Phytotoxic ent-Isopimarane-Type Diterpenoids from Euphorbia hylonoma

Discovery of a Hybrid Molecule with Phytotoxic Activity by Genome Mining, Heterologous Expression, and OSMAC Strategy

Genome mining in association with the OSMAC (one strain, many compounds) approach provides a feasible strategy to extend the chemical diversity and novelty of natural products. In this study, we identified the biosynthetic gene cluster (BGC) of restricticin, a promising antifungal agent featuring a reactive primary amine, from the fungus Aspergillus sclerotiorum LZDX-33-4 by genome mining. Combining heterologous expression and the OSMAC strategy resulted in the production of a new hybrid product (1), along with N-acetyl-restricticin (2) and restricticinol (3). The structure of 1 was determined by spectroscopic data, including optical rotation and electronic circular dichroism (ECD) calculations, for configurational assignment. Compound 1 represents a fusion of restricticin and phytotoxic cichorin. The biosynthetic pathway of 1 was proposed, in which the condensation of a primary amine of restricticin with a precursor of cichorine was postulated. Compound 1 at 5 mM concentration inhibited the growth of the shoots and roots of Lolium perenne, Festuca arundinacea, and Lactuca sativa with inhibitory rates of 71.3 and 88.7% for L. perenne, 79.4 and 73.0% for F. arundinacea, and 58.2 and 52.9% for L. sativa. In addition, compound 1 at 25 μg/mL showed moderate antifungal activity against Fusarium fujikuroi and Trichoderma harzianum with inhibition rates of 22.6 and 31.6%, respectively. These results suggest that heterologous expression in conjunction with the OSMAC approach provides a promising strategy to extend the metabolite novelty due to the incorporation of endogenous metabolites from the host strain with exogenous compounds, leading to the production of more complex compounds and the acquisition of new physiological functions.

Phytotoxic phenols from the needles of Cedrus deodara

During the course of screening for anti-seed germination phytochemicals, the methanol fraction of the Cedrus deodara fresh needles showed potent activity. Bioactivity-guided fractionation led to the isolation of thirty-eight phenolic compounds. Four ones were identified as previously undescribed including (7S,8S)-3-methoxy-9'-acetoxy-3',7-epoxy-8,4'-oxyneoligna-4,9-diol (7), (7S,8R)-dihydro-3'-hydroxy-8-acetoxymethyl-7-(4-hydroxy-3-methoxy-phenyl)-1'-benzofuranpropanol (10), (8S)-4,9,9'-trihydroxy-3,3'-dimethoxy-8,4'-oxyneolignan (11) and (7S,8S)-4,7,9'-trihydroxy-3,3'-dimethoxy-9-acetoxy-8,4'-oxyneolignan (16), respectively. The potential phytotoxic effects of these compounds on the seed germination and root elongation of Arabidopsis thaliana were evaluated by the filter paper assay developed in our laboratory. Bioassay results indicated that caffeic acid (36) displayed most significant inhibitory activities against the seed germination and root elongation of A. thaliana, stronger than those of the commercial herbicides acetochlor and glyphosate at the same concentration of 200 μg/mL. Ditetrahydrofuran lignan (1), dihydrochalcone (25), and eight simple phenols (28, 29, 31, 33-35, 37 and 38) completely inhibited the seed germination of A. thaliana at the concentration of 400 μg/mL, which were as active as acetochlor. Dihydroflavone (21) and the simple phenols 32-34 displayed stronger inhibitory effects on the root elongation of A. thaliana than that of glyphosate. The inhibitory effects of these active compounds on the seed germination and root elongation of Amaranthus tricolor and Lactuca sativa were evaluated as well. The phytotoxic activity of 11, 16, 22, 25, 31, 34, 37 and 38 were detected for the first time. In addition, the structure-activity relationships of the same class of these phytochemicals were discussed.

