Fungi offer a deep source of natural products but remain underutilized. Most biosynthetic gene clusters (BGCs) that can be detected are silent or “cryptic” in standard lab cultures and their products ...are thus not interrogated in routine screens. As genetic alterations are difficult and some strains can only be grown on agar, we have herein applied an agar‐based high‐throughput chemical genetic screen to identify inducers of fungal BGCs. Using R. solani and S. sclerotiorum as test cases, we report 13 cryptic metabolites in four compound groups, including sclerocyclane, a natural product with a novel scaffold. Steroids were the best elicitors and follow‐up studies showed that plant‐steroids trigger sclerocyclane synthesis, which shows antibiotic activity against B. plantarii, an ecological competitor of S. sclerotiorum. Our results open new paths to exploring the chemical ecology of fungal‐plant interactions and provide a genetics‐free approach for uncovering cryptic fungal metabolites.
Fungi encode a diverse array of secondary metabolites that remain to be mined. The first agar‐based high‐throughput elicitor screen with two fungal strains was conducted and led to the identification of FDA‐approved drugs as strong enhancers of secondary metabolism. The elicitors enabled the discovery of 13 novel cryptic metabolites, notably sclerocyclane with an unprecedented azatropane scaffold and antimicrobial activity against an ecological competitor of fungi.
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Natural products provide an important source of pharmaceuticals and chemical tools. Traditionally, assessment of unexplored microbial phyla has led to new natural products. However, with every new ...microbe, the number of orphan biosynthetic gene clusters (BGC) grows. As such, the more difficult proposition is finding new molecules from well‐studied strains. Herein, we targeted Streptomyces rimosus, the widely‐used oxytetracycline producer, for the discovery of new natural products. Using MALDI‐MS‐guided high‐throughput elicitor screening (HiTES), we mapped the global secondary metabolome of S. rimosus and structurally characterized products of three cryptic BGCs, including momomycin, an unusual cyclic peptide natural product with backbone modifications and several non‐canonical amino acids. We elucidated important aspects of its biosynthesis and evaluated its bioactivity. Our studies showcase HiTES as an effective approach for unearthing new chemical matter from “drained” strains.
Microbial producers of pharmaceuticals still code for dozens of yet‐to‐be identified natural products. Herein, three groups of cryptic metabolites were uncovered from Streptomyces rimosus, the industrial producer of oxytetracycline, using high‐throughput elicitor screening, notably momomycin, a novel cyclic peptide with antiproliferative properties.
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Covering: up to June 2021A wide variety of mushrooms have traditionally been recognized as edible fungi with high nutritional value and low calories, and abundantly produce structurally diverse and ...bioactive secondary metabolites. However, accidental ingestion of poisonous mushrooms can result in serious illnesses and even death. Chemically, mushroom poisoning is associated with secondary metabolites produced in poisonous mushrooms, causing specific toxicity. However, many poisonous mushrooms have not been fully investigated for their secondary metabolites, and the secondary metabolites of poisonous mushrooms have not been systematically summarized for details such as chemical composition and biosynthetic mechanisms. The isolation and identification of secondary metabolites from poisonous mushrooms have great research value since these compounds could be lethal toxins that contribute to the toxicity of mushrooms or could provide lead compounds with remarkable biological activities that can promote advances in other related disciplines, such as biochemistry and pharmacology. In this review, we summarize the structures and biological activities of secondary metabolites identified from poisonous mushrooms and provide an overview of the current information on these metabolites, focusing on their chemistry, bioactivity, and biosynthesis.
The absolute-configuration determination of natural products and synthetic compounds with stereogenic centers is very important because stereoisomers dramatically and differentially affect many ...crucial properties, such as physical behaviors and biological functions. Despite several established methods for determining the absolute configuration, significant unmet needs for new methods still exist owing to the specific limitations of established methodologies. Here, we present a simple, optimized, new chemical-derivative method that utilizes competing enantioselective acylation followed by LC/MS analysis, and we demonstrate its successful application in determining the absolute configuration of a secondary alcohol in natural products with multiple reactive functional groups. This new development relies on the enantiomeric pair of homobenzotetramisole (HBTM) catalysts exhibiting adequate kinetic resolution for acylation of the secondary alcohol, and then the fast reaction was quantitatively confirmed via LC/MS as the characterization technique for the enantioselective transformations. Our new approach was successfully applied to determine the absolute configuration of one secondary alcohol in compound 1, which has other hydroxyl groups to be reacted. The identified stereocenter of 1 was verified by previously established methods including quantum chemical electronic-circular-dichroism (ECD) calculations, computational NMR-chemical-shift calculations followed by DP4+ calculations, and modified Mosher’s method. In addition, our method was applied to five known naturally occurring compounds, which led to the successful verification of their absolute configurations. Our newly developed method using the HBTM catalyst provides a highly sensitive, simple, and cost- and time-effective approach and an applicable and convenient analytical method for determining the absolute configuration of one secondary alcohol in natural products.
