Isocoumarindole A, a Chlorinated Isocoumarin and Indole Alkaloid Hybrid Metabolite from an Endolichenic Fungus Aspergillus sp

Steroids and Epicoccarines from Penicillium aurantiancobrunneum

Lichens are symbiotic organisms comprised of mycobionts and photobiont partners. They are known to produce bioactive secondary metabolites and most of these are biosynthesized by mycobionts. Investigations of cultures of isolated lichen-associated fungi have shown promise for the discovery of cytotoxic compounds. Thus, the lichen-associated fungus Penicillium aurantiacobrunneum was studied for its potential to produce novel compounds and the new sterols (20S*)-hydroxy-24(28)-dehydrocampesterol (1), 7α-methoxy-8β-hydroxypaxisterol (2), 14-nor-epicoccarine A (3) and 14-nor-epicoccarine B (4), as well as the known compound PF1140 (5), were isolated. The structures of these compounds were elucidated using methods including nuclear magnetic resonance (NMR) spectroscopy and high-resolution electrospray ionization mass spectrometry (HRESIMS). Following cytotoxicity assays, compound 1 demonstrated activity against the pancreatic adenocarcinoma epithelial HPAC cell line at 17.76 ± 5.35 μM. Since the structures of compounds 3 and 4 were very similar to tetramic acid derivatives that were reported to be biosynthesized from a polyketide synthase- non-ribosomal peptide synthetase (PKS-NRPS) hybrid pathway, a plausible biosynthetic route for production in P. aurantiacobrunneum is proposed herein.

Three new isocoumarin analogues from an endolichenic fungus Aspergillus flavus CPCC 400810

Five isocoumarin derivatives including three new compounds, aspermarolides A-C (1-3), and two known analogues, 8-methoxyldiaporthin (4) and diaporthin (5) were obtained from the culture extract of Aspergillus flavus CPCC 400810. The structures of these compounds were elucidated by spectroscopic methods. The double bond geometry of 1 and 2 were assigned by the coupling constants. The absolute configuration of 3 was determined by electronic circular dichroism experiment. All compounds showed no cytotoxic activities against the two human cancer cells HepG2 and Hela.

Three undescribed compounds from Diaporthe biguttusis T-24, an endophytic fungus isolated from Ligularia fischeri

Diaporthpyran A (1), diaporthester E (2) and diaporthester F (3), three new compounds along with four known compounds (4-7) were isolated from the crude extract of Diaporthe biguttusis T-24, an endophytic fungus isolated from Ligularia fischeri. The planar structures of compounds 1-3 including the relative and absolute configurations were elucidated on the basis of HRMS, NMR, J-based coupling constant analysis, CD, and calculated ECD analysis. In addition, compounds 1 and 3 were evaluated for their cytotoxic activities against four human cancer cell lines.

OSMAC Strategy: A promising way to explore microbial cyclic peptides

Microbial secondary metabolites are pivotal for the development of novel drugs. However, conventional culture techniques, have left a vast array of unexpressed biosynthetic gene clusters (BGCs) in microorganisms, hindering the discovery of metabolites with distinct structural features and diverse biological functions. To address this limitation, several innovative strategies have been emerged. The "One Strain Many Compounds" (OSMAC) strategy, which involves altering microbial culture conditions, has proven to be particularly effective in mining numerous novel secondary metabolites for the past few years. Among these, microbial cyclic peptides stand out. These peptides often comprise rare amino acids, unique chemical structures, and remarkable biological function. With the advancement of the OSMAC strategy, a plethora of new cyclic peptides have been identified from diverse microbial genera. This work reviews the progress in mining novel compounds using the OSMAC strategy and the applications of this strategy in discovering 284 microbial cyclic peptides from 63 endophytic strains, aiming to offer insights for the further explorations into novel active cyclic peptides.

Endolichenic Fungi: A Promising Medicinal Microbial Resource to Discover Bioactive Natural Molecules-An Update

Lichens are some of the most unique fungi and are naturally encountered as symbiotic biological organisms that usually consist of fungal partners (mycobionts) and photosynthetic organisms (green algae and cyanobacteria). Due to their distinctive growth environments, including hot deserts, rocky coasts, Arctic tundra, toxic slag piles, etc., they produce a variety of biologically meaningful and structurally novel secondary metabolites to resist external environmental stresses. The endofungi that live in and coevolve with lichens can also generate abundant secondary metabolites with novel structures, diverse skeletons, and intriguing bioactivities due to their mutualistic symbiosis with hosts, and they have been considered as strategically significant medicinal microresources for the discovery of pharmaceutical lead compounds in the medicinal industry. They are also of great importance in the fundamental research field of natural product chemistry. In this work, we conducted a comprehensive review and systematic evaluation of the secondary metabolites of endolichenic fungi regarding their origin, distribution, structural characteristics, and biological activity, as well as recent advances in their medicinal applications, by summarizing research achievements since 2015. Moreover, the current research status and future research trends regarding their chemical components are discussed and predicted. A systematic review covering the fundamental chemical research advances and pharmaceutical potential of the secondary metabolites from endolichenic fungi is urgently required to facilitate our better understanding, and this review could also serve as a critical reference to provide valuable insights for the future research and promotion of natural products from endolichenic fungi.