Pleosmaranes A-R, Isopimarane and 20-nor Isopimarane Diterpenoids with Anti-inflammatory Activities from the Mangrove Endophytic Fungus Pleosporales sp. HNQQJ-1

Pleosmaranes A-R (1-18), 18 new isopimarane-type diterpenoids, together with four known analogs (19-22), were isolated from the mangrove endophytic fungus Pleosporales sp. HNQQJ-1. Their structures and absolute configurations were established by analysis of their spectroscopic data and electronic circular dichroism (ECD) calculations. Compounds 1-9 possess an unusual aromatic B ring and a 20-nor-isopimarane skeleton. Compounds 15-17 contain a unique 2-oxabicyclo[2.2.2]octane moiety. Compound 18 features an unexpected 2-oxabicyclo[3.2.1]octane moiety. Compounds 8 and 12 exhibited a moderate inhibitory effect against LPS-induced NO production, with IC50 values of 19 and 25 μM, respectively.

Discovery of Ingenane Diterpenoids from Euphorbia hylonoma as Antiadipogenic Agents

Thirteen new Euphorbia diterpenoids, euphylonanes A-M (1-13), and eight known ones were isolated from the whole plants of Euphorbia hylonoma. Compounds 1 and 2 are two rearranged ingenanes bearing a rare 6/6/7/3-fused ring system. Compound 3 represents the first example of a 9,10-epoxy tigliane, while 4-21 are typical ingenanes varying with substituents. Structures were elucidated using a combination of spectroscopic, computational, and chemical methods. Most ingenanes exerted a significant antiadipogenic effect in 3T3-L1 adipocytes, among which 4 was the most active with an EC50 value of 0.60 ± 0.27 μM. Mechanistic study revealed that 4 inhibited the adipogenesis and lipogenesis in adipocytes via activation of the AMPK signaling pathway.

Yuexiandajisu diterpenoids from Euphorbia ebracteolata Hayata (Langdu roots): An overview

The roots of the plant Euphorbia ebracteolata Hayata (Yue Xian Da Ji) are commonly used in traditional Chinese medicine to treat multiple diseases such as chronic liver diseases, oedema, pulmonary diseases and cancer. It is the main ingredient of the TCM called Langdu which can be prepared also from roots of E. fischeriana Steud. and occasionally from Stellera chamaejasme species. Numerous bioactive natural products have been isolated from E. ebracteolata including a large diversity of diterpenoids with anti-inflammatory and anticancer properties. One little series of compounds has been named yuexiandajisu (A, B, C, D, D₁, E, F) which comprises two casbane-, one isopimarane-, two abietane-, and two rosane-type diterpenes including a dimeric molecule. The origin, structural diversity and properties of these little-known natural products is discussed here. Several of these compounds have been identified in the roots of other Euphorbia species, notably the potent phytotoxic agent yuexiandajisu C. The abietane diterpenes yuexiandajisu D-E exhibit marked anticancer properties but their mechanism of action remains unresolved. The dimeric compound, renamed yuexiandajisu D₁, also exhibit anti-proliferative properties against cancer cell lines, unlike the rosane diterpene yuexiandajisu F. The structural or functional analogy with other diterpenoids is discussed.

Euphylonoids A and B, Two Highly Modified Jatrophane Diterpenoids with Potent Lipid-Lowering Activity from Euphorbia hylonoma

Euphylonoids A (1) and B (2), two highly modified jatrophane diterpenoids, were isolated from Euphorbia hylonoma. 1 represents a new 9(10→18)-abeo-8,12-cyclojatrophane skeleton containing a cage-like 3,8-dioxatricyclo[5.1.2.0^4,9]decane core, while 2 is a 14(13→20)-abeo-8,12-cyclojatrophane featuring an unusual 17-oxatetracyclo[12.2.1.0^1,5.0^9,13]heptadecane framework. Their structural elucidation was completed by spectroscopic, chemical, computational, and single-crystal X-ray diffraction means. 2 significantly inhibited early adipogenesis in 3T3-L1 adipocytes via activating AMP-activated protein kinase signaling.

Phytochemical and pharmacological review of diterpenoids from the genus Euphorbia Linn (2012-2021)

ETHNOPHARMACOLOGICAL RELEVANCE

Euphorbia is one of the major genera in angiosperms, which is widely distributed all over the world, including Asia, Africa and Central and South America. The roots or tubers of Euphorbia are famous for medicinal purposes, especially in China. Many of them, such as Euphorbia pekinensis Rupr, Euphorbia fischeriana Steud and Euphorbia Kansui S.L.Liou ex S.B.Ho. . are used as Chinese herbal medicines.

