New Lactone and Xanthone Derivatives Produced by a Mangrove Endophytic Fungus Phoma sp. SK3RW1M from the South China Sea

Phoma spp. an untapped treasure of cytotoxic compounds: current status and perspectives

The genus Phoma has been explored for a wide range of secondary metabolites signifying a huge range of bioactivities. Phoma sensu lato is a major group that secretes several secondary metabolites. The genus Phoma mainly includes Phoma macrostoma, P. multirostrata, P. exigua, P. herbarum, P. betae, P. bellidis, P. medicaginis, P. tropica, and many more species from the genus that are continuously being identified for their potential secondary metabolites. The metabolite spectrum includes bioactive compounds like phomenon, phomin, phomodione, cytochalasins, cercosporamide, phomazines, and phomapyrone reported from various Phoma spp. These secondary metabolites show a broad range of activities including antimicrobial, antiviral, antinematode, and anticancer. The present review is aimed to emphasize the importance of Phoma sensu lato fungi, as a natural source of biologically active secondary metabolites, and their cytotoxic activities. So far, cytotoxic activities of Phoma spp. have not been reviewed; hence, this review will be novel and useful for the readers to develop Phoma-derived anticancer agents. KEY POINTS: • Different Phoma spp. contain a wide variety of bioactive metabolites. • These Phoma spp. also secrete cytotoxic and antitumor compounds. • The secondary metabolites can be used for the development of anticancer agents.

Muyocoxanthones O-S: Undescribed xanthones with antioxidative damage bioactivity to cardiomyocytes from the endophytic fungus Muyocopron laterale

The metabolites from the endophytic fungus Muyocopron laterale hosted in the medicinal plant Tylophora ovata were investigated, and five undescribed xanthones, muyocoxanthones O-S, along with seven known compounds were isolated. Their structures were elucidated by HR-ESI-MS, NMR, and ECD calculations. Compounds were evaluated for their anti-cardiomyocyte oxidative damage activity using a model of oxidative damage induced by cell hypoxia incubation. Muyocoxanthones O-Q and blennolide L exhibited moderate activity against oxidative damage to cardiomyocytes with relative viabilities of 62.4, 54.8, 60.3 and 54.9%, respectively.

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.

An Updated Review on Biologically Promising Natural Oxepines

Benzo-oxepines and dibenzo-oxepines, a unique class of naturally occurring secondary metabolites, are distributed mainly in plants and fungi and have received much attention from phytochemists and biologists based on their fascinating structural features and health-promoting functions. This review summarizes 100 oxepine derivatives comprising three categories: benzo-oxepine, dibenzo-oxepine, and pyrano-oxepine. Studies on various structural features and pharmacological activities of oxepine derivatives promote further in-depth research on these potent natural products. This review portrays the natural occurrence, bioactivity and biosynthesis of oxepines reported from 1984 to 2021.

Secondary metabolites from mangrove-associated fungi: source, chemistry and bioactivities

Covering 1989 to 2020The mangrove forests are a complex ecosystem occurring at tropical and subtropical intertidal estuarine zones and nourish a diverse group of microorganisms including fungi, actinomycetes, bacteria, cyanobacteria, algae, and protozoa. Among the mangrove microbial community, mangrove associated fungi, as the second-largest ecological group of the marine fungi, not only play an essential role in creating and maintaining this biosphere but also represent a rich source of structurally unique and diverse bioactive secondary metabolites, attracting significant attention of organic chemists and pharmacologists. This review summarizes the discovery relating to the source and characteristics of metabolic products isolated from mangrove-associated fungi over the past thirty years (1989-2020). Its emphasis included 1387 new metabolites from 451 papers, focusing on bioactivity and the unique chemical diversity of these natural products.

