Stilbene and dihydrophenanthrene derivatives from Pholidota chinensis and their nitric oxide inhibitory and radical-scavenging activities

Unambiguous Characterization of Commercial Natural (Dihydro)phenanthrene Compounds Is Vital in the Discovery of AMPK Activators

These days, easy access to commercially available (poly)phenolic compounds has expanded the scope of potential research beyond the field of chemistry, particularly in the area of their bioactivity. However, the quality of these compounds is often overlooked or not even considered. This issue is illustrated in this study through the example of (dihydro)phenanthrenes, a group of natural products present in yams, as AMP-activated protein kinase (AMPK) activators. A study conducted in our group on a series of compounds, fully characterized using a combination of chemical synthesis, NMR and MS techniques, provided evidence that the conclusions of a previous study were erroneous, likely due to the use of a misidentified commercial compound by its supplier. Furthermore, we demonstrated that additional representatives of the (dihydro)phenanthrene phytochemical classes were able to directly activate AMPK, avoiding the risk of misinterpretation of results based on analysis of a single compound alone.

Dimeric phenanthrenoids: possible biogenetic pathway and missing compounds

Secondary metabolites extracted from plants have historically been critical for drug discovery, but their isolation involves expensive and complicated procedures in terms of time and labor resources. Thus, the biogenetic pathway offers the possibility of identifying specific compounds that have not yet been isolated and predicting their isolation from specific natural sources. In plants, biphenanthrenes represent a relatively small group of aromatic secondary metabolites that are considered as important taxonomic markers with promising biological activities. To date, 38 mixed phenanthrenoid dimers have been identified, the biosynthesis of which involves the radical coupling of the two subunits, namely, a phenanthrene and a dihydrophenanthrene. For each of the compounds, it is possible to identify the single phenanthrenic and dihydrophenanthrenic units constituting the considered dimer. Based on the biogenetic pathway, it is possible to identify 19 phenanthrenes and 17 dihydrophenanthrenes, and to distinguish those already known from those not yet isolated. By comparing the results of the possible biosynthetic pathway for each compound with the data in the literature, it is possible to identify three known phenanthrenes and seven known dihydrophenanthrenes, as well as eleven new phenanthrenes and five new dihydrophenanthrenes, and to identify from which plant it is possible to isolate them. This could direct the work of researchers seeking to identify known or new molecules useful for their possible biological properties, and ultimately, to confirm the veracity of the proposed and generally accepted biosynthetic pathway.

Dihydrophenanthrene Dimers: Why and Where It Is Possible to Isolate Their Precursors

An interesting class of compounds of natural origin is dihydrophenanthrene dimers, which are characterized by a series of remarkable biological properties. Considering the hypothesis that each dimer is obtained through a biosynthetic mechanism that involves the coupling of the corresponding radicals of the single dihydrophenanthrene unit, we identified 29 dihydrophenanthrenes. Of these dihydrophenanthrenes, 11 were new compounds that could be isolated from 10 different plant species; 11 had already been identified, but not yet isolated in the 17 different plant species from which the corresponding dimers had been isolated; and 7 were known and had been isolated in the same plant sources of the corresponding dimers. A targeted analysis of several natural extracts from specific plant sources would allow the identification of known or new molecules with potential and/or specific biological activities and, in a final analysis, would confirm the relative biosynthetic mechanism.

Dihydrophenanthrenes from a Sicilian Accession of Himantoglossum robertianum (Loisel.) P. Delforge Showed Antioxidant, Antimicrobial, and Antiproliferative Activities

The peculiar aspect that emerges from the study of Orchidaceae is the presence of various molecules, which are particularly interesting for pharmaceutical chemistry due to their wide range of biological resources. The aim of our study was to investigate the properties of two dihydrophenanthrenes, isolated, for the first time, from Himantoglossum robertianum (Loisel.) P. Delforge (Orchidaceae) bulbs and roots. Chemical and spectroscopic study of the bulbs and roots of Himantoglossumrobertianum (Loisel.) P. Delforge resulted in the isolation of two known dihydrophenanthrenes-loroglossol and hircinol-never isolated from this plant species. The structures were evaluated based on ¹H-NMR, ¹³C-NMR, and two-dimensional spectra, and by comparison with the literature. These two molecules have been tested for their possible antioxidant, antimicrobial, antiproliferative, and proapoptotic activities. In particular, it has been shown that these molecules cause an increase in the activity of superoxide dismutase (SOD), catalase (CAT), and glutathione S-transferase (GST) in polymorphonuclear leukocytes (PMN); show antimicrobial activity against Escherichia coli and Staphylococcus aureus, and have anti-proliferative effects on gastric cancer cell lines, inducing apoptosis effects. Therefore, these two molecules could be considered promising candidates for pharmaceutical and nutraceutical preparations.

