Secondary Metabolites from an Endophytic Fungus Nigrospora sp

Anthrol reductases: discovery, role in biosynthesis and applications in natural product syntheses

Covering: up to 2023Short-chain dehydrogenase/reductases (SDR) are known to catalyze the regio- and stereoselective reduction of a variety of substrate types. Investigations of the deoxygenation of emodin to chrysophanol has led to the discovery of the anthrol reductase activity of an SDR, MdpC involved in monodictyphenone biosynthesis of Aspergillus nidulans and provided access to (R)-dihydroanthracenone, a putative biosynthetic intermediate. This facilitated the identification of several MdpC-related enzymes involved in the biosynthesis of aflatoxins B1, cladofulvin, neosartorin, agnestins and bisanthraquinones. Because of their ability to catalyze the reduction of hydroanthraquinone (anthrols) using NADPH, they were named anthrol reductases. This review provides a comprehensive summary of all the anthrol reductases that have been identified and characterized in the last decade along with their role in the biosynthesis of natural products. In addition, the applications of these enzymes towards the chemoenzymatic synthesis of flavoskyrins, modified bisanthraquinones, 3-deoxy anthraquinones, chiral cycloketones and β-halohydrins have been discussed.

Antioxidant, Anti-Inflammatory and Anti-Diabetic Activities of Tectona grandis Methanolic Extracts, Fractions, and Isolated Compounds

Tectona grandis is a traditional Dai medicine plant belonging to the Lamiaceae family, which can be used to treat malaria, inflammation, diabetes, liver disease, bronchitis, tumors, cholelithiasis, jaundice, skin disease and as an anti-helminthic. To find more novel therapeutic agents contained in this medicinal plant, the antioxidant, anti-inflammatory and anti-diabetic activities of T. grandis methanolic extract, fractions and compounds were evaluated. In this study, 26 compounds were isolated from the leaves and branches of T. grandis. Their structures were identified based on extensive spectral experiments, including NMR, ESI-MS and comparison with published spectral data. Among them, compounds 1–2, 4–6, 9–14 and 16–22 were reported for the first time for this plant. The antioxidant activity screening results showed that compounds 5, 15 and 23 had potent antioxidant capacities, with SC50 values from 0.32 to 9.92 µmol/L, 0.92 to 1.10 mmol Trolox/L and 1.02 to 1.22 mmol Trolox/L for DPPH, ABTS and FRAP, respectively. In addition, their anti-inflammatory effects were investigated by releasing TNF-α, IL-1β and IL-6 through the use of mouse monocytic macrophages (RAW 264.7). Compounds 1, 13, 18 and 23 had the effects of reducing the expression of inflammatory factors. Compounds 13 and 18 were reported for the first time for their anti-inflammatory activities. Furthermore, the methanolic extract (ME), petroleum ether extract (PEE) and EtOAc extract (EAE) of T. grandis showed significant glucose uptake activities; compounds 21 and 23 significantly promoted glucose uptake of 3T3-L1 adipocytes at 40 µM. Meanwhile, compounds 4, 5 and 7 showed significant inhibitory activities against α-glucosidase, with IC50 values of 14.16 ± 0.34 µmol/L, 19.29 ± 0.26 µmol/L and 3.04 ± 0.08 µmol/L, respectively. Compounds 4 and 5 were reported for the first time for their α-glucosidase inhibitory activities. Our investigation explored the possible therapeutic material basis of T. grandis to prevent oxidative stress and related diseases, especially inflammation and diabetes.

Secondary metabolites of the genus Nigrospora from terrestrial and marine habitats: Chemical diversity and biological activity

Secondary metabolites produced by the ascomycetes have attracted wide attention from researchers. Their diverse chemical structures and rich biological activities are essential in medicine, food, and agriculture. The monophyletic Nigrospora genus belongs to the Apiosporaceae family and is a rich source of novel and diverse bioactive metabolites. It occurs as a common plant pathogen, endophyte, and saprobe distributed in many ecosystems worldwide. Researchers have focused on discovering new species and secondary metabolites in the past ten years. The host diseases caused by Nigrospora species are also investigated. This review describes 50 references from Web of Science, CNKI, Google Scholar and PubMed related to the secondary metabolites from Nigrospora. Here, a total of 231 compounds isolated from five known species and 21 unidentified species of Nigrospora from January 1991 to June 2022 are summarized. Their structures are attributed to polyketides, terpenoids, steroids, N-containing compounds, and fatty acids. Meanwhile, 77 metabolites exhibited various biological activities like cytotoxic, antifungal, antibacterial, antiviral, antioxidant, anti-inflammatory, antileukemic, antimalarial, phytotoxic, enzyme inhibitory, etc. Notably, this review presents a comprehensive literature survey focusing on the chemistry and bioactivity of secondary metabolites from Nigrospora.

