Stilbenoids: Chemistry and bioactivities

Stilbenes Against Alzheimer's Disease: A Comprehensive Review of Preclinical Studies of Natural and Synthetic Compounds Combined with the Contributions of Developed Nanodrug Delivery Systems

This review covers preclinical studies of stilbene derivative compounds (both natural and synthetic) with potential preventive and therapeutic effects against Alzheimer's disease (AD). AD is a worldwide neurodegenerative disease characterized by the destruction of nerve cells in the brain and the loss of cognitive function due to aging. Stilbenes are a unique class of natural phenolic compounds distinguished by a C6-C2-C6 (1,2-diphenylethylene) structure and two aromatic rings connected by an ethylene bridge. Stilbenes' distinct features make them an intriguing subject for pharmacological research and development. Several preclinical studies have suggested that stilbenes may have neuroprotective effects by reducing Aβ generation and oligomerization, enhancing Aβ clearance, and regulating tau neuropathology through the prevention of aberrant tau phosphorylation and aggregation, as well as scavenging reactive oxygen species. Synthetic stilbene derivatives also target multiple pathways involved in neuroprotection and have demonstrated promising biological activity in vitro. However, some properties of stilbenes, such as sensitivity to physiological conditions, low solubility, poor permeability, instability, and low bioavailability, limit their usefulness in clinical applications. To address this issue, current investigations have developed new drug delivery systems based on stilbene derivative molecules. This review aims to shed light on the development of next-generation treatment strategies by examining in detail the role of stilbenes in Alzheimer's pathophysiology and their therapeutic potential.

Stilbenes: A new strategy for protecting light-sensitive foods, a review of their structure classification and singlet oxygen quenching mechanism

Natural stilbenes have been studied extensively as a result of their complicated structures and diverse biological activities. Singlet oxygen (1O2), a kind of reactive oxygen species (ROS) has a strong destructive effect on food systems (especially for light-sensitive foods). Many cutting-edge scientific studies have found that some stilbenes not only have extensive quenching properties for ROS, but also can selectively quench 1O2. However, the industry devoted too much energy on the development of more new stilbenes, lacking in-depth summaries and reflections on the characteristics of their basic structure and the mechanism of their extraordinary 1O2 quenching abilities. Therefore, we summarized the classification methods for stilbene compounds and evaluated similarities, differences and possible limitations of different classification methods. In addition, we described the role of different functional groups in stilbenes in quenching of 1O2 and summarized the quenching mechanism of 1O2 by stilbenes. By the way, the current application of stilbene compounds and their potential risks in the food industry were also mentioned in this article. The stilbenes can be used as antioxidants (especially new strategies against 1O2 oxidation) in food systems to improve the shelf life. At this stage, it is necessary to develop more effective and safe food antioxidant stilbenes based on their quenching mechanism.

Biomimetic oxidative copolymerization of hydroxystilbenes and monolignols

Hydroxystilbenes are a class of polyphenolic compounds that behave as lignin monomers participating in radical coupling reactions during the lignification. Here, we report the synthesis and characterization of various artificial copolymers of monolignols and hydroxystilbenes, as well as low-molecular-mass compounds, to obtain the mechanistic insights into their incorporation into the lignin polymer. Integrating the hydroxystilbenes, resveratrol and piceatannol, into monolignol polymerization in vitro, using horseradish peroxidase to generate phenolic radicals, produced synthetic lignins [dehydrogenation polymers (DHPs)]. Copolymerization of hydroxystilbenes with monolignols, especially sinapyl alcohol, by in vitro peroxidases notably improved the reactivity of monolignols and resulted in substantial yields of synthetic lignin polymers. The resulting DHPs were analyzed using two-dimensional NMR and 19 synthesized model compounds to confirm the presence of hydroxystilbene structures in the lignin polymer. The cross-coupled DHPs confirmed both resveratrol and piceatannol as authentic monomers participating in the oxidative radical coupling reactions during polymerization.

