Bioactive hydroanthraquinones and anthraquinone dimers from a soft coral-derived Alternaria sp. fungus

Cytotoxic Compounds from Marine Fungi: Sources, Structures, and Bioactivity

Marine fungi, such as species from the Penicillium and Aspergillus genera, are prolific producers of a diversity of natural products with cytotoxic properties. These fungi have been successfully isolated and identified from various marine sources, including sponges, coral, algae, mangroves, sediment, and seawater. The cytotoxic compounds derived from marine fungi can be categorized into five distinct classes: polyketides, peptides, terpenoids and sterols, hybrids, and other miscellaneous compounds. Notably, the pre-eminent group among these compounds comprises polyketides, accounting for 307 out of 642 identified compounds. Particularly, within this collection, 23 out of the 642 compounds exhibit remarkable cytotoxic potency, with IC50 values measured at the nanomolar (nM) or nanogram per milliliter (ng/mL) levels. This review elucidates the originating fungal strains, the sources of isolation, chemical structures, and the noteworthy antitumor activity of the 642 novel natural products isolated from marine fungi. The scope of this review encompasses the period from 1991 to 2023.

Marine Natural Products from the Beibu Gulf: Sources, Chemistry, and Bioactivities

Marine natural products (MNPs) play an important role in the discovery and development of new drugs. The Beibu Gulf of South China Sea harbors four representative marine ecosystems, including coral reefs, mangroves, seaweed beds, and coastal wetlands, which are rich in underexplored marine biological resources that produce a plethora of diversified MNPs. In our ongoing efforts to discover novel and biologically active MNPs from the Beibu Gulf, we provide a systematic overview of the sources, chemical structures, and bioactive properties of a total of 477 new MNPs derived from the Beibu Gulf, citing 133 references and covering the literature from the first report in November 2003 up to September 2022. These reviewed MNPs were structurally classified into polyketides (43%), terpenoids (40%), nitrogen-containing compounds (12%), and glucosides (5%), which mainly originated from microorganisms (52%) and macroorganisms (48%). Notably, they were predominantly found with cytotoxic, antibacterial, and anti-inflammatory activities. This review will shed light on these untapped Beibu Gulf-derived MNPs as promising lead compounds for the development of new drugs.

Fluorinated derivatives of tetrahydroaltersolanol molecule on COVID-19, HIV, and HTLV protease by DFT and molecular docking approaches

Structural, optoelectronic, and biological properties of tetrahydroaltersolanol (C₁₆H₂₀O₇) and fluorinated derivatives are calculated using density functional theory (DFT) and molecular docking approaches. It is shown that the pure C₁₆H₂₀O₇ molecule has a direct HOMO-LUMO energy gap about 3.1 eV. The substitution of F atom at A category decreases the electronic energy gap, while it is constant at B category. In A category, the behavior of the pure molecule changed from insulator to semiconductor with various substitution of F atom. The electronic properties were depended on the F sites in the pure molecule. The molecular electrical transport properties and charge-transfer possibilities increase with decreasing energy gap. The pure C₁₆H₂₀O₇ molecule with high energy gap has low chemical reactivity and substitution of F atom at considered molecule increases chemical reactivity. Obtained results show that F-O bonds in trifurcation bonds of C₁₆H₁₉O₇(F14), C₁₆H₁₉O₇(F16), and C₁₆H₁₉O₇(F17) molecules play a key role in confronting with COVID-19, HIV, and HTLV proteases, respectively. Optical spectra, such as the dielectric functions, electron energy-loss spectroscopy, refractive index, extinction coefficient, and reflection spectra show that fluorinated derivatives of C₁₆H₂₀O₇ at B category can be used in the new drugs.

Secondary Metabolites from Coral-Associated Fungi: Source, Chemistry and Bioactivities

Our study of the secondary metabolites of coral-associated fungi produced a valuable and extra-large chemical database. Many of them exhibit strong biological activity and can be used for promising drug lead compounds. Serving as an epitome of the most promising compounds, which take the ultra-new skeletons and/or remarkable bioactivities, this review presents an overview of new compounds and bioactive compounds isolated from coral-associated fungi, covering the literature from 2010 to 2021. Its scope included 423 metabolites, focusing on the bioactivity and structure diversity of these compounds. According to structure, these compounds can be roughly classified as terpenes, alkaloids, peptides, aromatics, lactones, steroids, and other compounds. Some of them described in this review possess a wide range of bioactivities, such as anticancer, antimicrobial, antifouling, and other activities. This review aims to provide some significant chemical and/or biological enlightenment for the study of marine natural products and marine drug development in the future.

Alternarialone A, a new curvularin-type metabolite from the mangrove-derived fungus Alternaria longipes

Alternarialone A (1), one new curvularin derivative, and two known compounds (2 and 3) were isolated from the crude extract of the mangrove-derived fungus Alternaria longipes. Their structures were elucidated by comprehensive spectroscopic analyses, including MS and NMR spectroscopic data. The absolute configuration of 1 was assigned by ¹³C NMR calculations and a comparison of electronic circular dichroism (ECD) spectra. All compounds were evaluated for their antibacterial activities against Helicobacter pylori. Compounds 2 and 3 showed antibacterial activities against H. pylori G27 with MIC values of 8 and 16 µg/ml, respectively, while compound 3 also displayed antibacterial activity against H. pylori BHKS159 with the MIC value of 16 µg/ml.

