Antioxidant galloylated flavonol glycosides from Calliandra haematocephala

1,5-Anhydro-d-glucitol derivative and galloylated flavonoids isolated from the leaves of Acer ginnala Maxim. as dual inhibitors of PTP1B and α-glucosidase enzymes: In vitro and in silico studies

Four undescribed compounds (two 1,5-anhydro-d-glucitol derivatives and two galloyl derivatives) and fourteen known compounds were isolated and structurally identified from leaves of Acer ginnala Maxim. (Amur maple). Structures and absolute configurations of the four undescribed compounds were determined using extensive analysis of NMR spectroscopic, HRESI-MS, modified Mosher ester method, and comparison with spectroscopic data of known compounds. Bioactivity evaluation revealed that the isolated 1,5-anhydro-d-glucitol derivative, galloylated flavonol rhamnosides, and galloylated flavanols had inhibitory effects on both protein tyrosine phosphatase-1B (PTP1B, IC₅₀ values ranging of 3.46-12.65 μM) and α-glucosidase (IC₅₀ values ranging of 0.88-6.06 μM) in comparison with a positive control for PTP1B (ursolic acid, IC₅₀ = 5.10 μM) or α-glucosidase (acarbose, IC₅₀ = 141.62 μM). A combination of enzyme kinetic analysis and molecular docking provided additional evidence in favor of their inhibitory activities and mechanism. These data demonstrate that A. ginnala Maxim. together with its constituents are promising sources of potent candidates for developing novel anti-diabetic medications.

Promising antioxidant activity of crude extract from Calliandra tweedii Benth

The interest in medicinal plants encourages new research studies on plant extracts, as they are sources for treatments in medicine, agriculture, and veterinary. Calliandra tweedii is a native Brazilian species with broad use in folk medicine. This study aimed to examine the leaf crude extract (CE) of C. tweedii and its methanolic (MP) and hexane (HP) phases concerning total phenolic compounds (TPC), proanthocyanidins (PRO), and flavonoid profile, and correlate it to their antioxidant activity (DPPH and FRAP). CE and MP revealed high contents of TPC, PRO and high antioxidant activity (DPPH and FRAP) in relation to HP. Opposite, HP showed reduced antioxidant activity, according to the scarce phenolic constituents obtained from the partition. Five flavonols were detected by HPLC-UV-DAD, being quercitrin the major constituent. Also, one kaempferol derivate, and a series of three quercetin derivates were detected. Strong positive correlations were observed between DPPH, FRAP, and phenolic compounds. These discoveries are important to highlight the promising antioxidant activity of CE of C. tweedii, which could contribute to the expansion of popular herbal medicines and new drug discovery.

Insulin secretory and antidiabetic actions of Heritiera fomes bark together with isolation of active phytomolecules

In folklore, Heritiera fomes (H. fomes) has been extensively used in treatment of various ailments such as diabetes, cardiac and hepatic disorders. The present study aimed to elucidate the antidiabetic actions of hot water extract of H. fomes (HWHF), including effects on insulin release from BRIN BD11 cells and isolated mouse islets as well as glucose homeostasis in high-fat-fed rats. Molecular mechanisms underlying anti-diabetic activity along with isolation of active compounds were also evaluated. Non-toxic concentrations of HWHF stimulated concentration-dependent insulin release from isolated mouse islets and clonal pancreatic β-cells. The stimulatory effect was potentiated by glucose and isobutyl methylxanthine (IBMX), persisted in presence of tolbutamide or a depolarizing concentration of KCl but was attenuated by established inhibitors of insulin release such as diazoxide, verapamil, and Ca2+ chelation. HWHF caused depolarization of the β-cell membrane and increased intracellular Ca2+. The extract also enhanced glucose uptake and insulin action in 3T3-L1 differentiated adipocytes cells and significantly inhibited in a dose-dependent manner starch digestion, protein glycation, DPP-IV enzyme activity, and glucose diffusion in vitro. Oral administration of HWHF (250 mg/5ml/kg b.w.) to high-fat fed rats significantly improved glucose tolerance and plasma insulin responses and it inhibited plasma DPP-IV activity. HWHF also decreased in vivo glucose absorption and intestinal disaccharidase activity while increasing gastrointestinal motility and unabsorbed sucrose transit. Compounds were isolated from HWHF with similar molecular weights to quercitrin (C21 H20 O11) ranging from 447.9 to 449.9 Da which stimulated the insulin release in vitro and improved both glucose tolerance and plasma insulin responses in mice. In conclusion, H. fomes and its water-soluble phytochemicals such as quercitrin may exert antidiabetic actions mediated through a variety of mechanisms which might be useful as dietary adjunct in the management of type 2 diabetes.