LC-HRMS/MS-Based Metabolomics Approaches Applied to the Detection of Antifungal Compounds and a Metabolic Dynamic Assessment of Orchidaceae

The liquid chromatography-mass spectrometry (LC-MS)-based metabolomics approach is a powerful technology for discovering novel biologically active molecules. In this study, we investigated the metabolic profiling of Orchidaceae species using LC-HRMS/MS data combined with chemometric methods and dereplication tools to discover antifungal compounds. We analyze twenty ethanolic plant extracts from Vanda and Cattleya (Orchidaceae) genera. Molecular networking and chemometric methods were used to discriminate ions that differentiate healthy and fungal-infected plant samples. Fifty-three metabolites were rapidly annotated through spectral library matching and in silico fragmentation tools. The metabolomic profiling showed a large production of polyphenols, including flavonoids, phenolic acids, chromones, stilbenoids, and tannins, which varied in relative abundance across species. Considering the presence and abundance of metabolites in both groups of samples, we can infer that these constituents are associated with biochemical responses to microbial attacks. In addition, we evaluated the metabolic dynamic through the synthesis of stilbenoids in fungal-infected plants. The tricin derivative flavonoid- and the loliolide terpenoidfound only in healthy plant samples, are promising antifungal metabolites. LC-HRMS/MS, combined with state-of-the-art tools, proved to be a rapid and reliable technique for fingerprinting medicinal plants and discovering new hits and leads.

Molecular encapsulation and bioactivity of gnetol, a resveratrol analogue, for use in foods

BACKGROUND

Gnetol is a stilbene whose characterization and bioactivity have been poorly studied. It shares some bioactivities with its analogue resveratrol, such as anti-inflammatory, anti-thrombotic, cardioprotective and anti-cancer activities. However, the low solubility of stilbenes may limit their potential applications in functional foods. Encapsulation in cyclodextrins could be a solution.

RESULTS

The antioxidant activity of gnetol was evaluated by 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) radical cation and ferric reducing antioxidant power methods (Trolox equivalents 13.48 μmol L^-1 and 37.08 μmol L^-1 respectively at the highest concentration) and it was higher than that of resveratrol, and depending on the method, similar or higher to that of oxyresveratrol. Spectrophotometric and spectrofluorimetric characterization of gnetol is published for the first time. Moreover, its water solubility was determined and improved almost threefold after its molecular encapsulation in cyclodextrins, as well as its stability after storage for a week. A physicochemical and computational study revealed that cyclodextrins complex gnetol in a 1:1 stoichiometry, with better affinity for like 2-hydroxypropyl-β-cyclodextrin (K_F  = 4542.90 ± 227.15 mol^-1  L). Temperature and pH affected the encapsulation constants.

CONCLUSION

These results could increase interest of gnetol as an alternative to the most studied stilbene, resveratrol, as well as aid in the development of more stable inclusion complexes that improve its aqueous solubility and stability so that it can be incorporated into functional foods. © 2022 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Antibacterial activities of polyphenols against foodborne pathogens and their application as antibacterial agents

Polyphenols are secondary metabolites produced in higher plants. They are known to possess various functional properties in the human body. Polyphenols also exhibit antibacterial activities against foodborne pathogens. Their antibacterial mechanism is based on inhibiting bacterial biofilm formation or inactivating enzymes. Food-derived polyphenols with such antibacterial activity are natural preservatives and can be used as an alternative to synthetic preservatives that can cause side effects, such as allergies, asthma, skin irritation, and cancer. Studies have reported that polyphenols have positive effects, such as decreasing harmful bacteria and increasing beneficial bacteria in the human gut microbiota. Polyphenols can also be used as natural antibacterial agents in food packaging system in the form of emitting sachets, absorbent pads, and edible coatings. We summarized the antibacterial activities, mechanisms and applications of polyphenols as antibacterial agents against foodborne bacteria.

Naturally occurring prenylated stilbenoids: food sources, biosynthesis, applications and health benefits

Prenylated stilbenoids are a unique class of natural phenolic compounds consisting of C6-C2-C6 skeleton with prenyl substitution. They are potential nutraceuticals and dietary supplements presented in some edible plants. Prenylated stilbenoids demonstrate promising health benefits, including antioxidant, anti-cancer, anti-inflammatory, anti-microbial activities. This review reports the structure, bioactivity and potential application of prenylated stilbeniods in food industry. Edible sources of these compounds are compiled and summarized. Structure-activity relationship of prenylated stilbenoids are also highlighted. The biosynthesis strategies of prenylated stilbenoids are reviewed. The findings of these compounds as food preservative, nutraceuticals and food additive are discussed. This paper combines the up-to-date information and gives a full image of prenylated stilbenoids.