Dihydrophenanthrenes from medicinal plants of Orchidaceae: A review

The plants of Orchidaceae are widely distributed in the world, 47 species of which have been used as folk medicines with a long history. The tubers and stems of them exhibit diverse efficacy, including clearing heat and resolving toxin, moistening lung and relieving cough and promoting blood circulation. Since dihydrophenanthrenes were responsible for the medical purposes, the characteristic skeletons, pharmacological effects and clinical applications of dihydrophenanthrenes were summarized in this review, so as to provide a theoretical basis for the comprehensive study, development and application of DPs from medicinal plants of Orchidaceae.

Six phenanthrenes from the roots of Cymbidium faberi Rolfe. and their biological activities

A new phenanthrene compound, 7-(4-hydroxybenzyl)-8-methoxy-9,10- dihydrophenanthrene-2,5-diol (HMD), along with five known compounds (Coelonin, DD, Shancidin, HDP and MDD) were isolated from the roots of Cymbidium faberi Rolfe. (CFR). Their structures were identified using various spectroscopic methods. These compounds were reported for the first time in the genus. All isolated compounds were tested by radical-scavenging ability against 1,1-diphenyl-2-picryl-hydrazyl (DPPH), cytotoxic activity against three human cancer cell lines and inflammatory activity. Among them, Shancidin exhibited the stronger DPPH-scavenging activity (IC₅₀=6.67 ± 0.84 μΜ) and cytotoxic activity against three tumour cell lines. Except for HDP, all compounds dose-dependently suppressed production of NO, TNF-α, IL-6 in LPS induced mouse primary peritoneal macrophage and showed anti-inflammatory activity. Moreover, 18 compounds were identified by UHPLC-LTQ-Orbitrap-MS combined with MS database, which provides a basis for further research.

Three new phenanthrenes from Pholidota chinensis Lindl. and their antibacterial activity

Three new phenanthrenes were isolated from Pholidota chinensis Lindl. Their structures were elucidated on the basis of spectroscopic techniques and comparison of their data to the values reported in the literature. From the 95% EtOH extract, three new compounds, namely 9, 10-dihydro-2, 4, 6-trihydroxy-7-methoxyphenanthrene (1), 11-methoxyflaccidin (2), and 2-methoxy-3,7-dihydroxy-5H phenanthro[4,5-bcd] pyran (3), were identified. Compound 3 showed an MIC₅₀ of 68.39 µM against Staphylococcus aureus subsp. Aureus.

Dihydro-stilbene gigantol relieves CCl4-induced hepatic oxidative stress and inflammation in mice via inhibiting C5b-9 formation in the liver

In general, anti-inflammatory treatment is considered for multiple liver diseases despite the etiology. But current drugs for alleviating liver inflammation have defects, making it necessary to develop more potent and safer drugs for liver injury. In this study, we screened a series of (dihydro-)stilbene or (dihydro-)phenanthrene derivatives extracted from Pholidota chinensis for their potential biological activities. Among 31 compounds, the dihydro-stilbene gigantol exerted most potent protective effects on human hepatocytes against lithocholic acid toxicity, and exhibited solid antioxidative and anti-inflammatory effect in vitro. In mice with CCl₄-induced acute liver injury, pre-administration of gigantol (10, 20, 40 mg· kg^-1· d^-1, po, for 7 days) dose-dependently decreased serum transaminase levels and improved pathological changes in liver tissues. The elevated lipid peroxidation and inflammatory responses in the livers were also significantly alleviated by gigantol. The pharmacokinetic studies showed that gigantol was highly concentrated in the mouse livers, which consisted with its efficacy in preventing liver injury. Using a label-free quantitative proteomic analysis we revealed that gigantol mainly regulated the immune system process in liver tissues of CCl₄-treated mice, and the complement and coagulation cascades was the predominant pathway; gigantol markedly inhibited the expression of complement component C9, which was a key component for the formation of terminal complement complex (TCC) C5b-9. These results were validated by immunohistochemistry (IHC) or real time-PCR. Confocal microscopy analysis showed that gigantol significantly inhibited the vascular deposition of TCC in the liver. In conclusion, we demonstrate for the first time that oral administration of gigantol potently relieves liver oxidative stress and inflammation, possibly via a novel mechanism of inhibiting the C5b-9 formation in the liver.