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In our ongoing research to discover natural products with neuroprotective effects, hyperoside (quercetin 3-O-galactoside) was isolated from Acer tegmentosum, which has been used in Korean traditional ...medicine to treat liver-related disorders. Here, we demonstrated that hyperoside protects cultured dopaminergic neurons from death via reactive oxygen species (ROS)-dependent mechanisms, although other relevant mechanisms of hyperoside activity remain largely uncharacterized. For the first time, we investigated the neuroprotective effects of hyperoside on 6-hydroxydopamine (6-OHDA)-induced neurotoxicity in neurons, and the possible underlying mechanisms. Hyperoside significantly ameliorated the loss of neuronal cell viability, lactate dehydrogenase release, excessive ROS accumulation and mitochondrial membrane potential dysfunction associated with 6-OHDA-induced neurotoxicity. Furthermore, hyperoside treatment activated the nuclear erythroid 2-related factor 2 (Nrf2), an upstream molecule of heme oxygenase-1 (HO-1). Hyperoside also induced the expression of HO-1, an antioxidant response gene. Remarkably, we found that the neuroprotective effects of hyperoside were weakened by an Nrf2 small interfering RNA, which blocked the ability of hyperoside to inhibit neuronal death, indicating the vital role of HO-1. Overall, we show that hyperoside, via the induction of Nrf2-dependent HO-1 activation, suppresses neuronal death caused by 6-OHDA-induced oxidative stress. Moreover, Nrf2-dependent HO-1 signaling activation represents a potential preventive and therapeutic target in Parkinson's disease management.
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A pregnane steroid, 3α-hydroxy-pregn-7-ene-6,20-dione (1), was isolated from a Hydractinia-associated Cladosporium sphaerospermum SW67 by repetitive column chromatographic separation and ...high-performance liquid chromatography (HPLC) purification. The planar structure of 1 was elucidated from the analysis of the spectroscopic data (1D and 2D NMR spectra) and LC-MS data. The absolute configuration of 1 was determined by interpretation of ROESY spectrum of 1, together with the comparison of reported spectroscopic values in previous studies. To the best of our knowledge, this is the first report of the identification of the pregnane scaffold from C. sphaerospermum, a natural source. Compound 1 was evaluated for its effects on lipid metabolism and adipogenesis during adipocyte maturation and showed that compound 1 substantially inhibited lipid accumulation compared to the control. Consistently, the expression of the adipocyte marker gene (Adipsin) was reduced upon incubation with 1. Further, we evaluated the effects of 1 on lipid metabolism by measuring the transcription of lipolytic and lipogenic genes. The expression of the lipolytic gene ATGL was significantly elevated upon exposure to 1 during adipogenesis, whereas the expression of lipogenic genes FASN and SREBP1 was significantly reduced upon treatment with 1. Thus, our findings provide experimental evidence that the steroid derived from Hydractinia-associated C. sphaerospermum SW67 is a potential therapeutic agent for obesity. KCI Citation Count: 4
Three new macrocyclic trichothecenes (1–3) and five known related compounds (4–8) were isolated from the MeOH extract of a plate culture of the fungus Podostroma cornu-damae, a deadly poisonous ...mushroom. Miophytocen D (1) is a rearranged macrocyclic type D trichothecene, featuring a bicyclo-6.5dodecahydrocyclopentabchromene scaffold, and the structures of new compounds (1–3) were delineated by the combination of 1D and 2D NMR spectroscopic experiments and HRESIMS, modified Mosher’s esterification, and quantum chemical ECD calculations. The isolated compounds (1–8) were evaluated for cytotoxicity against four human breast cancer cell lines (Bt549, HCC70, MDA-MB-231, and MDA-MB-468). Compounds 4, 6, and 8 exhibited significant cytotoxic effects against the breast cancer cell lines, with IC50 values in the range of 0.02–80 nM, which is stronger than doxorubicin, the positive control, and a structure–activity relationship was suggested.