Theoretical study on the radical scavenging activity and mechanism of four kinds of Gnetin molecule

As an important subgroup of resveratrol oligomers, Gnetins received much attention due to their antioxidants. The four Gnetin molecules are divided into two major categories according to different structures, type-A (Gnetin-C, Gnetin-D) and type-B (Gnetin-L, Gnetin-F). Density functional theory (DFT) has been performed thermodynamically and kinetically in detail to analyze the structure and antioxidant activity of four Gnetins toward OH/OOH radical in the gas and solvents phase with four possible antioxidant mechanisms, namely, Hydrogen-atom transfer (HAT), Single electron transfer followed by proton transfer (SET-PT), Sequential proton-loss electron transfer (SPLET), and Radical adduct formation (RAF). From these calculations; Gnetins' order of antioxidant activity was estimated as: Gnetin-C ≈ Gnetin-L > Resveratrol > Gnetin-D > Gnetin-F. All investigations suggested that type A has a higher radical scavenging activity compared to type B. On the basis of the structure-activity relationship, type A structure may have more vital antioxidant potential in the future.

Discovery of bletillain, an unusual benzyl polymer with significant autophagy-inducing effects in A549 lung cancer cells through the Akt/GSK-3β/β-catenin signaling pathway

Lung cancer is one of the most malignant tumors with the highest mortality and morbidity. The tubers of Bletilla striata are known as "an excellent medicine for lung diseases" in traditional Chinese medicine. This study performed a targeted study to explore compounds with anti-lung cancer activity and the molecular mechanisms using A549 cells. Eighteen bibenzyl derivatives, including four new compounds (13, 14, 16, and 18), were isolated from the tubers of B. striata. Analysis of the structure-activity relationship indicated that the cytotoxicity of the bibenzyls against A549 cells increased gradually as the number of the benzyl groups in the structures increased. Bletillain (18), an unusual benzyl polymer, was found to be the most active compound. Further flow cytometric analysis, dual-luciferase assays, real-time PCR assays, and western blot assays revealed that bletillain induced autophagy in A549 cells by regulating the Akt/GSK-3β/β-catenin signaling pathway. Beclin 1, LC3, and p62 are downstream autophagy factors of Akt, and Beclin 1 was the key autophagy factor. These results suggested that bibenzyls of B. striata play important roles in the treatment of lung cancer and provided scientific evidence illustrating why the tubers of B. striata are a suitable medicine for the treatment of lung cancer in traditional Chinese medicine.

Resveratrol Production in Yeast Hosts: Current Status and Perspectives

Resveratrol is a plant secondary metabolite known for its therapeutic applications as an antioxidant, anti-cancer, anti-inflammatory, anti-aging, cardio-protective, and neuroprotective agent. Topical formulas of resveratrol are also used for skin disease management and in cosmetic industries. Due to its importance, high resveratrol production is urgently required. Since the last decade, intensive efforts have been devoted to obtaining resveratrol from microorganisms by pathway and metabolic engineering. Yeasts were proven to be excellent host candidates for resveratrol production. In addition to the similar intracellular compartments between yeasts and plants, yeasts exhibit the ability to express genes coding for plant-derived enzymes and to perform post-translational modification. Therefore, this review summarizes the attempts to use yeasts as a platform for resveratrol synthesis as the next promising route in producing high titers of resveratrol from genetically engineered strains.

The Role of Polyphenols in Abiotic Stress Response: The Influence of Molecular Structure

Abiotic stressors such as extreme temperatures, drought, flood, light, salt, and heavy metals alter biological diversity and crop production worldwide. Therefore, it is important to know the mechanisms by which plants cope with stress conditions. Polyphenols, which are the largest group of plant-specialized metabolites, are generally recognized as molecules involved in stress protection in plants. This diverse group of metabolites contains various structures, from simple forms consisting of one aromatic ring to more complex ones consisting of large number of polymerized molecules. Consequently, all these molecules, depending on their structure, may show different roles in plant growth, development, and stress protection. In the present review, we aimed to summarize data on how different polyphenol structures influence their biological activity and their roles in abiotic stress responses. We focused our review on phenolic acids, flavonoids, stilbenoids, and lignans.

