norsesquiterpene characterized by an unprecedented tricyclic-6/5/5-[4.3.1.0^1,6]-decane skeleton. Their structures were elucidated by extensive spectroscopic analyses, while the absolute configuration of novel 1 was determined by the comparison of experimental and calculated ECD spectra. The novel 1 and known 2 and 3 showed significant antifungal activities against Colletotrichum lagrnarium with MIC values of 8, 16, and 16 μg/mL respectively, even better than those of the commonly used synthetic fungicide carbendazim with 32 μg/mL. They also exhibited antifungal potential against carbendazim-resistant Botrytis cinerea. Cyclodepsipeptides 7-9 showed moderate nematicidal activities against the southern root-knot nematode (Meloidogyne incognita). This study constitutes the first report on the antagonistic effects of metabolites from T. Longibrachiatum against soil-borne pathogens, also highlighting the integrated antagonistic potential of marine-derived T. Longibrachiatum as a biocontrol agent.

Antibacterial harziane diterpenoids from a fungal symbiont Trichoderma atroviride isolated from Colquhounia coccinea var. mollis

Fungal endophytes from plants are an important source for discovery of novel bioactive natural products. In this study, five undescribed harziane diterpenoids with a 4/7/5/6 tetracyclic scaffold, harzianols F‒J and three known derivatives, were obtained from the liquid fermentation of an endophytic fungus Trichoderma atroviride B7, which was isolated from the healthy flower of a Lamiaceae plant Colquhounia coccinea var. mollis. Their structures were elucidated by comprehensive spectroscopic analyses and X-ray crystallographic diffraction in the case of harzianol F. Harzianol I exhibited significant antibacterial effect against the growth of Staphylococcus aureus (EC₅₀ = 7.7 ± 0.8 μg/mL), Bacillus subtilis (EC₅₀ = 7.7 ± 1.0 μg/mL), and Micrococcus luteus (EC₅₀ = 9.9 ± 1.5 μg/mL). Meanwhile, cytotoxic activity of harzianol I against three cancer cell lines was also observed. A plausible biosynthetic pathway for harziane diterpenoids was proposed.

l-Phenylalanine Alters the Privileged Secondary Metabolite Production in the Marine-Derived Fungus Trichoderma erinaceum F1-1

The effects of a single-amino-acid culture strategy on secondary metabolite production in the marine-derived fungus Trichoderma erinaceum F1-1 were investigated by culturing the fungus in GPY medium supplemented or not supplemented with l-phenylalanine. A suite of secondary metabolites, including seven terpenoids (1-7) and one polyketide (8), among which are four new compounds, harziandione A (1), cyclonerodiols A and B (3, 4), and trichodermaerin A (6), were isolated from the GPY medium without l-phenylanine, whereas 18 aromatic compounds (9-26), including six new compounds, trichoderolides A-F (9, 10, and 14-17), were isolated from the culture grown in the GPY medium with l-phenylalanine. The structures of the new compounds were determined by high-resolution mass spectrometry, NMR spectroscopic analysis, optical rotation calculations, chemical methods, and X-ray crystallography. Compounds 10, 12, 13, and 26 exhibited cytotoxic activities against MDA-MB-435 human melanocyte cancer cells. Compound 26 was cytotoxic to A549 adenocarcinomic human alveolar basal epithelial cells.

Total Synthesis and Structural Revision of a Harziane Diterpenoid

The first total synthesis of nominal harziane diterpenoid 1 is disclosed, whose spectral characteristics did not match those of the reported natural product. Stereochemical analysis and subsequent synthesis of the epimeric tertiary alcohol led to reassignment of configuration of the natural product as shown for 2. At the heart of the synthesis is an enyne cycloisomerization that sets a key quaternary stereocenter within a cyclobutane with high diastereocontrol. The route features strategies for the synthesis of the highly congested 6-5-7-4 carbon skeleton characteristic of the caged harziane diterpenoids.

Asperienes A-D, Bioactive Sesquiterpenes from the Marine-Derived Fungus Aspergillus flavus

Marine-derived fungi of the genera Aspergillus could produce novel compounds with significant bioactivities. Among these fungi, the strain Aspergillus flavus is notorious for its mutagenic mycotoxins production. However, some minor components with certain toxicities from A. flavus have not been specifically surveyed and might have potent biological activities. Our investigation of the marine-derived fungus Aspergillus flavus CF13-11 cultured in solid medium led to the isolation of four C-6′/C-7′ epimeric drimane sesquiterpene esters, asperienes A–D (1–4). Their absolute configurations were assigned by electronic circular dichroism (ECD) and Snatzke’s methods. This is the first time that two pairs of C-6′/C-7′ epimeric drimane sesquiterpene esters have successfully been separated. Aperienes A–D (1–4) displayed potent bioactivities towards four cell lines with the IC₅₀ values ranging from 1.4 to 8.3 μM. Interestingly, compounds 1 and 4 exhibited lower toxicities than 2 and 3 toward normal GES-1 cells, indicating more potential for development as an antitumor agent in the future.

