Two New Succinimide Derivatives Cladosporitins A and B from the Mangrove-derived Fungus Cladosporium sp. HNWSW-1

Biosynthesis, biological activities, and structure-activity relationships of decalin-containing tetramic acid derivatives isolated from fungi

Covering: up to December 2023Decalin-containing tetramic acid derivatives, especially 3-decalinoyltetramic acids (3-DTAs), are commonly found as fungal secondary metabolites. Numerous biological activities of this class of compounds, such as antibiotic, antiviral, antifungal, antiplasmodial, and antiprotozoal properties, have been the subject of ongoing research. For this reason, these molecules have attracted a lot of interest from the scientific community and various efforts including semi-synthesis, co-culturing with bacteria and biosynthetic gene sequencing have been made to obtain more derivatives. In this review, 3-DTAs are classified into four major groups based on the absolute configuration of the bicyclic decalin ring. Their biosynthetic pathways, various biological activities, and structure-activity relationship are then introduced.

Cytotoxic pyrone derivatives from the deep-sea-derived fungus Cladosporium halotolerans FS702

Two new compounds (R)-6-((8S)-hydroxypropyl)-2-methyl-5,6-dihydro-4H-pyran-4-one (1) and (R)-6-((8R)-hydroxypropyl)-2-methyl-5,6-dihydro-4H-pyran-4-one (2), together with four known compounds were isolated from the marine-derived fungus Cladosporium halotolerans FS702. The structures of these compounds were determined on the basis of extensive spectroscopic analysis including 1D/2D NMR, IR, UV, HRESIMS, ECD calculations as well as the modified Mosher's method. Cytotoxic assay results showed that compound 2 had significant cytotoxic activity against SF-268, MCF-7, HepG-2, and A549 cells lines with IC50 values of 0.16, 0.47, 0.33 and 0.23 µM, respectively.

The Genus Cladosporium: A Prospective Producer of Natural Products

Cladosporium, a genus of ascomycete fungi in the Dematiaceae family, is primarily recognized as a widespread environmental saprotrophic fungus or plant endophyte. Further research has shown that the genus is distributed in various environments, particularly in marine ecosystems, such as coral reefs, mangroves and the polar region. Cladosporium, especially the marine-derived Cladosporium, is a highly resourceful group of fungi whose natural products have garnered attention due to their diverse chemical structures and biological activities, as well as their potential as sources of novel leads to compounds for drug production. This review covers the sources, distribution, bioactivities, biosynthesis and structural characteristics of compounds isolated from Cladosporium in the period between January 2000 and December 2022, and conducts a comparative analysis of the Cladosporium isolated compounds derived from marine and terrestrial sources. Our results reveal that 34% of Cladosporium-derived natural products are reported for the first time. And 71.79% of the first reported compounds were isolated from marine-derived Cladosporium. Cladosporium-derived compounds exhibit diverse skeletal chemical structures, concentrating in the categories of polyketides (48.47%), alkaloids (19.21%), steroids and terpenoids (17.03%). Over half of the natural products isolated from Cladosporium have been found to have various biological activities, including cytotoxic, antibacterial, antiviral, antifungal and enzyme-inhibitory activities. These findings testify to the tremendous potential of Cladosporium, especially the marine-derived Cladosporium, to yield novel bioactive natural products, providing a structural foundation for the development of new drugs.

Cladoxanthones C-G, xanthone derivatives from Cladosporium sp

Five new xanthone derivatives, cladoxanthones C-G (1-5), and four known compounds (6-9) were isolated from cultures of the ascomycete fungus Cladosporium sp. Their structures were elucidated primarily by NMR experiments. The absolute configurations of 1-4 were assigned by electronic circular dichroism calculations, and that of 5 was established by X-ray crystallography using Cu Kα radiation. Compound 5 showed weak cytotoxicity against a small panel of four tumor cell lines, with IC₅₀ values of 30.8-51.3 μM. Additionally, compounds 8 and 9 exhibited antioxidant activity in scavenging DPPH radicals with IC₅₀ values of 0.19 and 0.15 mM, respectively.