Ellagitannins and Oligomeric Proanthocyanidins of Three Polygonaceous Plants

The aim of this study was to characterize hydrolyzable tannins in Polygonaceous plants, as only a few plants have previously been reported to contain ellagitannins. From Persicaria chinensis, a new hydrolyzable tannin called persicarianin was isolated and characterized to be 3-O-galloyl-4,6-(S)-dehydrohexahydroxydiphenoyl-d-glucose. Interestingly, acid hydrolysis of this compound afforded ellagic acid, despite the absence of a hexahydroxydiphenoyl group. From the rhizome of Polygonum runcinatum var. sinense, a large amount of granatin A, along with minor ellagitannins, helioscpoinin A, davicratinic acids B and C, and a new ellagitannin called polygonanin A, were isolated. Based on 2D nuclear magnetic resonance (NMR) spectroscopic examination, the structure of polygonanin A was determined to be 1,6-(S)-hexahydroxydiphenoyl-2,4-hydroxychebuloyl-β-d-glucopyranose. These are the second and third hydrolyzable tannins isolated from Polygonaceous plants. In addition, oligomeric proanthocyanidins of Persicaria capitatum and P. chinensis were characterized by thiol degradation. These results suggested that some Polygonaceous plants are the source of hydrolyzable tannins not only proanthocyanidins.

Effects of Rhus coriaria L. hydroalcoholic extract on the lipid and antioxidant profile in high fat diet-induced hepatic steatosis in rats

Oxidative stress is related to increased fat deposition in the liver, known as hepatic steatosis. The present study is an evaluation of the anti-oxidative and antihyperlipidemic effects of the hydroalcoholic extract of Rhus coriaria L. (HARE) in rats on a high-fat diet (HFD). Twenty male Wistar rats were divided into four groups: control, HFD, HFD + HARE 50 mg/kg/day, and HFD + HARE 250 mg/kg/day for 12 weeks. Animals were weighed weekly and treated with the HARE extract for 12 weeks by gavage. Subsequently, the histopathological changes, oxidative markers, and lipid profile were evaluated. Statistical analysis was performed using the one-way analysis of variance (ANOVA) for multiple comparisons. First, the active ingredients of the extract were determined by HPLC. Then, the levels in the serum lipid profile (TG, cholesterol, HDL, and LDL) in rats fed with the HFD + HARE were analyzed where a significant reduction was observed. The HFD proved to increase the activity of the liver enzymes, the serum lipid levels, and the malondialdehyde (MDA) level. The ferric-reducing antioxidant activity power (FRAP), catalase (CAT), and superoxide dismutase (SOD) catalytic activity were reduced in the liver homogenate of HFD rats compared to the controls. Additionally, the aforementioned liver enzymes activities were reduced in response to HARE. Evaluation of oxidative stress determined a reduction in the MDA level while a raised FRAP was confirmed. In accordance with the present results, histopathological observations have also demonstrated that HARE ameliorated grade-1 hepatic steatosis induced by HFD. Taken together, the findings of this study introduce HARE as a future potential therapeutic agent in treating hepatic steatosis and reducing oxidative damages of an HFD in the liver.

