Cytotoxic sesquiterpene lactones from Eupatorium lindleyanum

Targeting thioredoxin reductase by eupalinilide B promotes apoptosis of colorectal cancer cells in vitro and in vivo

Aberrant activation of thioredoxin reductase (TrxR) is correlated with tumor occurrence and progression, suggesting that TrxR inhibitors can be used as antitumor agents. In this study, we evaluated the anticancer efficacy of eupalinilides B on colorectal cancer cells. Eupalinilides B primarily targeted the conserved selenocysteine 498 residues in TrxR. Besides, it inhibited the enzyme activity in an irreversible manner. After eupalinilides B was used to pharmacologically inhibit TrxR, reactive oxygen species accumulated, and the intracellular redox balance was broken, finally causing oxidative stress-induced tumor cell apoptosis. Significantly, eupalinilides B treatment inhibited in vivo tumor growth. Targeting TrxR by eupalinilides B reveals the new mechanism underlying eupalinilides B and provides insight in developing eupalinilides B as the candidate antitumor chemotherapeutic agent for the treatment of cancer.

Mechanistic study on the side arm effect in a palladium/Xu-Phos-catalyzed enantioselective alkoxyalkenylation of γ-hydroxyalkenes

Recently, the asymmetric bifunctionalization of alkenes has received much attention. However, the development of enantioselective alkoxyalkenylation has posed a considerable challenge and has lagged largely behind. Herein, we report a new palladium-catalyzed enantioselective alkoxyalkenylation reaction, using a range of primary, secondary, and tertiary γ-hydroxy-alkenes with alkenyl halides. By employing newly identified Xu-Phos (Xu8 and Xu9) with a suitable side-arm adjacent to the PCy2 motif, a series of allyl-substituted tetrahydrofurans were obtained in good yields with up to 95% ee. Besides (E)-alkenyl halides, (Z)-alkenyl halide was also examined and provided the corresponding (Z)-product as a single diastereomer, supporting a stereospecific oxidative addition and reductive elimination step. Moreover, deuterium labeling and VCD experiments were employed to determine a cis-oxypalladation mechanism. DFT calculations helped us gain deeper insight into the side-arm effect on the chiral ligand. Finally, the practicability of this method is further demonstrated through a gram-scale synthesis and versatile transformations of the products.

Regio- and Stereoselective Hydrochlorination/Cyclization of 1,n-Enynes by FeCl3 Catalysis

A highly regio- and stereoselective hydrochlorination/cyclization of enynes has been reported by FeCl₃ catalysis. A variety of enynes undergo this cyclization transformation with acetic chloride as the chlorine source and H₂O providing protons via a cationic pathway. This protocol provides a cheap, simple, stereospecific, and effective cyclization to afford heterocyclic alkenyl chloride compounds as Z isomers with high yields (≤98%) and regioselectivity.

Asymmetric Total Synthesis of Eupalinilide E, a Promoter of Human HSPC Expansion

A concise and scalable asymmetric total synthesis of eupalinilde E from (R)-(-)-carvone in 12 steps is reported with an overall yield of 20%. The key steps of the synthesis are a tandem Favorskii rearrangement-elimination reaction in the chromatography-free synthesis of carvone-derived 2-cyclopentene carbaldehyde and its catalyst-free stereospecific tandem allylboration-lactonization using recyclable trifluoroethanol as a promoter and solvent affording β-hydroxymethyl-α-methylene-γ-butyrolactone.

Eupalinilide B as a novel anti-cancer agent that inhibits proliferation and epithelial–mesenchymal transition in laryngeal cancer cells

Objective

To investigate the anti-cancer effects and potential mechanisms of eupalinilide B in laryngeal cancer cells.

Methods

Laryngeal cancer cell lines were selected to study the anti-tumor effects of eupalinilide B in vitro and in vivo. Lysine-specific demethylase 1 (LSD1) activity was assessed in vitro and dialysis experiments were performed to identify the anti-tumor target of the drug.