Preparative Isolation of Piceatannol Derivatives from Passion Fruit (Passiflora edulis) Seeds by High-Speed Countercurrent Chromatography Combined with High-Performance Liquid Chromatography and Screening for α-Glucosidase Inhibitory Activities

Passiflora edulis Sims (passion fruit) seeds are often discarded as byproducts during juice processing. In fact, the seeds are of considerable commercial value in the food and cosmetics industry because of their rich polyphenols, especially piceatannol. In this study, high-speed countercurrent chromatography (HSCCC) was applied for the separation of stilbene polyphenols from passion fruit seeds. The n-hexane-ethyl acetate-methanol-water (1:2:1:2.8, v/v) was found to be the optimum two-phase solvent for the preparation of two major stilbenes, scirpusin B (8) and piceatannol (9) with purities of 90.2% and 94.8%, respectively. In addition, a continuous semipreparative HPLC was applied to further purify the HSCCC fractions containing minor stilbenes and obtain four new piceatannol derivatives (1-4) along with three known ones (5-7). The structures of these new compounds were determined using spectroscopic methods, including NMR, high-resolution electrospray ionization mass spectrometry (HR-ESI-MS), and circular dichroism (CD). The isolated compounds were evaluated for α-glucosidase inhibitory activities in vitro. The result suggested that all of them exhibited more significant activity than acarbose, and passiflorinol B (2) had the strongest activity, with a IC₅₀ value of 1.7 μM.

Whole-cell biocatalytic, enzymatic and green chemistry methods for the production of resveratrol and its derivatives

Resveratrol and the biosynthetically related stilbenes are plant secondary metabolites with diverse pharmacological effects. The versatile functions of these compounds in plant defense mechanisms as phytoalexins on one hand, and in human health as potential pharmaceutical agents on the other, have attracted lots of interest in recent years to understand their biosynthetic pathways and their biological properties. Because of difficulties in obtaining resveratrol and its glucosylated derivatives as well as oligomeric forms in sufficient amounts for evaluation of their activity by plant sourcing or total synthesis, biotechnology may provide a competitive approach for the large-scale and low cost production of biologically active stilbenes. Additionally, one major limitation in the use of resveratrol and related aglycone derivatives as therapeutic agents is associated with their inherent poor aqueous solubility and low bioavailability. This article examines approaches for the synthesis of potential pharmacologically resveratrol derivatives in vivo by exploiting whole microorganisms, enzymatic and biocatalytic approaches allowing their full utilization for medicine, food and cosmetic applications. These methods also have the advantage of enabling the one-step production of stilbene compounds, compared to the time-consuming and environmentally unfriendly procedures used for their total synthesis or their extraction from plants. Increasing the desired products yield and biological activity through glucosylation (β-D-glucosides versus α-D-glucosides) and oligomerization methodologies of resveratrol including green chemistry methods in organic solvent-free media are discussed as well.

Parallel in vitro and in silico investigations into anti-inflammatory effects of non-prenylated stilbenoids

Stilbenoids represent a large group of bioactive compounds, which occur in food and medicinal plants. Twenty-five stilbenoids were screened in vitro for their ability to inhibit COX-1, COX-2 and 5-LOX. Piceatannol and pinostilbene showed activity comparable to the zileuton and ibuprofen, respectively. The anti-inflammatory potential of stilbenoids was further evaluated using THP-1 human monocytic leukemia cell line. Tests of the cytotoxicity on the THP-1 and HCT116 cell lines showed very low toxic effects. The tested stilbenoids were evaluated for their ability to attenuate the LPS-stimulated activation of NF-κB/AP-1. Most of the tested substances reduced the activity of NF-κB/AP-1 and later attenuated the expression of TNF-α. The effects of selected stilbenoids were further investigated on inflammatory signaling pathways. Non-prenylated stilbenoids regulated attenuation of NF-ĸB/AP-1 activity upstream by inhibiting the phosphorylation of MAPKs. A docking study used to in silico analyze the tested compounds confirmed their interaction with NF-ĸB, COX-2 and 5-LOX.

Uptake and distribution of phenanthrene and pyrene in roots and shoots of maize (Zea mays L.)