Unexpected Noremestrin with a Sulfur-Bearing 15-Membered Macrocyclic Lactone from Emericella sp. 1454

Two previous unreported epipolythiodioxopiperazines of the emestrin family, namely, noremestrin A (1) and secoemestrin E (2), were successfully isolated from the fungal source Emericella sp. 1454. Employing comprehensive spectroscopic techniques, such as high-resolution electrospray ionization mass spectrometry, infrared, and nuclear magnetic resonance (NMR), along with NMR and electronic circular dichroism calculations, the chemical structures of compounds 1 and 2 were elucidated. Particularly noteworthy is the distinctive nature of noremestrin A, representing the inaugural instance of a noremestrin variant incorporating a sulfur-bearing 15-membered macrocyclic lactone moiety. Compounds 1 and 2 exhibited weak cytotoxic activities against the human chronic myelocytic leukemia cell lines MEG-01 and K562.

Meroterpenoids with divers' rings systems from Phyllosticta capitalensis and their anti-inflammatory activity

Four undescribed sesquiterpene-shikimates (1-4), eight undescribed monoterpene-shikimates (5-12), together with two known ones were isolated and identified from the 95% ethanol extract of the plant endophytic fungus Phyllosticta capitalensis cultured in rice medium. Capitalensis A (1) was identified as the first sesquiterpene-shikimate-conjugated spirocyclic meroterpenoid degradation product, while capitalensis B (2) is a sesquiterpene-shikimate-conjugated spirocyclic meroterpenoid with a unique D-ring formed by a C-2-O-C-9' connection. The structures of these previously undescribed compounds were elucidated by multiple techniques, including IR, HR-ESI-MS, and NMR analysis. Furthermore, their absolute configurations were established through the comprehensive approach that involved the calculations of ECD spectra, optical rotation values, and single-crystal X-ray analysis. Moreover, the anti-inflammatory activity of all isolated compounds was evaluated using a lipopolysaccharide (LPS)-induced inflammation model in BV2 microglial cells. Meanwhile, these compounds exhibited activity in inhibiting NO production. Four compounds, capitalensis C (3), capitalensis D (4), 15-hydroxyl tricycloalternarene 5b (13) and guignarenone A (14) showed strong inhibitory effects with IC50 values of 21.6 ± 1.33, 12.2 ± 1.08, 18.6 ± 1.27, and 15.8 ± 1.20 μM, respectively. In addition, the structure-activity relationship of the anti-inflammatory activity of the compounds was discussed.

Unravelling the Secrets of α-Pyrones from Aspergillus Fungi: A Comprehensive Review of Their Natural Sources, Biosynthesis, and Biological Activities

Aspergillus, one of the most product-rich and genetically robust genera, contains a diverse range of species with potential economic and ecological implications. Chemically, Aspergillus is one of the essential sources of polyketides, alkaloids, diphenyl ethers, diketopiperazines, and other miscellaneous compounds, displaying a variety of pharmacological activities. The α-pyrones are unsaturated six-membered lactones. Although α-pyrone has a small structure, it is responsible for the structural diversity of several natural and synthetic compounds and multiple biological activities. In this review, we have summarized approximately 178 α-pyrone containing metabolites derivatives identified/reported from terrestrial, marine, endophytic, and filamentous Aspergillus species, including their sources, biological properties, and biosynthetic pathways until mid-2023, for the first time. This review is the first to compile and analyze the available data on α-pyrone metabolites from Aspergillus, which could facilitate further research and innovation in this field. Additionally, it offers a valuable source of scaffolds for future bioactive drug development, as some of these metabolites have shown potent antimicrobial, anti-inflammatory, and anticancer effects. Therefore, this review has significant implications for the advancement of natural product chemistry, pharmacology, biotechnology, and medicine.

Alashanines A-C, Three Quinone-Terpenoid Alkaloids from Syringa pinnatifolia with Cytotoxic Potential by Activation of ERK

Three quinone-terpenoid alkaloids, alashanines A-C (1-3), possessing an unprecedented 6/6/6 tricyclic conjugated backbone and quinone-quinoline-fused characteristic, were isolated from the peeled stems of Syringa pinnatifolia. Their structures were elucidated by analysis of extensive spectroscopic data and quantum chemical calculations. A hypothesis of biosynthesis pathways for 1-3 was proposed on the basis of the potential precursor iridoid and benzoquinone. Compound 1 exhibited antibacterial activities against Bacillus subtilis and cytotoxicity against HepG2 and MCF-7 human cancer cell lines. The results of the cytotoxic mechanism revealed that compound 1 induced apoptosis of HepG2 cells through activation of ERK.

An indole diketopiperazine alkaloid and a bisabolane sesquiterpenoid with unprecedented skeletons from Aspergillus fumigatus

Fumitryprostatin A (1), the first example of an indole diketopiperazine alkaloid with a tricyclic 5/6/5 skeleton characterized by a dipyrrolo[1,2-a:1',2'-d]pyrazine-5,10-dione ring system decorated with a prenylated indole moiety, and fuminoid A (2), a sesquiterpenoid with a bicyclo[3.2.1]octane ring featuring a novel carbon skeleton via the transformation of the methyl, were isolated from the fungus Aspergillus fumigatus along with six known diketopiperazine alkaloids. The structure with the absolute configuration of 1 was determined based on spectroscopic analyses and X-ray crystallographic analysis, while the configuration of 2 was assigned tentatively by ¹³C NMR data with DP4+ probability analyses and ECD calculations. A plausible biosynthetic pathway for 1 was proposed starting from L-Trp and L-Pro via normal indole diketopiperazine. Compound 1 exhibited moderate cytotoxic activity with an IC₅₀ value of 14.6 μM, while compound 8 exhibited moderate immunosuppressive activity in vitro.

