Natural resorcylic lactones derived from alternariol

In this overview, naturally occurring resorcylic lactones biosynthetically derived from alternariol and almost exclusively produced by fungi, are discussed with view on their isolation, structure, biological activities, biosynthesis, and total syntheses. This class of compounds consists until now of 127 naturally occurring compounds, with very divers structural motifs. Although only a handful of these toxins (i.e., alternariol and its 9-O-methyl ether, altenusin, dehydroaltenusin, altertenuol, and altenuene) were frequently found and isolated as fungal contaminants in food and feed and have been investigated in significant detail, further metabolites, which were much more rarely found as natural products, similarly show interesting biological activities.

Antibacterial Polyketides from the Deep-Sea Cold-Seep-Derived Fungus Talaromyces sp. CS-258

Thirty-two fungal polyketide derivatives, including eleven new compounds, namely (3R,5'R)-5-hydroxytalaroflavone (1), talaroisochromenols A-C (3, 5, and 11), (8R,9R,10aR)-5-hydroxyaltenuene (13), (8R,9R,10aS)-5-hydroxyaltenuene (14), (8R,9S,10aR)-5-hydroxyaltenuene (15), nemanecins D and E (25 and 26), 2,5-dimethyl-8-iodochromone (27), and talarofurolactone A (29), together with one new naturally occurring but previously synthesized metabolite, 6-hydroxy-4-methoxycoumarin (28), were isolated and identified from the deep-sea cold-seep-derived fungus Talaromyces sp. CS-258. Among them, racemic ((±)-11) or epimeric (13-15, 25, and 26) mixtures were successfully separated by chiral or gradient elution HPLC. Meanwhile, compound 27 represents a rarely reported naturally occurring iodinated compound. Their planar structures as well as absolute configurations were determined by extensive analysis via NMR, MS, single-crystal X-ray diffraction, Mosher's method, and ECD or NMR calculation (with DP4+ probability analysis). Possible biosynthetic routes of some isolated compounds, which are related to chromone or isochromone biosynthetic pathways, were put forward. The biological analysis results revealed that compounds 7, 9, 10, 18-22, 24, 30, and 31 showed broad-spectrum antibacterial activities against several human and aquatic pathogens with MIC ranges of 0.5-64 μg/mL.

Cytotoxic and antimicrobial mycophenolic acid derivatives from an endophytic fungus Penicillium sp. MNP-HS-2 associated with Macrozamia communis

Macrozamia communis and its associated endophytic fungi are untapped sources of bioactive metabolites with great potential for medicinal exploitation. Chemical investigation of the mycelial extract derived from an endophytic fungus Penicillium sp. MNP-HS-2 associated with M. communis fruit afforded four mycophenolic acid derivatives recognized as previously undescribed natural products (1-4), together with nine known metabolites (5-13). Chemical structures of isolated compounds were determined based on extensive spectroscopic analyses, including 1D/2D NMR and HRESIMS. The absolute stereochemistry of alternatain E (1) was unambiguously established by comparing its experimental and calculated time-dependent density functional theory electronic circular dichroism spectra (TDDFT-ECD). All isolated compounds were assessed for their antimicrobial and cytotoxic activities, where mycophenolic acid methyl ester (7), displayed significant cytotoxic activity against seven different cell lines with IC50 values in the low micromolar to nanomolar range. Mycophenolene A (3) exhibited significant antibacterial activity against Staphylococcus aureus (MIC = 2.1 μg/mL).

Mangrove-associated endomycota: diversity and functional significance as a source of novel drug leads

Endophytic fungi are known for their unprecedented ability to produce novel lead compounds of clinical and pharmaceutical importance. This review focuses on the unexplored fungal diversity associated with mangroves, emphasizing their biodiversity, distribution, and methodological approaches targeting isolation, and identification. Also highlights the bioactive compounds reported from the mangrove fungal endophytes. The compounds are categorized according to their reported biological activities including antimicrobial, antioxidant and cytotoxic property. In addition, protein kinase, α-glucosidase, acetylcholinesterase, tyrosinase inhibition, antiangiogenic, DNA-binding affinity, and calcium/potassium channel blocking activity are also reported. Exploration of these endophytes as a source of pharmacologically important compounds will be highly promising in the wake of emerging antibiotic resistance among pathogens. Thus, the aim of this review is to present a detailed report of mangrove derived endophytic fungi and to open an avenue for researchers to discover the possibilities of exploring these hidden mycota in developing novel drug leads.