Results

Eupalinilide B concentration-dependently inhibited the proliferation of laryngeal cancer cells, exhibiting potent inhibitory activity against TU686 (IC₅₀ = 6.73 µM), TU212 (IC₅₀ = 1.03 µM), M4e (IC₅₀ = 3.12 µM), AMC-HN-8 (IC₅₀ = 2.13 µM), Hep-2 (IC₅₀ = 9.07 µM), and LCC cells (IC₅₀ = 4.20 µM). Subsequent target verification experiments demonstrated that eupalinilide B selectively and reversibly inhibited LSD1. Furthermore, eupalinilide B, as a natural product, suppressed epithelial–mesenchymal transition in TU212 cells. An in vivo experiment further indicated that eupalinilide B could significantly reduce the growth of tumors in TU212 xenograft mouse models.

Conclusions

Eupalinilide B might be a novel LSD1 inhibitor for treating laryngeal cancer.

Mechanism and Origins of Enantioselectivity of Cobalt-Catalyzed Intermolecular Hydroacylation/Cyclization of 1,6-Enynes with Aldehydes

Density functional theory calculations were performed to investigate the cobalt-catalyzed intermolecular hydroacylation/cyclization of 1,6-enynes. The computations show that the initial oxidative cyclization constitutes the rate-determining step of the overall reaction....

An insight into cytotoxic activity of flavonoids and sesquiterpenoids from selected plants of Asteraceae species

Cancer continues to be a disease that is difficult to cure and the current therapeutic regimen is associated with severe side effects and the issue of emerging drug resistance. According to the World Health Organization fact sheet 2017, cancer is the second major cause of morbidity and death and a 70% rise in new cases is expected over the next 20 years. The quest for new anticancer chemical entities is a thrust area identified by many government agencies and industry research and development groups. Nature-derived entities have played a very important role in therapeutics especially cancer Asteraceae is a large family consisting of around 1700 genera and more than 24,000 species. Several genera belonging to this family have ethnopharmacological uses such as cytotoxicity, antidiabetic, hepatoprotective and antioxidant. This review highlights the cytotoxic potential of structurally novel flavonoids and sesquiterpenes isolated from some selected species of Asteraceae plants native to Asia, Europe, parts of Africa and America. The existing literature suggests that sesquiterpenes and flavonoids from various species of Asteraceae represent a viable class of secondary metabolites with strong cytotoxic potential. These have demonstrated potent activity in cell cycle arrest, inhibition of neoangiogenesis and induction of apoptosis. The sesquiterpenoids exhibiting potent cytotoxic activity were found to contain an α- methylene-butyrolactone conjugated with an exomethylene group and the flavonoids obtained from various plant species of Blumea suggest that a dihydroxy ring system present in structure is essential for activity. Most of the published literature contains in vitro data of extracts/secondary metabolites with very few in vivo studies. Additionally, there is dearth of knowledge on mechanisms of cytotoxic activity and molecular targets impacted by the active secondary metabolites. This review hopes to fuel interest in researchers to take up detailed investigations on these scaffolds that could contribute significantly as potential leads in anticancer drug development.

Simultaneous determination of eight pyrrolizidine alkaloids in various parts of Eupatorium lindleyanum by ultra high performance liquid chromatography tandem mass spectrometry and risk assessments based on a real-life exposure scenario

Pyrrolizidine alkaloids are toxins having hepatotoxic and carcinogenic effects on human health. A ultra high performance liquid chromatography tandem mass spectrometry technique was developed for the first time for the simultaneous determination of eight pyrrolizidine alkaloids, including four diastereoisomers (intermedine, lycopsamine, rinderine, and echinatine) and their respective N-oxide forms, in different parts of Eupatorium lindleyanum. The risk assessment method for pyrrolizidine alkaloids in Eupatorium lindleyanum was explored using the margin of exposure strategy for the first time based on a real-life exposure scenario. Differences were found in all eight pyrrolizidine alkaloids in various parts of Eupatorium lindleyanum. Besides, the total levels of pyrrolizidine alkaloids in Eupatorium lindleyanum followed the order of root > flower > stem > leaf. Moreover, the risk assessment data revealed that the deleterious effects on human health were unlikely at exposure times of less than 200, 37, and 12 days during the lifetimes of Eupatorium lindleyanum leaves, stems, and flowers, respectively. This study reported both the contents of and risk associated with Eupatorium lindleyanum pyrrolizidine alkaloids. The comprehensive application of the novel ultra high performance liquid chromatography tandem mass spectrometry technique alongside the risk assessment approach provided a scientific basis for quality evaluation and rational utilization of toxic pyrrolizidine alkaloids in Eupatorium lindleyanum to improve public health safety.