Plant-Derived Bioactives and Oxidative Stress-Related Disorders: A Key Trend towards Healthy Aging and Longevity Promotion

Plants and their corresponding botanical preparations have been used for centuries due to their remarkable potential in both the treatment and prevention of oxidative stress-related disorders. Aging and aging-related diseases, like cardiovascular disease, cancer, diabetes, and neurodegenerative disorders, which have increased exponentially, are intrinsically related with redox imbalance and oxidative stress. Hundreds of biologically active constituents are present in each whole plant matrix, providing promissory bioactive effects for human beings. Indeed, the worldwide population has devoted increased attention and preference for the use of medicinal plants for healthy aging and longevity promotion. In fact, plant-derived bioactives present a broad spectrum of biological effects, and their antioxidant, anti-inflammatory, and, more recently, anti-aging effects, are considered to be a hot topic among the medical and scientific communities. Nonetheless, despite the numerous biological effects, it should not be forgotten that some bioactive molecules are prone to oxidation and can even exert pro-oxidant effects. In this sense, the objective of the present review is to provide a detailed overview of plant-derived bioactives in age-related disorders. Specifically, the role of phytochemicals as antioxidants and pro-oxidant agents is carefully addressed, as is their therapeutic relevance in longevity, aging-related disorders, and healthy-aging promotion. Finally, an eye-opening look into the overall evidence of plant compounds related to longevity is presented.

Screening and Isolation of Natural Antioxidants from Acer Ginnala Max by TLC-MS/MS Guided Bioautographic Method

A rapid and simple method has been developed for the screening and identification of natural antioxidants from the leaves of Acer ginnala Maxim (AG). The process is that upon reaction with 1,1-diphenyl-2-picrylhydrazyl (DPPH), the white yellow spots of compounds with potential antioxidant effects will be significantly observed on the thin-layer chromatography (TLC), and possible structures will be presumed by the ESI/MS technique. Using the improved approach, 6 compounds in the AG extract were found to possess a potential antioxidant activity. They were speculated as quercetin-3-O-α-L-(3"-galloyl)-rhamnoside (1), quercetin-3-O-α-L-(2"-galloyl)-rhamnoside (2), quercetin-3-O-α-L-(2"-galloyl)-arabinopyranoside (3), acertannin (4), gallic acid (5), and methyl gallate (6). In addition, we were still found that compounds 2, 3, and 5 had favorable antioxidant activity from the scannogram of the DPPH reaction plate. As a result, the isolated 6 compounds structures were in accordance with the presumed structures. Furthermore, the free radical scavenging capacities of the available identified compounds were also investigated. Compounds 2, 3, and 5 showed significant DPPH.Scavenging capacities, with IC50 values of 2.83 μg/mL, 2.34 μg/mL, and 1.86μg/mL, respectively. The results indicated that this newly improved method could be widely applied for rapid screening and identification of natural antioxidants from Chinese herbal medicines.

A new phenolic compound from Phedimus middendorffianus with antiproliferative activity

A new phenolic compound (1) and together with 12 known compounds-eight flavonoids (2 ∼ 9), two phenolic compounds (10 and 11) and two benzoic acid (12 and 13)-were isolated from Phedimus middendorffianus (Maxim.). The structures of all compound were determined on the basis of spectroscopic (MS and NMR) analyses. Compounds 4, 5, 7 and 11 ∼ 13 were showed anti-proliferative activities against MCF-7 than PC-3 cell line. Also compound 12 and 13 showed the significant cytotoxic activities against two cancer cell lines, PC-3 and MCF-7.

Exploiting fruit byproducts for eco-friendly nanosynthesis: Citrus × clementina peel extract mediated fabrication of silver nanoparticles with high efficacy against microbial pathogens and rat glial tumor C6 cells