Marine and terrestrial endophytic fungi: a mine of bioactive xanthone compounds, recent progress, limitations, and novel applications

Endophytic fungi are a kind of fungi that colonizes living plant tissues presenting a myriad of microbial adaptations that have been developed in such a hidden environment. Owing to its large diversity and particular habituation, they present a golden mine for research in the field of drug discovery. Endophytic fungal communities possess unique biocatalytic machinery that furnishes a myriad of complex natural product scaffolds. Xanthone compounds are examples of endophytic secondary metabolic products with pronounced biological activity to include: antioxidant, antimicrobial, anti-inflammatory, antithrombotic, antiulcer, choleretic, diuretic, and monoamine oxidase inhibiting activity.The current review compiles the recent progress made on the microbiological production of xanthones using fungal endophytes obtained from both marine and terrestrial origins, with comparisons being made among both natural resources. The biosynthesis of xanthones in endophytic fungi is outlined along with its decoding enzymes. Biotransformation reactions reported to be carried out using different endophytic microbial models are also outlined for xanthones structural modification purposes and the production of novel molecules.A promising application of novel computational tools is presented as a future direction for the goal of optimizing microbial xanthones production to include establishing metabolic pathway databases and the in silico analysis of microbial interactions. Metagenomics methods and related bioinformatics platforms are highlighted as unexplored tools for the biodiversity analysis of endophytic microbial communities that are difficult to be cultured.

Bioactive polyketides from the mangrove endophytic fungi Phoma sp. SYSU-SK-7

Five new polyketides, colletotric B (2), 3-hydroxy-5-methoxy-2,4,6-trimethylbenzoic acid (3), colletotric C (4), chaetochromone D (6) and 8-hydroxy-pregaliellalactone B (9), together with four known analogues (1, 5 and 7-8) were isolated from the mangrove endophytic fungus Phoma sp. SYSU-SK-7. Their structures were elucidated by analysis of extensive spectroscopic data and mass spectrometric data. Compounds 1-2 showed strong antimicrobial activity against the P. aeruginosa, MRSA and C. albicans with the MIC values in the range of 1.67-6.28 μg/ml. Furthermore, Compounds 1-5 also exhibited significant α-glucosidase inhibitory activity with the IC₅₀ values in the range of 36.2-90.6 μM. Compound 7 was found to inhibited radical scavenging activity against DPPH with the EC₅₀ value of 11.8 μM.

Structural Revision of Wentiquinone C and Related Congeners from Anthraquinones to Xanthones Using Chemical Derivatization and NMR Analysis

Wentiquinone C, which was previously isolated from the marine brown alga-derived endophytic fungus Aspergillus wentii EN-48, was found to be a potent antioxidant against α,α-diphenyl-picrylhydrazyl (DPPH) radical. The structure of wentiquinone C was originally assigned as an anthraquinone derivative (1,10-dihydroxy-3-(hydroxymethyl)-8-methoxydibenzo [b,e]oxepine-6,11-dione, 1) by 1D and 2D NMR experiments. However, the minor differences of the chemical shifts between xanthones and anthraquinones were queried, leading to the structure of 1 to be revised as a xanthone analog (8-hydroxy-6-(hydroxymethyl)-3-methoxy-9-oxo-9H-xanthene-1-carboxylic acid, 2) on the basis of a methylation and subsequent NMR measurements, and was confirmed by X-ray crystallographic analysis. The method established in this paper could be applied to the structural re-examination or revision for some of the reported seco-anthraquinone derivatives.

Marine-derived Phoma-the gold mine of bioactive compounds

The genus Phoma contains several species ubiquitously present in soil, water, and environment. There are two major groups of Phoma, viz., terrestrial and marine. After 1981 researchers all over the world have focused on marine-derived Phoma for their bioactive compounds. The marine Phoma are very rich sources for novel bioactive secondary metabolites, which could potentially be used as drugs. Recently, a large number of structurally unique metabolites with potential biological and pharmacological activities have been isolated from the marine Phoma species particularly Phoma herbarum, P. sorghina, and P. tropica. These metabolites mainly include diterpenes, enolides, lactones, quinine, phthalate, and anthraquinone. Most of these compounds possess antimicrobial, anticancer, radical scavenging, and cytotoxic properties. The present review has been focused on the general background of Phoma, current approaches used for its identification and their limitations, difference between terrestrial and marine Phoma species. In addition, this review summarizes the novel bioactive compounds derived from marine Phoma and their biological activities.