AIM OF THE STUDY

This paper reviews the diterpenoids isolated from the genus Euphorbia species and the pharmacological activities of these compounds to evaluate its traditional use and potential future development.

MATERIALS AND METHODS

Information on the studies of the genus Euphorbia Linn was collected from scientific journals, books and reports via library and electronic data search (Scifinder, Web of Science, PubMed, Elsevier, Scopus, Google Scholar, Springer, Science Direct, Wiley, ACS, CNKI and Kew Plants of the Word Online). Meanwhile, it was also obtained from published works of material medica, folk records, ethnophmacological literatures, Ph.D. and Masters dissertations.

RESULTS

Known as the main constituents of the genus Euphorbia Linn, Diterpenoids possess many pharmacological properties such as anti-inflammation, antiviral activities and cytotoxicity. To date, various types of diterpenoids were identified from this genus, including isopimarane, rosane, abietane, ent-kaurane, ent-atisane. cembrane, casbane, lathyrane, myrsinane, jatropholane, tigliane, ingenane, jatrophane, paraliane, pepluane, and euphoractin.

CONCLUSIONS

This review describes 14 types of diterpenoid isolated from 45 Euphorbia species from 2012 to 2021, a total of 615 compounds. Among them, mainly include jatrophane (171), lathyrane (92), myrsinane (62), abietane (70), ent-atisane (36), ent-kaurane (7), tigliane (26) and ingenane (19). The possible biological pathways of these compounds were presumed. At the same time, more than 10 biological activities of these compounds were summarized, such as anti-inflammation, antiviral activities and cytotoxicity.

Euphorbia diterpenoids: isolation, structure, bioactivity, biosynthesis, and synthesis (2013-2021)

Covering: 2013 to 2021As the characteristic metabolites of Euphorbia plants, Euphorbia diterpenoids have always been a hot topic in related science communities due to their intriguing structures and broad bioactivities. In this review, we intent to provide an in-depth and extensive coverage of Euphorbia diterpenoids reported from 2013 to the end of 2021, including 997 new Euphorbia diterpenoids and 78 known ones with latest progress. Multiple aspects will be summarized, including their occurrences, chemical structures, bioactivities, and syntheses, in which the structure-activity relationship and biosynthesis of this class will be discussed for the first time.

Pimarane, abietane, and labdane diterpenoids from Euphorbia pekinensis Rupr. and their anti-tumor activities

Chemical investigation of the roots of Euphorbia pekinensis Rupr. led to the isolation of five undescribed labdane diterpenoids "(4S, 5S, 9R, 10S, 13R)-18-O-galloyl-labda-8(17), 14(15)-dien-13-ol; (4S, 5S, 9R, 10S, 13R)-13-hydroxy-labda-8(17), 14(15)-dien-18-one; (4S, 5S, 9R, 10S, 13R)-18-O-acetyl-labda-8(17), 14(15)-dien-13-ol; (4S, 5S, 9R, 10S)-labda-8(17), 13(16), 14(15)-trien-18-ol; (5R, 6R, 9R, 10S, 13R)-labda-8(17), 14(15)-dien-6,13-diol", two undescribed pimarane diterpenoids "(2R, 5S, 9R, 10S, 12R, 13R)-2,12-dihydroxy-isopimara-7,15-dien-3-one; (5S, 9R, 10S, 12R, 13R)-2, 12-dihydroxy-isopimara-1, 7, 15-trien-3-one)", together with nine known diterpenoids, including three pimarane-type "(3β,11α,13α)-3,11-dihydroxypimara-7,15-diene-2,12-dione; (11R, 12S)-2,11,12-trihydroxy-ent-isopimara-1,7,15-trien-3-one; isopimara-7,15-dien-3β-ol)", five abietane-type "helioscopinolide A-C; helioscopinolide E; helioscopinolide I″, and one lathyrane-type "jolkinol B". The structures of these compounds were elucidated by analysis of HRESIMS, 1D NMR, 2D NMR, and X-ray diffraction. These sixteen compounds were evaluated for cytotoxic activity in vitro against three human cancer cell lines, U-937, LOVO, and K-562. Jolkinol B exhibited IC₅₀ of 3.60 μM and 8.44 μM against U-937 and LOVO cell lines, (4S, 5S, 9R, 10S, 13R)-18-O-galloyl-labda-8(17), 14(15)-dien-13-ol displayed IC₅₀ of 5.92 μM against U-937 cell lines, isopimara-7,15-dien-3β-ol showed IC₅₀ of 0.87 μM against K-562 cell lines.

