Flavonoid Aglycones Research Articles

Phenolic Profile and In Vivo Cytotoxic Activity of Rice Straw Extract

Background: Previous work of our team exhibited that rice straw (RS) has antitumor activity in vitro and inhibit proliferation of liver, lung, prostate, and breast cancer human cell lines. In this work, we extended our research to screen the antitumor activity of RS ethanol extract as a single treatment and in the presence of combined radiotherapy with a low dose of gamma radiation against murine Ehrlich solid carcinoma (EAC) model. Objective: To evaluate the most common waste in Egypt RS to screen out its in vivo cytotoxic activity and as combined therapy with radiotherapy. Method: Tested sample RS was investigated for its content of phenolics by LC/MS/MS, in addition, ethanolic extracts of the tested sample were investigated as antitumor on female mice inoculated with EAC cells as a single treatment and in the presence of combined radiotherapy with a low dose of gamma radiation (LDR). Results: LC/MS/MS revealed that rice straw was rich in phenolic acids (vanillic, p-coumaric, ferulic, and sinapic acid) along with catechin and flavonoids aglycones (quercetin, apigenin, and kaempferol). Rice straw and/or exposure to a low dose of γ-radiation caused a marked suppression of tumor growth and induced significant reduction in VEGF level & in IL-6 level with significant elevation in IL-10 serum level. Rice straw caused a significant down regulation in the gene transcription level of MCL1 and b-catenin, and a significant up-regulation of Caspase-3 and Bax gene expression. RS extract and LDR (EC + RS + R group) revealed that there was a mild form of necrosis with severe apoptosis in the tumor cells. Conclusion: From the aforementioned results, it can be concluded that RS/LDR effectively and synergistically work towards inhibition of cancer cell proliferation. These findings were well supported with histopathological studies suggesting that RS/low dose gamma radiation can serve as a good therapeutic agent against cancer but still need further clinical studies.

The Effect of Flavonoid Aglycones on the CYP1A2, CYP2A6, CYP2C8 and CYP2D6 Enzymes Activity.

Cytochromes P450 are major metabolic enzymes involved in the biotransformation of xenobiotics. The majority of xenobiotics are metabolized in the liver, in which the highest levels of cytochromes P450 are expressed. Flavonoids are natural compounds to which humans are exposed through everyday diet. In the previous study, selected flavonoid aglycones showed inhibition of CYP3A4 enzyme. Thus, the objective of this study was to determine if these flavonoids inhibit metabolic activity of CYP1A2, CYP2A6, CYP2C8, and CYP2D6 enzymes. For this purpose, the O-deethylation reaction of phenacetin was used for monitoring CYP1A2 enzyme activity, coumarin 7-hydroxylation for CYP2A6 enzyme activity, 6-α-hydroxylation of paclitaxel for CYP2C8 enzyme activity, and dextromethorphan O-demethylation for CYP2D6 enzyme activity. The generated metabolites were monitored by high-performance liquid chromatography coupled with diode array detection. Hesperetin, pinocembrin, chrysin, isorhamnetin, and morin inhibited CYP1A2 activity; apigenin, tangeretin, galangin, and isorhamnetin inhibited CYP2A6 activity; and chrysin, chrysin-dimethylether, and galangin inhibited CYP2C8. None of the analyzed flavonoids showed inhibition of CYP2D6. The flavonoids in this study were mainly reversible inhibitors of CYP1A2 and CYP2A6, while the inhibition of CYP2C8 was of mixed type (reversible and irreversible). The most prominent reversible inhibitor of CYP1A2 was chrysin, and this was confirmed by the docking study.

In vitro antigenotoxic activity, in silico ADME prediction and protective effects against aflatoxin B1 induced hepatotoxicity in rats of an Erythrina latissima stem bark extract