Process byproducts from the fruit industry may represent a cheap and reliable source of green reducing agents to be used in current bio-nanosynthesis. This study reports the use of orange (Citrus × clementina) peel aqueous extract (OPE) for one-pot green synthesis of silver nanoparticles (AgNPs) with high effectiveness against various microbial pathogens as well as rat glial tumor C6 cells. The effects of various operational parameters on the synthesis of AgNPs were systematically investigated. The morphology, particle size, and properties of synthesized AgNPs were characterized using UV-visible spectroscopy, x-ray diffraction, x-ray photoelectron spectroscopy, field emission scanning electron microscopy, energy-dispersive x-ray spectroscopy, and Fourier transform infrared spectroscopy. High-resolution transmission electron microscopy shows that the nanoparticles are mostly spherical in shape and monodispersed, with an average particle size of 15-20 nm. Notably, the OPE-synthesized AgNPs were stable up to 6 months without change in their properties. Low doses of OPE-AgNPs inhibited the growth of human pathogens Escherichia coli, Bacillus cereus, and Staphylococcus aureus. The minimum inhibitory concentration and minimum bactericidal concentration of AgNPs against selected pathogenic bacteria were determined. OPE-AgNPs exhibited strong antioxidant activity in terms of ABTS (2,2'-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid)) radical scavenging (IC₅₀ 49.6 μg/mL) and DPPH (1,1-diphenyl-2-picrylhydrazyl) radical scavenging (IC₅₀ 63.4 μg/mL). OPE-AgNPs showed dose-dependent response against rat glial tumor C6 cells (LD₅₀ 60 μg/mL) showing a promising potential as anticancer agents. Overall, the current investigation highlighted a cheap green technology route to synthesize AgNPs using OPE byproducts and could potentially be utilized in biomedical, cosmetic, and pharmaceutical industry.

Flavonoids as Potent Scavengers of Hydroxyl Radicals

Oxidative stress is a fundamental principle in the pathophysiology of many diseases. It occurs when the production of reactive oxygen species exceeds the capacity of the cell defense system. The hydroxyl radical is a reactive oxygen species that is commonly formed in vivo and can cause serious damage to biomolecules, such as lipids, proteins, and nucleic acids. It plays a role in inflammation-related diseases, like chronic inflammation, neurodegeneration, and cancer. To overcome excessive oxidative stress and thus to prevent or stop the progression of diseases connected to it, scientists try to combat oxidative stress and to find antioxidant molecules, including those that scavenge hydroxyl radical or diminish its production in inflamed tissues. This article reviews various methods of hydroxyl radical production and scavenging. Further, flavonoids, as natural plant antioxidants and essential component of the human diet, are reviewed as compounds interacting with the production of hydroxyl radicals. The relationship between hydroxyl radical scavenging and the structure of the flavonoids is discussed. The structural elements of the flavonoid molecule most important for hydroxyl radical scavenging are hydroxylation of ring B and a C2-C3 double bond connected with a C-3 hydroxyl group and a C-4 carbonyl group. Hydroxylation of ring A also enhances the activity, as does the presence of gallate and galactouronate moieties as substituents on the flavonoid skeleton.

Mechanism(s) of action underlying the gastroprotective effect of ethyl acetate fraction obtained from the crude methanolic leaves extract of Muntingia calabura

Background

Muntingia calabura L. (family Muntingiaceae), commonly known as Jamaican cherry or kerukup siam in Malaysia, is used traditionally to treat various ailments. The aim of this study is to elucidate the possible underlying gastroprotective mechanisms of ethyl acetate fraction (EAF) of Muntingia calabura methanolic leaves extract (MEMC).

Methods

MEMC and its fractions were subjected to HPLC analysis to identify and quantify the presence of its phyto-constituents. The mechanism of gastroptotection of EAF was further investigated using pylorus ligation-induced gastric lesion rat model (100, 250, and 500 mg/kg). Macroscopic analysis of the stomach, evaluation of gastric content parameters such as volume, pH, free and total acidity, protein estimation, and quantification of mucus were carried out. The participation of nitric oxide (NO) and sulfhydryl (SH) compounds was evaluated and the superoxide dismutase (SOD), gluthathione (GSH), catalase (CAT), malondialdehyde (MDA), prostaglandin E₂ (PGE₂) and NO level in the ethanol induced stomach tissue homogenate was determined.