Asymmetric Cobalt-Catalyzed Regioselective Hydrosilylation/Cyclization of 1,6-Enynes

We report an enantioselective cobalt-catalyzed hydrosilylation/cyclization reaction of 1,6-enynes with secondary and tertiary hydrosilanes employing a catalyst generated in situ from the combination of Co(acac)₂ and (R,S_p )-Josiphos. A wide range of oxygen-, nitrogen-, and carbon-tethered 1,6-enynes reacted with Ph₂ SiH₂ , (EtO)₃ SiH, or (RO)₂ MeSiH to afford the corresponding chiral organosilane products in high yields and up to >99 % ee. This cobalt-catalyzed hydrosilylation/cyclization also occurred with prochiral secondary hydrosilane PhMeSiH₂ to yield chiral alkylsilanes containing both carbon- and silicon-stereogenic centers with excellent enantioselectivity, albeit with modest diastereoselectivity. The chiral organosilane products from this cobalt-catalyzed asymmetric hydrosilylation/cyclization could be converted to a variety of chiral five-membered heterocyclic compounds by stereospecific conversion of their C-Si and Si-H bonds without loss of enantiopurity.

Traditional Applications, Phytochemistry, and Pharmacological Activities of Eupatorium lindleyanum DC.: A Comprehensive Review

Eupatorium lindleyanum DC. (EL) has a long history of traditional use in China to cure coughs, chronic bronchitis, lobar pneumonia, and hypertension. Because of this extensive use of EL in traditional medicine, this present review gives a systematic overview of the conventional applications, phytochemistry, and pharmacological effects of the herb. Literature was systematically searched using the scientific databases ScienceDirect, SciFinder, CNKI, Wiley, Baidu Scholar, SpringerLink, PubMed, Web of Science, and other professional websites. Information was also gathered from books on traditional Chinese herbal medicine, the Chinese Pharmacopoeia and Chinese Materia Medica. To date, many preparations of EL have been widely used clinically to treat various diseases of the respiratory system. More than 100 compounds have been isolated from the herb, including triterpenes, sesquiterpenes, sesquiterpene lactones, flavonoids, acyclic diterpenoids, sterols, and so on. Among them, terpenoids are considered to be the most important bioactive substances in EL. The pharmacological functions of EL, including anti-asthmatic, anti-tussive, anti-inflammatory, anti-hyperlipidemic, anti-hypertensive, anti-virus, and anti-tumor activities, have been widely investigated. However, most of the studies are preclinical research. Further studies are required to examine the underlying mechanisms of action. Traditionally, EL is used for treating many diseases, especially respiratory diseases. Unfortunately, up to now, modern studies have not yet well elucidated the conventional usage of EL. Most importantly, its biological activities and the corresponding constituents are still unclear. Moreover, studies on the pharmacokinetics and toxicity of EL are few, so data on the clinical safety of EL are lacking. Taken together, research work on EL is quite preliminary. More in-depth studies of phytochemistry, pharmacological activities, pharmacokinetics, and toxicity of the herb are needed. This review aims to provide valuable information on EL to guide future investigations and applications.

Cytotoxic sesquiterpene lactones from Campuloclinium macrocephalum (=Eupatorium macrocephalum)

Three undescribed germacranolide sesquiterpene lactones, named macrocephalides A-C, along with known steroids, triterpenes and flavonoids were isolated from the aerial parts of Campuloclinium macrocephalum. The structures of the undescribed compounds were elucidated with basis on their 1D and 2D-NMR, and HR-ESI-MS data. Their absolute configurations were assigned by comparison of experimental and calculated electronic circular dichroism (ECD) spectra. Additionally, macrocephalides A-C were evaluated for their in vitro cytotoxic activities against nine human cancer cell lines. Macrocephalides A and B exhibited moderate to potent cytotoxic activity, inhibiting 50% of cell growth (GI₅₀) at concentrations ranging from 0.576 to 6.37 μM.