Integrated Strategy of UHPLC-Q-TOF-MS and Molecular Networking for Identification of Diterpenoids from Euphorbia fischeriana Steud. and Prediction of the Anti-Breast-Cancer Mechanism by the Network Pharmacological Method

Breast cancer is one of the most common malignancies in women worldwide. Traditional Chinese medicine has been used as adjunctive or complementary therapy for breast cancer. Diterpenoids from Euphorbia fischeriana Steud. have been demonstrated to possess anti-breast-cancer activity. This research was aimed to systematically explore the diterpenoids from E. fischeriana and study the multiple mechanisms on breast cancer. The structures of diterpenoids were identified by the integrated strategy of UHPLC-Q-TOF-MS and molecular networking. A total of 177 diterpenoids belonging to 13 types were collected. In silico ADME analysis was performed on these compounds. It indicated that 130 of 177 diterpenoids completely adjusted to Lipinski's rule. The targets of compounds were obtained from PharmMapper. The targets of breast cancer were collected from GeneCards. Then, 197 compounds-related targets and 544 breast cancer-related targets were identified. After the intersection process, 58 overlapping targets between compounds-related targets and breast cancer-related targets were acquired. The STRING database was applied to predict the protein-protein interactions. The GO and KEGG pathway enrichment analysis were performed by using the KOBAS database. It indicated that these predicted pathways were closely related to breast cancer. The treatment effect of E. fischeriana on breast cancer might be performed through signaling pathways, such as IL-17 signaling pathway, MAPK signaling pathway, and PI3K-Akt signaling pathway. The predicted top genes such as EGFR, ESR, MAPK, SRC, CASP3, CDK2, and KDR were involved in cell proliferation, gene transcription, apoptosis, signal transduction, DNA damage and repair, tumor differentiation, metastasis, and cell cycle, which indicated that E. fischeriana might treat breast cancer comprehensively. A compounds-KEGG pathways-related targets network was built by using cytoHubba to analyze the hub compounds and targets. It concluded that E. fischeriana treated breast cancer not only by the main components but also by the microconstituents, which reflected the overall regulatory role of multicomponents treating breast cancer. To estimate the binding affinities, binding sites, and binding postures, molecular docking simulations between 177 diterpenoids and top 19 targets were carried out. The results are basically in line with expectations. In conclusion, these results can serve as references for researchers studying potential targets of diterpenoids from E. fischeriana on breast cancer in the future.

Euphorfistrines A-G, cytotoxic and AChE inhibiting triterpenoids from the roots of Euphorbia fischeriana

Seven new triterpenoids including two cycloartanes (1-2), a lanostane (3), a tirucallane (4), a dammarane (5), an ursane (6), and an oleanane (7), along with nineteen known triterpenoids (8-26), have been obtained from the roots of Euphorbia fischeriana. Their structures were established by NMR, HRESIMS, single-crystal X-ray diffraction analysis, Mosher's method, NMR calculations, ECD analysis, and comparison with structurally related known analogues. Among them, compounds 1 and 8 were a pair of cycloartane-type triterpenoids epimers. Our bioassays have established that compounds 1-5 and 10 displayed moderate cytotoxic effects, and the structure-activity relationships of cycloartane-type triterpenoids (CTTs) were further examined. Notably, some triterpenoids displayed moderate inhibitory effects against AChE by an in vitro screened experiment. Triterpenoid 7 (Euphorfistrine G, ETG) displayed the potent inhibitory effect with IC₅₀ = 2.45 and K_i = 2.30 μM (inhibition kinetic). And, in silico docking analyses have been performed to investigate the inhibitory mechanism of compound 7.