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.

Exploring the Mangrove Fruit: From the Phytochemicals to Functional Food Development and the Current Progress in the Middle East

Nowadays, the logarithmic production of existing well-known food materials is unable to keep up with the demand caused by the exponential growth of the human population in terms of the equality of access to food materials. Famous local food materials with treasury properties such as mangrove fruits are an excellent source to be listed as emerging food candidates with ethnomedicinal properties. Thus, this study reviews the nutrition content of several edible mangrove fruits and the innovation to improve the fruit into a highly economic food product. Within the mangrove fruit, the levels of primary metabolites such as carbohydrates, protein, and fat are acceptable for daily intake. The mangrove fruits, seeds, and endophytic fungi are rich in phenolic compounds, limonoids, and their derivatives as the compounds present a multitude of bioactivities such as antimicrobial, anticancer, and antioxidant. In the intermediary process, the flour of mangrove fruit stands as a supplementation for the existing flour with antidiabetic or antioxidant properties. The mangrove fruit is successfully transformed into many processed food products. However, limited fruits from species such as Bruguiera gymnorrhiza, Rhizophora mucronata, Sonneratia caseolaris, and Avicennia marina are commonly upgraded into traditional food, though many more species demonstrate ethnomedicinal properties. In the Middle East, A. marina is the dominant species, and the study of the phytochemicals and fruit development is limited. Therefore, studies on the development of mangrove fruits to functional for other mangrove species are demanding. The locally accepted mangrove fruit is coveted as an alternate food material to support the sustainable development goal of eliminating world hunger in sustainable ways.

Structures and absolute configurations of butenolide derivatives from the isopod-associated fungus Pidoplitchkoviella terricola

In this research, twenty aromatic and branched aliphatic polyketides, including seven previously undescribed butenolide derivatives, piterriones A-G and one known analogue, along with twelve known altenusin derivatives, were isolated from the isopod-associated fungus Pidoplitchkoviella terricola. Their structures were elucidated by analysis of NMR (1D and 2D) and mass spectrometry data, and their absolute configurations were determined by Mosher's method, microscale derivatization, and comparison of their specific rotations and ECD spectra. Dihydroaltenuene B exhibited mushroom tyrosinase inhibitory activity with an IC₅₀ value of 38.33 ± 1.59 μM, which was comparable to that of the positive control, kojic acid (IC₅₀ = 39.72 ± 1.34 μM). A molecular-docking study disclosed the hydrogen bonding interactions between the 3-OH and 4'-OH of dihydroaltenuene B and the His244, Met280 and Gly281 residues of tyrosinase.

Anti-diabetic activities of phenolic compounds of Alternaria sp., an endophyte isolated from the leaves of desert plants growing in Egypt

Six phenolic compounds (talaroflavone (1), alternarienoic acid (2), altenuene (3), altenusin (4), alternariol (5), and alternariol-5-O-methyl ether (6)) were isolated from the solid rice culture media of Alternaria sp., an endophyte isolated from the fresh leaves of three desert plants, Lycium schweinfurthii Dammer (Solanaceae), Pancratium maritimum L. (Amaryllidaceae) and Cynanchum acutum L. (Apocynaceae). Compounds 2, 3, and 4 exhibited potent α-glucosidase and lipase inhibitory activities suggesting that they might act as naturally occurring anti-diabetic candidates. The same compounds showed potent binding in the active site for both enzymes with desirable pharmacokinetic properties. The isolated bioactive compounds were not exclusive to a certain host plant which reveals the dominant ecological standpoints for consequent optimization. This could lead to a cost-effective and reproducible yield applicable to commercial scale-up.

Six phenolic compounds were isolated from the solid rice culture media of Alternaria sp., an endophyte isolated from the leaves of three desert plants, Lycium schweinfurthii Dammer (Solanaceae), Pancratium maritimum L. (Amaryllidaceae) and Cynanchum acutum L. (Apocynaceae).

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.