Polycyclic aromatic hydrocarbons as byproducts of carbon-based fuel combustion are an important group of pollutants with wide distribution in the environment. Polycyclic aromatic hydrocarbons are known as toxic compounds for almost all organisms. Different plant species can uptake polycyclic aromatic hydrocarbons by roots and translocate them to various aerial parts. The aim of this study is to investigate the uptake, translocation, and accumulation of pyrene and phenanthrene in maize under controlled conditions. Seeds were cultivated in perlite containing 25, 50, 75, and 100 ppm of phenanthrene and pyrene, and their concentrations in the roots and shoots of the plants were measured using high-performance liquid chromatography technique after 7, 14, and 21 days. The results revealed that phenanthrene naturally existed in maize and its concentration showed a time-dependent decrease in shoots and roots. In contrast, the concentration of pyrene was increased in the roots and reduced in the shoots. Although pyrene had higher uptake than phenanthrene in roots of maize, the translocation factor value for pyrene was lower than for phenanthrene. According to these findings, phenanthrene could be metabolized in maize in the shoot and root tissues, but pyrene had more tendency to be accumulated in roots.

Synthesis of Indole-, Benzo[ b]thiophene-, and Benzo[ b]selenophene-Based Analogues of the Resveratrol Dimers Viniferifuran and (±)-Dehydroampelopsin B

A convenient synthetic strategy to obtain viniferifuran and (±)-dehydroampelopsin B analogues based on the heterocyclic cores of indole, benzo[ b]thiophene, and benzo[ b]selenophene is presented. The key transformations utilized in the described syntheses include Sonogashira couplings, Cacchi and alkyne electrophilic cyclizations, Horner-Wadsworth-Emmons (HWE) reaction, chemoselective Suzuki-Miyaura couplings, and acid-promoted intramolecular cyclization to form the seven-membered ring of (±)-dehydroampelopsin B.

Update on Phytochemistry and Pharmacology of Naturally Occurring Resveratrol Oligomers

Resveratrol oligomers (REVs), a major class of stilbenoids, are biosynthesized by regioselective oxidative coupling of two to eight units of resveratrol monomer. Due to their unique structures and pleiotropic biological activities, natural product chemists are increasingly focusing on REVs in the last few decades. This study presents a detailed and thorough examination of REVs, including chemical structures, natural resources, and biological activities, during the period of 2010–2017. Ninety-two new REVs compounds, including 39 dimers, 23 trimers, 13 tetramers, six resveratrol monomers, six hexamers, four pentamers, and one octamer, have been reported from the families of Dipterocarpaceae, Paeoniaceae, Vitaceae, Leguminosae, Gnetaceae, Cyperaceae, Polygonaceae Gramineae, and Poaceae. Amongst these families, Dipterocarpaceae, with 50 REVs, accounts for the majority, and seven genera of Dipterocarpaceae are involved, including Vatica, Vateria, Shorea, Hopea, Neobalanocarpus, Dipterocarpus, and Dryobalanops. These REVs have shown a wide range of bioactivities. Pharmacological studies have mainly focused on potential efficacy on tumors, bacteria, Alzheimer’s disease, cardiovascular diseases, and others. The information updated in this review might assist further research and development of novel REVs as potential therapeutic agents.

Two New Stilbenoids from the Aerial Parts of Arundina graminifolia (Orchidaceae)

Two new phenanthrene derivatives, a phenanthrenequinone named arundiquinone (1) and a 9,10-dihydrophenanthrene named arundigramin (2) together with a known lignin dimer (3) and seven known stilbenoids (4–10) were isolated from the aerial parts of the Asian orchid Arundina graminifolia. The structures of the isolated compounds were elucidated by spectroscopic methods, including extensive 1D, 2D NMR (heteronuclear single quantum coherence (HSQC), heteronuclear multiple-bond correlation spectroscopy (HMBC), and HR-ESI-MS techniques, as well as comparison with respective literature reports. The cytoprotective activity of the isolated compounds were evaluated for their ability to reduce beta amyloid induced toxicity on undifferentiated PC12 cells. Compound 8 showed moderate cytoprotective activity at 0.5 µmol/L (71% of cell viability) while the other compounds showed no significant activity at the highest concentration tested.