Recent advances in the discovery, biosynthesis, and therapeutic potential of isocoumarins derived from fungi: a comprehensive update

Microorganisms still remain the main hotspots in the global drug discovery avenue. In particular, fungi are highly prolific producers of vast structurally diverse specialized secondary metabolites, which have displayed a myriad of biomedical potentials. Intriguingly, isocoumarins is one distinctive class of fungal natural products polyketides, which demonstrated numerous remarkable biological and pharmacological activities. This review article provides a comprehensive state-of-the-art over the period 2000-2022 about the discovery, isolation, classifications, and therapeutic potentials of isocoumarins exclusively reported from fungi. Indeed, a comprehensive list of 351 structurally diverse isocoumarins were documented and classified according to their fungal sources [16 order/28 family/55 genera] where they have been originally discovered along with their reported pharmacological activities wherever applicable. Also, recent insights around their proposed and experimentally proven biosynthetic pathways are also briefly discussed.

The current scenario of naturally occurring indole alkaloids with anticancer potential

Naturally occurring indole alkaloids are ubiquitously present in nature and possess extensive biological properties and structural diversity. Mechanistically, naturally occurring indole alkaloids have the potential to inhibit cancer cell proliferation, arrest cell cycle and induce apoptosis. Accordingly, naturally occurring indole alkaloids exhibit promising activity against both drug-sensitive and drug-resistant cancers including multidrug-resistant forms. Therefore, naturally occurring indole alkaloids constitute an important source of anticancer drug leads and candidates. The goal of this review is to highlight the current scenario of naturally occurring indole alkaloids with anticancer potential, covering articles published from 2018 to present. The names, sources, and antiproliferative activity are discussed to continuously open up a map for the remarkable exploration of more effective candidates.

Exploration of the Main Antibiofilm Substance of Lactobacillus plantarum ATCC 14917 and Its Effect against Streptococcus mutans

Dental plaque, a complex biofilm system established by cariogenic bacteria such as Streptococcus mutans (S. mutans), is the initiator of dental caries. Studies have found that the cell-free supernatant (CFS) of Lactobacilli could inhibit S. mutans biofilm formation. However, the main antibiofilm substance of the Lactobacilli CFS that acts against S. mutans is unclear. The present study found that the CFS of Lactobacillus plantarum (L. plantarum) ATCC 14917 had the strongest antibiofilm effect among the five tested oral Lactobacilli. Further bioassay-guided isolation was performed to identify the main antibiofilm substance. The antibiofilm effect of the end product, named 1-1-4-3, was observed and the structure of it was elucidated by using Q-TOF MS, 2D NMR and HPLC. The results showed that several components in the CFS had an antibiofilm effect; however, the effect of 1-1-4-3 was the strongest, as it could reduce the generation of exopolysaccharides and make the biofilm looser and thinner. After structure elucidation and validation, 1-1-4-3 was identified as a mixture of lactic acid (LA) and valine. Additionally, LA was shown to be the main antibiofilm substance in 1-1-4-3. In summary, this study found that the antibiofilm effect of the L. plantarum CFS against S. mutans was attributable to the comprehensive effect of multiple components, among which LA played a dominant role.

Cytotoxic hexadepsipeptides and anti-coronaviral 4-hydroxy-2-pyridones from an endophytic Fusarium sp

Three new hexadepsipeptides (1-3), along with beauvericin (4), beauvericin D (5), and four 4-hydroxy-2-pyridone derivatives (6-9) were isolated from the endophytic fungus Fusarium sp. CPCC 400857 that derived from the stem of tea plant. Their structures were determined by extensive 1D and 2D NMR, and HRESIMS analyses. The absolute configuration of hexadepsipeptides were elucidated by the advanced Marfey's method and chiral HPLC analysis. Compounds 4, and 7-9 displayed the cytotoxicity against human pancreatic cancer cell line, AsPC-1 with IC₅₀ values ranging from 3.45 to 29.69 μM, and 7 and 8 also showed the antiviral activity against the coronavirus (HCoV-OC43) with IC₅₀ values of 13.33 and 6.65 μM, respectively.

Recent advances in research for potential utilization of unexplored lichen metabolites

Several research studies have shown that lichens are productive organisms for the synthesis of a broad range of secondary metabolites. Lichens are a self-sustainable stable microbial ecosystem comprising an exhabitant fungal partner (mycobiont) and at least one or more photosynthetic partners (photobiont). The successful symbiosis is responsible for their persistence throughout time and allows all the partners (holobionts) to thrive in many extreme habitats, where without the synergistic relationship they would be rare or non-existent. The ability to survive in harsh conditions can be directly correlated with the production of some unique metabolites. Despite the potential applications, these unique metabolites have been underutilised by pharmaceutical and agrochemical industries due to their slow growth, low biomass availability and technical challenges involved in their artificial cultivation. However, recent development of biotechnological tools such as molecular phylogenetics, modern tissue culture techniques, metabolomics and molecular engineering are opening up a new opportunity to exploit these compounds within the lichen holobiome for industrial applications. This review also highlights the recent advances in culturing the symbionts and the computational and molecular genetics approaches of lichen gene regulation recognized for the enhanced production of target metabolites. The recent development of multi-omics novel biodiscovery strategies aided by synthetic biology in order to study the heterologous expressed lichen-derived biosynthetic gene clusters in a cultivatable host offers a promising means for a sustainable supply of specialized metabolites.