Targeting pharmacophore with probe-reactivity-guided fractionation to precisely identify electrophilic sesquiterpenes and its activity of anti-TNBC

INTRODUCTION

Innovative strategy is urgently needed to precisely discover novel natural products as lead compounds for development of new drugs against orphan diseases such as triple-negative breast cancer (TNBC). Herein, we describe a targeting pharmacophore with probe-reactivity-guided strategy for the discovery of electrophilic sesquiterpene (ES), a class of bioactive natural product.

OBJECTIVE

This study aimed to identify pharmacophore, based on pharmacophore with probe-reactivity-guided strategy for precisely discovering ESs from ethyl acetate extract of Eupatorium chinense L. (EEEChL) METHODOLOGY: MTT assay combined with ultra-performance liquid chromatography (UPLC) analysis was used to identify pharmacophore. UPLC-mass spectrometry (MS) was applied to carefully compare the intrinsic reactivity characteristics of two chemoselective nucleophilic probes: glutathione (GSH) and 4-bromothiophenol (BTP) reaction with ESs. ESs was isolated and identified from EEEChL by phytochemical methods. Furthermore, stoichiometric ratio and binding site of one typical ES 8β-[4'-hydroxytigloyloxy]-5-desoxy-8-desacyleuparotin (HDDE) reaction with BTP were studied by UPLC-quadrupole time-of-flight (Q-TOF)-MS and two-dimensional nuclear magnetic resonance (NMR).

RESULTS

Eleven ESs were identified from EEEChL, MTT assay illustrated that all of the 11 ESs possess fairly good anti-TNBC activity CONCLUSIONS: Electrophilic groups were confirmed as pharmacophore of bioactive compounds contained in EEEChL. An optimised halogenated aromatic probe BTP furnishes ES-BTP conjugates that are highly conspicuous via MS by virtue of a unique isotopic bromine signature, conjugates also have a considerable separation on C18 column. The new probe-reactivity-guided strategy can effectively improve the traditional bioassay-guided approaches, and significantly increase the probability of obtaining designated bioactive compounds.

Directing Stem Cell Fate: The Synthetic Natural Product Connection

Stem cells possess remarkable potential for the treatment of a broad array of diseases including many that lack therapeutic options. However, the use of cell-based products derived from stem cells as therapeutics has limitations including rejection, sufficient availability, and lack of appropriate engraftment. Chemical control of stem cells provides potential solutions for overcoming many of the current limitations in cell-based therapeutics. The development of exogenous molecules to control stem cell self-renewal or differentiation has arrived at natural product-based agents as an important class of modulators. The ex vivo production of cryopreserved cellular products for use in tissue repair is a relatively new area of medicine in which the conventional hurdles to implementing chemicals to effect human health are changed. Translational challenges centered on chemistry, such as pharmacokinetics, are reduced. Importantly, in many cases the desired human tissues can be evaluated against new chemicals, and approaches to cellular regulation can be validated in the clinically applicable system. As a result linking new and existing laboratory syntheses of natural products with findings of the compounds' unique abilities to regulate stem cell fate provides opportunities for developing improved methods for tissue manufacture, accessing probe compounds, and generating new leads that yield manufactured cells with improved properties. This review provides a summary of natural products that have shown promise in controlling stem cell fate and which have also been fully synthesized thereby providing chemistry platforms for further development.

Cobalt-Catalyzed Asymmetric Hydroboration/Cyclization of 1,6-Enynes with Pinacolborane

We report a cobalt-catalyzed asymmetric hydroboration/cyclization of 1,6-enynes with catalysts generated from Co(acac)₂ and chiral bisphosphine ligands and activated in situ by reaction with pinacolborane (HBpin). A variety of oxygen-, nitrogen-, and carbon-tethered 1,6-enynes underwent this asymmetric transformation, yielding both alkyl- and vinyl-substituted boronate esters containing chiral tetrahydrofuran, cyclopentane, and pyrrolidine moieties with high to excellent enantioselectivities (86%-99% ee).