Potent Phytotoxic Harziane Diterpenes from a Soft Coral-Derived Strain of the Fungus Trichoderma harzianum XS-20090075

Two new harziane diterpene lactones, possessing a 6/5/7/5-fused carbocyclic core containing a lactone ring system, harzianelactones A and B (1 and 2), and five new harziane diterpenes, harzianones A-D (3-6) and harziane (7), were isolated from the soft coral-derived fungus Trichoderma harzianum XS-20090075. Their structures were determined by extensive NMR spectroscopic data, ECD and OR calculations, as well as X-ray diffraction. The isolated compounds exhibited potent phytotoxicity against seedling growth of amaranth and lettuce. Harziane diterpenes were rarely reported for their remarkably bioactivities, and it was the first report to study the phytotoxicity of harziane diterpenes, which provide a new application of such compounds in agriculture for future research.

Bioactive Compounds Isolated from Marine-Derived Microbes in China: 2009-2018

This review outlines the research that was carried out regarding the isolation of bioactive compounds from marine-derived bacteria and fungi by China-based research groups from 2009-2018, with 897 publications being surveyed. Endophytic organisms featured heavily, with endophytes from mangroves, marine invertebrates, and marine algae making up more than 60% of the microbial strains investigated. There was also a strong focus on fungi as a source of active compounds, with 80% of publications focusing on this area. The rapid increase in the number of publications in the field is perhaps most notable, which have increased more than sevenfold over the past decade, and suggests that China-based researchers will play a major role in marine microbial natural products drug discovery in years to come.

Deoxytrichodermaerin, a harziane lactone from the marine algicolous fungus Trichoderma longibrachiatum A-WH-20-2

Three metabolites deoxytrichodermaerin (a new harziane lactone), harzianol A and harzianone were obtained from Trichoderma longibrachiatum A-WH-20-2, an endophyte from marine red alga Laurencia okamurai. Their structures and relative configurations were unequivocally assigned by spectroscopic techniques, and the absolute configuration of deoxytrichodermaerin was established by analysis of the ECD curve aided by quantum chemical calculations. Deoxytrichodermaerin represents the second harziane lactone with an ester linkage between C-10 and C-11. Harzianol A occurs as a natural product of Trichoderma for the first time. Harzianone has been previously discovered from T. longibrachiatum cf-11. These isolates exhibited potent inhibition of some marine plankton species.

Seven chromanoid norbisabolane derivatives from the marine-alga-endophytic fungus Trichoderma asperellum A-YMD-9-2

An examination of the endophytic fungus Trichoderma asperellum A-YMD-9-2 obtained from the marine red alga Gracilaria verrucosa led to the isolation of seven new chromanoid norbisabolane derivatives, trichobisabolins I-L (1-4) and trichaspsides C-E (5-7). Their structures and relative configurations were established on the basis of spectroscopic techniques, mainly including 1D/2D NMR and MS, and the absolute configuration of 1 was assigned by X-ray crystallographic analysis using Cu Kα radiation. All of these isolates feature a 1,9-epoxy ring system, and 5-7 represent the second occurrence of norbisabolane aminoglycosides. Compounds 1-7 exhibited potent inhibition of several marine phytoplankton species.

Cyclonerane Derivatives from the Algicolous Endophytic Fungus Trichoderma asperellum A-YMD-9-2

Seven previously unreported cyclonerane derivatives, namely, 3,7,11-trihydroxycycloneran-10-one, cycloneran-3,7,10,11-tetraol, cycloneran-3,7,11-triol, 11,12,15-trinorcycloneran-3,7,10-triol, 7,10S-epoxycycloneran-3,15-diol, 7,10R-epoxycycloneran-3,15-diol, and (10Z)-15-acetoxy-10-cycloneren-3,7-diol, were isolated in addition to the known (10Z)-cyclonerotriol, (10E)-cyclonerotriol, catenioblin C, and chokol E from the culture of Trichoderma asperellum A-YMD-9-2, an endophytic fungus obtained from the marine red alga Gracilaria verrucosa. The structures of previously unreported compounds were established by spectroscopic techniques, including 1D/2D NMR, MS, and IR. The isolation of these new cyclonerane derivatives greatly adds to the structural diversity of unusual cyclonerane sesquiterpenes, and several isolates exhibit potent inhibition against some marine phytoplankton species.

Nitrogenous cyclonerane sesquiterpenes from an algicolous strain of Trichoderma asperellum

Eight new nitrogenous cyclonerance derivatives (1–8) including two unprecedented hydroxamic acids (1 and 2) with potent algicidal activity were characterized from the algicolous fungus Trichoderma asperellum.