Stem bark of Erythrina latissima E. Mey (Leguminosae) contains a wide range of prenylated flavonoids able to counteract the genotoxic properties of aflatoxin B1 (AFB1). Thus, the hypothesis was raised that E. latissima stem bark extracts (ELBE) may counteract the in vivo hepatotoxic effects of aflatoxins, contaminants in food and feed. An HPLC-DAD method was developed and validated to determine the level of flavonoid aglycones (11.82%) and glycosides (16.17%). ADME, pharmacokinetic and drug-likeness assessment of major flavonoids of ELBE, using the web tool SwissADME, showed good oral bioavailability. The protective effect of ELBE against AFB1 induced genotoxicity in the Vitotox assay after metabolic activation was confirmed (IC50 of 44.32 μg/ml), followed by evaluation of its inhibitory effect on hepatotoxicity in rats induced by the same agent. Male Wistar rats were orally treated with ELBE (20 mg/kg, 50 mg/kg and 100 mg/kg) or curcumin (500 mg/kg) combined with piperine (20 mg/kg) - positive control, for 8 days prior to AFB1 exposure (1 mg/kg). The ELBE group showed a decreased activity of ALP and γ-GT compared to the AFB1 group. Histopathological examination of the liver demonstrated ameliorative effects of ELBE. Thus, ELBE could have a protective effect against hepatotoxins such as AFB1.

Natural Products Diversity in Plant-Insect Interaction between Tithonia diversifolia (Asteraceae) and Chlosyne lacinia (Nymphalidae).

The chemical ecology of plant-insect interactions has been driving our understanding of ecosystem evolution into a more comprehensive context. Chlosyne lacinia (Lepidoptera: Nymphalidae) is an olygophagous insect herbivore, which mainly uses host plants of Heliantheae tribe (Asteraceae). Herein, plant-insect interaction between Tithonia diversifolia (Heliantheae) and Chlosyne lacinia was investigated by means of untargeted LC-MS/MS based metabolomics and molecular networking, which aims to explore its inherent chemical diversity. C. lacinia larvae that were fed with T. diversifolia leaves developed until fifth instar and completed metamorphosis to the adult phase. Sesquiterpene lactones (STL), flavonoids, and lipid derivatives were putatively annotated in T. diversifolia (leaves and non-consumed abaxial surface) and C. lacinia (feces, larvae, pupae, butterflies, and eggs) samples. We found that several furanoheliangolide-type STL that were detected in T. diversifolia were ingested and excreted in their intact form by C. lacinia larvae. Hence, C. lacinia caterpillars may have, over the years, developed tolerance mechanisms for STL throughout effective barriers in their digestive canal. Flavonoid aglycones were mainly found in T. diversifolia samples, while their glycosides were mostly detected in C. lacinia feces, which indicated that the main mechanism for excreting the consumed flavonoids was through their glycosylation. Moreover, lysophospholipids were predominately found in C. lacinia samples, which suggested that they were essential metabolites during pupal and adult stages. These findings provide insights into the natural products diversity of this plant-insect interaction and contribute to uncovering its ecological roles.

Velutin, an Aglycone Extracted from Korean Mistletoe, with Improved Inhibitory Activity against Melanin Biosynthesis.

The abnormal regulation of melanin synthesis leads to a wide range of pigmentary disorders. Although various melanin biosynthesis inhibitors have been developed, their efficacy and long-term safety needs to be further improved, and thus the goal of this study is to develop promising natural compound inhibitors of melanin biosynthesis. Here, we obtained aglycone flavonoid extract through the microwave-assisted hydrolysis of glycoside extract from Korean mistletoe in acidic condition. The aglycone extract inhibited tyrosinase activity more efficiently with better antioxidant activity than glycoside extract in vitro. The microwave-assisted aglycone extract of mistletoe was further analyzed for in vivo activity, and the results showed the aglycone extract inhibited both early melanocyte development and melanin synthesis more efficiently in zebrafish embryo in a dose-dependent manner. Our in vivo toxicity assay quantitatively measured cell death in zebrafish embryos and showed that the microwave-assisted aglycone extract of mistletoe had no significant effect on cell death (p < 0.001), indicating that aglycone extract is more biocompatible than glycoside extract. Furthermore, our in vitro and in vivo analyses successfully identified and characterized velutin, an aglycone of a homoflavoyadorinin B glycoside, as a major inhibitory component in the microwave-assisted mistletoe extract. Ultimately, this study showed that the novel natural compound inhibitor velutin, which was generated through microwave-assisted extraction from mistletoe, improved the efficacy of melanin biosynthesis inhibition with little toxicity.

Kaempferol: A Key Emphasis to Its Anticancer Potential.