Synthetic Route Development for the Laboratory Preparation of Eupalinilide E

Following the discovery that the guaianolide natural product eupalinilide E promotes the expansion of hematopoietic stem and progenitor cells; the development of a synthetic route to provide laboratory access to the natural product became a priority. Exploration of multiple synthetic routes yielded an approach that has permitted a scalable synthesis of the natural product. Two routes that failed to access eupalinilide E were triaged either as a result of providing an incorrect diastereomer or due to lack of synthetic efficiency. The successful strategy relied on late-stage allylic oxidations at two separate positions of the molecule, which significantly increased the breadth of reactions that could be used to this point. Subsequent to C-H bond oxidation, adaptations of existing chemical transformations were required to permit chemoselective reduction and oxidation reactions. These transformations included a modified Luche reduction and a selective homoallylic alcohol epoxidation.

2-Hydroxyeupatolide attenuates inflammatory responses via the inhibiting of NF-κB signaling pathways

2-Hydroxyeupatolide (2-HE), a sesquiterpene lactone, is a potential agent to improve LPS-induced acute mouse inflammation damage.

Synthesis of Eupalinilide E, a Promoter of Human Hematopoietic Stem and Progenitor Cell Expansion

Improving the ex vivo and in vivo production of hematopoietic stem and progenitor cells (HSPCs) has the potential to address the short supply of these cells that are used in the treatment of various blood diseases and disorders. Eupalinilide E promotes the expansion of human HSPCs and inhibits subsequent differentiation, leading to increased numbers of clinically useful cells. This natural product represents an important tool to uncover new methods to drive expansion while inhibiting differentiation. However, in the process of examining these effects, which occur through a novel mechanism, the natural product was consumed, which limited additional investigation. To provide renewed and improved access to eupalinilide E, a laboratory synthesis has been developed and is reported herein. The synthetic route can access >400 mg in a single batch, employing reactions conducted on useful scales in a single vessel. Key transformations enabling the approach include a diastereoselective borylative enyne cyclization and a late-stage double allylic C-H oxidation as well as adapted Luche reduction and aluminum-mediated epoxidation reactions to maximize the synthetic efficiency. Retesting of the synthetic eupalinilide E confirmed the compound's ability to expand HSPCs and inhibit differentiation.

New thymol derivatives and cytotoxic constituents from the root of Eupatorium cannabinum ssp. asiaticum

Two new thymol (=5-methyl-2-(1-methylethyl)phenol) derivatives, 8,10-didehydro-9-(3-methylbutanoyl)thymol 3-O-tiglate (1) and 9-O-angeloyl-8-methoxythymol 3-O-isobutyrate (2), were isolated from the root of Eupatorium cannabinum ssp. asiaticum, together with six known compounds, 3-8. The structures of 1 and 2 were determined through extensive 1D/2D-NMR and MS analyses. Among the isolates, 9-acetoxy-8,10-epoxythymol 3-O-tiglate (3) was the most cytotoxic, with IC50 values of 0.02±0.01, 1.02±0.07, and 1.36±0.12 μg/ml, respectively, against DLD-1, CCRF-CEM, and HL-60 cell lines. In addition, 10-acetoxy-9-O-angeloyl-8-hydroxythymol (4) and eupatobenzofuran (6) exhibited cytotoxicities, with IC50 values of 1.14±0.16 and 2.63±0.22, and 7.63±0.94 and 2.31±0.14 μg/ml, respectively, against DLD-1 and CCRF-CEM cell lines.

Eupalinilide E inhibits erythropoiesis and promotes the expansion of hematopoietic progenitor cells

Hematopoietic stem cells (HSCs) are the progenitor cells that give rise to all blood cells. The ability to control HSC differentiation has the potential to improve the success of bone marrow transplants and the production of functional blood cells ex vivo. Here we performed an unbiased screen using primary human CD34(+) hematopoietic stem and progenitor cells (HSPCs) to identify natural products that selectively control their differentiation. We identified a plant-derived natural product, eupalinilide E, that promotes the ex vivo expansion of HSPCs and hinders the in vitro development of erythrocytes. This activity was additive with aryl hydrocarbon receptor (AhR) antagonists, which are also known to expand HSCs and currently in clinical development. These findings reveal a new activity for eupalinilide E, and suggest that it may be a useful tool to probe the mechanisms of hematopoiesis and improve the ex vivo production of progenitors for therapeutic purposes.