Prenylemestrins A and B: Two Unexpected Epipolythiodioxopiperazines with a Thioethanothio Bridge from Emericella sp. Isolated by Genomic Analysis

Prenylemestrins A and B (1 and 2, respectively), two unusual epipolythiodioxopiperazines featuring a thioethanothio bridge instead of a polysulfide bridge, were isolated from the fungus Emericella sp. CPCC 400858 guided by genomic analysis. Their structures were determined by extensive spectroscopic data, NMR and ECD calculations, and X-ray diffraction analysis. A plausible biosynthetic pathway for 1 and 2 was proposed on the basis of gene cluster analysis. Prenylemestrins A and B exhibited cytotoxicities against human chronic myelocytic leukemia cell lines K562 and MEG-01.

Four new fatty acid derivatives from Diaporthe sp. T24, an endophytic fungus isolated from Ligularia fischer

The endophytic fungus Diaporthe sp. is known to contain many secondary metabolites, but fatty acid derivatives have rarely been found. In this study, four new fatty acid derivatives (1-4), together with four known compounds (5-8), were isolated from Diaporthe sp., which was obtained from the stem of Ligularia fischeri. The absolute configurations of the new compounds 1-4 were deduced based on spectroscopic technique and J-based coupling constant analysis. Moreover, compound 1 exhibited cytotoxic activities against HCT-8 and MCF-7 cancer cells, and compounds 3 and 4 showed modest selectivity for HCT-8 cells by MTT assay.

The synthesis of indole-3-carbinols (I3C) and their application to access unsymmetrical bis(3-indolyl)methanes (BIMs) bearing a quaternary sp3-carbon

In the present study, the novel synthesis of tert-indole-3-carbinols is reported through the DDQ-mediated oxidation of the allylic C-H bond/aromatization/hydroxylation at the indolyl carbon using water as the hydroxyl source. The reaction is highly efficient and high yielding and it works under mild reaction conditions. Furthermore, the synthetic value of such indole-based tert-carbinols is explored through their use as excellent electrophilic methylene surrogates to develop medicinally important unsymmetrical bis(3-indolyl)methanes containing an all carbon quaternary center.

Dehydromevalonolactone ameliorates liver fibrosis and inflammation by repressing activation of NLRP3 inflammasome

Liver fibrosis is an important process in chronic liver disease and is strongly related to poor prognosis. Dehydromevalonolactone (C8) is a natural product isolated from a fungus of Fusarium sp. CPCC 401218, and its pharmacological activity has never been reported before. In this study, the potential of C8 as an anti-hepatic fibrosis agent was investigated. In human hepatic stellate cell (HSC) line LX-2, C8 suppressed the increased expression of COL1A1 and α-SMA induced by TGFβ1, which indicated that C8 could repress the activation of HSCs. In bile duct ligated rats, C8 administration (100 mg/kg, i.p.) markedly attenuated liver injury, fibrosis, and inflammation, and suppressed the expression of the macrophage surface marker F4/80. In terms of mechanism, C8 treatment blocked the activation of the NLRP3 inflammasome, which was stimulated by LPS and nigericin in bone marrow-derived macrophages (BMDMs) and companied by the release of active IL-1β. In addition, the activation of LX-2 cells induced by IL-1β released from BMDMs was also inhibited after C8 administration, which indicated that C8 repressed HSCs activation by inhibiting the activation of NLRP3 inflammasome in macrophages. Furthermore, C8 exhibited the effects of anti-fibrosis and inhibiting the expression of NLRP3 inflammasome in non-alcoholic steatohepatitis (NASH) mice. Finally, C8 can be commendably absorbed in vivo and was safe for mice at the concentration of 1000 mg/kg (p.o.). In summary, our study reveals that C8 ameliorates HSCs activation and liver fibrosis in cholestasis rats and NASH mice by inhibiting NLRP3 inflammasome in macrophages, and C8 might be a safe and effective candidate for the treatment of liver fibrosis.

