Xanthanolides and xanthane epoxide derivatives from Xanthium strumarium

Xanthanolides in Xanthium L.: Structures, Synthesis and Bioactivity

Xanthanolides were particularly characteristic of the genus Xanthium, which exhibited broad biological effects and have drawn much attention in pharmacological application. The review surveyed the structures and bioactivities of the xanthanolides in the genus Xanthium, and summarized the synthesis tactics of xanthanolides. The results indicated that over 30 naturally occurring xanthanolides have been isolated from the genus Xanthium in monomeric, dimeric and trimeric forms. The bioassay-guided fractionation studies suggested that the effective fractions on antitumor activities were mostly from weak polar solvents, and xanthatin (1) was the most effective and well-studied xanthanolide. The varieties of structures and structure-activity relationships of the xanthanolides had provided the promising skeleton for the further study. The review aimed at providing guidance for the efficient preparation and the potential prospects of the xanthanolides in the medicinal industry.

Biologically Active Constituents from Plants of the Genus Xanthium

Herbaceous annual plants of the genus Xanthium are widely distributed throughout the world and have been employed medicinally for millennia. This contribution aims to provide a systematic overview of the diverse structural classes of Xanthium secondary metabolites, as well as their pharmacological potential. On searching in various reference databases with a combination of three keywords "Xanthium", "Phytochemistry", and "Pharmacology", relevant publications have been obtained subsequently. From the 1950s to the present, phytochemical investigations have focused mainly on 15 Xanthium species, from which 300 compounds have been isolated and structurally resolved, primarily using NMR spectroscopic methodology. Xanthium constituents represent several secondary metabolite types, including simple phenols, sulfur and nitrogen-containing compounds, lignans, sterols, flavonoids, quinones, coumarins, and fatty acids, with terpenoids being the most common of these. Among the 174 terpenoids characterized, xanthanolide sesquiterpenoids are abundant, and most of the compounds isolated containing sulfur were found to be new in Nature. The ethnomedical uses of Xanthium crude extracts are supported by the in vitro and in vivo effects of their constituents, such as cytotoxicity, antioxidant, antibacterial, antifungal, antidiabetes, and hepatoprotective activities. Toxicological results suggest that Xanthium plant extracts are generally safe for use. In the future, additional phytochemical investigations, along with further assessments of the biological profiles and mechanism of action studies of the components of Xanthium species, are to be expected.

Antiprotozoal and Antitumor Activity of Natural Polycyclic Endoperoxides: Origin, Structures and Biological Activity

Polycyclic endoperoxides are rare natural metabolites found and isolated in plants, fungi, and marine invertebrates. The purpose of this review is a comparative analysis of the pharmacological potential of these natural products. According to PASS (Prediction of Activity Spectra for Substances) estimates, they are more likely to exhibit antiprotozoal and antitumor properties. Some of them are now widely used in clinical medicine. All polycyclic endoperoxides presented in this article demonstrate antiprotozoal activity and can be divided into three groups. The third group includes endoperoxides, which show weak antiprotozoal activity with a reliability of up to 70%, and this group includes only 1.1% of metabolites. The second group includes the largest number of endoperoxides, which are 65% and show average antiprotozoal activity with a confidence level of 70 to 90%. Lastly, the third group includes endoperoxides, which are 33.9% and show strong antiprotozoal activity with a confidence level of 90 to 99.6%. Interestingly, artemisinin and its analogs show strong antiprotozoal activity with 79 to 99.6% confidence against obligate intracellular parasites which belong to the genera Plasmodium, Toxoplasma, Leishmania, and Coccidia. In addition to antiprotozoal activities, polycyclic endoperoxides show antitumor activity in the proportion: 4.6% show weak activity with a reliability of up to 70%, 65.6% show an average activity with a reliability of 70 to 90%, and 29.8% show strong activity with a reliability of 90 to 98.3%. It should also be noted that some polycyclic endoperoxides, in addition to antiprotozoal and antitumor properties, show other strong activities with a confidence level of 90 to 97%. These include antifungal activity against the genera Aspergillus, Candida, and Cryptococcus, as well as anti-inflammatory activity. This review provides insights on further utilization of polycyclic endoperoxides by medicinal chemists, pharmacologists, and the pharmaceutical industry.