Chemical diversity, medicinal potentialities, biosynthesis, and pharmacokinetics of anthraquinones and their congeners derived from marine fungi: a comprehensive update

Marine fungi receive excessive attention as prolific producers of structurally unique secondary metabolites, offering promising potential as substitutes or conjugates for current therapeutics, whereas existing research has only scratched the surface in terms of secondary metabolite diversity and potential industrial applications as only a small share of bioactive natural products have been identified from marine-derived fungi thus far. Anthraquinones derived from filamentous fungi are a distinct large group of polyketides containing compounds which feature a common 9,10-dioxoanthracene core, while their derivatives are generated through enzymatic reactions such as methylation, oxidation, or dimerization to produce a large variety of anthraquinone derivatives. A considerable number of reported anthraquinones and their derivatives have shown significant biological activities as well as highly economical, commercial, and biomedical potentialities such as anticancer, antimicrobial, antioxidant, and anti-inflammatory activities. Accordingly, and in this context, this review comprehensively covers the state-of-art over 20 years of about 208 structurally diverse anthraquinones and their derivatives isolated from different species of marine-derived fungal genera along with their reported bioactivity wherever applicable. Also, in this manuscript, we will present in brief recent insights centred on their experimentally proved biosynthetic routes. Moreover, all reported compounds were extensively investigated for their in-silico drug-likeness and pharmacokinetics properties which intriguingly highlighted a list of 20 anthraquinone-containing compounds that could be considered as potential drug lead scaffolds.

Halo- and Thiocarbazomycins from Coral- and Coral Reef Sands-Derived Actinomycetes

Four actinomycete strains isolated from the coral Acropora austera and coral sand samples from the South China Sea, were found to produce a series of halogenated compounds baring similar ultraviolet absorption based on the analysis of HPLC and LC-MS. The production titers of halogenated compounds from Streptomyces diacarni SCSIO 64983 exceeded those of other similar strains leading us to focus on SCSIO 64983. Four new thiocarbazomycins A–B (1–2), chlocarbazomycin E (3), and brocarbazomycin A (4), together with three known chlocarbazomycins A–C (5–7) containing a carbazole core were identified, and their structures were determined using a combination of spectroscopic analysis including HRESIMS, 1D and 2D NMR. Structurally speaking, compounds 1 and 2 have the rare sulfur-containing carbazole nuclei, and 3 and 4 contain Cl and Br atoms, respectively. Although these compounds have not yet been found to have obvious biological activity, their discovery highlights the role of molecular libraries in subsequent drug discovery campaigns.

Altereporenes A-E, five epoxy octa-hydronaphthalene polyketides produced by an endophytic fungus Alternaria sp. YUD20002

Five previously undescribed epoxy octa-hydronaphthalene polyketides, altereporenes A-E (1-5) were isolated from rice culture of the endophytic fungus Alternaria sp. YUD20002 derived from the tubers of Solanum tuberosum. Their structures were determined on the basis of comprehensive spectroscopic analyses, while the absolute configurations were elucidated by the comparison of experimental and calculated specific rotations. Meanwhile, the antimicrobial, cytotoxic, anti-inflammatory and acetylcholinesterase inhibitory activities of compounds 1-5 were also investigated.

Anthraquinones and Their Analogues from Marine-Derived Fungi: Chemistry and Biological Activities

Anthraquinones are an interesting chemical class of polyketides since they not only exhibit a myriad of biological activities but also contribute to managing ecological roles. In this review article, we provide a current knowledge on the anthraquinoids reported from marine-derived fungi, isolated from various resources in both shallow waters such as mangrove plants and sediments of the mangrove habitat, coral reef, algae, sponges, and deep sea. This review also tentatively categorizes anthraquinone metabolites from the simplest to the most complicated scaffolds such as conjugated xanthone–anthraquinone derivatives and bianthraquinones, which have been isolated from marine-derived fungi, especially from the genera Apergillus, Penicillium, Eurotium, Altenaria, Fusarium, Stemphylium, Trichoderma, Acremonium, and other fungal strains. The present review, covering a range from 2000 to 2021, was elaborated through a comprehensive literature search using the following databases: ACS publications, Elsevier, Taylor and Francis, Wiley Online Library, MDPI, Springer, and Thieme. Thereupon, we have summarized and categorized 296 anthraquinones and their derivatives, some of which showed a variety of biological properties such as enzyme inhibition, antibacterial, antifungal, antiviral, antitubercular (against Mycobacterium tuberculosis), cytotoxic, anti-inflammatory, antifouling, and antioxidant activities. In addition, proposed biogenetic pathways of some anthraquinone derivatives are also discussed.

Marine fungal metabolites as a source of drug leads against aquatic pathogens

Aquatic pathogens, including Vibrio, Edwardsiella, Pseudomonas, and Aeromonas, which could result in bacterial diseases to aquaculture, have seriously threatened the world aquaculture production. Marine-derived fungi, which could produce novel secondary metabolites with significant antibacterial activity, may be an important source for finding effective agents against aquatic pathogens. In this review, a systematically overview of the harm of several aquatic pathogens, and 134 antibacterial secondary metabolites against aquatic pathogens from 13 genera of marine-derived fungi, were summarized and concluded. The aim of this review is to find out the relationships between activity and structural type, between bioactive compounds and their hosts, and so on. Altogether, 95 references published during 1997-2021 were cited. KEY POINTS: •Aquatic pathogens, which could result in bacterial diseases to aquaculture, were described. •Marine fungal metabolites with activities against aquatic pathogens were summarized. •The distributions of these bioactive marine fungal metabolites were analyzed.

Seawater fungi-derived compound screening to identify novel small molecules against dengue virus NS5 methyltransferase and NS2B/NS3 protease

Dengue fever is a virus spread by mosquitoes that has no effective treatment or vaccination. Several dengue cases combined with the current COVID-19 pandemic, exacerbates this problem. Two proteins, NS5 methyltransferase and NS2B/NS3 primary protease complexes, are crucial for dengue viral replication and are the target sites for antiviral development. Thus, this study screened published literature and identified 162 marine fungus-derived compounds with active bioavailability. Following Lipinski's rules and antiviral property prediction, 41 compounds were selected for docking with NS5 methyltransferase and NS2B/NS3 protease (PDB ID: 6IZZ and 2FOM) to evaluate compounds that could stop the action of dengue viral protein complexes. To find the best candidates, computational ADME, toxicity, and drug target prediction were performed to estimate the potential of the multi-targeting fungal-derived natural compounds. Analyzing the result from 41 compounds, Chevalone E (−13.5 kcal/mol), Sterolic acid (−10.3 kcal/mol) showed higher binding energy against dengue NS2B/NS3 protease; meanwhile, Chevalone E (−12.0 kcal/mol), Brevione K (−7.4 kcal/mol), had greater binding affinity against NS5 methyltransferase. Consequently, this study suggests that Chevalone E is an effective inhibitor of NS5 methyltransferase and NS2B/NS3 protease. Ligand-based virtual screening from DrugBank was utilized to predict biologically active small compounds against dengue virus NS2B/NS3 major protease and NS5 methyltransferase. Both licensed medications, estramustine (DB01196) and quinestrol (DB04575), were found to be similar to Chevalone E, with prediction scores of 0.818 and 0.856, respectively. In addition, cholic acid (DB02659), acitretin (DB00459), and mupirocin (DB00410) are similar to Sterolic acid, zidovudine (DB00495), imipenem (DB01598), and nadolol (DB01203) are similar to Brocazine A, and budesonide (DB01222) and colchicine (DB01394) are related to Brevione K. These findings suggest that these could be feasible dengue virus treatment options, meaning that more research is needed.