A marked decrease in human cancers, including breast cancer, bone cancer, and cervical cancer, has been linked to the consumption of vegetable and fruit, and the corresponding chemoprotective effect has been associated with the presence of several active molecules, such as kaempferol. Kaempferol is a major flavonoid aglycone found in many natural products, such as beans, bee pollen, broccoli, cabbage, capers, cauliflower, chia seeds, chives, cumin, moringa leaves, endive, fennel, and garlic. Kaempferol displays several pharmacological properties, among them antimicrobial, anti-inflammatory, antioxidant, antitumor, cardioprotective, neuroprotective, and antidiabetic activities, and is being applied in cancer chemotherapy. Specifically, kaempferol-rich food has been linked to a decrease in the risk of developing some types of cancers, including skin, liver, and colon. The mechanisms of action include apoptosis, cell cycle arrest at the G2/M phase, downregulation of epithelial-mesenchymal transition (EMT)-related markers, and phosphoinositide 3-kinase/protein kinase B signaling pathways. In this sense, this article reviews data from experimental studies that investigated the links between kaempferol and kaempferol-rich food intake and cancer prevention. Even though growing evidence supports the use of kaempferol for cancer prevention, further preclinical and clinical investigations using kaempferol or kaempferol-rich foods are of pivotal importance before any public health recommendation or formulation using kaempferol.

Effects of heat treatment of mandarin peel on flavonoid profiles and lipid accumulation in 3T3-L1 adipocytes

Citrus peel, a primary byproduct of citrus fruits, contains a variety of flavonoids. Heat treatment is a favorable food processing for solid peel to release bioactive compounds from tissues and intensify nutritional effects. In this study, we explored alterations of flavonoids by thermal treatment of mandarin peel and their effects on lipid accumulation and intracellular levels during differentiation of 3T3-L1 cells to adipocytes. The heat-treated sample showed stronger inhibition on the formation of lipid droplets than the non-treated sample, along with enhanced intracellular levels of flavonoids. Overall flavonoids, especially flavonoid aglycones showing better efficacy, were found to increase in the peel after heat-treatment. Our findings indicate thermal processing could help release flavonoids from citrus peel and convert them into aglycone forms, leading to efficient cellular uptake and suppression of lipid accumulation in 3T3-L1 cells. This study provides useful information of heat-treated citrus peel as potential dietary supplements with anti-obesity-related effects.

Low-copy nuclear sequence data confirm complex patterns of farina evolution in notholaenid ferns (Pteridaceae)

Notholaenids are an unusual group of ferns that have adapted to, and diversified within, the deserts of Mexico and the southwestern United States. With approximately 40 species, this group is noted for being desiccation-tolerant and having “farina”—powdery exudates of lipophilic flavonoid aglycones—that occur on both the gametophytic and sporophytic phases of their life cycle. The most recent circumscription of notholaenids based on plastid markers surprisingly suggests that several morphological characters, including the expression of farina, are homoplasious. In a striking case of convergence, Notholaena standleyi appears to be distantly related to core Notholaena, with several taxa not before associated with Notholaena nested between them. Such conflicts can be due to morphological homoplasy resulting from adaptive convergence or, alternatively, the plastid phylogeny itself might be misleading, diverging from the true species tree due to incomplete lineage sorting, hybridization, or other factors. In this study, we present a species phylogeny for notholaenid ferns, using four low-copy nuclear loci and concatenated data from three plastid loci. A total of 61 individuals (49 notholaenids and 12 outgroup taxa) were sampled, including 31 out of 37 recognized notholaenid species. The homeologous/allelic nuclear sequences were retrieved using PacBio sequencing and the PURC bioinformatics pipeline. Each dataset was first analyzed individually using maximum likelihood and Bayesian inference, and the species phylogeny was inferred using *BEAST. Although we observed several incongruences between the nuclear and plastid phylogenies, our principal results are broadly congruent with previous inferences based on plastid data. By mapping the presence of farina and their biochemical constitutions on our consensus phylogenetic tree, we confirmed that the characters are indeed homoplastic and have complex evolutionary histories. Hybridization among recognized species of the notholaenid clade appears to be relatively rare compared to that observed in other well-studied fern genera.

Bioconversion of Flavonoid Glycosides from Hippophae rhamnoides Leaves into Flavonoid Aglycones by Eurotium amstelodami.