Discovery of structurally diverse and bioactive compounds from plant resources in China

This review describes the major discoveries of structurally diverse and/or biologically significant compounds from plant resources in China, mainly from the traditional Chinese medicines (TCMs) since the establishment of our research group in 1999. In the past decade, a large array of biologically significant and novel structures has been identified from plant resources (or TCM) in our laboratory. The structural modification of several biologically important compounds led to more than 400 derivatives, some of which exhibited significantly improved activities and provided opportunities to elucidate the structure-activity relationship of the related compound class. These findings are important for drug discovery and help us understand the biological basis for the traditional applications of these plants in TCM.

Three new acyclic diterpenoids from Eupatorium lindleyanum DC

Three new acyclic diterpenoids were isolated from the whole plant of Eupatorium lindleyanum DC. The structures of the compounds were elucidated by means of (1)H and (13)C NMR spectroscopic analyses, including 2D NMR experiments.

Thymol, benzofuranoid, and phenylpropanoid derivatives: anti-inflammatory constituents from Eupatorium cannabinum

Five new compounds, 9-O-angeloyl-8,10-dehydrothymol (1), 9-(3-methylbutanoyl)-8,10-dehydrothymol (2), eupatobenzofuran (3), 2-hydroxy-2,6-dimethylbenzofuran-3(2H)-one (4), and 1-(2-hydroxy-4-methylphenyl)propan-1,2-dione (5), have been isolated from the aerial part of Eupatorium cannabinum subsp. asiaticum, together with 16 known compounds (6-21). Compounds 6-8, 11, 13, and 15 exhibited inhibition (IC50 values≤18.4 μM) of superoxide anion generation by human neutrophils in response to formyl-L-methionyl-L-leucyl-L-phenylalanine/cytochalasin B (fMLP/CB). Compounds 2, 3, 10, 13, and 15 inhibited fMLP/CB-induced elastase release with IC50 values≤18.3 μM.

An unusual dimeric guaianolide with antiprotozoal activity and further sesquiterpene lactones from Eupatoriumperfoliatum

The CH(2)Cl(2) extract of aerial parts of Eupatorium perfoliatum L. exhibits antiprotozoal activity under in vitro conditions, especially against Plasmodium falciparum (IC(50)=2.7μg/ml). The search for active compounds yielded seven sesquiterpene lactones: Four structurally similar guaianolides, one dimeric guaianolide, and two germacranolides. The guaianolides differ in the degree of oxidation at C-14, ranging from a hydroxyl group up to a free carboxylic acid. The dimeric guaianolide, structurally closely related to the monomers, displays an unusual type of interguaianolide linkage between C-14 and C-4. Except for the germacranolide euperfolitin, all STLs described here were hitherto unknown. Furthermore, the flavonoid aglycones eupafolin, hispidulin, patuletin, and kaempferol were identified in the extract, which, except for kaempferol, have not been described as constituents of E. perfoliatum before. The dimeric guaianolide was shown to be the most active constituent against Plasmodium falciparum (IC(50) = 2.0μM) and was less cytotoxic against rat skeletal myoblasts (IC(50) = 16.2μM, selectivity index of about 8).

Bioactive Sesquiterpene Lactones from Eupatorium Kiirunense

Four new sesquiterpene lactones, two heliangolides, one eudesmanolide and one germacranolide, were isolated by chromatographic fractionation of an acetone extract of Eupatorium kiirunense and named eupakirunsins F, G H and I (1–4). They were identified as 8β-(3-hydroxy-2-methylen-butanoyloxy)-1β,10α-epoxy-3α-hydroxy-6βH,7αH-heliang-4Z,11(13)-dien-6,12-olide (1), 8β-tigloyloxy-1β,10α-epoxy-3β,15-dihydroxy-6βH,7αH-heliang-4Z,11(13)-dien-6,12-olide (2), 8β-tigloyloxy-1 β,3β-dihydroxy-6βH,7αH-eudesman-4(15),11(13)-dien-6,12-olide (3) and 8βtigloyloxy-3βhydroxy-1β,10β-epoxy-14-oxo-6βH,7αH-germacra-4E,11(13)-dien-6,12-olide (4). The structures and the relative configurations of the new metabolites were elucidated through extensive spectral analysis and by comparison with known spectral data. Among the isolated compounds, 1 and 3 exhibited potent cytotoxicity against WiDr and MCF-7 human tumor cell lines.