Vascular Epiphytic Medicinal Plants as Sources of Therapeutic Agents: Their Ethnopharmacological Uses, Chemical Composition, and Biological Activities

This is an extensive review on epiphytic plants that have been used traditionally as medicines. It provides information on 185 epiphytes and their traditional medicinal uses, regions where Indigenous people use the plants, parts of the plants used as medicines and their preparation, and their reported phytochemical properties and pharmacological properties aligned with their traditional uses. These epiphytic medicinal plants are able to produce a range of secondary metabolites, including alkaloids, and a total of 842 phytochemicals have been identified to date. As many as 71 epiphytic medicinal plants were studied for their biological activities, showing promising pharmacological activities, including as anti-inflammatory, antimicrobial, and anticancer agents. There are several species that were not investigated for their activities and are worthy of exploration. These epipythes have the potential to furnish drug lead compounds, especially for treating cancers, and thus warrant indepth investigations.

Two new stilbenoids from Bletilla striata

Two new stilbenoids bletilol D (1) and bletilol E (2), together with five known compounds were isolated from Bletilla striata. Three of them (3, 4, and 7) were obtained from this genus for the first time. Their structures were elucidated by spectroscopic methods and comparing with data reported in literatures. The cytotoxic activities of compounds 1-7 against MCF-7 (human breast cancer) and A549 (human lung carcinoma) cell lines were evaluated by MTT assay. Compound 2 showed weak cytotoxicity against MCF-7 and A549 cell lines with IC₅₀ values of 36.32 ± 1.17 and 36.48 ± 1.12 μM, respectively, and 5 exhibited weak cytotoxicity against MCF-7 cell line with IC₅₀ value of 57.09 ± 2.03 μM.

Phenanthrenes: A Promising Group of Plant Secondary Metabolites

Although phenanthrenes are considered to constitute a relatively small group of natural products, discovering new phenanthrene derivatives and evaluating their prospective biological activities have become of great interest to many research groups worldwide. Based on 160 references, this review covers the phytochemistry and pharmacology of 213 naturally occurring phenanthrenes that have been isolated between 2008 and 2016. More than 40% of the 450 currently known naturally occurring phenanthrenes were identified during this period. The family Orchidaceae is the most abundant source of these compounds, although several new plant families and genera have been involved in the search for phenanthrenes. The presence of certain substituent patterns may be restricted to specific families; vinyl-substituted phenanthrenes were reported only from Juncaceae plants, and prenylated derivatives occur mainly in Euphorbiaceae species. Therefore, these compounds also can serve as chemotaxonomic markers. Almost all of the newly isolated compounds have been studied for their biological activities (e.g., potential cytotoxic, antimicrobial, anti-inflammatory, and antioxidant effects), and many of them showed multiple activities. According to the accumulated data, denbinobin, with a novel mechanism of action, has great potential as a lead compound for the development of a new anticancer agent.

Chemical Compounds in Natural Medicines That Affect Macropharges and Adipocyte Cells