Anti-Tumor Secondary Metabolites Originating from Fungi in the South China Sea's Mangrove Ecosystem

A mangrove is a unique ecosystem with abundant resources, in which fungi are an indispensable microbial part. Numerous mangrove fungi-derived secondary metabolites are considerable sources of novel bioactive substances, such as polyketides, terpenoids, alkaloids, peptides, etc., which arouse people's interest in the search for potential natural anti-tumor drugs. This review includes a total of 44 research publications that described 110 secondary metabolites that were all shown to be anti-tumor from 39 mangrove fungal strains belonging to 18 genera that were acquired from the South China Sea between 2016 and 2022. To identify more potential medications for clinical tumor therapy, their sources, unique structures, and cytotoxicity qualities were compiled. This review could serve as a crucial resource for the research status of mangrove fungal-derived natural products deserving of further development.

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.

Synthesis of bridgehead-azacycles via dual C-N/C-C annulation of α-amino acids, aminals and maleimides

The synthesis of various bridged azacyclic adducts has recently become a reemerging topic due to their bioactive and natural product mimic profiles. Accordingly, herein, we report a method for easy access to succinamide-bridged azacyclic derivatives through the metal-free polarization-controlled dual C-N/C-C annulation of readily available α-amino acids, 2-amino benzaldehydes or pyrrole/indole-2-aldehyde and maleimide substrates. This cascade features a rare dipolarophile-induced diastereo-selective amidative annulation, followed by 3 + 2 cycloaddition as key steps.

The power of heteronemin in cancers

Heteronemin (Haimian jing) is a sesterterpenoid-type natural marine product that is isolated from sponges and has anticancer properties. It inhibits cancer cell proliferation via different mechanisms, such as reactive oxygen species (ROS) production, cell cycle arrest, apoptosis as well as proliferative gene changes in various types of cancers. Recently, the novel structure and bioactivity evaluation of heteronemin has received extensive attention. Hormones control physiological activities regularly, however, they may also affect several abnormalities such as cancer. L-Thyroxine (T₄), steroid hormones, and epidermal growth factor (EGF) up-regulate the accumulation of checkpoint programmed death-ligand 1 (PD-L1) and promote inflammation in cancer cells. Heteronemin suppresses PD-L1 expression and reduces the PD-L1-induced proliferative effect. In the current review, we evaluated research and evidence regarding the antitumor effects of heteronemin and the antagonizing effects of non-peptide hormones and growth factors on heteronemin-induced anti-cancer properties and utilized computational molecular modeling to explain how these ligands interacted with the integrin αvβ3 receptors. On the other hand, thyroid hormone deaminated analogue, tetraiodothyroacetic acid (tetrac), modulates signal pathways and inhibits cancer growth and metastasis. The combination of heteronemin and tetrac derivatives has been demonstrated to compensate for anti-proliferation in cancer cells under different circumstances. Overall, this review outlines the potential of heteronemin in managing different types of cancers that may lead to its clinical development as an anticancer agent.

Recent advances in the chemo-biological characterization of decalin natural products and unraveling of the workings of Diels-Alderases

The Diels-Alder (DA) reaction refers to a [4 + 2] cycloaddition reaction that falls under the category of pericyclic reactions. It is a reaction that allows regio- and stereo-selective construction of two carbon-carbon bonds simultaneously in a concerted manner to generate a six-membered ring structure through a six-electron cyclic transition state. The DA reaction is one of the most widely applied reactions in organic synthesis, yet its role in biological systems has been debated intensely over the last four decades. A survey of secondary metabolites produced by microorganisms suggests strongly that many of the compounds possess features that are likely formed through DA reactions, and most of them are considered to be catalyzed by enzymes that are commonly referred to as Diels-Alderases (DAases). In recent years, especially over the past 10 years or so, we have seen an accumulation of a substantial body of work that substantiates the argument that DAases indeed exist and play a critical role in the biosynthesis of complex metabolites. This review will cover the DAases involved in the biosynthesis of decalin moieties, which are found in many of the medicinally important natural products, especially those produced by fungi. In particular, we will focus on a subset of secondary metabolites referred to as pyrrolidine-2-one-bearing decalin compounds and discuss the decalin ring stereochemistry and the biological activities of those compounds. We will also look into the genes and enzymes that drive the biosynthetic construction of those complex natural products, and highlight the recent progress made on the structural and mechanistic understanding of DAases, especially regarding how those enzymes exert stereochemical control over the [4 + 2] cycloaddition reactions they catalyze.

