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Antioxidant flavonoids and phenolic acids from leaves of Leea guineense G. Don (Leeaceae)
Abstract
From leaves of Leea guineense (Leeaceae) three hydrophilic flavonoids were isolated and identified as quercetin-3'-sulphate-3-O-alpha-L-rhamnopyranoside, quercetin-3,3'-disulphate and a new flavonoid sulphate, quercetin-3,3',4'-trisulphate, together with kaempferol, quercetin, quercitrin, mearnsitrin, gallic acid and ethyl gallate. The structures were established by spectroscopic analysis (UV, MS, (1)H-NMR, (13)C-NMR and 2D-NMR). Their antioxidant effect on free radical scavenging was evaluated in the DPPH assay.
... Ascorbic acid 100 mg/ml AME 80 mg/ml AME 60 mg/ml AME 40 mg/ml AME 20 mg/ml AME pared to other aglycone derivatives with more methoxylated groups. Methylation of free OH groups in fl avonoids substantially reduces the antioxidant activity of the compounds (Op de Beck et al., 2003). In line with this observation, compounds 11, 12, and 13 with a 3-OMe beside a 3'-OMe group in case of 11, 6,3',4'-OMe group in case of 12, and 6,7,3',4'-OMe group in case of 13 did not inhibit 50% of DPPH scavenging capacity at concentrations up to 100 mg ml -1 . ...
... In line with this observation, compounds 11, 12, and 13 with a 3-OMe beside a 3'-OMe group in case of 11, 6,3',4'-OMe group in case of 12, and 6,7,3',4'-OMe group in case of 13 did not inhibit 50% of DPPH scavenging capacity at concentrations up to 100 mg ml -1 . The weak activity exhibited by these compounds could be linked to the methylation of some of their phenolic OH groups (Op de Beck et al., 2003). Methylation of the 3-OH group of compounds 11 -13 reduced the activity signifi cantly when compared with compounds 9 and 10 with a free 3-OH group. ...
... Compound 8 has the same oxygenation pattern as its fi ve derivatives 9 -13, but all its OH groups are free and this signifi cantly enhances its antioxidant activity. This observation agrees with an earlier structure-activity study (Op de Beck et al., 2003). Our results indicate that only compounds 9 and 10 had strong antioxidant activity but they are still less active than compound 8 (quercetin). ...
3
Phytochemical investigations of Calotropis procera leaves have led to the isolation of two new compounds: quercetagetin-6-methyl ether 3-O-β-D-⁴C1-galacturonopyranoside () and (E)-3-(4-methoxyphenyl-2-O-β-D-⁴C1-glucopyranoside)-methyl propenoate (4), along with eleven known metabolites: nine flavonol and two cinnamic acid derivatives. All metabolites were isolated for the first time from the genus Calotropis, except for 1 isolated previously from Calotropis gigantea. The structures were determined by spectroscopic methods (UV, ESI-MS, ¹H, ¹³C NMR, ¹H-¹H COSY, HSQC, and HMBC). The radical scavenging activity of the aqueous methanol extract and compounds 8 - 13 was measured by the 1,1-diphenyl- 2-picrylhydrazyl (DPPH) method. Cytotoxic screening of the same compounds was carried out on brine shrimps as well
... These flavonoids were isolated from leaves of Leea guineense [48] Flavonoids ...
... These five lignans were isolated from the ethanolic extract of the aerial parts of Leea aequata [39] Gallic acid (33), Ethyl gallate (34) These phenolic compounds were isolated from leaves of Leea guineense [48] Phenolics These phenolic compounds were identified from butanol and aqueous fraction of ethanolic extract of Leea macrophylla root tubers [49] Phenolics These phenolic compounds were identified from ethyl acetate and methanol extract of Leea macrophylla seeds [52] Tannin ...
... Therefore, it is difficult to carry out a detailed chemical literature review of all the plants belong to this family. Due to this shortcoming, an extensive chemical review of the Leea plants available in Bangladesh was carried out and claimed to possess mainly flavonoids, glycosides, phenols, terpenoids, steroids, volatile oils, alkaloids, tannins, saponins, and many other organic compounds [46,47,48] (Figure 2, Table 2). These phytoconstituents are well known to produce many pharmacological activities, which is the evidence of the importance of this genus. ...
Objectives
Plants have been used as traditional medicine (TM) since ancient times and TM remains an effective treatment option in the primary health care system in developing countries, including Bangladesh. There are several reasons to use plants as TM, which are cheaply and easily available and have a cultural heritage of their uses across generations. Leea, a genus of the Vitaceae family, possesses a large number of medicinal plants. In this review, the literature data on the traditional uses and pharmacological activities of Leea species and their phytochemicals are compiled. All the information was collected from the scientific databases.
Results
Leea species are endemic that have opened a promising research field to identify new leads against different diseases. Leea contains approximately 70 species, which are widely distributed throughout the Northern and Eastern Australia, South and Southeast Asia and parts of Africa. The Leea plants are used traditionally in different ailments such as fever, diarrhea, dysentery, joint pain, rheumatism, diabetes, bone fracture, body ache, wound, sexual disorders, and so on. The majority of the Leea species are the medicinal plants, which have anticancer, cytotoxic, antimicrobial, antidiabetic, hepatoprotective, cardiovascular, and CNS activity. Moreover, phytochemicals such as flavonoids, glycosides, phenols, terpenoids, steroids, volatile oils, alkaloids, proteins, quinine derivatives, tannins, saponins, and many other organic compounds have been reported in the Leea species (Leea indica, Leea macrophylla, Leea asiatica, Leea aequata, Leea rubra and Leea guineensis). The presence of phytochemicals and the in vitro and in vivo biological activities reported of these plants support their use as TM. Though original research articles related to the Leea genus are available, supportive reviews on phytochemicals and pharmacological activities remain scarce.