Endolichenic Fungal Community Analysis by Pure Culture Isolation and Metabarcoding: A Case Study of Parmotrema tinctorum

Lichen is a symbiotic mutualism of mycobiont and photobiont that harbors diverse organisms including endolichenic fungi (ELF). Despite the taxonomic and ecological significance of ELF, no comparative investigation of an ELF community involving isolation of a pure culture and high-throughput sequencing has been conducted. Thus, we analyzed the ELF community in Parmotrema tinctorum by culture and metabarcoding. Alpha diversity of the ELF community was notably greater in metabarcoding than in culture-based analysis. Taxonomic proportions of the ELF community estimated by metabarcoding and by culture analyses showed remarkable differences: Sordariomycetes was the most dominant fungal class in culture-based analysis, while Dothideomycetes was the most abundant in metabarcoding analysis. Thirty-seven operational taxonomic units (OTUs) were commonly observed by culture- and metabarcoding-based analyses but relative abundances differed: most of common OTUs were underrepresented in metabarcoding. The ELF community differed in lichen segments and thalli in metabarcoding analysis. Dissimilarity of ELF community intra lichen thallus increased with thallus segment distance; inter-thallus ELF community dissimilarity was significantly greater than intra-thallus ELF community dissimilarity. Finally, we tested how many fungal sequence reads would be needed to ELF diversity with relationship assays between numbers of lichen segments and saturation patterns of OTU richness and sample coverage. At least 6000 sequence reads per lichen thallus were sufficient for prediction of overall ELF community diversity and 50,000 reads per thallus were enough to observe rare taxa of ELF.

Xylarins A-D, Two Pairs of Diastereoisomeric Isoindoline Alkaloids from the Endolichenic Fungus Xylaria sp

Two pairs of diastereoisomeric isoindoline alkaloids, xylarins A-D (1-4), were isolated from the endolichenic fungus Xylaria sp. Xylarins A and B (1 and 2) possess a previously undescribed 5/6/5-5/6 polycyclic scaffold, featuring a combination of a novel dihydrobenzofurone unit and an isoindoline unit, while xylarins C and D (3 and 4) contain an additional N,N-dimethylaniline at the C-3' position. Their structures were elucidated by comprehensive spectroscopic analyses combined with single-crystal X-ray diffraction and electronic circular dichroism calculations. The plausible biosynthetic pathways and gene clusters for 1-4 were proposed. Compound 1 exhibited significant antithrombotic activity.

New lignans from the fruits of Leonurus japonicus and their hepatoprotective activities

Twelve tetrahydrofuran lignans (1-12), including six new compounds (1-6), were isolated from the 70% EtOH extract of the fruits of Leonurus japonicus. Spectroscopic analyses and ECD and OR calculations were used to determine their structures. Compounds 5 and 6 were unusual alkaloidal lignans with a butyrolactam unit. Based on the beneficial effects of the fruits of L. japonicus (Chongweizi in Chinese) on the liver in traditional Chinese medicine (TCM), the hepatocyte protective activities of the isolates were studied by MTT, Hoechst 33,342 staining, and western blotting. The MTT results revealed that compounds 1, 2, 7, and 8 significantly increased the survival rates of HL-7702 cells injured by acetaminophen, with EC₅₀ values of 10.41 ± 0.90 μM, 19.86 ± 3.13 μM, 9.68 ± 1.93 μM, and 21.35 ± 3.58 μM, respectively. In the Hoechst 33,342 fluorescence staining, compounds 1 and 7 suppressed the apoptosis of the injured HL-7702 cells. Furthermore, the western blot analysis showed that compounds 1 and 7 increased the Bcl-2/Bax protein expression ratio and procaspase-3 protein expression, indicating that compounds 1 and 7 may exert hepatoprotective activity by regulating the mitochondrial apoptotic pathway.

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.

Inhibition of Isoleucyl-tRNA Synthetase by the Hybrid Antibiotic Thiomarinol

Hybrid antibiotics are an emerging antimicrobial strategy to overcome antibiotic resistance. The natural product thiomarinol A is a hybrid of two antibiotics: holothin, a dithiolopyrrolone (DTP), and marinolic acid, a close analogue of the drug mupirocin that is used to treat methicillin-resistant Staphylococcus aureus (MRSA). DTPs disrupt metal homeostasis by chelating metal ions in cells, whereas mupirocin targets the essential enzyme isoleucyl-tRNA synthetase (IleRS). Thiomarinol A is over 100-fold more potent than mupirocin against mupirocin-sensitive MRSA; however, its mode of action has been unknown. We show that thiomarinol A targets IleRS. A knockdown of the IleRS-encoding gene, ileS, exhibited sensitivity to a synthetic analogue of thiomarinol A in a chemical genomics screen. Thiomarinol A inhibits MRSA IleRS with a picomolar K_i and binds to IleRS with low femtomolar affinity, 1600 times more tightly than mupirocin. We find that thiomarinol A remains effective against high-level mupirocin-resistant MRSA and provide evidence to support a dual mode of action for thiomarinol A that may include both IleRS inhibition and metal chelation. We demonstrate that MRSA develops resistance to thiomarinol A to a substantially lesser degree than mupirocin and the potent activity of thiomarinol A requires hybridity between DTP and mupirocin. Our findings identify a mode of action of a natural hybrid antibiotic and demonstrate the potential of hybrid antibiotics to combat antibiotic resistance.