Traditional Uses, Botany, Phytochemistry, Pharmacology, Pharmacokinetics and Toxicology of Xanthium strumarium L.: A Review

Xanthium strumarium L. (Asteraceae) is a common and well-known traditional Chinese herbal medicine usually named Cang-Er-Zi, and has been used for thousands of years in China. The purpose of this paper is to summarize the progress of modern research, and provide a systematic review on the traditional usages, botany, phytochemistry, pharmacology, pharmacokinetics, and toxicology of the X. strumarium. Moreover, an in-depth discussion of some valuable issues and possible development for future research on this plant is also given. X. strumarium, as a traditional herbal medicine, has been extensively applied to treat many diseases, such as rhinitis, nasal sinusitis, headache, gastric ulcer, urticaria, rheumatism bacterial, fungal infections and arthritis. Up to now, more than 170 chemical constituents have been isolated and identified from X. strumarium, including sesquiterpenoids, phenylpropenoids, lignanoids, coumarins, steroids, glycosides, flavonoids, thiazides, anthraquinones, naphthoquinones and other compounds. Modern research shows that the extracts and compounds from X. strumarium possess wide-ranging pharmacological effects, including anti- allergic rhinitis (AR) effects, anti-tumor effects, anti-inflammatory and analgesic effects, insecticide and antiparasitic effects, antioxidant effects, antibacterial and antifungal effects, antidiabetic effects, antilipidemic effects and antiviral effects. However, further research should focus on investigating bioactive compounds and demonstrate the mechanism of its detoxification, and more reasonable quality control standards for X. strumarium should also be established.

Phytotoxic Compounds Isolated from Leaves of the Invasive Weed Xanthium spinosum

The aim of this study was to identify bioactive compounds from leaves of the invasive plant Xanthium spinosum and assess their phytotoxic activity. Activity-guided fractionation led to the isolation of 6 bioactive compounds: xanthatin (1), 1α,5α-epoxyxanthatin (2), 4-epiisoxanthanol (3), 4-epixanthanol (4), loliolide (5) and dehydrovomifoliol (6). Of them, compounds 2–6 were isolated from the X. spinosum for the first time. The structures of 1–6 were elucidated on the basis of extensive NMR studies and ESI-MS measurements as well as comparison with literature data. All of compounds were evaluated for their phytotoxic activity. Among them, compounds 1–4 exhibited stronger activity on 2 receiver plants compared with the other 2 compounds, with xanthatin (1) being the most potent compound, which suppressed root growth of the dicot plant Amaranthus retroflexus by 32.5%, 39.4%, 84.7% when treated xanthatin (1) at 5, 20, and 100 µg/mL, while for the monocot plant, root growth was inhibited by 14.7%, 28.0%, and 40.0%, respectively. Seedling growth was nearly completely inhibited when the concentration of xanthanolides increased to 500 µg/mL, whereas there was still some seedling growth when loliolide (5) and dehydrovomifoliol (6) were applied at the same concentration. Dehydrovomifoliol (6) did not negatively affect seedling growth of P. annua at all tested concentrations, and root length was still 42.0% of the control when the highest concentration 500 µg/mL was used. This is the first report of the phytotoxicity of 1α,5α-epoxyxanthatin (2), 4-epiisxanthanol (3) and 4-epixanthanol (4). These compounds have the potential to be utilized as natural herbicides, especially 4-epiisoxanthanol (3), which exhibited significant selective activity between the dicot and monocot plants. On the other hand, whether these bioactive substances serve as allelochemicals to facilitate the invasion success of X. spinosum needs to be further studied.