From natural products to HDAC inhibitors: An overview of drug discovery and design strategy

Histone deacetylases (HDACs) play a key role in the homeostasis of protein acetylation in histones and have recently emerged as a therapeutic target for numerous diseases. The inhibition of HDACs may block angiogenesis, arrest cell growth, and lead to differentiation and apoptosis in tumour cells. Thus, HDAC inhibitors (HDACi) have received increasing attention and many of which are developed from natural sources. In the past few decades, naturally occurring HDACi have been identified to have potent anticancer activities, some of which have demonstrated promising therapeutic effects on haematological malignancies. In this review, we summarized the discovery and modification of HDAC inhibitors from natural sources, novel drug design that uses natural products as parent nuclei, and dual target design strategies that combine HDAC with non-HDAC targets.

Identification, Characterization, and Evaluation of Nematophagous Fungal Species of Arthrobotrys and Tolypocladium for the Management of Meloidogyne incognita

Root-knot nematodes belonging to the genus Meloidogyne are agriculturally important pests, and biocontrol strategies offer safer alternatives for their management. In the present study, two fungal species from Indian soils were identified as Arthrobotrys thaumasia and Tolypocladium cylindrosporum based on morphological characteristics and further confirmed using molecular markers. In vitro evaluation of A. thaumasia against M. incognita and Caenorhabditis elegans showed 82 and 73% parasitism, respectively, whereas T. cylindrosporum gave 65.2 and 57.7% parasitism, respectively. Similarly, culture filtrates of A. thaumasia caused 57.7 and 53.7% mortality of M. incognita and C. elegans, respectively, whereas T. cylindrosporum caused higher mortality of 87.3 and 64%, respectively. Besides, greenhouse evaluation of both fungi against M. incognita infecting tomato significantly reduced nematode disease burden reflecting parasitic success measured as the total number of galls, egg masses, eggs per egg mass, and derived nematode multiplication factor. Application of A. thaumasia and T. cylindrosporum reduced nematode multiplication factor by 80 and 95%, respectively, compared with control. General metabolite profiling of tested fungi using gas chromatography–mass spectrometry and ultra-performance liquid chromatography–quadrupole/time of flight mass spectrometry reported for the first time here showed presence of various volatile and non-volatile compounds with nematicidal activity, viz., trimethyl-heptadiene, methyl-hexadecanol, dodecadienal, decane, terpendole E, dodecane, acetamido-6-anthraquinone, and hexadecanol. Also, other compounds such as undecane, dibutyl-disulfide, octadecenal, paganin, talathermophilin, dactylarin, tolypyridone A, tolypyridone B, pyridoxatin, and destruxin were identified, reported in the literature to possess antibacterial, antifungal, and insecticidal properties. This is the first report of the occurrence of both fungi from India and pioneer demonstration of T. cylindrosporum for root-knot nematode management.

Diversity and chemical fingerprinting of endo-metabolomes from endophytes associated with Ampelopsis grossedentata (Hand.-Mazz.) W. T. Wang possessing antibacterial activity against multidrug resistant bacterial pathogens

BACKGROUND

Serious infections caused by bacteria and their resistance to antibiotics are one of the biggest healthcare threats to mankind. Therefore, the present study aimed to isolate endophytes from medicinal plant Ampelopsis grossedentata, an endemic species of Western Hubei, China and to investigate its antibacterial efficacy and chemical diversity of the secondary metabolites.

METHODS

The antibacterial potential of the endophytes was evaluated by disc diffusion method against a panel of eleven type strains and some multidrug resistant pathogenic bacteria. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) were estimated by broth microdilution using iodonitrotetrazolium chloride assay. Further, the chemical diversity of the metabolites was estimated using LC-Q-TOF-MS/MS and GC-MS fingerprinting.

RESULTS

Four endophytic fungi were isolated from the tender shoot of A. grossedentata; they were identified as Fusarium graminearum TC-1, Phomopsis mali TC-3, Pestalotiopsis maculans TC-5 and Alternaria alternata TC-11. Among the endophytes screened, A. alternata TC-11 exhibited significant antibacterial activity with the zones of inhibition ranging from 13.72 ± 0.30 to 21.76 ± 0.53 mm against all the tested type strains and multidrug resistant bacterial pathogens. Further, it showed significant antibacterial activity with MIC values ranging from 0.37 to 3.00 μg/mL. The combined LC-Q-TOF-MS/MS and GC-MS analyses of active extract revealed that alternarian acid, altertenuol, dimethyl sulfone, docosane, dodecane, duclauxin, ergosta-4,6,8(14),22-tetraen-3-one, ethyl 6-cyano-5-oxo-1-phenyl-7-thiophen-2-yl-[1,2,4]triazolo[4,3-a]pyrimidine-3-carboxylate, heptacosane, linoleic acid, neodecanoic acid, oxiranylmethyl ester, pentadecane, verrulactone E, 2,6,11-Trimethyldodecane and 4-[(E,4R,6R)-11-(furan-3-yl)-6-hydroxy-4,8-dimethylundec-8-enyl]-2-hydroxy-2H-furan-5-one were the most abundant compounds present which were responsible for the significant antibacterial activity.