The flowering process has been reported to play crucial roles in improving the flavor and efficacy of fermented tea. Hippophae rhamnoides leaves containing many beneficial ingredients are a suitable plant source for tea processing. In this study, we isolated a β-glucosidase-producing fungus Eurotium amstelodami BSX001 from the fermented tea and used Hippophae rhamnoides leaves (HRL) as a substrate to explore the detailed process of bioconversion of some important functional factors. The results show that the contents of total phenolic compounds and flavonoids increased significantly after seven days, especially flavonoid aglycones (e.g., quercetin, kaempferol, and isorhamnetin). Such compounds greatly enhance the antioxidative activity of fermented products. Metabolic analysis of the standard compounds (rutin, quercetin-3-glucoside, kaempferol-3-glucoside, quercetin, isorhamnetin-3-glucoside, isorhamnetin, and kaempferol) further confirmed the effective biotransformation by E. amstelodami. Mechanisms of the bioconversion could be involved in deglycosylation, dihydroxylation, and O-methylation. Our findings expand the understanding of tea fermentation process and provide further guidance for the fermented tea industry.

Classification of edible chrysanthemums based on phenolic profiles and mechanisms underlying the protective effects of characteristic phenolics on oxidatively damaged erythrocyte.

In this study, phenolic profiles of chrysanthemums derived from five main species were determined for characterization of rationality of their application in tea, beverages and functional foods. A total of 41 phenolics including 3 phenolic acids, 17 flavones, 9 flavanones, 1 dihydroflavonol, 4 flavonols, 4 chalcones and 3 aurones were identified. The contents of 22 characteristic phenolics were simultaneously determined. Chrysanthemum morifolium cv. 'Qiju' (with abundant phenolics) and Coreopsis tinctoria Nutt. (with unique and abundant flavonoid aglycones and glycosides), exhibited excellent cellular antioxidant activities and strong market potentials. Chlorogenic acid, 3,5-dicaffeoylquinic acid and luteolin-7-O-glucoside largely contributing to cellular antioxidant activity of 'Qiju' by forming protective membrane around erythrocyte should be markers for quality control of 'Qiju'. Okanin, the gut microbial-produced metabolite of marein, possessed strong protective effect on oxidatively damaged erythrocyte via incorporating in membrane and entering cytoplasm. Okanin and marein should be markers for quality control of C. tinctoria.

Chemical composition and cytotoxic screening of Musa cavendish green peels extract: Antiproliferative activity by activation of different cellular death types

Musa cavendish, commonly known as banana, is a fruit with nutritional and therapeutic properties. We investigated the chemical composition and in vitro cytotoxic effect of M. cavendish green peel extract (MHE) on cancer cells for the first time. The compounds characterization was performed by HPLC-UV/Vis and FIA-ESI-IT-MSn. We investigated in vitro cytotoxic effect of Musa cavendish green peels extract (MHE) in HepG2, A-375, MCF-7 and Caco-2 cancer cells. We evaluated the effect of MHE on proliferation of different cell lines through apoptosis, necrosis, mitochondrial membrane potential (MMP) and reactive oxygen species (ROS) content determination. We identified 12 compounds from different classes in the extract, including derivatives of phenolic acids, aglycone flavonoids, glycoside flavonoids and catecholamines. Our results indicate that MHE exerts, after 48 h treatment, an accentuated antiproliferative effect from the dose of 100 μg/mL in all cell lines tested. In HepG2 cells, these effects were related to the induction of cell death, both necrotic and apoptotic, and remarkable changes in cell morphology. Depolarization of MMP and high ROS content were also observed in the cells in a dose-dependent manner. Our results show that MHE may be used as a source of new drugs with anticancer activity.