Cytotoxic dimeric xanthanolides from fruits of Xanthium chinense

Nine dimeric xanthanolides, pungiolides F-N, and five known analogues, pungiolides A-E, were isolated from fruits of Xanthium chinense. Their structures were elucidated through spectroscopic and electronic circular dichroism (ECD) analyses. Pungiolide F is a xanthanolide dimer with an acyclic linkage. Five of the dimers, pungiolides H, L, A, C and E, exhibited moderate cytotoxicities with IC₅₀ values in the range of 0.90-6.84 μM using taxol as the positive control, which had, by comparison, IC₅₀ values in the range of 0.00118-0.0675 μM. These findings enrich the structural diversity of dimeric sesquiterpene lactones.

PDK1 in NF-κB signaling is a target of Xanthium strumarium methanolic extract-mediated anti-inflammatory activities

ETHNOPHARMACOLOGICAL RELEVANCE

Xanthium strumarium L. (Asteraceae) has traditionally been used to treat bacterial infections, nasal sinusitis, urticaria, arthritis, chronic bronchitis and rhinitis, allergic rhinitis, edema, lumbago, and other ailments. However, the molecular mechanisms by which this plant exerts its anti-inflammatory effects are poorly characterized. Here we studied the immunopharmacological activities of the methanolic extract of the aerial parts of this plant (Xs-ME) and validated its pharmacological targets.

MATERIALS AND METHODS

To evaluate the anti-inflammatory activity of Xs-ME, we employed lipopolysaccharide (LPS)-treated macrophages and an HCl/EtOH-induced mouse model of gastritis. We also used HPLC to identify the potentially active anti-inflammatory components of this extract. The molecular mechanisms of its anti-inflammatory activity were studied by kinase assays, reporter gene assays, immunoprecipitation analysis, and overexpression of target enzymes.

RESULTS

The production of nitric oxide (NO) and prostaglandin E2 (PGE2) were both suppressed by Xs-ME. Moreover, orally administered Xs-ME ameliorated HCl/EtOH-induced gastric lesions. Furthermore, this extract downregulated the expression of inducible NO synthase (iNOS) and cyclooxygenase (COX)-2 and reduced the nuclear levels of NF-κB. Signaling events upstream of NF-κB translocation, such as phosphorylation of AKT and the formation of PDK1-AKT signaling complexes, were also inhibited by Xs-ME. Moreover, Xs-ME suppressed the enzymatic activity of PDK1. Additionally, PDK1-induced luciferase activity and Akt phosphorylation were both inhibited by Xs-ME. We also identified the polyphenol resveratrol as a likely active anti-inflammatory component in Xs-ME that targets PDK1.

CONCLUSION

Xs-ME exerts anti-inflammatory activity in vitro and in vivo by inhibiting PDK1 kinase activity and blocking signaling to its downstream transcription factor, NF-κB.

Differential microRNA Analysis of Glandular Trichomes and Young Leaves in Xanthium strumarium L. Reveals Their Putative Roles in Regulating Terpenoid Biosynthesis

The medicinal plant Xanthium strumarium L. (X. strumarium) is covered with glandular trichomes, which are the sites for synthesizing pharmacologically active terpenoids such as xanthatin. MicroRNAs (miRNAs) are a class of 21-24 nucleotide (nt) non-coding RNAs, most of which are identified as regulators of plant growth development. Identification of miRNAs involved in the biosynthesis of plant secondary metabolites remains limited. In this study, high-throughput Illumina sequencing, combined with target gene prediction, was performed to discover novel and conserved miRNAs with potential roles in regulating terpenoid biosynthesis in X. strumarium glandular trichomes. Two small RNA libraries from leaves and glandular trichomes of X. strumarium were established. In total, 1,185 conserved miRNAs and 37 novel miRNAs were identified, with 494 conserved miRNAs and 18 novel miRNAs being differentially expressed between the two tissue sources. Based on the X. strumarium transcriptome data that we recently constructed, 3,307 annotated mRNA transcripts were identified as putative targets of the differentially expressed miRNAs. KEGG (Kyoto Encyclopedia of Genes and Genomes) pathway analysis suggested that some of the differentially expressed miRNAs, including miR6435, miR5021 and miR1134, might be involved in terpenoid biosynthesis in the X. strumarium glandular trichomes. This study provides the first comprehensive analysis of miRNAs in X. strumarium, which forms the basis for further understanding of miRNA-based regulation on terpenoid biosynthesis.