CONCLUSIONS

To our knowledge, this is the first report of fungal endophytes isolated from the tender shoot of A. grossedentata with bacteriostatic and bactericidal activities. Our finding provides a new insight into the antibacterial potential of endophytes and envisages the possibility of using them for drug discovery.

Antiviral fungal metabolites and some insights into their contribution to the current COVID-19 pandemic

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) outbreak, which started in late 2019, drove the scientific community to conduct innovative research to contain the spread of the pandemic and to care for those already affected. Since then, the search for new drugs that are effective against the virus has been strengthened. Featuring a relatively low cost of production under well-defined methods of cultivation, fungi have been providing a diversity of antiviral metabolites with unprecedented chemical structures. In this review, we present viral RNA infections highlighting SARS-CoV-2 morphogenesis and the infectious cycle, the targets of known antiviral drugs, and current developments in this area such as drug repurposing. We also explored the metabolic adaptability of fungi during fermentation to produce metabolites active against RNA viruses, along with their chemical structures, and mechanisms of action. Finally, the state of the art of research on SARS-CoV-2 inhibitors of fungal origin is reported, highlighting the metabolites selected by docking studies.

Molecular docking of secondary metabolites from Indonesian marine and terrestrial organisms targeting SARS-CoV-2 ACE-2, M pro, and PL pro receptors

With the uncontrolled spread of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), development and distribution of antiviral drugs and vaccines have gained tremendous importance. This study focused on two viral proteases namely main protease (Mpro) and papain-like protease (PLpro) and human angiotensin-converting enzyme (ACE-2) to identify which of these are essential for viral replication. We screened 102 secondary metabolites against SARS-CoV-2 isolated from 36 terrestrial plants and 36 marine organisms from Indonesian biodiversity. These organisms are typically presumed to have antiviral effects, and some of them have been used as an immunomodulatory activity in traditional medicine. For the molecular docking procedure to obtain Gibbs free energy value (∆G), toxicity, ADME and Lipinski, AutoDock Vina was used. In this study, five secondary metabolites, namely corilagin, dieckol, phlorofucofuroeckol A, proanthocyanidins, and isovitexin, were found to inhibit ACE-2, Mpro, and PLpro receptors in SARS-CoV-2, with a high affinity to the same sites of ptilidepsin, remdesivir, and chloroquine as the control molecules. This study was delimited to molecular docking without any validation by simulations concerned with molecular dynamics. The interactions with two viral proteases and human ACE-2 may play a key role in developing antiviral drugs for five active compounds. In future, we intend to investigate antiviral drugs and the mechanisms of action by in vitro study.

Marine Natural Products as a Source of Drug Leads against Respiratory Viruses: Structural and Bioactive Diversity

Respiratory viruses, including influenza virus, respiratory syncytial virus, coronavirus, etc., have seriously threatened the human health. For example, the outbreak of severe acute respiratory syndrome coronavirus, SARS, affected a large number of countries around the world. Marine organisms, which could produce secondary metabolites with novel structures and abundant biological activities, are an important source for seeking effective drugs against respiratory viruses. This report reviews marine natural products with activities against respiratory viruses, the emphasis of which was put on structures and antiviral activities of these natural products. This review has described 167 marinederived secondary metabolites with activities against respiratory viruses published from 1981 to 2019. Altogether 102 references are cited in this review article.

Species Diversity and Secondary Metabolites of Sarcophyton-Associated Marine Fungi

Soft corals are widely distributed across the globe, especially in the Indo-Pacific region, with Sarcophyton being one of the most abundant genera. To date, there have been 50 species of identified Sarcophyton. These soft corals host a diverse range of marine fungi, which produce chemically diverse, bioactive secondary metabolites as part of their symbiotic nature with the soft coral hosts. The most prolific groups of compounds are terpenoids and indole alkaloids. Annually, there are more bio-active compounds being isolated and characterised. Thus, the importance of the metabolite compilation is very much important for future reference. This paper compiles the diversity of Sarcophyton species and metabolites produced by their associated marine fungi, as well as the bioactivity of these identified compounds. A total of 88 metabolites of structural diversity are highlighted, indicating the huge potential these symbiotic relationships hold for future research.

Marine Anthraquinones: Pharmacological and Toxicological Issues

The marine ecosystem, populated by a myriad of animals, plants, and microorganisms, is an inexhaustible reservoir of pharmacologically active molecules. Among the multiple secondary metabolites produced by marine sources, there are anthraquinones and their derivatives. Besides being mainly known to be produced by terrestrial species, even marine organisms and the uncountable kingdom of marine microorganisms biosynthesize anthraquinones. Anthraquinones possess many different biological activities, including a remarkable antitumor activity. However, due to their peculiar chemical structures, anthraquinones are often associated with toxicological issues, even relevant, such as genotoxicity and mutagenicity. The aim of this review is to critically describe the anticancer potential of anthraquinones derived from marine sources and their genotoxic and mutagenic potential. Marine-derived anthraquinones show a promising anticancer potential, although clinical studies are missing. Additionally, an in-depth investigation of their toxicological profile is needed before advocating anthraquinones as a therapeutic armamentarium in the oncological area.

Marine endophytic fungal metabolites: A whole new world of pharmaceutical therapy exploration

The growing threat arises due to diseases such as cancer and the infections around the world leading to a critical requirement for novel and constructive compounds with unique ways of action capable of combating these deadly diseases. At present, it is evident that endophytic fungi constitute an enormous as well as comparatively untapped source of great biodiversity that can be considered as a wellspring of effective novel natural products for medical, agricultural and industrial use. Marine endophytic fungi have been found in every marine plants (algae, seagrass, driftwood, mangrove plants), marine vertebrates (mainly, fish) or marine invertebrates (mainly, sponge and coral) inter- and intra-cellular without causing any palpable symptoms of illness. Since evolution of microbes and eukaryotes to a higher level, coevolution has resulted in specific interaction mechanisms. Endophytic fungi are known to influence the life cycle and are necessary for the homeostasis of their eukaryotic hosts and the chemical signals of their host have been shown to activate gene expression in endophytes to induce expression of endophytic secondary metabolites. Marine endophytic fungi are receiving increasing attention by chemists because of their varied and structurally unmatched compounds that have strong biological roles in life as lead pharmaceutical compounds, including anticancer, antiviral, insulin mimetic, antineurodegenerative, antimicrobial, antioxidant and immuno-suppressant compounds. Moreover, fungal endophytes proved to have different biological activities for exploitation in the environmental and agricultural sustainability.