Results

HPLC analysis confirmed the presence of quercetin and gallic acid in EAF. In pylorus-ligation model, EAF significantly (p <0.001) prevent gastric lesion formation. Volume of gastric content and total protein content reduced significantly (p < 0.01 and p < 0.05, respectively), while free and total acidity reduced in the doses of 250 and 500 mg/kg (p <0.001 and p <0.05, respectively). EAF also augmented the mucus content significantly (p < 0.001). Pre-treatment with N-nitro-L-arginine methyl ester (L-NAME) or N-ethylmaleimide (NEM) reversed the gastroprotective activity of EAF. EAF treatment markedly ameliorated the SOD, GSH and CAT activity and PGE₂ and NO level while attenuating MDA level, relative to the vehicle group.

Conclusions

In conclusion, the underlying gastroprotective mechanisms of EAF could be associated with the antisecretory, participation of mucus, antiperoxidative, improvement of antioxidant status, modulation of NO and SH compounds, stimulation of PGE₂ as well as presence of quercetin and gallic acid.

Histopathological studies of acute and chronic effects of Calliandra portoricensis leaf extract on the stomach and pancreas of adult Swiss albino mice

OBJECTIVE

To evaluate the consequence of oral administration of Calliandra portoricensis (C. portoricensis) leaf extract on the stomach and pancreas in Swiss albino mice.

METHODS

Three groups of mice (B, C and D) were treated with 4 mg/kg of C. portoricensis extract. Group A was the control and received an equivalent volume of distilled water. Group B received C. portoricensis leaf extract for 7 days, Group C received C. portoricensis leaf extract for 14 days, and Group D received C. portoricensis leaf extract for 28 days. At different stages in the study, the mice were sacrificed and the stomach and pancreas were excised and fixed in 10% formol saline for histological analysis.

RESULTS

The result showed a normal microstructural outline in groups B and C as compared with the control. However, animals in group D showed disorganization of the mucosa and discontinuation of epithelial lining of the stomach while the islets of Langerans in the pancreas were at various degree of degeneration as compared with the control mice.

CONCLUSIONS

The present finding suggests that chronic administration (28 days as seen in this study) of C. portoricensis leaf extract may inhibit the proper function of the stomach and pancreas.

Effect of topical application of quercetin-3-O-(2″-gallate)-α-l-rhamnopyranoside on atopic dermatitis in NC/Nga mice

BACKGROUND

Quercetin-3-O-(2″-gallate)-α-l-rhamnopyranoside (QGR) is a new quercetin derivative which is isolated from the leaves of Acer ginnala Maxim, a native plant of Korea. Quercetin has several biological effects including antioxidative, anti-inflammatory, and anti-allergic effects. However, the topical effect of QGR on atopic dermatitis (AD) like skin lesion in NC/Nga mice has not been studied.

OBJECTIVE

To evaluate the anti-inflammatory and anti-allergic effect of QGR in a murine model of atopic dermatitis.

METHODS

We measured inducible nitric oxide synthase (iNOS) and cyclooxygenase -2(COX-2) level in RAW264.7 cell with QGR treatment. And after induction of AD like skin lesions with Dermatophagoides farina (Df) ointment, mice were treated with QGR and control drugs. Clinical scores, interleukin (IL) 4, 5, and 13, serum IgE, eosinophil levels, iNOS and COX-2 level were evaluated.

RESULTS

Results show that mRNA level of iNOS and COX-2 in vitro were decreased after QGR treatment. Topical QGR markedly decreased the iNOS and COX-2 mRNA expressions in the skin. QGR also significantly suppressed the increase in the level of total plasma IgE and eosinophils. In addition, topical application of QGR down-regulated the expressions of the cytokines, IL-4,5 and 13, which were induced by Df ointment stimulation.

CONCLUSIONS

In the present study, we showed that topical application of QGR ameliorated Df-induced AD-like inflammatory responses in NC/Nga mice. These results demonstrate that QGR might be beneficial in the treatment of AD.