Bioactive Sesquiterpenes and Lignans from the Fruits of Xanthium sibiricum

Seven new sesquiterpenes (1, 3-8), a new sesquiterpene natural product (2), and two new lignans (9 and 10), together with 15 known compounds, were isolated from the fruits of Xanthium sibiricum. The structures of the new compounds were established by NMR spectroscopic analysis, ECD calculations, and Mo2(OAc)4-induced circular dichroism, with the structures of 1 and 4 confirmed by single-crystal X-ray diffraction. Compound 1 is the first example of a 3/5/6/5 tetracyclic eudesmane sesquiterpene lactone formed at C-6 and C-7. In turn, compound 4 is the first example of a natural xanthane tetranorsesquiterpene, while compounds 5-8 are the first xanthane trinorsesquiterpenes found to date. Compounds 8, 11-15, 17, and 24 exhibited indirect anti-inflammatory activity by suppressing the lipopolysaccharide-induced proinflammatory factors in BV2 microglial cells, with IC50 values between 1.6 and 8.5 μM. Furthermore, compounds 13 and 17 exhibited anti-inflammatory activity against ear edema in mice produced by croton oil, with inhibition rates of 46.9% and 37.7%, respectively. Compounds 8, 11, 12, 23, and 24 exhibited potent activity against influenza A virus (A/FM/1/47, H1N1) with IC50 values between 3.7 and 8.4 μM.

Anti-arthritic activity of Xanthium strumarium L. extract on complete Freund׳s adjuvant induced arthritis in rats

ETHNOPHARMACOLOGICAL RELEVANCE

Xanthium strumarium L. fruit (Xanthiu fruit) has been traditionally used as a medicinal herb in China for the treatment of many ailments including rheumatoid arthritis. However, the anti-arthritic activity of Xanthium strumarium fruit has still not been demonstrated. In the present study, we confirmed that the extract of Xanthium strumarium (EXS) prevents rheumatoid arthritis induced by Complete Freund׳s Adjuvant (CFA) in rats.

MATERIALS AND METHODS

Male Wistar rats (160±10 g) were immunized by intradermal injection of 0.1 mL of CFA into the left hind metatarsal footpad. EXS was administered orally at a dose of 300 and 75 mg/kg once a day after the induction of adjuvant arthritis. Methotrexate (3 mg/kg, twice a week) was used as a positive control. Paw swelling, arthritic score, body weight loss, spleen index, thymus index, serum cytokines, inflammatory mediators and histological change were measured. The chemical profile of EXS was analyzed by HPLC-DAD.

RESULTS

We found that the EXS significantly suppressed paw swelling and arthritic score, increased body weight loss and decreased the thymus index. The overproduction of TNF-α and IL-1β were remarkably suppressed in the serum of all EXS-treated rats, and in contrast IL-10 was markedly increased. The level of COX-2 and 5-LOX was also decreased with EXS treatment. Ten phenolic acid derivatives were identified from 14 detected peaks by HPLC-DAD with the reference substances and verified by LC-MS.

CONCLUSIONS

These results suggest the potential effect of EXS as an anti-arthritis agent towards CFA-induced arthritis in rats. Xanthium strumarium has the potential to be regarded as a candidate for use in general therapeutics and as an immune-modulatory medicine in rheumatoid arthritis.

Peroxy natural products

This review covers the structures and biological activities of peroxy natural products from a wide variety of terrestrial fungi, higher plants, and marine organisms. Syntheses that confirm or revise structures or stereochemistries have also been included, and 406 references are cited.