Emerging paradigms of viral diseases and paramount role of natural resources as antiviral agents

In the current scenario, the increasing prevalence of diverse microbial infections as well as emergence and re-emergence of viral epidemics with high morbidity and mortality rates are major public health threat. Despite the persistent production of antiviral drugs and vaccines in the global market, viruses still remain as one of the leading causes of deadly human diseases. Effective control of viral diseases, particularly Zika virus disease, Nipah virus disease, Severe acute respiratory syndrome, Coronavirus disease, Herpes simplex virus infection, Acquired immunodeficiency syndrome, and Ebola virus disease remain promising goal amidst the mutating viral strains. Current trends in the development of antiviral drugs focus solely on testing novel drugs or repurposing drugs against potential targets of the viruses. Compared to synthetic drugs, medicines from natural resources offer less side-effect to humans and are often cost-effective in the productivity approaches. This review intends not only to emphasize on the major viral disease outbreaks in the past few decades and but also explores the potentialities of natural substances as antiviral traits to combat viral pathogens. Here, we spotlighted a comprehensive overview of antiviral components present in varied natural sources, including plants, fungi, and microorganisms in order to identify potent antiviral agents for developing alternative therapy in future.

Antioxidant Molecules from Marine Fungi: Methodologies and Perspectives

The marine environment represents a prosperous existing resource for bioprospecting, covering 70% of the planet earth, and hosting a huge biodiversity. Advances in the research are progressively uncovering the presence of unknown microorganisms, which have evolved unique metabolic and genetic pathways for the production of uncommon secondary metabolites. Fungi have a leading role in marine bioprospecting since they represent a prolific source of structurally diverse bioactive metabolites. Several bioactive compounds from marine fungi have already been characterized including antibiotics, anticancer, antioxidants and antivirals. Nowadays, the search for natural antioxidant molecules capable of replacing those synthetic currently used, is an aspect that is receiving significant attention. Antioxidants can inactivate reactive oxygen and nitrogen species, preventing the insurgence of several degenerative diseases including cancer, autoimmune disorders, cardiovascular and neurodegenerative diseases. Moreover, they also find applications in different fields, including food preservation, healthcare and cosmetics. This review focuses on the production of antioxidants from marine fungi. We begin by proposing a survey of the available tools suitable for the evaluation of antioxidants, followed by the description of various classes of marine fungi antioxidants together with their extraction strategies. In addition, a view of the future perspectives and trends of these natural products within the "blue economy" is also presented.

Fungal Bioactive Anthraquinones and Analogues

This review, covering the literature from 1966 to the present (2020), describes naturally occurring fungal bioactive anthraquinones and analogues biosynthesized by the acetate route and concerning several different functionalized carbon skeletons. Hydrocarbons, lipids, sterols, esters, fatty acids, derivatives of amino acids, and aromatic compounds are metabolites belonging to other different classes of natural compounds and are generated by the same biosynthetic route. All of them are produced by plant, microorganisms, and marine organisms. The biological activities of anthraquinones and analogues comprise phytotoxic, antibacterial, antiviral, anticancer, antitumor, algicide, antifungal, enzyme inhibiting, immunostimulant, antiplatelet aggregation, cytotoxic, and antiplasmodium activities. The review also covers some practical industrial applications of anthraquinones.

Secondary Metabolites with Nitric Oxide Inhibition from Marine-Derived Fungus Alternaria sp. 5102

Two new benzofurans, alternabenzofurans A and B (1 and 2) and two new sesquiterpenoids, alternaterpenoids A and B (3 and 4), along with 18 known polyketides (5−22), were isolated from the marine-derived fungus Alternaria sp. 5102. Their structures were elucidated on the basis of extensive spectroscopic analyses (1D and 2D NMR, HR-ESIMS, and ECD) and X-ray crystallography, as well as the modified Mosher’s method. Compounds 2, 3, 5, 7, 9–18, and 20–22 exhibited potent anti-inflammatory activity by inhibiting the production of NO in RAW264.7 cells activated by lipopolysaccharide with IC₅₀ values in the range from 1.3 to 41.1 μM. Structure-activity relationships of the secondary metabolites were discussed.

Ten-Year Research Update Review: Antiviral Activities from Marine Organisms

Oceans cover more than 70 percent of the surface of our planet and are characterized by huge taxonomic and chemical diversity of marine organisms. Several studies have shown that marine organisms produce a variety of compounds, derived from primary or secondary metabolism, which may have antiviral activities. In particular, certain marine metabolites are active towards a plethora of viruses. Multiple mechanisms of action have been found, as well as different targets. This review gives an overview of the marine-derived compounds discovered in the last 10 years. Even if marine organisms produce a wide variety of different compounds, there is only one compound available on the market, Ara-A, and only another one is in phase I clinical trials, named Griffithsin. The recent pandemic emergency caused by SARS-CoV-2, also known as COVID-19, highlights the need to further invest in this field, in order to shed light on marine compound potentiality and discover new drugs from the sea.

Streptomyces albogriseolus SY67903 Produces Eunicellin Diterpenoids Structurally Similar to Terpenes of the Gorgonian Muricella sibogae, the Bacterial Source

Microeunicellols A (1) and B (2), two undescribed eunicellin diterpenoids, were isolated from the culture of a bacterial symbiont, Streptomyces albogriseolus SY67903. Their structures, including absolute configurations revealed by spectroscopic data and single-crystal X-ray diffraction analysis, are closely related with the diterpenoids from its host, a South China Sea gorgonian, Muricella sibogae. This is the first report of eunicellin diterpenoids, commonly coral-derived, from a bacterial symbiont of coral. The chemical metabolic relationship between the bacterium and its host is discussed. Biological evaluation revealed that compound 1 possessed cytotoxicities against several human cancer cell lines.