A critical review on the use of DP4+ in the structural elucidation of natural products: the good, the bad and the ugly. A practical guide

Covering: 2015 up to the end of 2020Even in the golden age of NMR, the number of natural products being incorrectly assigned is becoming larger every day. The use of quantum NMR calculations coupled with sophisticated data analysis provides ideal complementary tools to facilitate the elucidation process in challenging cases. Among the current computational methodologies to perform this task, the DP4+ probability is a popular and widely used method. This updated version of Goodman's DP4 synergistically combines NMR calculations at higher levels of theory with the Bayesian analysis of both scaled and unscaled data. Since its publication in late 2015, the use of DP4+ to solve controversial natural products has substantially grown, with several predictions being confirmed by total synthesis. To date, the structures of more than 200 natural products were determined with the aid of DP4+. However, all that glitters is not gold. Besides its intrinsic limitations, on many occasions it has been improperly used with potentially important consequences on the quality of the assignment. Herein we present a critical revision on how the scientific community has been using DP4+, exploring the strengths of the method and how to obtain optimal results from it. We also analyze the weaknesses of DP4+, and the paths to by-pass them to maximize the confidence in the structural elucidation.

Antimicrobial Compounds Isolated from Endolichenic Fungi: A Review

A lichen is a symbiotic relationship between a fungus and a photosynthetic organism, which is algae or cyanobacteria. Endolichenic fungi are a group of microfungi that resides asymptomatically within the thalli of lichens. Endolichenic fungi can be recognized as luxuriant metabolic artists that produce propitious bioactive secondary metabolites. More than any other time, there is a worldwide search for new antibiotics due to the alarming increase in microbial resistance against the currently available therapeutics. Even though a few antimicrobial compounds have been isolated from endolichenic fungi, most of them have moderate activities, implying the need for further structural optimizations. Recognizing this timely need and the significance of endolichenic fungi as a promising source of antimicrobial compounds, the activity, sources and the structures of 31 antibacterial compounds, 58 antifungal compounds, two antiviral compounds and one antiplasmodial (antimalarial) compound are summarized in this review. In addition, an overview of the common scaffolds and structural features leading to the corresponding antimicrobial properties is provided as an aid for future studies. The current challenges and major drawbacks of research related to endolichenic fungi and the remedies for them have been suggested.

Neuroprotective Activities of Constituents from Phyllosticta capitalensis, an Endophyte Fungus of Loropetalum chinense var. rubrum

One new dioxolanone derivative, guignardianone G (1) and twelve known compounds (2-13) were isolated from the 95 % ethanol extract of the plant endophytic fungus Phyllosticta capitalensis cultured in rice medium. Among these known compounds, isoaltenuene (3), brassicasterol (7), 5,6-epoxyergosterol (8), citreoanthrasteroid A (9), demethylincisterol A (10), and chaxine C (11) were reported from Phyllosticta sp. for the first time. The structure of 1 was elucidated by 1D- and 2D-NMR experiments and HR-ESI-MS data analysis, and its absolute configuration was established through the comprehensive use of the methods of modified Mosher methods, calculations of ECD spectra and optical rotation values. The neuroprotective activity of compounds (1-9, 11-13) were evaluated on PC12 cells damage induced by glutamate, and compounds 9 and 12 showed potential neuroprotective activities with half effective concentration (EC₅₀ ) of 24.2 and 33.9 μM, respectively.

New phenol and chromone derivatives from the endolichenic fungus Daldinia species and their antiviral activities

Three new phenolic metabolites, daldispols A–C (1–3), two new chromone derivatives, (5R,7R)-5,7-dihydroxy-2-methyl-5,6,7,8-tetrahydro-4H-chromen-4-one (9) and (5R,7R)-5,7-dihydroxy-2-propyl-5,6,7,8-tetrahydro-4H-chromen-4-one (10), together with five known phenolic compounds (4–8) and two known chromone compounds (11 and 12) were isolated from the endolichenic fungus Daldinia sp. CPCC 400770. Their structures were elucidated on the basis of spectroscopic methods, electronic circular dichroism (ECD), and comparison with reported data. Compounds 1, 3, 4, 9, and 11 exhibited significant anti-influenza A virus (IAV) activities with IC₅₀ values of 12.7, 6.4, 12.5, 16.1, and 9.0 μM, respectively, and compound 8 displayed significant anti-ZIKV activity with inhibitory ratio of 42.7% at 10 μM. The results demonstrated that the fungus Daldinia sp. CPCC 400770 might be a rich source for discovering anti-IAV secondary metabolites as potential novel leading compounds.

Eight phenols including three new ones (1–3) and four chromones including two new ones (9 and 10) were isolated from endolichenic fungus Daldinia sp. CPCC 400770, and some of them showed significant antiviral activities.

Structurally Diverse Sesquiterpenoids with Anti-neuroinflammatory Activity from the Endolichenic Fungus Cryptomarasmius aucubae

Two new sterpurane sesquiterpenoids named sterpurol D (1) and sterpurol E (2), and one skeletally new sesquiterpene, cryptomaraone (3), bearing a 5,6-fused bicyclic ring system, along with five known ones, sterpurol A (4), sterpurol B (5), paneolilludinic Acid (6), murolane-2α, 9β-diol-3-ene (7) and (-)-10,11-dihydroxyfarnesol (8) were isolated from an endolichenic fungus Cryptomarasmius aucubae. The structures of the new compounds were elucidated by analysis of NMR spectroscopic spectra and HRESIMS data. The absolute configurations of 1 and 2 were established by spectroscopic data analysis and comparison of specific optical rotation, as well as the biosynthetic consideration. Additionally, compounds 1, 2, 4-6, and 8 showed significant nitric oxide (NO) production inhibition in Lipopolysaccharide (LPS)-induced BV-2 microglial cells with the IC50 values ranging from 9.06 to 14.81 μM.