Role of carbohydrate-cleaving enzymes in phenolic mobilization of guava leaves tea during solid state bio-processing with Monascus anka and Bacillus sp

• Solid-state bio-processing (SSB) increased soluble phenolic contents (SPC) of guava leaves tea (GLT). • Relationship between SPC and carbohydrate-cleaving enzyme was investigated during SSB. • High levels of α -amylase and total cellulase activities were observed during SSB. • Good correlations between SPC and α -amylase, cellulase and β -glucosidase activity. • Low correlation on between SPC and xylanase activity. The purpose of this study was to investigate the effect of carbohydrate-cleaving enzymes produced by Monascus anka and Bacillus sp. in the phenolic mobilization during guava leaves tea (GLT) bio-processing. The results showed solid state bio-processing (SSB) greatly increased the contents of soluble phenolic and flavonoid aglycone in GLT. During SSB, the activities of α -amylase (83.05 U/g) and total cellulase (31.32 U/g) were high, while those of xylanase (5.27 U/g) and β -glucosidase (0.19 U/g) were relatively lower. There was a good correlation between the content of soluble phenolic released from GLT and the activities of α -amylase, cellulase and β -glucosidase, while a low correlation between the content of soluble phenolic and the activity of xylanase. Moreover, the contents of soluble phenolic, especially quercetin and kaempferol, in GLT treated with mixture of pure enzymes significantly increased. The study provides theoretical basis for the phenolic mobilization of plant matrices during SSB and lays a solid foundation for seeking more efficient methods for enhancing the efficacy of tea infusions.

Deep supercooling enabled by surface impregnation with lipophilic substances explains the survival of overwintering buds at extreme freezing.

The frost survival mechanism of vegetative buds of angiosperms was suggested to be extracellular freezing causing dehydration, elevated osmotic potential to prevent freezing. However, extreme dehydration would be needed to avoid freezing at the temperatures down to −45°C encountered by many trees. Buds of Alnus alnobetula, in common with other frost hardy angiosperms, excrete a lipophilic substance, whose functional role remains unclear. Freezing of buds was studied by infrared thermography, psychrometry, and cryomicroscopy. Buds of A. alnobetula did not survive by extracellular ice tolerance but by deep supercooling, down to −45°C. An internal ice barrier prevented ice penetration from the frozen stem into the bud. Cryomicroscopy revealed a new freezing mechanism. Until now, supercooled buds lost water towards ice masses that form in the subtending stem and/or bud scales. In A. alnobetula, ice forms harmlessly inside the bud between the supercooled leaves. This would immediately trigger intracellular freezing and kill the supercooled bud in other species. In A. alnobetula, lipophilic substances (triterpenoids and flavonoid aglycones) impregnate the surface of bud leaves. These prevent extrinsic ice nucleation so allowing supercooling. This suggests a means to protect forestry and agricultural crops from extrinsic ice nucleation allowing transient supercooling during night frosts.

Antibacterial potential of the phenolics extracted from the Paulownia tomentosa L. leaves as studied with use of high-performance thin-layer chromatography combined with direct bioautography

Paulownia tomentosa (Thunb.) Steud. is a medicinal plant with a very long established and considerable position in traditional Chinese medicine (TCM) and in those of the other Far East Asian countries (mainly in Vietnam, Laos, Japan, and Korea). In Europe, Americas and Australia, P. tomentosa is known as princess tree, empress tree, or foxglove tree, and it is cultivated as a beautifully blossoming ornamental tree. In TCM, all parts of P. tomentosa (i.e., timber, bark, leaves, flowers and fruits) are used for curative purposes. From a literature survey, a conclusion can be drawn that in phytochemical and ethnopharmaceutical studies relatively less attention has been paid to investigating the chemical composition and biological activity of the leaves than that of the other parts of this medicinal plant and for this reason, our research was focused on antibacterial properties of the phenolics extracted from the P. tomentosa leaves. There are two important novelties of our approach. One novelty is that the phenolics extract from the P. tomentosa leaves was fractionated into six fractions (I–VI, expectedly containing flavonoid aglycons, free phenolic acids, non-polar flavonoid glycosides, polar flavonoid glycosides and phenolic acids liberated by the acidic and basic hydrolysis, respectively). The other novelty is that antibacterial assay was performed for each isolated fraction with the use of high-performance thin-layer chromatography combined with direct bioautography (HPTLC-DB). The best separations were obtained for fractions I and II, somewhat worse separations were obtained for fractions III–V, and the lack of characteristic bands was observed with fraction VI. In the antibacterial assay performed upon the HPTLC fingerprints, the Gram positive Bacillus subtilis and the Gram negative Aliivibrio fischeri bacteria were used. Well pronounced antibacterial activity was established with the selected fingerprint zones derived from fractions I–IV, whereas a lack of antibacterial activity was observed with fractions V and VI. Identification of apigenin and p-coumaric acid in the chromatographic zones from fractions I and II was performed with use of HPTLC and HPLC-DAD-MS, aided by external standards. Fractions III and IV were found to have similar chromatographic patterns, which suggests the presence of semi-polar flavonoid sugar conjugates in the P. tomentosa leaves.