Fungi as a Potential Source of Pigments: Harnessing Filamentous Fungi

The growing concern over the harmful effects of synthetic colorants on both the consumer and the environment has raised a strong interest in natural coloring alternatives. As a result the worldwide demand for colorants of natural origin is rapidly increasing in the food, cosmetic and textile sectors. Natural colorants have the capacity to be used for a variety of industrial applications, for instance, as dyes for textile and non-textile substrates such as leather, paper, within paints and coatings, in cosmetics, and in food additives. Currently, pigments and colorants produced through plants and microbes are the primary source exploited by modern industries. Among the other non-conventional sources, filamentous fungi particularly ascomycetous and basidiomycetous fungi (mushrooms), and lichens (symbiotic association of a fungus with a green alga or cyanobacterium) are known to produce an extraordinary range of colors including several chemical classes of pigments such as melanins, azaphilones, flavins, phenazines, and quinines. This review seeks to emphasize the opportunity afforded by pigments naturally found in fungi as a viable green alternative to current sources. This review presents a comprehensive discussion on the capacity of fungal resources such as endophytes, halophytes, and fungi obtained from a range or sources such as soil, sediments, mangroves, and marine environments. A key driver of the interest in fungi as a source of pigments stems from environmental factors and discussion here will extend on the advancement of greener extraction techniques used for the extraction of intracellular and extracellular pigments. The search for compounds of interest requires a multidisciplinary approach and techniques such as metabolomics, metabolic engineering and biotechnological approaches that have potential to deal with various challenges faced by pigment industry.

Chemical and Bioactive Marine Natural Products of Coral-Derived Microorganisms (2015-2017)

Coral-derived microorganisms are known for their inherent ability to produce novel products of pharmaceutical importance. Nearly 260 marine natural products (MNPs) have been isolated from coral-derived microorganisms till 2014. In the last three years, 118 MNPs have been isolated from coral-associated microorganisms including 46 new compounds, two with a novel skeleton, and four new natural products. Most of them exhibited in vitro or in vivo activities against tumor cell lines, parasites, pathogenic bacteria, fungi and virus. We reviewed the natural products reported from 2015 to 2017 that have a wide range of bioactivities against different biological targets.

Secondary Metabolites from Marine-Derived Fungi from China

Marine-derived fungi play an important role in the search for structurally unique secondary metabolites, some of which show promising pharmacological activities that make them useful leads for drug discovery. Marine natural product research in China in general has made enormous progress in the last two decades as described in this chapter on fungal metabolites. This contribution covers 613 new natural products reported from 2001 to 2017 from marine-derived fungi obtained from algae, sponges, corals, and other marine organisms from Chinese waters. The genera Aspergillus (170 new natural products, 28%) and Penicillium (70 new natural products, 11%) were the main fungal producers of new natural products during the time period covered, whereas sponges (184 new natural products, 30%) were the most abundant source of new natural products, followed by corals (154 new natural products, 25%) and algae (130 new natural products, 21%). Close to 40% of all natural products covered in this contribution displayed various bioactivities. The major bioactivities reported were cytotoxicity against different cancer cell lines, antimicrobial (mainly antibacterial) activity, and antiviral activity, which accounted for 13%, 9%, and 3% of all natural products reported. In terms of structural classes, polyketides (188 new natural products, 31%) play a dominant role, and if prenylated polyketides and nitrogen-containing polyketides (included in meroterpenes and alkaloids in this contribution) are taken into account, their total number even exceeds 50%. Nitrogen-containing compounds including peptides (65 new natural products, 10%) and alkaloids (103 new natural products, 17%) are the second largest group.

Two new unsaturated fatty acids from the mangrove rhizosphere soil-derived fungus Penicillium javanicum HK1-22

Two new unsaturated fatty acids, 6R,8R-dihydroxy-9Z,12Z-octadecadienoic acid (1) and methyl-6R,8R-dihydroxy-9Z,12Z-octadecadienoate (2), and two known 9Z,12Z-octadecadienoic acid analogues (3, 4) together with a known sesquiterpenoid (5) were isolated from the mangrove rhizosphere soil-derived fungus Penicillium javanicum HK1-22. An acetonide derivative (1a) from 1 was also prepared. The relative configuration of 1 was determined by analysis of the 1D and 2D NOE spectra of 1a. The absolute configuration of 1 was assigned on the basis of biogenetic considerations. The antifungal activity of the high yield compound 5 was evaluated against four strains of crop pathogens and it showed significant antifungal activities against all the tested strains.

Coral and Coral-Associated Microorganisms: A Prolific Source of Potential Bioactive Natural Products

Marine invertebrates and their associated microorganisms are rich sources of bioactive compounds. Among them, coral and its associated microorganisms are promising providers of marine bioactive compounds. The present review provides an overview of bioactive compounds that are produced by corals and coral-associated microorganisms, covering the literature from 2010 to March 2019. Accordingly, 245 natural products that possess a wide range of potent bioactivities, such as anti-inflammatory, cytotoxic, antimicrobial, antivirus, and antifouling activities, among others, are described in this review.

Coral and Coral-Associated Microorganisms: A Prolific Source of Potential Bioactive Natural Products

Marine invertebrates and their associated microorganisms are rich sources of bioactive compounds. Among them, coral and its associated microorganisms are promising providers of marine bioactive compounds. The present review provides an overview of bioactive compounds that are produced by corals and coral-associated microorganisms, covering the literature from 2010 to March 2019. Accordingly, 245 natural products that possess a wide range of potent bioactivities, such as anti-inflammatory, cytotoxic, antimicrobial, antivirus, and antifouling activities, among others, are described in this review.