New furo[3,2-h]isochroman from the mangrove endophytic fungus Aspergillus sp. 085242

Four new compounds, asperisocoumarin G (1), asperisocoumarin H (2), (±)-asperisocoumarin I [(±)-3], along with the known pergillin (4) and penicisochroman L (5) were isolated from a mangrove endophytic fungus Aspergillus sp. 085242 by further chemical investigation. The structures of the new compounds, including their absolute configurations, were established by analysis of HR-ESI-MS and NMR spectroscopic data, and ECD calculation. Asperisocoumarins G-I (1-3) were new isocoumarins belonging to the class of furo[3, 2-h]isocoumarins which are rarely found in natural sources. All of the isolated compounds were evaluated for their α-glucosidase inhibitory effects, and compounds 1 and 4 showed moderate α-glucosidase inhibitory activity, respectively. In an antimicrobial test, the racemate of 3 showed antibacterial activity against Salmonella.

Natural isocoumarins: Structural styles and biological activities, the revelations carry on …

Isocoumarins and dihydroisocoumarins are lactonic phytochemicals plentiful in microbes and higher plants. These are an amazing small scaffolds consecrated with all types of pharmacological applications. Our previous review covered the period 2000-2016, documenting the then known natural products of this class; the current article is a critical account of discovery of known as well as undescribed structural types and pharmacological activities reported in the course of 2016-2020. The classification revealed in our previous review based on the biogenetic origin is further buttressed by discovery of new members of each class and some new structural types hitherto unknown have also been identified. Similarly, the biological activities and SAR conclusions identified were found to be valid as well, nonetheless with new accompaniments. The most recent available literature on the structural diversity and biological activity of these natural products has been included. The information documented in this article are collected from scientific journals, books, electronic search engines and scientific databases.

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.

Amentotaxins C-V, Structurally Diverse Diterpenoids from the Leaves and Twigs of the Vulnerable Conifer Amentotaxus argotaenia and Their Cytotoxic Effects

A phytochemical investigation of the MeOH extract of the leaves and twigs of Amentotaxus argotaenia, a relict vulnerable coniferous species endemic to China, led to the isolation and characterization of 35 diterpenoids/norditerpenoids. Twenty of these are new, including 11 ent-kaurane-type (amentotaxins C-M, 1-11, respectively), three icetexane-type [= 9(10→20)abeo-abietane-type (amentotaxins N-P, 12-14, respectively)], four ent-labdane-type (amentotaxins Q-T, 15-18, respectively), and two isopimarane-type [amentotaxins U (19) and V (20)] compounds. Their structures were elucidated on the basis of spectroscopic data, single-crystal X-ray diffraction, the modified Mosher's method, and electronic circular dichroism data analyses. Compounds 1-9 are rare 18-nor-ent-kaurane-type diterpenoids featuring a 4β,19-epoxy ring. All the isolates were evaluated for their cytotoxic effects against a small panel of cultured human cancer cell lines (HeLa, A-549, MDA-MB-231, SKOV3, Huh-7, and HCT-116), and some of them exhibited cytotoxicities with IC₅₀ values ranging from 1.5 to 10.0 μM.

Polyketides from Alternaria alternata MT-47, an endophytic fungus isolated from Huperzia serrata

Four new polyketides, alternatains A-D (1-4), along with 17 known compounds (5-21) were obtained from the solid substrate fermentation cultures of Alternaria alternata MT-47, an endophytic fungus isolated from the medicinal plant of Huperzia serrata. Their structures were elucidated by extensive spectroscopic and spectrometric techniques (1D and 2D NMR, IR, and HRESIMS) and calculated electronic circular dichroism (ECD) method. Compounds 4, 6, 15, and 21 exhibited inhibitory activities on ATP release of thrombin-activated platelets with IC₅₀ values in the range of 18.2-68.8 μM.

Two New Altenusin/Thiazole Hybrids and a New Benzothiazole Derivative from the Marine Sponge-Derived Fungus Alternaria sp. SCSIOS02F49

Two novel altenusin-thiazole hybrids named altenusinoides A and B (1 and 2), a new benzothiazole derivative (3), and three known altenusin derivatives (4–6) have been obtained from the solid culture of the marine sponge-derived fungal strain, Alternaria sp. SCSIOS02F49. The structures of these new compounds were characterized by NMR, HRESIMS, and X-ray single crystal analysis. Compounds 1 and 2 possess an unusual altenusin-thiazole-fused skeleton core (6/6/5), and compound 3 represents the first benzothiazole derivative from fungi. Compounds 4 and 5 showed significant DPPH free-radical-scavenging activities with the prominent IC₅₀ values of 10.7 ± 0.09 μM and 100.6 ± 0.025 μM, respectively. Additionally, compound 5 exhibited COX-2 inhibitory activity with an IC₅₀ value of 9.5 ± 0.08 μM.