Description of Chromolaena odorata L. R.M King and H. Robinson as medicinal plant: A Review

Chromolaena odorata L. belongs to Asteraceae family (sunflower family) is an important and serious perennial herb in the world, while this weed also acts as medicinal plant. Several parts of this plant widely used to treat wound, burns, skin infections as well as to possess anticancer, antidiabetic, anti-hepatotoxic, anti-inflammatory, antimicrobial, and antioxidant properties. Native to North America and has been introduced to Asia, West Africa and Australia. Siam weed is one of common name of Chromolaena odorata L. grown as medical herbs and ornamental plant. The medicinal values of Chromolaena odorata L. lie in their phytochemicals component, the dried leaf of Chromolaena odorata contained flavonoid aglycones (flavanones, flavonols, flavones) including acacetin, chalcones, eupatilin, luteolin, naringenin, kaempferol, quercetin, quercetagetin, and sinensetin, terpenes and terpenoids, essential oils, and other phenolic compounds, which produce define physiological action in our body. Therefore, this review study provides detail information on general description of Chromolaena odorata L as medicinal plant.

Analysis of Distribution of Selected Bioactive Compounds in Camelina sativa from Seeds to Pomace and Oil

Camelina sativa is an oilseed plant that produces seed oil rich in vitamins, UFA (unsaturated fatty acids), phytosterols, and polyphenols. Most, but not all, bioactive compounds are soluble in oil. So far, studies have been based analyzing the profile of bioactive compounds only in oil. As part of this work, it was decided to examine the seeds, oil, and pomace of four genotypes of Camelina sativa (three spring genotypes and one winter cultivar). The transmission of bioactive compounds to oil and pomace was compared to their content in seeds. The quantitative profile of selected bioactive compounds was analyzed: eight flavonoid aglycons, 11 phenolic acids, three carotenoids, and 19 fatty acids. As a result of pressing more than 80% of flavonoids entered oil, whereas 20% remained in the pomace. When the content of phenolic acids in seeds and in oil was compared, it turned out that on average 50% of these compounds entered oil. Among all the phenolic acids under analysis the highest contents of chlorogenic, caffeic, and sinapic acids were found both in camelina seeds and oil. Similarly to the other bioactive compounds, more than 70% of fat-soluble carotenoids were extracted from camelina seeds with oil. Most of the genotypes had the fatty acid composition and the ω-6/ω-3 ratio characteristic of camelina oil. Camelina oil is characterized by properties that enable its extensive use in the food industry.

Purification, structural elucidation, antioxidant capacity and neuroprotective potential of the main polyphenolic compounds contained in Achyrocline satureioides (Lam) D.C. (Compositae).

Achyrocline satureioides (Lam) D.C (Compositae) is a native medicinal plant of South America traditionally utilized for its anti-inflammatory, sedative and anti-atherosclerotic properties among others. Neuroprotective effects have been reported in vivo and could be associated to its elevated content of flavonoid aglycones. In the present study we performed the isolation and structure elucidation of the major individual flavonoids of A. satureioides along with the in vitro characterization of their individual antioxidant and neuroprotective properties in order to see their putative relevance for treating neurodegeneration. Exact mass, HPLC-MS/MS and 1H NMR identified dicaffeoyl quinic acid isomers, quercetin, luteolin, isoquercitrin, and 3-O-methylquercetin as the mayor polyphenols. Flavonoids intrinsic redox properties were evaluated in the presence of the endogenous antioxidants GSH and Ascorbate. Density Functional Theory (DFT) molecular modeling and electron density studies showed a theoretical basis for their different redox properties. Finally, in vitro neuroprotective effect of each isolated flavonoid was evaluated against hydrogen peroxide-induced toxicity in a primary neuronal culture paradigm. Our results showed that quercetin was more efficacious than luteolin and isoquercitrin, while 3-O-methylquercetin was unable to afford neuroprotection significantly. This was in accordance with the susceptibility of each flavonoid to be oxidized and to react with GSH. Overall our results shed light on chemical and molecular mechanisms underlying bioactive actions of A. satureioides main flavonoids that could contribute to its neuroprotective effects and support the positive association between the consumption of A. satureioides as a natural dietary source of polyphenols, and beneficial health effect.

