Anthraquinones, Diphenyl Ethers, and Their Derivatives from the Culture of the Marine Sponge-Associated Fungus Neosartorya spinosa KUFA 1047

Meirols A-C: Bioactive Catecholic Compounds from the Marine-Derived Fungus Meira sp. 1210CH-42

Three new catecholic compounds, named meirols A-C (2-4), and one known analog, argovin (1), were isolated from the marine-derived fungus Meira sp. 1210CH-42. Their structures were determined by extensive analysis of 1D, 2D NMR, and HR-ESIMS spectroscopic data. Their absolute configurations were elucidated based on ECD calculations. All the compounds exhibited strong antioxidant capabilities with EC50 values ranging from 6.01 to 7.47 μM (ascorbic acid, EC50 = 7.81 μM), as demonstrated by DPPH radical scavenging activity assays. In the α-glucosidase inhibition assay, 1 and 2 showed potent in vitro inhibitory activity with IC50 values of 184.50 and 199.70 μM, respectively (acarbose, IC50 = 301.93 μM). Although none of the isolated compounds exhibited cytotoxicity against one normal and six solid cancer cell lines, 1 exhibited moderate cytotoxicity against the NALM6 and RPMI-8402 blood cancer cell lines with GI50 values of 9.48 and 21.00 μM, respectively. Compound 2 also demonstrated weak cytotoxicity against the NALM6 blood cancer cell line with a GI50 value of 29.40 μM.

The Chemical Space of Marine Antibacterials: Diphenyl Ethers, Benzophenones, Xanthones, and Anthraquinones

The emergence of multiresistant bacteria and the shortage of antibacterials in the drug pipeline creates the need to search for novel agents. Evolution drives the optimization of the structure of marine natural products to act as antibacterial agents. Polyketides are a vast and structurally diverse family of compounds that have been isolated from different marine microorganisms. Within the different polyketides, benzophenones, diphenyl ethers, anthraquinones, and xanthones have shown promising antibacterial activity. In this work, a dataset of 246 marine polyketides has been identified. In order to characterize the chemical space occupied by these marine polyketides, molecular descriptors and fingerprints were calculated. Molecular descriptors were analyzed according to the scaffold, and principal component analysis was performed to identify the relationships among the different descriptors. Generally, the identified marine polyketides are unsaturated, water-insoluble compounds. Among the different polyketides, diphenyl ethers tend to be more lipophilic and non-polar than the remaining classes. Molecular fingerprints were used to group the polyketides according to their molecular similarity into clusters. A total of 76 clusters were obtained, with a loose threshold for the Butina clustering algorithm, highlighting the large structural diversity of the marine polyketides. The large structural diversity was also evidenced by the visualization trees map assembled using the tree map (TMAP) unsupervised machine-learning method. The available antibacterial activity data were examined in terms of bacterial strains, and the activity data were used to rank the compounds according to their antibacterial potential. This potential ranking was used to identify the most promising compounds (four compounds) which can inspire the development of new structural analogs with better potency and absorption, distribution, metabolism, excretion, and toxicity (ADMET) properties.

Advances in Natural Products from the Marine-Sponge-Associated Microorganisms with Antimicrobial Activity in the Last Decade

Microorganisms are the dominating source of food and nutrition for sponges and play an important role in sponge structure, chemical defense, excretion and evolution. In recent years, plentiful secondary metabolites with novel structures and specific activities have been identified from sponge-associated microorganisms. Additionally, as the phenomenon of the drug resistance of pathogenic bacteria is becoming more and more common, it is urgent to discover new antimicrobial agents. In this paper, we reviewed 270 secondary metabolites with potential antimicrobial activity against a variety of pathogenic strains reported in the literature from 2012 to 2022. Among them, 68.5% were derived from fungi, 23.3% originated from actinomycetes, 3.7% were obtained from other bacteria and 4.4% were discovered using the co-culture method. The structures of these compounds include terpenoids (13%), polyketides (51.9%), alkaloids (17.4%), peptides (11.5%), glucosides (3.3%), etc. Significantly, there are 124 new compounds and 146 known compounds, 55 of which have antifungal activity in addition to antipathogenic bacteria. This review will provide a theoretical basis for the further development of antimicrobial drugs.