Galloylated flavonol rhamnosides from the leaves of Calliandra tergemina with antibacterial activity against methicillin-resistant Staphylococcus aureus (MRSA)

Galloylated flavonol rhamnosides identified as kaempferol-3-O-(2″,3″,4″-tri-O-galloyl)-α-l-rhamnopyranoside, quercetin-3-O-(3″,4″-di-O-galloyl)-α-l-rhamnopyranoside, and quercetin-3-O-(2″,3″,4″-tri-O-galloyl)-α-l-rhamnopyranoside, together with five known galloylated and non-galloylated flavonol rhamnosides, were isolated from leaves of Calliandra tergemina (L.) Benth. Their structures were established using spectroscopic methods and their antibacterial activities against methicillin-resistant Staphylococcus aureus (MRSA) were evaluated by a microdilution method.

HPLC-DAD-ESI-MS/MS screening of bioactive components from Rhus coriaria L. (Sumac) fruits

Rhus coriaria L. (sumac) is an important crop widely used in the Mediterranean basin as a food spice, and also in folk medicine, due to its health-promoting properties. Phytochemicals present in plant foods are in part responsible for these consequent health benefits. Nevertheless, detailed information on these bioactive compounds is still scarce. Therefore, the present work was aimed at investigating the phytochemical components of sumac fruit epicarp using HPLC-DAD-ESI-MS/MS in two different ionisation modes. The proposed method provided tentative identification of 211 phenolic and other phyto-constituents, most of which have not been described so far in R. coriaria fruits. More than 180 phytochemicals (tannins, (iso)flavonoids, terpenoids, etc.) are reported herein in sumac fruits for the first time. The obtained results highlight the importance of R. coriaria as a promising source of functional ingredients, and boost its potential use in the food and nutraceutical industries.

Electrospray ionization and collision-induced dissociation tandem mass spectrometric discrimination of polyphenolic glycosides: exact acylation site determination of the O-acylated monosaccharide residues

RATIONALE

Acylated monosaccharide residues are structural subunits of natural products or synthetic intermediates that have received much attention in past years. Determination of the acylation sites of these residues still relies heavily on the comparison of their characteristic NMR signals with those of known standards and synthesized acylated glycosides. It is important to develop a rapid analytical method for determining the acylation sites for these compounds, and this is described in this study.

METHODS

Six known polyphenolic glycosides were used for the electrospray ionization and collision-induced dissociation tandem mass spectrometry (ESI-CID-MS/MS) discrimination of the acylated monosaccharide residues with different acylation sites. A combination of ESI-CID-MS/MS, using a triple quadrupole mass spectrometer, with ultra-performance liquid chromatography (UPLC) and photo-diode array (PDA) detection (UPLC-PDA) has been applied to the identification or characterization of polyphenolic glycosides in Polygonum capitatum that possess an acylated monosaccharide residue.

RESULTS

An ESI-MS and CID-MS/MS method has been developed for the determination of the acylation sites of polyphenolic glycosides that possess an acylated monosaccharide residue. Twelve polyphenolic glycosides including four new ones have been identified or characterized in P. capitatum. Eight (including the new ones) of the twelve glycosides were reported for the first time from this plant.

CONCLUSIONS

The developed ESI-MS and CID-MS/MS method provided a very useful strategy for the determination of the sites of polyphenolic glycosides that possess an acylated monosaccharide residue. The acylation site could be determined by the characteristic product ion spectra of the in-source CID-generated O-acyl monosaccharide ion [B(1)](+). The presented work may facilitate the structural characterization of these types of compounds.

Evaluation of antioxidant and free radical scavenging capacities of polyphenolics from pods of Caesalpinia pulcherrima