Anthraquinone Derivatives from a Marine-Derived Fungus Sporendonema casei HDN16-802

Five new anthraquinone derivatives, auxarthrols D-H (1-5), along with two known analogues (6-7), were obtained from the culture of the marine-derived fungus Sporendonema casei. Their structures, including absolute configurations, were established on the basis of NMR, HRESIMS, and circular dichroism (CD) spectroscopic techniques. Among them, compound 4 represents the second isolated anthraquinone derivative with a chlorine atom, which, with compound 6, are the first reported anthraquinone derivatives with anticoagulant activity. Compounds 1 and 3 showed cytotoxic activities with IC₅₀ values from 4.5 μM to 22.9 μM, while compounds 1, 3-4, and 6-7 showed promising antibacterial activities with MIC values from 12.5 μM to 200 μM. In addition, compound 7 was discovered to display potential antitubercular activity for the first time.

New Naphtho-γ-Pyrones Isolated from Marine-Derived Fungus Penicillium sp. HK1-22 and Their Antimicrobial Activities

Three novel monomeric naphtho-γ-pyrones, peninaphones A–C (compounds 1–3), along with two known bis-naphtho-γ-pyrones (compounds 4 and 5) were isolated from mangrove rhizosphere soil-derived fungus Penicillium sp. HK1-22. The absolute configurations of compounds 1 and 2 were determined by electronic circular dichroism (ECD) spectra, and the structure of compound 3 was confirmed by single-crystal X-ray diffraction analysis. Compounds 4 and 5 are a pair of hindered rotation isomers. A hypothetical biosynthetic pathway for the isolated monomeric and dimeric naphtho-γ-pyrones is also discussed in this study. Compounds 1–3 showed antibacterial activity against Staphylococcus aureus (ATCC 43300, 33591, 29213, and 25923) with minimum inhibitory concentration (MIC) values in the range of 12.5–50 μg/mL. Compound 3 exhibited significant activity against the rice sheath blight pathogen Rhizoctonia solani.

Bioactive Meroterpenoids and Isocoumarins from the Mangrove-Derived Fungus Penicillium sp. TGM112

Two new meroterpenoids, penicianstinoids A and B (1 and 2), and eight new isocoumarins, peniciisocoumarins A-H (3-10), together with 10 known analogues (11-20) were obtained from the mangrove-derived fungus Penicillium sp. TGM112. The structures and absolute configurations of 1-10 were determined by interpretation of detailed NMR, MS spectroscopic data, X-ray diffraction analyses, modified Mosher's method, and calculated electronic circular dichroism data. Compounds 1-4, 7, 8, 10, 12, 13, and 16 showed growth inhibition activity against newly hatched larvae of Helicoverpa armigera Hubner with IC₅₀ values ranging from 50 to 200 μg/mL, respectively. Compounds 1, 2, and 11-15 displayed activity against Caenorhabditis elegans with EC₅₀ values ranging from 9.4 (± 1.0) to 38.2 (± 0.6) μg/mL, respectively. Compound 1 represents an austinoid-like meroterpenoid that is reported here for the second time, in which a carbon-carbon double bond was oxidized to a carbonyl group at C-1'-C-2'.

Bialternacins A-F, Aromatic Polyketide Dimers from an Endophytic Alternaria sp

Six novel aromatic polyketide dimers, bialternacins A-F (1-6), were isolated from a plant endophytic Alternaria sp. The structures of compounds 1-6 were elucidated on the basis of extensive spectroscopic analysis, single-crystal X-ray diffraction, and electronic circular dichroism analysis. Compounds 1, 2, 5, and 6 were characterized as four pairs of racemic mixtures. Compound (+)-5 was demonstrated to show acetylcholinesterase inhibitory activity with an IC₅₀ value of 15.5 μM. A putative biosynthetic pathway for these compounds was proposed.

Anthraquinone derivatives from a coral associated fungus Stemphylium lycopersici

Two new anthraquinone derivatives, alterporriol Y (1) and macrosporin 2-O-α-D-glucopyranoside (2), together with five known analogues (3-7) were isolated from the fungus Stemphylium lycopersici associated with the gorgonian coral Dichotella gemmacea collected from the South China Sea. Their structures were determined on the basis of detailed spectroscopic analysis and comparison with reported data. The absolute configurations were determined by the ECD method. In an in vitro cytotoxic assay, compound 3 and 4 showed potent effects against HCT-116 and MCF-7 cell lines. Compound 4 also exhibited cytotoxicity toward Huh7 stem cell-like cells.

Novel anthraquinone derivatives as inhibitors of protein tyrosine phosphatases and indoleamine 2,3-dioxygenase 1 from the deep-sea derived fungusAlternaria tenuissimaDFFSCS013

A novel hydroanthraquinone possessing an unprecedented hexacyclic spiro-fused ring system, anthrininone A (1), and two new anthraquinones, anthrininones B and C (2and3), were obtained from the deep-sea derived fungusAlternaria tenuissima.

Bioactive Secondary Metabolites from Octocoral-Associated Microbes-New Chances for Blue Growth

Octocorals (Cnidaria, Anthozoa Octocorallia) are magnificent repositories of natural products with fascinating and unusual chemical structures and bioactivities of interest to medicine and biotechnology. However, mechanistic understanding of the contribution of microbial symbionts to the chemical diversity of octocorals is yet to be achieved. This review inventories the natural products so-far described for octocoral-derived bacteria and fungi, uncovering a true chemical arsenal of terpenes, steroids, alkaloids, and polyketides with antibacterial, antifungal, antiviral, antifouling, anticancer, anti-inflammatory, and antimalarial activities of enormous potential for blue growth. Genome mining of 15 bacterial associates (spanning 12 genera) cultivated from Eunicella spp. resulted in the identification of 440 putative and classifiable secondary metabolite biosynthetic gene clusters (BGCs), encompassing varied terpene-, polyketide-, bacteriocin-, and nonribosomal peptide-synthase BGCs. This points towards a widespread yet uncharted capacity of octocoral-associated bacteria to synthetize a broad range of natural products. However, to extend our knowledge and foster the near-future laboratory production of bioactive compounds from (cultivatable and currently uncultivatable) octocoral symbionts, optimal blending between targeted metagenomics, DNA recombinant technologies, improved symbiont cultivation, functional genomics, and analytical chemistry are required. Such a multidisciplinary undertaking is key to achieving a sustainable response to the urgent industrial demand for novel drugs and enzyme varieties.