Enhancing the Yield of Bioactive Compounds from Sclerocarya birrea Bark by Green Extraction Approaches.

Sclerocarya birrea is a tree indigenous to Southern Africa with significant importance in rural livelihoods for food, medicine, and carving. The bark, which contains 10–20% tannin, provides several pharmacological benefits as an antidiabetic, anti-inflammatory, antimicrobial, anti-atherogenic, and antioxidant medication, among others. This study compared different extraction techniques used to recover bioactive compounds from marula bark. For this purpose, solid–liquid extraction, supercritical fluid extraction (SFE), and pressurized liquid extraction (PLE) were performed under selected conditions, using only “food-grade” solvents. The potential use of the proposed extraction methodologies was evaluated in term of yield, and the individual phenolic composition determined by HPLC–ESI–TOF–MS. PLE provided a high extraction yield in all experimental conditions. With regard to bioactive compounds composition, a total of 71 compounds, a significant percentage of which in a galloyl form, were distributed in five major categories. The largest number of compounds, mostly flavonoid aglycones, were extracted by PLE, generally when the extraction was developed at low temperatures. SFE did prove effective as a way of extracting antidiabetic proanthocyanidins. Advanced extraction techniques represent a powerful tool to obtain bioactive compounds from S. birrea bark, which can be used as supplements or food ingredients, promoting the valorization of this crop.

The overlooked rotational isomerism of C-glycosyl flavonoids

C-glycosyl flavonoids are important secondary plant metabolites with a wide range of biological activities. Rotational isomerism, arising from restricted bond rotation, has been observed on a portion of C-glycosyl flavonoids. NMR technique contributes most to the observation and research of this phenomenon. Signal duplication in NMR spectra may be the key characteristic of C-glycosyl flavonoids existing as rotamers. Bulky steric hindrance from the substituents at position 7 and sugar moieties are responsible for the restricted bond rotation. There are other influence factors including temperature, solvents, H-bonds and π-stacking, but these are of lesser importance. Difference exists between 8-C-glycosyl flavonoids and their 6-C-glycosyl isomers despite sharing the same flavonoid aglycone and sugar moiety. 8-C-glycosyl flavonoids are more likely to suffer from restricted rotation. The energy barriers between rotamers of C-glycosyl flavonoids seem not high enough for atropisomerism to be realized and the isolation of rotamers should be difficult.

A novel poly-oxygenated flavone glucoside from aerial parts of the Brazilian plant Neoglaziovia variegata (Bromeliaceae)

Neoglaziovia variegata is endemic to northeastern Brazil. The drought resistant plant produces edible fruits and is used as a fibre plant by rural communities in the Caatinga region where a variety of products are made from the white, soft and flexible fibres. Extracts of N. variegata have been reported to be of low toxicity and to exhibit antinociceptive effect, photoprotective potential, antioxidant effect, gastroprotective effects and antibacterial effect against both Gram-positive and Gram-negative bacteria, however, the chemical constituents of this species are mainly unknown. The novel poly-oxygenated flavone glucoside 5,6,7,4'-tetrahydroxy-3',5'-dimethoxy-flavone 7-O-β-glucopyranoside in addition to the rare poly-oxygenated flavone 5,4'-dihydroxy-6,7,3'-trimethoxyflavone 4'-O-β-glucopyranoside and the flavonol quercetin 3-O-(6''-rhamnopyranosyl-β-glucopyranoside) have been characterised from the leaves of N. variegata. 5,6,7,4'-tetrahydroxy-3',5'-dimethoxy-flavone, which comprises the core structure of the novel compound, is a new flavonoid aglycone in nature. The structure determinations were based on extensive use of 2D NMR spectroscopic techniques and high-resolution mass spectrometry. Both substances exhibited toxicity towards MOLM-13 acute myeloid leukaemia cells.