Multigene Phylogeny Reveals Endophytic Xylariales Novelties from Dendrobium Species from Southwestern China and Northern Thailand

Xylariales are common endophytes of Dendrobium. However, xylarialean species resolution remains difficult without sequence data and poor sporulation on artificial media and asexual descriptions for only several species and old type material. The surface-sterilized and morph-molecular methods were used for fungal isolation and identification. A total of forty-seven strains were identified as twenty-three species belonging to Apiosporaceae, Hypoxylaceae, Induratiaceae, and Xylariaceae. Five new species—Annulohypoxylon moniliformis, Apiospora dendrobii, Hypoxylon endophyticum, H. officinalis and Nemania dendrobii were discovered. Three tentative new species were speculated in Xylaria. Thirteen known fungal species from Hypoxylon, Nemania, Nigrospora, and Xylaria were also identified. Another two strains were only identified at the genus and family level (Induratia sp., Hypoxylaceae sp.). This study recorded 12 new hosts for xylarialean endophytes. This is the first report of Xylariales species as endophytes from Dendrobium aurantiacum var. denneanum, D. cariniferum, D. harveyanum, D. hercoglossum, D. moniliforme, and D. moschatum. Dendrobium is associated with abundant xylarialean taxa, especially species of Hypoxylon and Xylaria. We recommend the use of oat agar with low concentrations to induce sporulation of Xylaria strains.

A biocatalytic approach towards the preparation of natural deoxyanthraquinones and their impact on cellular viability

Natural deoxyanthraquinones synthesized using a chemoenzymatic approach and tested for cell viability shows less toxicity compared to the respective anthraquiones.

Neuroprotective Metabolites from Vietnamese Marine Derived Fungi of Aspergillus and Penicillium Genera

Low molecular weight secondary metabolites of marine fungi Aspergillus flocculosus, Aspergillus terreus and Penicillium sp. from Van Phong and Nha Trang Bays (Vietnam) were studied and a number of polyketides, bis-indole quinones and terpenoids were isolated. The structures of the isolated compounds were determined by 1D and 2D NMR and HR-ESI-MS techniques. Stereochemistry of some compounds was established based on ECD data. A chemical structure of asterriquinone F (6) was thoroughly described for the first time. Anthraquinone (13) was firstly obtained from a natural source. Neuroprotective influences of the isolated compounds against 6-OHDA, paraquat and rotenone toxicity were investigated. 4-Hydroxyscytalone (1), 4-hydroxy-6-dehydroxyscytalone (2) and demethylcitreoviranol (3) have shown significant increasing of paraquat- and rotenone-treated Neuro-2a cell viability and anti-ROS activity.

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.

Napthrene Compounds from Mycelial Fermentation Products of Marasmius berteroi

The metabolites of the genus Marasmius are diverse, showing good research prospects for finding new bioactive molecules. In order to explore the active metabolites of the fungi Marasmius berteroi, the deep chemical investigation on the bioactive compounds from its cultures was undertaken, which led to the isolation of three new naphthalene compounds dipolynaphthalenes A-B (1,2) and naphthone C (3), as well as 12 known compounds (4-15). Compounds 1, 2, and 4 are dimeric naphthalene compounds. Their structures were elucidated by MS, 1D and 2D NMR spectroscopic data, as well as ECD calculations. Compounds 2-4 and 7 exhibited acetylcholinesterase (AChE) inhibitory activities at the concentration of 50 μg/mL with inhibition ratios of 42.74%, 44.63%, 39.50% and 51.49%, respectively. Compounds 5 and 7,8 showed weak inhibitory activities towards two tumor cell lines, with IC₅₀ of 0.10, 0.076 and 0.058 mM (K562) and 0.13, 0.18, and 0.15 mM (SGC-7901), respectively.

Cerebrosides and Steroids from the Edible Mushroom Meripilus giganteus with Antioxidant Potential

The detailed chemical analysis of the methanol extract of Meripilus giganteus (Pers.) P. Karst. led to the isolation of two new cerebrosides, mericeramides A (1) and B (2) together with cerebroside B (3), ergosterol (4), 3β-hydroxyergosta-7,22-diene (5), cerevisterol (6), 3β-hydroxyergosta-6,8(14),22-triene (7), 3β-O-glucopyranosyl-5,8-epidioxyergosta-6,22-diene (8) and (11E,13E)-9,10-dihydroxy-11,13-octadecadienoic acid (9). The structures of the compounds were determined on the basis of NMR and MS spectroscopic analysis. Mericeramide A (1) is the first representative of halogenated natural cerebrosides. The isolated fungal metabolites 1-9 were evaluated for their antioxidant activity using the oxygen radical absorbance capacity (ORAC) assay. Compounds 2, 5 and 9 proved to possess considerable antioxidant effects, with 2.50 ± 0.29, 4.94 ± 0.37 and 4.27 ± 0.05 mmol TE/g values, respectively. The result obtained gives a notable addition to the chemical and bioactivity profile of M. giganteus, highlighting the possible contribution of this species to a versatile and balanced diet.