Microalgal Microscale Model for Microalgal Growth Inhibition Evaluation of Marine Natural Products

Marine organisms especially sessile invertebrates, such as soft corals, gorgonians and sponges, can survive in the competitive environment mainly relying on their second metabolites with chemoecological effects including allelopathy and algal growth inhibition. It is well known that the microscale models are urgently needed in marine chemoecology assessment to evaluate the algal growth inhibition activity of trace quantity natural products. In this work, a microalgal growth inhibition model was established for microalgal inhibition evaluation of marine natural products with 96-well microplate by automatic fluorescence observation using microplate reader. Subsequently, this model was applied to bioassay-guided isolation and preliminary bioactivity screening of the secondary metabolites from soft corals, gorgonians, sponges and their symbiotic microbes collected from the South China Sea. As a result, fifteen compounds (1‒15) were found to exhibit microalgal growth inhibition activities against at least one of marine microalgae, Karenia mikimotoi, Isochrysis galbana, and Heterosigma akashiwo. Specifically, altersolanol C (13) demonstrated potent activity against K. mikimotoi with the 96h-EC₅₀ value of 1.16 µg/mL, more than four times stronger than that of the positive control K₂Cr₂O₇. It was suggested that the microalgal growth inhibition microscale model is suitable for bioassay-guided isolation and preliminary bioactivity screening of marine natural products.

Penicilindoles A-C, Cytotoxic Indole Diterpenes from the Mangrove-Derived Fungus Eupenicillium sp. HJ002

Three new indole diterpenes, penicilindoles A-C (1-3), were isolated from the mangrove-derived fungus Eupenicillium sp. HJ002. Their planar structures and absolute configurations were determined by interpretation of NMR spectroscopic data, HR-ESIMS, and X-ray diffraction analysis using Cu Kα radiation. The cytotoxic and antibacterial activities were evaluated in vitro; penicilindole A (1) showed cytotoxic activity against human A549 and HepG2 cell lines with IC₅₀ values of 5.5 and 1.5 μM, respectively.

First enantioselective total synthesis of altersolanol A

The first enantioselective total synthesis of altersolanol A was accomplished by Diels–Alder cycloaddition promoted by (R)-3,3′-BINOL/boron Lewis acid.

Harzianumnones A and B: two hydroxyanthraquinones from the coral-derived fungusTrichoderma harzianum

Two new hydroxyanthraquinones, harzianumnones A (1) and B (2), together with seven known analogs (3–9), were isolated from the soft coral-derived fungus Trichoderma harzianum (XS-20090075). Their chemical structures were elucidated by extensive spectroscopic investigation. The absolute configurations of 1 and 2 were determined by ECD calculation and single-crystal X-ray diffraction. Compounds 1 and 2 were identified as a pair of epimers, which are the first example of hydroanthraquinones from T. harzianum. Compounds 7 and 8 exhibited cytotoxicity against hepatoma cell line HepG2 with IC₅₀ values of 2.10 and 9.39 μM, respectively. Compound 7 was still found to show cytotoxicity against cervical cancer cell line HeLa with an IC₅₀ value of 8.59 μM.

Two new hydroxyanthraquinones were isolated from the soft coral-derived fungus Trichoderma harzianum, which are the first examples of hydroanthraquinones from T. harzianum.

Marine Pharmacology in 2012-2013: Marine Compounds with Antibacterial, Antidiabetic, Antifungal, Anti-Inflammatory, Antiprotozoal, Antituberculosis, and Antiviral Activities; Affecting the Immune and Nervous Systems, and Other Miscellaneous Mechanisms of Action

The peer-reviewed marine pharmacology literature from 2012 to 2013 was systematically reviewed, consistent with the 1998–2011 reviews of this series. Marine pharmacology research from 2012 to 2013, conducted by scientists from 42 countries in addition to the United States, reported findings on the preclinical pharmacology of 257 marine compounds. The preclinical pharmacology of compounds isolated from marine organisms revealed antibacterial, antifungal, antiprotozoal, antituberculosis, antiviral and anthelmitic pharmacological activities for 113 marine natural products. In addition, 75 marine compounds were reported to have antidiabetic and anti-inflammatory activities and affect the immune and nervous system. Finally, 69 marine compounds were shown to display miscellaneous mechanisms of action which could contribute to novel pharmacological classes. Thus, in 2012–2013, the preclinical marine natural product pharmacology pipeline provided novel pharmacology and lead compounds to the clinical marine pharmaceutical pipeline, and contributed significantly to potentially novel therapeutic approaches to several global disease categories.

Potential of small-molecule fungal metabolites in antiviral chemotherapy

Various viral diseases, such as acquired immunodeficiency syndrome, influenza, and hepatitis, have emerged as leading causes of human death worldwide. Scientific endeavor since invention of DNA-dependent RNA polymerase of pox virus in 1967 resulted in better understanding of virus replication and development of various novel therapeutic strategies. Despite considerable advancement in every facet of drug discovery process, development of commercially viable, safe, and effective drugs for these viruses still remains a big challenge. Decades of intense research yielded a handful of natural and synthetic therapeutic options. But emergence of new viruses and drug-resistant viral strains had made new drug development process a never-ending battle. Small-molecule fungal metabolites due to their vast diversity, stereochemical complexity, and preapproved biocompatibility always remain an attractive source for new drug discovery. Though, exploration of therapeutic importance of fungal metabolites has started early with discovery of penicillin, recent prediction asserted that only a small percentage (5-10%) of fungal species have been identified and much less have been scientifically investigated. Therefore, exploration of new fungal metabolites, their bioassay, and subsequent mechanistic study bears huge importance in new drug discovery endeavors. Though no fungal metabolites so far approved for antiviral treatment, many of these exhibited high potential against various viral diseases. This review comprehensively discussed about antiviral activities of fungal metabolites of diverse origin against some important viral diseases. This also highlighted the mechanistic details of inhibition of viral replication along with structure-activity relationship of some common and important classes of fungal metabolites.