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A new 28-norlupane triterpenoid, 3-acetate-28-norlup-20(29)-en-3β-hydroxy-17β-hydroperoxide (1) and a new tirucallane triterpenoid, cornusalterin M (2), together with one known triterpenoid, ...3-acetate-28-norlup-20(29)-en-3β,17β-diol (3), were isolated from a MeOH extract of the stems of Cornus walteri. The chemical structures of the new compounds (1 and 2) were elucidated based on comprehensive one- and two-dimensional (1D and 2D) NMR spectroscopic experiments and high resolution-electrospray ionization (HR-ESI)-MS. Among the isolates, compound 1 was a relatively rare triterpenoid identified as a 28-norlupane-type triterpene with a 17β-hydroperoxide group and compound 3 was previously reported but only as a synthetic product. The cytotoxic activities of the isolated compounds 1–3 were evaluated by determining their inhibitory effects on human tumor cell lines (A549 (non-small cell lung carcinoma), SK-OV-3 (ovary malignant ascites), SK-MEL-2 (skin melanoma), and HCT-15 (colon adenocarcinoma)).
Microbial secondary metabolite discovery is often conducted in pure monocultures. In a natural setting, however, where metabolites are constantly exchanged, biosynthetic precursors are likely ...provided by symbionts or hosts. In the current work, we report eight novel and architecturally unusual secondary metabolites synthesized by the bacterial symbiont Phaeobacter inhibens from precursors that, in a native context, would be provided by their algal hosts. Three of these were produced at low titres and their structures were determined de novo using the emerging microcrystal electron diffraction method. Some of the new metabolites exhibited potent algaecidal activity suggesting that the bacterial symbiont can convert algal precursors, tryptophan and sinapic acid, into complex cytotoxins. Our results have important implications for the parasitic phase of algal‐bacterial symbiotic interactions.
The emerging method MicroED was used in combination with NMR spectroscopy to elucidate the structures of eight novel and unusual alkaloids produced by the marine bacterial symbiont Phaeobacter inhibens when it is challenged with algal metabolites. Four of these molecules exhibited algaecidal activity, indicating that the bacteria can combine algal precursors to produce complex, hybrid natural products that kill the algal host.
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The fruits of the mulberry tree (
L.), known as white mulberry, have been consumed in various forms, including tea, beverages, and desserts, worldwide. As part of an ongoing study to discover ...bioactive compounds from
fruits, the anti-inflammatory effect of compounds from
were evaluated in lipopolysaccharide (LPS)-stimulated mouse RAW 264.7 macrophages. Phytochemical analysis of the ethanol extract of the
fruits led to the isolation of 22 compounds. Among the isolated compounds, to the best of our knowledge, compounds
,
,
,
,
,
, and
were identified from
fruits for the first time in this study. Inhibitory effects of 22 compounds on the production of the nitric oxide (NO) known as a proinflammatory mediator in LPS-stimulated RAW 264.7 macrophages were evaluated using NO assays. Western blot analysis was performed to evaluate the anti-inflammatory effects of cyclo(L-Pro-L-Val) (
). We evaluated whether the anti-inflammatory effects of cyclo(L-Pro-L-Val) (
) following LPS stimulation in RAW 264.7 macrophages occurred because of phosphorylation of IκB kinase alpha (IKKα), IκB kinase beta (IKKβ), inhibitor of kappa B alpha (IκBα), nuclear factor kappa B (NF-κB) and activations of inducible nitric oxide synthase (iNOS), and cyclooxygenase-2 (COX-2). Cyclo(L-Pro-L-Val) (
) significantly suppressed phosphorylations of IKKα, IKKβ, IκBα, and NF-κB and activations of iNOS and COX-2 in a concentration-dependent manner. Taken together, these results indicate that cyclo(L-Pro-L-Val) (
) can be considered a potential therapeutic agent for the treatment of inflammation-associated disorders.
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