Pyranonaphthoquinone and anthraquinone derivatives from Ventilago harmandiana and their potent anti-inflammatory activity

The chemical study on the heartwoods extract of Ventilago harmandiana (Rhamnaceae) resulted in the isolation of ten previously undescribed pyranonaphthoquinones (ventilanones A-J), an undescribed anthraquinone (ventilanone K), together with eight known anthraquinone derivatives. Their structures were elucidated by extensive analysis of their spectroscopic data. The absolute configuration of ventilanone A was established from single crystal X-ray crystallographic analysis of its p-bromobenzenesulfonate ester derivative using Cu Kα radiation. The absolute configurations of the other related compounds were identified by comparison of their ECD data with those of ventilanone A and related known compounds. Cytotoxic and anti-inflammatory activities of some of the isolated compounds were evaluated. Ventilanone A and ventilanone C exhibited moderate cytotoxicity against P-388 cell line. Ventilanone D exhibited significant anti-inflammatory activity while ventilanone A and ventilanone C showed moderate activity.

Secondary metabolites from Diaporthe lithocarpus isolated from Artocarpus heterophyllus

Fractionation and purification of the ethyl acetate extract of Diaporthe lithocarpus, an endophytic fungus from the leaves of Artocarpus heterophyllus, yielded one new compound, diaporthindoic acid (1), along with seven known compounds (2-8). The new compound was characterized and established by the basis of extensive spectroscopic methods including NMR (1D and 2D) and HRMS. Compound 6 showed the best citotoxicity against murine leukemia P-388 cells with an IC₅₀ value of 0.41 μg/mL. All compounds (1-8) were also tested for their antimicrobial activities. To the best of our knowledge, this is the first chemical evaluation of fungal Diaporthe derived from Artocarpus.

Assembling a plug-and-play production line for combinatorial biosynthesis of aromatic polyketides in Escherichia coli

Polyketides are a class of specialised metabolites synthesised by both eukaryotes and prokaryotes. These chemically and structurally diverse molecules are heavily used in the clinic and include frontline antimicrobial and anticancer drugs such as erythromycin and doxorubicin. To replenish the clinicians' diminishing arsenal of bioactive molecules, a promising strategy aims at transferring polyketide biosynthetic pathways from their native producers into the biotechnologically desirable host Escherichia coli. This approach has been successful for type I modular polyketide synthases (PKSs); however, despite more than 3 decades of research, the large and important group of type II PKSs has until now been elusive in E. coli. Here, we report on a versatile polyketide biosynthesis pipeline, based on identification of E. coli-compatible type II PKSs. We successfully express 5 ketosynthase (KS) and chain length factor (CLF) pairs-e.g., from Photorhabdus luminescens TT01, Streptomyces resistomycificus, Streptoccocus sp. GMD2S, Pseudoalteromonas luteoviolacea, and Ktedonobacter racemifer-as soluble heterodimeric recombinant proteins in E. coli for the first time. We define the anthraquinone minimal PKS components and utilise this biosynthetic system to synthesise anthraquinones, dianthrones, and benzoisochromanequinones (BIQs). Furthermore, we demonstrate the tolerance and promiscuity of the anthraquinone heterologous biosynthetic pathway in E. coli to act as genetically applicable plug-and-play scaffold, showing it to function successfully when combined with enzymes from phylogenetically distant species, endophytic fungi and plants, which resulted in 2 new-to-nature compounds, neomedicamycin and neochaetomycin. This work enables plug-and-play combinatorial biosynthesis of aromatic polyketides using bacterial type II PKSs in E. coli, providing full access to its many advantages in terms of easy and fast genetic manipulation, accessibility for high-throughput robotics, and convenient biotechnological scale-up. Using the synthetic and systems biology toolbox, this plug-and-play biosynthetic platform can serve as an engine for the production of new and diversified bioactive polyketides in an automated, rapid, and versatile fashion.

Antimicrobial anthraquinones from cultures of the ant pathogenic fungus Cordyceps morakotii BCC 56811

Five new anthraquinones, morakotins A-E (1-5), together with seven known compounds, lunatin (6), rheoemodin (7), YM187781 (8), bislunatin (9), 6-(1-hydroxypentyl)-4-methoxypyran-2-one, 9,11-dehydoergrosterol peroxide, and cerevisterol, were isolated from the insect pathogenic fungus Cordyceps morakotii BCC 56811. The morakotin structures were elucidated from NMR spectroscopic and mass spectrometric data. The absolute configurations of bianthraquinone compounds, morakotins C-E (3-5), were determined by application of the exciton chirality method. Compounds 3, 7, 8, and 9 showed weak to moderate antimycobacterial and antifungal activities. Compounds 4 and 8 exhibited antibacterial activity against both Bacillus cereus and Staphylococcus aureus (MIC 3.13-25 µg ml^-1), whereas compounds 3 and 9 were active against B. cereus (MIC 12.5 and 3.13 µg ml^-1, respectively), and compound 7 was active against Acinetobacter baumannii (MIC 12.5 µg ml^-1).