Marine natural products

Covering: January to December 2021This review covers the literature published in 2021 for marine natural products (MNPs), with 736 citations (724 for the period January to December 2021) 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 (1425 in 416 papers for 2021), together with the relevant biological activities, source organisms and country of origin. Pertinent reviews, biosynthetic studies, first syntheses, and syntheses that led to the revision of structures or stereochemistries, have been included. An analysis of the number of authors, their affiliations, domestic and international collection locations, focus of MNP studies, citation metrics and journal choices is discussed.

New Alkylpyridinium Anthraquinone, Isocoumarin, C-Glucosyl Resorcinol Derivative and Prenylated Pyranoxanthones from the Culture of a Marine Sponge-Associated Fungus, Aspergillus stellatus KUFA 2017

An unreported isocoumarin, (3S,4R)-4-hydroxy-6-methoxymellein (2), an undescribed propylpyridinium anthraquinone (4), and an unreported C-glucosyl resorcinol derivative, acetyl carnemycin E (5c), were isolated, together with eight previously reported metabolites including p-hydroxybenzaldehyde (1), 1,3-dimethoxy-8-hydroxy-6-methylanthraquinone (3a), 1,3-dimethoxy-2,8-dihydroxy-6-methylanthraquinone (3b), emodin (3c), 5[(3E,5E)-nona-3,5-dien-1-yl]benzene (5a), carnemycin E (5b), tajixanthone hydrate (6a) and 15-acetyl tajixanthone hydrate (6b), from the ethyl acetate extract of the culture of a marine sponge-derived fungus, Aspergillus stellatus KUFA 2017. The structures of the undescribed compounds were elucidated by 1D and 2D NMR and high resolution mass spectral analyses. In the case of 2, the absolute configurations of the stereogenic carbons were determined by comparison of their calculated and experimental electronic circular dichroism (ECD) spectra. The absolute configurations of the stereogenic carbons in 6a and 6b were also determined, for the first time, by X-ray crystallographic analysis. Compounds 2, 3a, 3b, 4, 5a, 5b, 5c, 6a, and 6b were assayed for antibacterial activity against four reference strains, viz. two Gram-positive (Staphylococcus aureus ATCC 29213, Enterococcus faecalis ATCC 29212) and two Gram-negative (Escherichia coli ATCC 25922, Pseudomonas aeruginosa ATCC 27853), as well as three multidrug-resistant strains. However, only 5a exhibited significant antibacterial activity against both reference and multidrug-resistant strains. Compound 5a also showed antibiofilm activity against both reference strains of Gram-positive bacteria.

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.

Bioactive Compounds from Terrestrial and Marine-Derived Fungi of the Genus Neosartorya †

Fungi comprise the second most species-rich organism group after that of insects. Recent estimates hypothesized that the currently reported fungal species range from 3.5 to 5.1 million types worldwide. Fungi can grow in a wide range of habitats, from the desert to the depths of the sea. Most develop in terrestrial environments, but several species live only in aquatic habitats, and some live in symbiotic relationships with plants, animals, or other fungi. Fungi have been proved to be a rich source of biologically active natural products, some of which are clinically important drugs such as the β-lactam antibiotics, penicillin and cephalosporin, the immunosuppressant, cyclosporine, and the cholesterol-lowering drugs, compactin and lovastatin. Given the estimates of fungal biodiversity, it is easy to perceive that only a small fraction of fungi worldwide have ever been investigated regarding the production of biologically valuable compounds. Traditionally, fungi are classified primarily based on the structures associated with sexual reproduction. Thus, the genus Neosartorya (Family Trichocomaceae) is the telemorphic (sexual state) of the Aspergillus section known as Fumigati, which produces both a sexual state with ascospores and an asexual state with conidiospores, while the Aspergillus species produces only conidiospores. However, according to the Melbourne Code of nomenclature, only the genus name Aspergillus is to be used for both sexual and asexual states. Consequently, the genus name Neosartorya was no longer to be used after 1 January 2013. Nevertheless, the genus name Neosartorya is still used for the fungi that had already been taxonomically classified before the new rule was in force. Another aspect is that despite the small number of species (23 species) in the genus Neosartorya, and although less than half of them have been investigated chemically, the chemical diversity of this genus is impressive. Many chemical classes of compounds, some of which have unique scaffolds, such as indole alkaloids, peptides, meroterpenes, and polyketides, have been reported from its terrestrial, marine-derived, and endophytic species. Though the biological and pharmacological activities of a small fraction of the isolated metabolites have been investigated due to the available assay systems, they exhibited relevant biological and pharmacological activities, such as anticancer, antibacterial, antiplasmodial, lipid-lowering, and enzyme-inhibitory activities.