Diterpenoids from the genus Euphorbia: Structure and biological activity (2013-2019)

Euphorbiaceae is one of the largest families of higher plants, including 7500 species, and many of them are used as medicines in China. From 2013 to 2019, a total of 455 previously undescribed diterpenoids were isolated from 53 species of Euphorbia, and some skeleton types were first discovered from the genus Euphorbia. Most of the diterpenoids isolated from Euphorbia spp. have been tested for their biological activity, and some of them were first reported for Euphorbia diterpenoids in recent years, such as neuroprotection, antimalarial activity and inhibition of osteoclast formation. In this review, we summarize all the isolated diterpenoids from the genus Euphorbia according to their skeleton types, classify all these diterpenoids into 26 normal classes and 37 novel skeleton types, and summarize their biological activity.

Euphnerins A and B, Diterpenoids with a 5/6/6 Rearranged Spirocyclic Carbon Skeleton from the Stems of Euphorbia neriifolia

Euphnerins A (1) and B (2), two extremely modified diterpenoids possessing an unprecedented 5/6/6 rearranged spirocyclic carbon skeleton, and a biosynthetically related known diterpenoid (3) were purified from the stems of Euphorbia neriifolia. Their structures were identified by NMR experiments and X-ray diffraction analysis, as well as experimental and calculated electronic circular dichroism data comparison. A putative biosynthetic relationship of 1 and 2 with their presumed precursor 3 is proposed. Compound 1 showed NO inhibitory effects in lipopolysaccharide-stimulated BV-2 cells with an IC₅₀ value of 22.4 μM.

Phytotoxic neo-clerodane diterpenoids from the aerial parts of Scutellaria barbata

Bioactivity guided the isolation of extracts from the aerial parts Scutellaria barbata D. Don to discover neo-clerodane diterpenoids with potent phytotoxic activity. Of the 34 isolates, 13 neo-clerodane diterpenoids were described for the first time. The structures of these undescribed compounds were elucidated by extensive analysis of NMR spectroscopic data, and the absolute configurations of scutebarbolides A and L and scutebata W were determined by X-ray diffraction. The phytotoxic activity of all compounds against the growth of the roots and shoots of L. perenne and L. sativa seedlings were first reported, and some compounds showed considerable inhibitory effects, especially scutebarbolide K, whose inhibition rates were higher than those of the positive control at concentrations ranging from 25 to 200 μg/mL. When L. perenne and L. sativa seedlings were treated at a concentration of 200 μg/mL, scutebarbolide K caused wilting symptoms on and finally death of these two tested plant seedlings. In addition, the structure-activity relationships of these neo-clerodane diterpenoids were also discussed.

Labdane-Type Diterpenoids from Leonurus japonicus and Their Plant-Growth Regulatory Activity

Thirteen new labdane-type diterpenoids 1-6, 9-11, 13, 14, 18, and 19 and seven known ones were isolated from the aerial parts of Leonurus japonicus. Compounds 1-5 represent rare examples of labdane-type diterpenoids, of which compounds 1-4 carry an N-chain linked at C-7 in their B-ring and compound 5 featured an α,β-unsaturated-γ-lactam moiety. The structures and absolute configurations of these new diterpenoids were characterized by a combination of spectroscopic techniques, X-ray crystallography, electronic circular dichroism, and calculated specific rotations. The plant-growth regulatory activity of these compounds on the growth of the roots and shoots of Lactuca sativa and Lolium perenne seedlings were evaluated. Compound 3 showed a broad-spectrum inhibitory activity with the inhibition rates ranging from 60 to 83.5% at a concentration of 200 μg/mL, which were as active as those of glyphosate. Compound 8 had a selective inhibitory activity against the growth of the roots of L. perenne seedlings with an inhibition rate of 81.7%. However, compounds 11 and 16 exhibited significant stimulation effects on the roots of L. sativa with stimulation rates of 59.8 and 65.3%, respectively. In addition, compounds 3 and 8 exhibited inhibitory effects on the germination of L. perenne seeds.

Phytotoxic Diterpenoids from Plants and Microorganisms

Phytotoxic natural products with either unique or various structures are one of the most abundant sources for the discovery of potential allelochemicals, natural herbicides, and plant growth regulators. Phytotoxic diterpenoids, a relatively large class of natural products, play an important role in the plant-plant or plant-microorganism interactions. This article argues that the phytotoxic diterpenoids isolated from the plants and microorganisms can either inhibit the seed germination and the growth of plant seedlings or lead to some disease symptoms on the tested plant tissues and plant seedlings.