Fusapyrone A, a γ-pyrone derived from a desert Fusarium sp

In this work, we isolated and characterized fusapyrone A (1), a new γ-pyrone derivative, along with six previously described compounds from the rice fermentation of Fusarium sp. CPCC 401218, a fungus collected from the desert. The structure of 1 was characterized using various spectroscopic analyses, such as MS, IR, 1D, and 2D NMR. The absolute configuration of 1 was determined through the use of ¹³C NMR chemical shifts, electronic circular dichroism (ECD) and optical rotation (OR) calculations. Compound 1 was found to have weak antiproliferative activity for Hela cells, with an IC₅₀ of 50.6 μM.[Formula: see text].

Microbial Transformation of neo-Clerodane Diterpenoid, Scutebarbatine F, by Streptomyces sp. CPCC 205437

Biotransformation of the neo-clerodane diterpene, scutebarbatine F (1), by Streptomyces sp. CPCC 205437 was investigated for the first time, which led to the isolation of nine new metabolites, scutebarbatine F₁–F₉ (2–10). Their structures were determined by extensive high-resolution electrospray ionization mass spectrometry (HRESIMS) and NMR data analyses. The reactions that occurred included hydroxylation, acetylation, and deacetylation. Compounds 2–4 and 8–10 possess 18-OAc fragment, which were the first examples of 13-spiro neo-clerodanes with 18-OAc group. Compounds 7–10 were the first report of 13-spiro neo-clerodanes with 2-OH. Compounds 1–10 were biologically evaluated for the cytotoxic, antiviral, and antibacterial activities. Compounds 5, 7, and 9 exhibited cytotoxic activities against H460 cancer cell line with inhibitory ratios of 46.0, 42.2, and 51.1%, respectively, at 0.3 μM. Compound 5 displayed a significant anti-influenza A virus activity with inhibitory ratio of 54.8% at 20 μM, close to the positive control, ribavirin.

DDQ/FeCl3-mediated tandem oxidative carbon-carbon bond formation for the Synthesis of indole-fluorene hybrid molecules

A series of diverse and complex hybrid structures of indole bearing fluorene were obtained in the presence of DDQ with high regioselectivity under mild conditions from biaryl tethered 3-(methylene)indoline in good to excellent yields. The strategy involves tandem allylic Csp³-H oxidation and subsequent intramolecular carbon-carbon bond formation. The yield of the product was dramatically improved in the presence of additives such as FeCl₃ and molecular sieves (4 Å). A possible mechanism is proposed for this tandem process.

Three new isocoumarin derivatives from the mangrove endophytic fungus Penicillium sp. YYSJ-3

Three new isocoumarin derivatives, (S)-6,8-dihydroxy-5-(methoxymethyl)-3,7-dimethylisochroman-1-one (1), (S)-6,8-dihydroxy-3,5,7-trimethyl-isochroman-1-one (2) and (R)-2-chloro-3-(8-hydroxy-6-methoxy-1-oxo-1H-isochromen-3-yl) propyl acetate (3), along with four known compounds (4-7) were isolated from a mangrove endophytic fungus Penicillium sp. YYSJ-3. Their structures were established on the basis of the extensive spectroscopic data and HR-ESI-MS analysis. The absolute configurations of 1-3 were further determined by X-ray diffraction analysis and optical rotations. Compounds 3, 6 and 7 showed promising inhibitory activity against α-glucosidase, which were stronger than that of the positive control 1-deoxynojirimycin (IC₅₀ 141.2 μmol·L^-1).

Xanthanoltrimer A–C: three xanthanolide sesquiterpene trimers from the fruits of Xanthium italicum Moretti isolated by HPLC-MS-SPE-NMR

Xanthanoltrimer A–C, first three xanthanolide sesquiterpene trimers from the fruits of Xanthium italicum Moretti, were isolated by HPLC-MS-SPE-NMR. Xanthanoltrimer A–C had an unprecedented 5/7/6/5/7/6/5/7 polycyclic scaffold.

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.

Survey of natural products reported by Asian research groups in 2019

The new natural products reported in 2019 in peer-reviewed articles in journals with good reputations were reviewed and analyzed. The advances made by Asian research groups in the field of natural products chemistry in 2019 were summarized. Compounds with unique structural features and/or promising bioactivities originating from Asian natural sources were discussed based on their structural classification.

Naturally Occurring Isocoumarins Derivatives from Endophytic Fungi: Sources, Isolation, Structural Characterization, Biosynthesis, and Biological Activities

Recently, the metabolites separated from endophytes have attracted significant attention, as many of them have a unique structure and appealing pharmacological and biological potentials. Isocoumarins represent one of the most interesting classes of metabolites, which are coumarins isomers with a reversed lactone moiety. They are produced by plants, microbes, marine organisms, bacteria, insects, liverworts, and fungi and possessed a wide array of bioactivities. This review gives an overview of isocoumarins derivatives from endophytic fungi and their source, isolation, structural characterization, biosynthesis, and bioactivities, concentrating on the period from 2000 to 2019. Overall, 307 metabolites and more than 120 references are conferred. This is the first review on these multi-facetted metabolites from endophytic fungi.