α-Glucosidase Inhibitors: Diphenyl Ethers and Phenolic Bisabolane Sesquiterpenoids from the Mangrove Endophytic Fungus Aspergillus flavus QQSG-3

Two new diphenyl ethers (1 and 2) and four new phenolic bisabolane sesquiterpenoids (3–6), together with five known related derivatives, were isolated from the culture of the endophytic fungus Aspergillus flavus QQSG-3 obtained from a fresh branch of Kandelia obobata, which was collected from Huizhou city in the province of Guangdong, China. The structures of compounds 1–6 were determined by analyzing NMR and HRESIMS data. The absolute configurations of 5 and 6 were assigned by comparing their experimental ECD spectra with those reported for similar compounds in the literature. All isolates were evaluated for their α-glucosidase inhibitory activity, of which compounds 3, 5, 10, and 11 showed strong inhibitory effects with IC₅₀ values in the range of 1.5–4.5 μM.

Perylenequione Derivatives with Anticancer Activities Isolated from the Marine Sponge-Derived Fungus, Alternaria sp. SCSIO41014

Seven new secondary metabolites classified as two perylenequinone derivatives (1 and 2), an altenusin derivative (3), two phthalide racemates (4 and 5), and two phenol derivatives (6 and 7), along with twenty-one known compounds (8–28) were isolated from cultures of the sponge-derived fungus, Alternaria sp. SCSIO41014. The structures and absolute configurations of these new compounds (1–7) were determined by spectroscopic analysis, X-ray single crystal diffraction, chiral-phase HPLC separation, and comparison of ECD spectra to calculations. Altertoxin VII (1) is the first example possessing a novel 4,8-dihydroxy-substituted perylenequinone derivative, while the phenolic hydroxy groups have commonly always substituted at C-4 and C-9. Compound 1 exhibited cytotoxic activities against human erythroleukemia (K562), human gastric carcinoma cells (SGC-7901), and hepatocellular carcinoma cells (BEL-7402) with IC₅₀ values of 26.58 ± 0.80, 8.75 ± 0.13, and 13.11 ± 0.95 μg/mL, respectively. Compound 11 showed selectively cytotoxic activity against K562, with an IC₅₀ value of 19.67 ± 0.19 μg/mL. Compound 25 displayed moderate inhibitory activity against Staphylococcus aureus with an MIC value of 31.25 μg/mL.

Peniisocoumarins A-J: Isocoumarins from Penicillium commune QQF-3, an Endophytic Fungus of the Mangrove Plant Kandelia candel

Ten new isocoumarins, named peniisocoumarins A-J (1-9 and 11), along with three known analogues (10, 12, and 13) were obtained from the fermentation of an endophytic fungus, Penicillium commune QQF-3, which was isolated from a fresh fruit of the mangrove plant Kandelia candel. Their structures were elucidated through extensive spectroscopic analysis. The absolute configurations of 1-7 were determined by single-crystal X-ray diffraction and modified Mosher's method, and those of 8, 9, and 11 were assigned on the basis of experimental and calculated electronic circular dichroism data. Compounds 1 and 2 were unusual dimeric isocoumarins with a symmetric four-membered core. These isolated compounds (1-13) were evaluated for their cytotoxicity and enzyme inhibitory activities against α-glucosidase and Mycobacterium tuberculosis protein tyrosine phosphatase B (MptpB). Among them, compounds 3, 7, 9, and 11 exhibited potent inhibitory effects against α-glucosidase with IC₅₀ values ranging from 38.1 to 78.1 μM, and compound 7 was found to inhibit MptpB with an IC₅₀ value of 20.7 μM.

Marine natural products

Covering: 2016. Previous review: Nat. Prod. Rep., 2017, 34, 235-294This review covers the literature published in 2016 for marine natural products (MNPs), with 757 citations (643 for the period January to December 2016) 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 (1277 in 432 papers for 2016), together with the relevant biological activities, source organisms and country of origin. Reviews, biosynthetic studies, first syntheses, and syntheses that led to the revision of structures or stereochemistries, have been included.