Xanthane sesquiterpenoids: structure, synthesis and biological activity

The aim of this review is to survey the naturally occurring xanthanes and xanthanolides, their structures, biological activities, structure–activity relationships and synthesis. There has been no comprehensive review of this topic previously. On the basis of 126 references, 112 compounds are summarized.

Synthesis of reduced xanthatin derivatives andin vitroevaluation of their antifungal activity

Abstract The synthesis of new xanthanolide derivatives is reported starting from xanthatin, a sesquiterpenic lactone isolated from Xanthium macrocarpum (Asteraceae). In vitro evaluation of their antifungal activity has been investigated.

A new heterocyclic glucoside from the fruits ofXanthiumpungens

A new thiazinedione glucoside, 7-(beta-D-glucopyranosyloxymethyl)-8,8-dimethyl-4,8-dihydrobenzo[1,4]thiazine-3,5-dione (1) and named xanthiside, was isolated from the methanol extract of the fruits of Xanthium pungens. Its structure was determined by spectroscopic techniques including, IR, CIMS, high-resolution-EIMS, and extensive 400 MHz one- and two-dimensional NMR-analysis (1H, 13C-NMR, DEPT, 1H-1H COSY, HMQC, COLOC, and NOE experiments).

Antileishmanial and antifungal activities of xanthanolides isolated from Xanthium macrocarpum

Seven xanthanolides, xanthinosin, xanthatin, 4-hydroxyxanthinosin, xanthinin, 4-epiisoxanthanol, 4-epixanthanol, 2-hydroxyxanthinosin and 4-oxobedfordia acid, were isolated from the fruits of Xanthium macrocarpum. A valuation of the antifungal activity of these xanthanolides against Candida albicans, Candida glabrata and Aspergillus fumigatus and of their antileishmanial activity against Leishmania infantum and Leishmania mexicana is presented.

Asymmetric Synthesis of (−)-Dihydroxanthatin by the Stereoselective Oshima−Utimoto Reaction

[reaction: see text]. The catalytic stereoselective Oshima-Utimoto reaction is useful for the construction of five-membered oxacycles from simple starting materials and was employed for the preparation of the lactone group in the asymmetric synthesis of (-)-11alpha,13-dihydroxanthatin. Completion of the synthesis is facilitated by ring-closing enyne metathesis and alkene cross metathesis reactions.

Sesquiterpene lactones from Montanoa hibiscifolia that inhibit the transcription factor NF-kappa B

The reinvestigation of the aerial parts of Montanoa hibiscifolia afforded four new eudesmanolides (1-4), three of them with a rare endoperoxide structural element and the fourth with a rare carbonyl function. It also afforded three unusual montabibisciolides (5-7), two (5 and 7) of which are new natural compounds. Additionally, seven germacrolides (8-10 and 12-15) and one melampolide (11) could be isolated, including two new germacrolides (8 and 9). Their structures were elucidated using 1D and 2D NMR measurement as well as ESI, CIMS, and HRMS analyses. Low-energy conformations were obtained by molecular mechanics calculations. The (13)C NMR data of five compounds are reported for the first time. Six sesquiterpene lactones (4, 6, 10, 11, 12, and 14) were investigated for their inhibitory activity on DNA binding of the transcription factor NF-kappa B using Jurkat T cells as well as RAW 264.7 cells. Besides the alpha-methylene-gamma-butyrolactone moiety the epoxy group in the acyl residue might take part in the NF-kappa B inhibitory activity of sesquiterpene lactones.

A review of plant species used to treat conjunctivitis

Conjunctivitis is a major occular external infection in tropical countries. Although not a very serious disease, it gives much discomfort and sometimes leads to partial blindness or blindness due to corneal involvement. Conjunctivitis has been known to occur in epidemic proportions in different parts of the world, mainly African and Asian regions. The indigenous cure of conjunctivitis using herbal products has been popular for centuries. This paper is an attempt to compile information on plants mentioned as a cure for conjunctivitis during ethnobotanical surveys between 1933 and 2000. Plants mentioned as a cure in various systems of medicine, namely Siddha and Ayurveda, are also included.