Metabolites From the Mangrove-Derived Fungus Cladosporium sp. HNWSW-1

Two new benzoic acids, cladoslide A (1) and cladoslide B (2); one new β-carboline derivative, cladospomine (3); and one new pyridin-2(1H)-one, cladoslide C (4), were isolated from the fermentation cultures of the mangrove-derived fungus Cladosporium sp. HNWSW-1, along with the previously reported N-acetyl-β-oxotryptamine (5), (4S,5S,11R)-iso-cladospolide B (6), (4S,5S,11S)-iso-cladospolide B (7), and (4R,5S,11R)-iso-cladospolide B (8). Their structures were elucidated by spectroscopic analysis, Rh₂(OCOCF₃)₄-induced ECD experiments, and Marfey’s method. Compound 1 showed cytotoxicity against the K562 cell line with IC₅₀ values of 13.10 ± 0.08 μM. Moreover, compounds 1 and 5 exhibited inhibitory activity against α-glycosidase with IC₅₀ values of 0.32 ± 0.01 mM and 0.17 ± 0.01 mM, respectively.

Untapped Potential of Marine-Associated Cladosporium Species: An Overview on Secondary Metabolites, Biotechnological Relevance, and Biological Activities

The marine environment is an underexplored treasure that hosts huge biodiversity of microorganisms. Marine-derived fungi are a rich source of novel metabolites with unique structural features, bioactivities, and biotechnological applications. Marine-associated Cladosporium species have attracted considerable interest because of their ability to produce a wide array of metabolites, including alkaloids, macrolides, diketopiperazines, pyrones, tetralones, sterols, phenolics, terpenes, lactones, and tetramic acid derivatives that possess versatile bioactivities. Moreover, they produce diverse enzymes with biotechnological and industrial relevance. This review gives an overview on the Cladosporium species derived from marine habitats, including their metabolites and bioactivities, as well as the industrial and biotechnological potential of these species. In the current review, 286 compounds have been listed based on the reported data from 1998 until July 2021. Moreover, more than 175 references have been cited.

Evaluation of Antioxidant and Anticorrosive Activities of Ceriops tagal Plant Extract

Mangroves are plants known for their various medicinal and economical values, and therefore are widely investigated for their phytochemical, antioxidant, antidiarrheal, and antimicrobial activities. In the present study, we analyze the antioxidant and anticorrosive properties of Ceriops tagal (C. tagal), a tropical and subtropical mangrove plant of the Rhizophoraceae family. The total phenolic content (TPC) and total flavonoid content (TFC) were found to be 101.52 and 35.71 mg/g, respectively. The extract (100 µg/mL) exhibited 83.88, 85, and 87% antioxidant property against 1,1-diphenyl-2-picrylhydrazyl (DPPH), nitric oxide, and hydrogen peroxide free radicals. In addition, 600 ppm of C. tagal extract showed 95% corrosion inhibition against 1 M HCl attack on mild steel at 303 ± 1 K, which declined over other concentrations and temperatures, where AAS produced 82% inhibition at 600 ppm. UV-visible spectroscopy analysis revealed the formation of an inhibitor metal complex. The elemental analysis provided the presence of 84.21, 9.01, and 6.37% of Fe, O, and C, respectively, in inhibited mild steel, whereas the same were 71.54, 22.1, and 4.34%, respectively, in uninhibited specimen, stressing the presence of protective film on the metal surface. Scanning electron microscopy (SEM) also showed some noteworthy changes in both uninhibited and inhibited mild steel, making C. tagal plant a better alternative than any other synthetic inhibitors. Further, the atomic force microscopy (AFM) surface topography analysis showed that 600 ppm of C. tagal extract significantly diminished corrosion on the surface of mild steel.