Insight into the Presence of Stilbenes in Medicinal Plants Traditionally Used in Croatian Folk Medicine

Over the last years, great interest has arisen concerning plant stilbenes, especially resveratrol, which has a whole spectrum of positive biological activities. In this study, we investigated the presence of resveratrol monomers (trans- and cis- form) and naturally occurring derivatives of fraas-resveratrol (piceid, astringin and isorhapontin) in phenolic extracts of twenty medicinal plants traditionally used in Croatian folk medicine. The investigated compounds were present in the samples, in free form or as glucosides, and the highest share was found in immortelle, common yarrow and Lamiaceae plants. The obtained results indicate that biological activity of selected medicinal plants can be related to the presence of this valuable group of phytochemicals.

Neuroprotective naphthalene and flavan derivatives from Polygonum cuspidatum

Ten naphthalene derivatives including two unusual glycosides possessing a naphthalene-fused piceid via a [C8'-O-C6-C5-C7']-trans-dihydrofuran ring, two flavan derivatives, as well as sixteen known phenolic compounds, were isolated from Polygonum cuspidatum. The structures were determined by extensive NMR, MS, CD data, and chemical evidence. In the in vitro neuroprotective assays, at the concentration of 10 μM, five of these compounds exhibited significant effects against PC12 cells injured by rotenone.

Solving the supply of resveratrol tetramers from Papua New Guinean rainforest anisoptera species that inhibit bacterial type III secretion systems

The supply of (-)-hopeaphenol (1) was achieved via enzymatic biotransformation in order to provide material for preclinical investigation. High-throughput screening of a prefractionated natural product library aimed to identify compounds that inhibit the bacterial virulence type III secretion system (T3SS) identified several fractions derived from two Papua New Guinean Anisoptera species, showing activity against Yersinia pseudotuberculosis outer proteins E and H (YopE and YopH). Bioassay-directed isolation from the leaves of A. thurifera, and similarly A. polyandra, resulted in three known resveratrol tetramers, (-)-hopeaphenol (1), vatalbinoside A (2), and vaticanol B (3). Compounds 1-3 displayed IC50 values of 8.8, 12.5, and 9.9 μM in a luminescent reporter-gene assay (YopE) and IC50 values of 2.9, 4.5, and 3.3 μM in an enzyme-based YopH assay, respectively, which suggested that they could potentially act against the T3SS in Yersinia. The structures of 1-3 were confirmed through a combination of spectrometric, chemical methods, and single-crystal X-ray structure determinations of the natural product 1 and the permethyl ether analogue of 3. The enzymatic hydrolysis of the β-glycoside 2 to the aglycone 1 was achieved through biotransformation using the endogenous leaf enzymes. This significantly enhanced the yield of the target bioactive natural product from 0.08% to 1.3% and facilitates ADMET studies of (-)-hopeaphenol (1).

Review of natural compounds for potential skin cancer treatment

Most anti-cancer drugs are derived from natural resources such as marine, microbial and botanical sources. Cutaneous malignant melanoma is the most aggressive form of skin cancer, with a high mortality rate. Various treatments for malignant melanoma are available, but due to the development of multi-drug resistance, current or emerging chemotherapies have a relatively low success rates. This emphasizes the importance of discovering new compounds that are both safe and effective against melanoma. In vitro testing of melanoma cell lines and murine melanoma models offers the opportunity for identifying mechanisms of action of plant derived compounds and extracts. Common anti-melanoma effects of natural compounds include potentiating apoptosis, inhibiting cell proliferation and inhibiting metastasis. There are different mechanisms and pathways responsible for anti-melanoma actions of medicinal compounds such as promotion of caspase activity, inhibition of angiogenesis and inhibition of the effects of tumor promoting proteins such as PI3-K, Bcl-2, STAT3 and MMPs. This review thus aims at providing an overview of anti-cancer compounds, derived from natural sources, that are currently used in cancer chemotherapies, or that have been reported to show anti-melanoma, or anti-skin cancer activities. Phytochemicals that are discussed in this review include flavonoids, carotenoids, terpenoids, vitamins, sulforaphane, some polyphenols and crude plant extracts.