New Dihydroisocoumarin Root Growth Inhibitors From the Sponge-Derived Fungus Aspergillus sp. NBUF87

Six new dihydroisocoumarins, aspergimarins A-F (1-6), were discovered together with five known analogs (7-11) from a monoculture of the sponge-derived fungus Aspergillus sp. NBUF87. The structures of these compounds were elucidated through comprehensive spectroscopic methods, and absolute configurations were assigned after X-ray crystallography, use of the modified Mosher's method, and comparison of electronic circular dichroism (ECD) data with literature values for previously reported analogs. Compounds 1-11 were evaluated in a variety of bioassays, and at 100 μM, both 1 and 5 showed significant inhibitory effects on the lateral root growth of Arabidopsis thaliana Columbia-0 (Col-0). Moreover, at 100 μM, 5 also possessed notable inhibition against the primary root growth of Col-0. Meanwhile, 1-11 were all found to be inactive in vitro against acetylcholinesterase (AChE) (IC50 > 100 μM), four different types of human-derived cancer cell lines (IC50 > 50 μM), as well as methicillin-resistant Staphylococcus aureus and Escherichia coli (MIC > 50 μg/mL), and Plasmodium falciparum W2 (EC50 > 100 μg/mL), in phenotypic tests.

Cytotoxic Indolyl Diketopiperazines from the Aspergillus sp. GZWMJZ-258, Endophytic with the Medicinal and Edible Plant Garcinia multiflora

Two new indolyl diketopiperazines, gartryprostatins A and B (1 and 2), with an unusual 2,3-furan-fused pyrano[2,3-g]pyrrolo[1″,2″:4',5']pyrazino[1',2':1,5]pyrrolo[2,3-b]indole nucleus, along with a new naturally occurring compound (gartryprostatin C, 3) were isolated from the solid culture of Aspergillus sp. GZWMJZ-258, an endophyte from Garcinia multiflora (Guttiferae). The structures of compounds 1-3 were determined by nuclear magnetic resonance, mass spectrometry, Marfey's analysis of amino acids, and chemical calculation. Compounds 1-3 displayed selective inhibition on human FLT3-ITD mutant AML cell line, MV4-11, with IC₅₀ values of 7.2, 10.0, and 0.22 μM, respectively.

The Purification, Characterization, and Biological Activity of New Polyketides from Mangrove-Derived Endophytic Fungus Epicoccum nigrum SCNU-F0002

Six new polyketides, including one coumarin (1), two isocoumarins (2 and 3), dihydroradicinin (4), and two benzofuranone derivatives (7 and 8), together with seven known analogues (5–6 and 9–13) were isolated from the culture of the mangrove endophytic fungus Epicoccum nigrum SCNU-F0002. The structures were elucidated on the interpretation of spectroscopic data. The absolute configuration of Compounds 2 and 3 were determined by comparison of their ECD spectra with the data of their analogue dihydroisocoumarins described in the literature. The absolute configuration of 4 was determined by single-crystal X-ray diffraction. All the compounds were screened for their antioxidant, antibacterial, anti-phytopathogenic fungi and cytotoxic activities. Using a DPPH radical-scavenging assay, Compounds 10–13 showed potent antioxidant activity with IC₅₀ values of 13.6, 12.1, 18.1, and 11.7 μg/mL, respectively. In addition, Compounds 6 and 7 showed antibacterial effects against Bacillus subtilis (ATCC 6538), Escherichia coli (ATCC 8739), and Staphylococcus aureus (ATCC 6538), with MIC values in the range of 25–50 μg/mL.

Cytotoxic and neuroprotective activities of constituents from Alternaria alternate, a fungal endophyte of Psidium littorale

Chemical investigation of the EtOAc extract of the plant-associated fungus Alternaria alternate in rice culture led to the isolation of a novel liphatic polyketone, alternin A (1), a new indole alkaloid (8), and a new sesquiterpene (11), together with 12 known compounds. Their structures were elucidated by the interpretation of extensive spectroscopic data, and the absolute configurations of 1-3 were established using calculations of ECD spectra, NMR data, and optical rotation values. Compound 1 possesses an unprecedented C25 liphatic polyketone skeleton. Compounds 5 and 10 exhibited potential cytotoxic activities against MCF-7 and HepG cells, and compounds 2, 7, and 9 exhibited potential neuroprotective activities in glutamate induced-PC12 injured cells.

Cytotoxic metabolites from the endophytic fungus Chaetomium globosum 7951

The following compounds were isolated from acetate extracts of Chaetomium globosum 7951 solid cultures: demethylchaetocochin C (1) and chaetoperazine A (3), two new epipolythiodioxopiperazine (ETP) alkaloids, a novel pyridine benzamide, 4-formyl-N-(3′-hydroxypyridin-2′-yl) benzamide (6), and three known ETP derivatives (2, 4, and 5). The structures of these compounds were determined using extensive spectroscopic data analysis. Compounds 1–3, and 6, inhibited the growth of MCF-7, MDA-MB-231, H460 and HCT-8 cells with an IC₅₀ of 4.5 to 65.0 μM.

Demethylchaetocochin C and chaetoperazine A, two new epipolythiodioxopiperazine alkaloids, and three known analogs were isolated from Chaetomium globosum 7951. Demethylchaetocochin C significantly inhibits human lung cancer cell growth.