Polyketide Derivatives from the Endophytic Fungus Phaeosphaeria sp. LF5 Isolated from Huperzia serrata and Their Acetylcholinesterase Inhibitory Activities

The secondary metabolites of Phaeosphaeria sp. LF5, an endophytic fungus with acetylcholinesterase (AChE) inhibitory activity isolated from Huperzia serrata, were investigated. Their structures and absolute configurations were elucidated by means of extensive spectroscopic data, including one- and two-dimensional nuclear magnetic resonance (NMR), high-resolution electrospray ionization mass spectrometry (HR-ESI-MS) analyses, and calculations of electronic circular dichroism (ECD). A chemical study on the solid-cultured fungus LF5 resulted in 11 polyketide derivatives, which included three previously undescribed derivatives: aspilactonol I (4), 2-(1-hydroxyethyl)-6-methylisonicotinic acid (7), and 6,8-dihydroxy-3-(1′R, 2′R-dihydroxypropyl)-isocoumarin (9), and two new natural-source-derived aspilactonols (G, H) (2, 3). Moreover, the absolute configuration of de-O-methyldiaporthin (11) was identified for the first time. Compounds 4 and 11 exhibited inhibitory activity against AChE with half maximal inhibitory concentration (IC₅₀) values of 6.26 and 21.18 µM, respectively. Aspilactonol I (4) is the first reported furanone AChE inhibitor (AChEI). The results indicated that Phaeosphaeria is a good source of polyketide derivatives. This study identified intriguing lead compounds for further research and development of new AChEIs.

Effects of Marine Antagonistic Fungi against Plant Pathogens and Rice Growth Promotion Activity

Ten marine-derived fungi crude extracts, namely Emericella stellatus KUFA0208, Eupenicillium parvum KUFA0237, Neosartorya siamensis KUFA0514, N. spinosa KUFA 0528, Talaromyces flavus KUFA 0119, T. macrosporus KUFA 0135, T. trachyspermus KUFA0304, Trichoderma asperellum KUFA 0559, T. asperellum KUFA 0559 and T. harzianum KUFA 0631 were determined for their fungicidal activity against five rice pathogens in vitro. The results showed that the extracts of E. stellatus KUFA0208 and N. siamensis KUFA0514 exhibited the best antifungal activity, causing complete cessation of the mycelial growth of Alternaria padwickii, Bipalaris oryzae, Fusarium semitectum, Pyricularia oryzae and Rhizoctonia solani at 10 g/L. The N. siamensis KUFA0514 extract was fractioned and antifungal compounds were found in the fractions derived from petroleum-ether and chloroform (7: 3) evidenced by inhibition zones against the mycelial growth of A. padwickii around the disc containing each fraction. Moreover, in rice growth promotion tests, diluted cultural broth of T. asperellum KUFA 0559 and T. harzianum KUFA 0631 were found to strongly promote rice shoot and root elongation; however, higher concentrations of all marine fungal broths resulted in significantly reduced rice seedling growth rather than promotion. Meanwhile, Trichoderma showed great indole-3-acetic acid (IAA) production leading to the optimum IAA values of 45.38 and 52.30 µg/ml at 11 and 13 days after inoculation, respectively. The results of this study indicated that marine fungi are promising agents having antagonistic mechanisms involving antibiosis production and plant growth promotion and may be developed as novel biocontrol agents for rice disease management.

The Discovery of Actinospene, a New Polyene Macrolide with Broad Activity against Plant Fungal Pathogens and Pathogenic Yeasts

Phytopathogenic fungi infect crops, presenting a worldwide threat to agriculture. Polyene macrolides are one of the most effective antifungal agents applied in human therapy and crop protection. In this study, we found a cryptic polyene biosynthetic gene cluster in Actinokineospora spheciospongiae by genome mining. Then, this gene cluster was activated via varying fermentation conditions, leading to the discovery of new polyene actinospene (1), which was subsequently isolated and its structure determined through spectroscopic techniques including UV, HR-MS, and NMR. The absolute configuration was confirmed by comparing the calculated and experimental electronic circular dichroism (ECD) spectra. Unlike known polyene macrolides, actinospene (1) demonstrated more versatile post-assembling decorations including two epoxide groups and an unusual isobutenyl side chain. In bioassays, actinospene (1) showed a broad spectrum of antifungal activity against several plant fungal pathogens as well as pathogenic yeasts with minimum inhibitory concentrations ranging between 2 and 10 μg/mL.