An unusual piceatannol dimer from Rheum austral D. Don with antioxidant activity

A novel dimer of piceatannol glycoside, named rheumaustralin (1) was isolated from the underground parts of the ethnomedicinal plant Rheum austral (Polygonaceae) collected from Tibet together with 17 known compounds, including rheumin (2), 2,5-dimethyl-7-hydroxychromone (3), 2,5-dimethylchromone-7-O-β-D-glucopyranoside (4), 7-hydroxy-2-(2'-hydroxypropyl)-5-methylchromone (5), torachrysone (6) torachrysone-8-O-β-D-glucopyranoside (7), 4-(4'-hydroxyphenyl)-2-butanone-4'-O-β-D-glucopyranoside (8), amabiloside (9), N-trans-feruloyl tyramine (10), chrysophanol (11), aloe-emodin (12), emodin (13), physcion (14), physcion-1-O-β-D-glucopyranoside (15), emodin-8-O-β-D-glucopyranoside (16), D-catechin (17) and gallic acid (18). Their structures were determined by combined spectroscopic methods and by comparison of their spectral data with those reported in literature. Compounds 1-10 were tested for their ability to scavenge 1, 1-diphenyl-2-picrylhydrazyl (DPPH) radical.

Cytotoxic deoxybenzoins and diphenylethylenes from Arundina graminifolia

Eight new C-4-alkylated deoxybenzoins (1-8), three new diphenylethylenes (9-11), and five known diphenylethylenes were isolated from Arundina graminifolia. The structures of 1-11 were elucidated by spectroscopic methods including extensive 1D and 2D NMR techniques. Compounds 9-11 are the first naturally occurring diphenylethylenes possessing a hydroxyethyl unit. Compounds 1-11 were evaluated for cytotoxicity against five human tumor cell lines. Compounds 4, 5, and 9-11 showed significant cytotoxicity against five cancer cell lines, with IC50 values ranging from 1.8 to 8.7 μM.

New resveratrol oligomer derivatives from the roots of Rheum lhasaense

Two new resveratrol trimer derivatives, named rheumlhasol A (1) and rheumlhasol B (2) were isolated from the methanolic extract of roots of Rheum lhasaense A. J. Li et P. K. Hsiao together with four known resveratrol dimer derivatives, including maximol A (3), gnetin C (4), ε-viniferin (5), and pallidol (6). The structures were determined by combined spectroscopic methods and by comparison of their spectral data with those reported in the literature. All the compounds isolated from R. lhasaense were tested for their ability to scavenge1,1-diphenyl-2-picrylhydrazyl (DPPH) radical.

Antiviral phenolic compounds from Arundina gramnifolia

Five new phenolic compounds, gramniphenols C-G (1-5), and eight known compounds (6-13) were isolated from the whole plant of Arundina gramnifolia. Compounds 1, 4, and 5 showed anti-tobacco mosaic virus activity, with IC(50) values of 20.8, 40.8, and 57.7 μM, respectively. Compounds 1-10 were also tested for their anti-HIV-1 activity; compounds 2, 3, and 6 displayed anti-HIV-1 activity with therapeutic index values above 100:1.

Natural stilbenoids: distribution in the plant kingdom and chemotaxonomic interest in Vitaceae

Stilbenoids, a family of polyphenols known for the complexity of their structure and for their diverse biological activities, occur with a limited but heterogeneous distribution in the plant kingdom. The most prominent stilbene containing plant family, the Vitaceae, represented by the famous wine producing grape vines Vitis vinifera L., is one of the richest sources of novel stilbenes currently known, together with other families, such as Dipterocarpaceae, Gnetaceae and Fabaceae. This review focuses on the distribution of stilbenes and 2-arylbenzofuran derivatives in the plant kingdom, the chemical structure of stilbenes in the Vitaceae family and their taxonomic implication.

Ex vivo study of the vasorelaxant activity induced by phenanthrene derivatives isolated from Maxillaria densa

The phenanthrenes gymnopusin (1), fimbriol A (2), and erianthridin (3) from Maxillaria densa were found to induce significant relaxant effects in a concentration-dependent and endothelium-independent manner on aortic rings precontracted with norepinephrine (NE, 0.1 μM) and KCl (80 mM). Compound 1 was the most active and also inhibited the cumulative concentration-response contraction of NE or CaCl(2). Contractions induced by FPL 64176, an agonist of L-type voltage-dependent calcium channels, were blocked by 1. The potassium channel blockers glibenclamide and TEA (tetraethylammonium) reduced the relaxations induced by 1. Nevertheless, the effect of 1 was not modified by 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one, a specific soluble guanylate cyclase inhibitor. The functional results obtained suggest that 1 induces relaxation through an endothelium-independent pathway by the control of cationic channels (calcium channel blockade and potassium channel opening) in the myogenic response of rat aortic rings.