Thirteen polyphenolics were isolated from fresh pods of Caesalpinia pulcherrima using various methods of column chromatography. The structures of these polyphenolics were elucidated as gallic acid (1), methyl gallate (2), 6-O-galloyl-d-glucoside (3), methyl 6-O-galloyl-β-d-glucoside (4), methyl 3,6-di-O-galloyl-α-d-glucopyranoside (5), gentisic acid 5-O-α-d-(6'-O-galloyl)glucopyranoside (6), guaiacylglycerol 4-O-β-d-(6'-O-galloyl)glucopyranoside (7), 3-methoxy-4-hydroxyphenol 1-O-β-d-(6'-O-galloyl) glucopyranoside (8), (+)-gallocatechin (9), (+)-catechin (10), (+)-gallocatechin 3-O-gallate (11), myricetin 3-rhamnoside (12), and ampelopsin (13). All isolated compounds were tested for their antioxidant activities in the 1,1-diphenyl-2-picrylhydrazyl (DPPH), hydroxyl, and peroxynitrite radicals scavenging assays. Among those compounds, 11, 12, and 2 exhibited the best DPPH-, hydroxyl-, and peroxynitrite radical-scavenging activities, respectively. Compound 7 is a new compound, and possesses better scavenging activities towards DPPH but has equivalent hydroxyl radical scavenging activity when compared to BHT. The paper is the first report on free radical scavenging properties of components of the fresh pods of Caesalpinia pulcherrima. The results obtained from the current study indicate that the free radical scavenging property of fresh pods of Caesalpinia pulcherrima may be one of the mechanisms by which this herbal medicine is effective in several free radical mediated diseases.

Antioxidant flavonol glycosides from Elaeocarpus serratus and Filicium decipiens

Chemical investigation of the leaves of Elaeocarpus serratus yielded myricitrin (1), mearnsetin 3-O-β-D-glucopyranoside (2), mearnsitrin (3), tamarixetin 3-O-α-L-rhamnopyranoside (4) and the fruits of Filicium decipiens yielded three flavonol glycosides, kaempferol 3-O-rutinoside (5), kaempferol 3-O-robinobioside (6) and trifolin (7). Compound 1 showed strong antioxidant activity against DPPH.

Identification of 2″-galloylated flavonol 3-o-glycosides accumulating in developing leaves of persimmon

INTRODUCTION

Dried leaves of persimmon, traditionally consumed as a herbal tea in Japan, contain bioactive galloylated flavonol glycosides. Investigation of the seasonal compositional changes in these compounds is important for determining the optimum harvest time.

OBJECTIVE

The three objectives were: (1) to elucidate the compositional changes of the flavonol glycosides in persimmon leaves collected in different seasons; (2) to develop an efficient method for separation of the constituents; and (3) to compare their antioxidant activities.

METHODOLOGY

Fresh persimmon leaves were collected at different growth stages in 2007 and 2008 in Niigata, Japan. Total flavonols were extracted with 70% aqueous acetone followed by ethyl acetate partitioning, and were analysed by high-performance liquid chromatography. Enzymatic transformation and chromatographic fractionation was performed to isolate the individual flavonols. Two antioxidant assays were performed.

RESULTS

Four nongalloylated flavonol glycosides were detected at the leaf-shooting stage, and four additional galloylated flavonol glycosides accumulated during leaf development, resulting in a total of eight constituents. Isolation of nongalloylated and galloylated constituents was successfully achieved through enzymatic transformation of the flavonol mixture using combinations of tannase, β-glucosidase and β-galactosidase, followed by chromatographic fractionation. The gallates were identified as regiospecific 2″-galloylated galactosides and glucosides of kaempferol and quercetin. A mixture of 2″-galloylated flavonol glycosides had a two-fold stronger antioxidant activity than the nongalloylated mixture.

CONCLUSION

This study showed that four 2″-galloylated flavonol glycosides had accumulated in developing leaves of persimmon by the end of May through a rapid 2″-galloylation of the corresponding nongalloylated flavonol glycosides.

HIV-1 ribonuclease H inhibitory phenolic glycosides from Eugenia hyemalis

Three new galloyl arbutins, hyemalosides A-C (1-3), along with nine known compounds were isolated from the evergreen tree Eugenia hyemalis. The structures of compounds 1-3 were determined by analysis of NMR and MS data. Compounds 1-3 inhibited HIV-1 RNase H in vitro with IC50 values of 1.46, >18, and 1.19 microM, respectively. However, in a XTT-based cell viability assay using the human T-cell line CEM-SS infected with HIV-1 RT, none of the compounds inhibited the cytopathic effect of HIV-1 infection at the highest dose tested (20 microg/mL).