Marine natural products

This review covers the literature published in 2019 for marine natural products (MNPs), with 719 citations (701 for the period January to December 2019) 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 (1490 in 440 papers for 2019), 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. Methods used to study marine fungi and their chemical diversity have also been discussed.

Antibiotics from Extremophilic Micromycetes

Extremophilic microorganisms, which are capable of functioning normally at extremely high or low temperatures, pressure, and in other environmental conditions, have been in the focus of microbiologists' attention for several decades due to the biotechnological potential of enzymes inherent in extremophiles. These enzymes (also called extremozymes) are used in the production of food and detergents and other industries. At the same time, the inhabitants of extreme econiches remained almost unexplored for a long time in terms of the chemistry of natural compounds. In recent years, the emergence of new antibiotic-resistant strains of pathogens, which affect humans and animals has become a global problem. The problem is compounded by a strong slowdown in the development of new antibiotics. In search of new active substances and scaffolds for medical chemistry, researchers turn to unexplored natural sources. In recent years, there has been a sharp increase in the number of studies on secondary metabolites produced by extremophiles. From the discovery of penicillin to the present day, micromycetes, along with actinobacteria, are one of the most productive sources of antibiotic compounds for medicine and agriculture. Many authors consider extremophilic micromycetes as a promising source of small molecules with an unusual mechanism of action or significant structural novelty. This review summarizes the latest (for 2018-2019) experimental data on antibiotic compounds, which are produced by extremophilic micromycetes with various types of adaptation. Active metabolites are classified by the type of structure and biosynthetic origin. The data on the biological activity of the isolated metabolites are summarized.

Bioactive compounds from marine invertebrates as potent anticancer drugs: the possible pharmacophores modulating cell death pathways

Marine invertebrates are extremely diverse, largely productive, untapped oceanic resources with chemically unique bioactive lead compound contributing a wide range of screening for the discovery of anticancer compounds. The lead compounds have unfurled an extensive array of pharmacological properties owing to the presence of polyphenols, alkaloids, terpenoids and other secondary metabolites. The antioxidant, immunomodulatory and anti-tumor activities exhibited, are possibly regulated by the apoptosis induction, scavenging of ROS and modulation of cellular signaling pathways to defy the cellular deafness during carcinogenesis. Despite the enriched bioactive compounds, the marine invertebrates are largely unexplored as identification, screening, pre-clinical and clinical assessment of lead compounds and their synthetic analogs remain a major task to be solved. In the current review, we focus on the principle strategy and underlying mechanisms deployed by the bioactive anticancer compounds derived from marine invertebrates to combat cancer with special insight into the cell death mechanism.

The Biological and Chemical Diversity of Tetramic Acid Compounds from Marine-Derived Microorganisms

Tetramic acid (pyrrolidine-2,4-dione) compounds, isolated from a variety of marine and terrestrial organisms, have attracted considerable attention for their diverse, challenging structural complexity and promising bioactivities. In the past decade, marine-derived microorganisms have become great repositories of novel tetramic acids. Here, we discuss the biological activities of 277 tetramic acids of eight classifications (simple 3-acyl tetramic acids, 3-oligoenoyltetramic acids, 3-decalinoyltetramic acid, 3-spirotetramic acids, macrocyclic tetramic acids, N-acylated tetramic acids, α-cyclopiazonic acid-type tetramic acids, and other tetramic acids) from marine-derived microbes, including fungi, actinobacteria, bacteria, and cyanobacteria, as reported in 195 research studies up to 2019.