Evaluation of the Combined Effects of Stilbenoid from Shorea gibbosa and Vancomycin against Methicillin-Resistant Staphylococcus aureus (MRSA)

The aim of this study is to determine the combined effects of stilbenoids from Shorea gibbosa and vancomycin against methicillin-resistant Staphylococcus aureus (MRSA). A total of nine pure compounds, five stilbenoid dimers ε-viniferin, ampelopsin A, balanocarpol, laevifonol and diptoindonesin G and four stilbenoid trimers α-viniferin, johorenol A, ampelopsin E and vaticanol G were evaluated for their antibacterial activities against ATCC 33591 and a HUKM clinical isolate. Minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) for each active compound were determined using the serial microdilution and plate-streak techniques. The combined effect of stilbenoids with vancomycin against MRSA was evaluated using the checkerboard assay to determine their fractional inhibitory concentration (FIC) index values. The MIC value of α-viniferin on both MRSA strains was 100 μg/mL, whereas those of johorenol A on ATCC 33591 and HUKM strain were 100 μg/mL and 200 μg/mL, respectively. The MIC values of ampelopsin E and vaticanol G were higher than 400 μg/mL. Out of the five stilbenoid dimers, only ε-viniferin was capable of inhibiting the growth of both MRSA strains at MIC 400 μg/mL. The MBC value of ε-viniferin, α-viniferin and johorenol A showed bacteriostatic action against MRSA. The FIC index value of ε-viniferin and α-viniferin in combination with vancomycin showed an additive effect (0.5 < FIC ≤ 2.0) against both MRSA strains. Johorenol A-vancomycin combination was also additive against HUKM strain, but it showed synergistic interaction with vancomycin against ATCC 33591 (FIC < 0.5). Stilbenoid compounds from Shorea gibbosa have anti-MRSA activity and huge potential as an alternative phytotherapy in combating MRSA infections.

Acuminatol and other antioxidative resveratrol oligomers from the stem bark of Shorea acuminata

A new resveratrol dimer, acuminatol (1), was isolated along with five known compounds from the acetone extract of the stem bark of Shorea acuminata. Their structures and stereochemistry were determined by spectroscopic methods, which included the extensive use of 2D NMR techniques. All isolated compounds were evaluated for their antioxidant activity using the 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity (RSA) and the β-carotene-linoleic acid (BCLA) assays, and compared with those of the standards of ascorbic acid (AscA) and butylated hydroxytoluene (BHT). All compounds tested exhibited good to moderate antioxidant activity in the DPPH assay (IC₅₀s 0.84 to 10.06 mM) and displayed strong inhibition of β-carotene oxidation (IC₅₀s 0.10 to 0.22 mM). The isolated compounds were evaluated on the Vero cell line and were found to be non-cytotoxic with LC₅₀ values between 161 to 830 µM.

Tannins of Constant Structure in Medicinal and Food Plants—Hydrolyzable Tannins and Polyphenols Related to Tannins

In addition to the commonly used classification as hydrolyzable tannins and condensed tannins, tannins can also be categorized into two other types: polyphenols of constant chemical structure (Type A) and polyphenols of variable composition (Type B). Both types of tannins and related polyphenols account for a large part of plant polyphenols, but accurate structure-activity correlations on a molecular basis can be determined mainly for type A compounds, among which are hydrolysable tannins such as the ellagitannins and their oxidized congeners, some gallotannins, epigallocatechin gallate, caffetannins, etc. Among the activities determined on a molecular basis are the chemical, biological and pharmacological actions such as superoxide anion scavenging, apoptosis, antitumor, anti-EVB, anti-MRSA and anti-plasmin inhibitory activities, etc., in addition to their fundamental activities, i.e., binding to proteins, large molecular compounds and metallic ions, and antioxidant activities. Some structure-specific activities were found for the condensation of dehydroellagitannins with co-existing compounds under mild conditions, and the host-mediated antitumor actions of ellagitannin oligomers. Structures and activities of metabolites of geraniin, a dehydroellagitannin, were revealed. Some stilbenoids and phlorotannins of firm structures have been known to have many activities similar to those of the type A tannins.