Novel Salt-Tolerant Xylanase from a Mangrove-Isolated Fungus Phoma sp. MF13 and Its Application in Chinese Steamed Bread

A novel glycosyl hydrolase family 11 xylanase gene, xynMF13A, was cloned from Phoma sp. MF13, a xylanase-producing fungus isolated from mangrove sediment. xynMF13A was heterologously expressed in Pichia pastoris, and the recombinant XynMF13A (rXynMF13A) was purified by Ni-affinity chromatography. The temperature and pH optima of purified rXynMF13A were 45 °C and pH 5.0, respectively. rXynMF13A showed a high level of salt tolerance, with maximal enzyme activity being seen at 0.5 M NaCl and as much as 53% of maximal activity at 4 M NaCl. The major rXynMF13A hydrolysis products from corncob xylan were xylobiose, xylotriose, xylotetraose, and xylopentaose, but no xylose was found. These hydrolysis products suggest an important potential for XynMF13A in the production of xylooligosaccharides (XOs). Furthermore, rXynMF13A had beneficial effects on Chinese steamed bread production, by increasing specific volume and elasticity while decreasing hardness and chewiness. These results demonstrate XynMF13A to be a novel xylanase with potentially significant applications in baking, XOs production, and seafood processing.

Bioactive natural products derived from mangrove-associated microbes

This review summarizes new findings concerning the sources and characteristics of various natural products that can be extracted from mangrove-associated microbes over the past three years (January 2011–December 2013).

Phomapyrrolidones A-C, antitubercular alkaloids from the endophytic fungus Phoma sp. NRRL 46751

Three new alkaloids, phomapyrrolidones A-C (1-3), bearing a cyclopenta[b]fluorene ring system were isolated from the mycelium extract of the endophytic fungal strain Phoma sp. NRRL 46751, inhabiting Saurauia scaberrinae. Methylation of 1 afforded its N-methyl derivative 4. The planar structures and relative configurations of 1-4 were elucidated by extensive spectroscopic analysis. Phomapyrrolidones B (2) and C (3) exhibited weak antitubercular activity at subcytotoxic concentrations.

Marine natural products

Covering: 2010. Previous review: Nat. Prod. Rep., 2011, 28, 196. This review covers the literature published in 2010 for marine natural products, with 895 citations (590 for the period January to December 2010) 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 (1003 for 2010), together with the relevant biological activities, source organisms and country of origin. Biosynthetic studies, first syntheses, and syntheses that lead to the revision of structures or stereochemistries, have been included.

Arthrinins A-D: novel diterpenoids and further constituents from the sponge derived fungus Arthrinium sp

Bioassay-guided fractionation of a methanolic extract of the fungus Arthrinium sp., isolated from the Mediterranean sponge Geodia cydonium, afforded 10 natural products including five new diterpenoids, arthrinins A-D (1-4) and myrocin D (5). In addition, five known compounds were obtained, which included myrocin A (6), norlichexanthone (7), anomalin A (8), decarboxycitrinone (9) and 2,5-dimethyl-7-hydroxychromone (10). The structures of all isolated compounds were unambiguously elucidated based on extensive 1D and 2D NMR and HR-MS analyzes. The absolute configuration of arthrinins A-D (1-4) was established by the convenient Mosher method performed in NMR tubes and by interpretation of the ROESY spectra. Antiproliferative activity of the isolated compounds was assessed in vitro against four different tumor cell lines, including mouse lymphoma (L5178Y), human chronic myelogenous leukemia (K562), human ovarian cancer (A2780) and cisplatin-resistant ovarian cancer cells (A2780CisR), using the MTT assay. Norlichexanthone (7) and anomalin A (8) exhibited the strongest activities with IC₅₀ values ranging from 0.40 to 74.0 μM depending on the cell line investigated. This was paralleled by the inhibitory activity of both compounds against 16 cancer related protein kinases including aurora-B, PIM1, and VEGF-R2. In vitro IC₅₀ values of 7 and 8 against these three protein kinases ranged from 0.3 to 11.7 μM. Further investigation of the potential antitumoral activity of compounds 5-8 was performed in an in vitro angiogenesis assay against human umbilical vascular endothelial cells (HUVEC) sprouting induced by vascular endothelial growth factor A (VEGF-A). Anomalin A (8), myrocin D (5) and myrocin A (6) inhibited VEGF-A dependent endothelial cell sprouting with IC₅₀ values of 1.8, 2.6 and 3.7 μM, respectively, whereas norlichexanthone (7) was inactive.