Macrophages play major roles in inflammation, immunity and host defense mechanisms. Once activated they produce and release cytokines, oxygen and nitrogen species, and eicosanoids. The best characterized stimuli to induce the transcription of genes encoding pro-inflammatory proteins in macrophages in vitro is bacterial lipopolysaccharide (LPS). LPS could be used alone or in combination with recombinant mouse interferon-γ (IFN-γ). Such stimulation results in cytokine release and the synthesis of enzymes such as cyclooxygenase-2 (COX-2) and inducible nitric oxide synthase (iNOS). The nitric oxide (NO) radical is known to play a central role in inflammatory and immune reactions for self-protection. However, the excessive production of NO may lead to tissue damage. In inflammatory diseases such as rheumatoid arthritis, excessive NO production by activated macrophages has been observed. Adipose tissue is composed of various cell types such as mature adipocytes, preadipocytes, fibroblasts, endothelial cells, vascular cells, and macrophages. Recent studies indicate that obesity is associated with low-grade chronic inflammation of adipose tissues, and that such inflammation is one of the potential mechanisms leading to the insulin resistance. It has been demonstrated that obese adipose tissue is characterized by the increased infiltration of macrophages. Therefore, we attempted to identify natural anti-inflammatory compounds that not only inhibit the secretion of NO from RAW 264.7 cells, but also inhibit triglyceride accumulation in 3T3-L1 adipocytes. This review describes the NO prpduction inhibitory activity or the TG accumulation inhibitory activity of the compounds obtained from 18 plants and a fungi that have been used as traditional medicines.

Antioxidant biomarkers from Vanda coerulea stems reduce irradiated HaCaT PGE-2 production as a result of COX-2 inhibition

Background

In our investigations towards the isolation of potentially biologically active constituents from Orchidaceae, we carried out phytochemical and biological analyses of Vanda species. A preliminary biological screening revealed that Vanda coerulea (Griff. ex. Lindl) crude hydro-alcoholic stem extract displayed the best DPPH /^•OH radical scavenging activity and in vitro inhibition of type 2 prostaglandin (PGE-2) release from UV_B (60 mJ/cm²) irradiated HaCaT keratinocytes.

Principal Findings

Bio-guided fractionation and phytochemical analysis led to the isolation of five stilbenoids: imbricatin (1) methoxycoelonin (2) gigantol (3) flavidin (4) and coelonin (5). Stilbenoids (1–3) were the most concentrated in crude hydro-alcoholic stem extract and were considered as Vanda coerulea stem biomarkers. Dihydro-phenanthropyran (1) and dihydro-phenanthrene (2) displayed the best DPPH/^•OH radical scavenging activities as well as HaCaT intracellular antioxidant properties (using DCFH-DA probe: IC₅₀ 8.8 µM and 9.4 µM, respectively) compared to bibenzyle (3) (IC₅₀ 20.6 µM). In turn, the latter showed a constant inhibition of PGE-2 production, stronger than stilbenoids (1) and (2) (IC₅₀ 12.2 µM and 19.3 µM, respectively). Western blot analysis revealed that stilbenoids (1–3) inhibited COX-2 expression at 23 µM. Interestingly, stilbenoids (1) and (2) but not (3) were able to inhibit human recombinant COX-2 activity.

Conclusions

Major antioxidant stilbenoids (1–3) from Vanda coerulea stems displayed an inhibition of UV_B-induced COX-2 expression. Imbricatin (1) and methoxycoelonin (2) were also able to inhibit COX-2 activity in a concentration-dependent manner thereby reducing PGE-2 production from irradiated HaCaT cells. Our studies suggest that stilbenoids (1–3) could be potentially used for skin protection against the damage caused by UV_B exposure.

Volatile Components of Selected Liverworts, and Cytotoxic, Radical Scavenging and Antimicrobial Activities of Their Crude Extracts

Crude extracts of the Tahitian liverworts Mastigophora Diclados and Frullania sp., the Indonesian Frullania sp., Dumortiera hirsuta and Marchantia sp., and the Japanese Porella perrottetiana were investigated chemically by using gas chromatography-mass spectrometry (GC-MS). All extracts contained various volatile sesqui- and diterpenoids and a few aromatic compounds. The Tahitian M. diclados and Frullania sp., and the Indonesian Frullania sp. exhibited cytotoxic activity against HL-60 and KB cell lines. The extracts of the Tahitian M. diclados and the Indonesian Marchantia sp. showed radical scavenging activity, whereas the crude extracts of the Tahitian M. diclados and Frullania sp., and the Indonesian Frullania and Marchantia sp. showed antimicrobial activity against Staphylococcus aureus and Bacillus subtilis.

Total synthesis of bulbophylol-B

The first total synthesis of bulbophylol-B (1) has been achieved with the longest linear sequence of 12 steps and an overall yield of 17.9% via a new and practical approach to construct the dihydrodibenz[b,f]oxepin skeleton employing Wittig, selective reduction, and intramolecular Ullmann reactions as key steps.