Conclusion
Leea species are used as TM in different ailments and have a real interest in their diverse pharmacological properties. Also, Leea species contain a remarkable number of bioactive compounds. This review has provided a comprehensive report on the plants of Leea genus to identify its therapeutic potential and future prospects for betterment research. However, chemical and biological investigations of several species of Leea genus remain unexplored. Therefore, further studies on these species are necessary, especially regarding pharmacological properties, isolation of the compounds and mechanism of action for the development of new drugs.
... The genus Leea was reported to possess several phytochemicals including coumarin, essential oils, flavonoids, hydrocarbons, and triterpenoids (Op de Beck et al. 1998, 2003Wong et al. 2012;Lakornwong et al. 2014;Mahmud et al. 2017;Kil et al. 2019;Singh et al. 2019). Op de Beck et al. (1998) earlier isolated a new flavonoid sulfate, quercitrin-3 0 -sulfate. ...
... Op de Beck et al. (1998) earlier isolated a new flavonoid sulfate, quercitrin-3 0 -sulfate. Later, three hydrophilic flavonoids, including a new flavonoid sulfate, quercetin-3,3 0 ,4 0 -trisulfate from the leaves of Leea manillensis (Op de Beck et al. 2003). Other compounds were also identified, such as kaempferol, quercetin, quercitrin, mearnsitrin, gallic acid, and ethyl gallate, which have shown antioxidant activities (Op de Beck et al. 2003). ...
... Later, three hydrophilic flavonoids, including a new flavonoid sulfate, quercetin-3,3 0 ,4 0 -trisulfate from the leaves of Leea manillensis (Op de Beck et al. 2003). Other compounds were also identified, such as kaempferol, quercetin, quercitrin, mearnsitrin, gallic acid, and ethyl gallate, which have shown antioxidant activities (Op de Beck et al. 2003). Borokini and Omotayo (2012) evaluated 23 medicinal plants in Nigeria. ...
Synonyms:
Leea aurantiaca Zoll. & Moritzi; Leea bulusanensis Elmer; Leea cuspidifera Baker; Leea dentata Craib; Leea euphlebia Merr.; Leea guineensis G.Don; Leea javanica Blume; Leea laeta Wall.; Leea luzonensis Elmer; Leea maculata Desf.; Leea negrosensis Elmer; Leea palawanensis Elmer; Leea pallidifolia Kaneh.; Leea parva Elmer; Leea parvifoliola Merr.; Leea schomburgkii Craib; Leea wrightii C. B.Clarke
... Various biological studies have reported the antibacterial, antioxidative, anthelmintic, cytotoxic, hepatoprotective, and nephroprotective effects of the Leea species. Several phytochemicals, including coumarin, essential oils, flavonoids, hydrocarbons, and triterpenoids have been determined from the extracts of diverse Leea species, such as L. thorelii [1,3], L. indica [4][5][6][7][8][9], L. macrophylla [10,11], and L. guineense [12,13]. Although several Leea species have been evaluated from both a biological and phytochemical perspective, relatively few studies have included L. asiatica (L.) Ridsdale in their analyses. ...
... From this point of view, the current study was designed to identify chemical constituents of L. asiatica and to provide their spectroscopic information. We describe here a novel compound (1) along with seven triterpenoids (2)(3)(4)(5)(6)(7)(8), eight flavonoids (9)(10)(11)(12)(13)(14)(15)(16), two phenolic gluocosides (17)(18), four diglycosidic compounds (19)(20)(21)(22), and two miscellaneous compounds (23)(24) (Figure 1). with seven triterpenoids (2)(3)(4)(5)(6)(7)(8), eight flavonoids (9)(10)(11)(12)(13)(14)(15)(16), two phenolic gluocosides (17)(18), four diglycosidic compounds (19)(20)(21)(22), and two miscellaneous compounds (23)(24) (Figure 1). ...
... We describe here a novel compound (1) along with seven triterpenoids (2)(3)(4)(5)(6)(7)(8), eight flavonoids (9)(10)(11)(12)(13)(14)(15)(16), two phenolic gluocosides (17)(18), four diglycosidic compounds (19)(20)(21)(22), and two miscellaneous compounds (23)(24) (Figure 1). with seven triterpenoids (2)(3)(4)(5)(6)(7)(8), eight flavonoids (9)(10)(11)(12)(13)(14)(15)(16), two phenolic gluocosides (17)(18), four diglycosidic compounds (19)(20)(21)(22), and two miscellaneous compounds (23)(24) (Figure 1). ...
Leea asiatica (L.) Ridsdale (Leeaceae) is found in tropical and subtropical countries and has historically been used as a traditional medicine in local healthcare systems. Although L. asiatica extracts have been found to possess anthelmintic and antioxidant-related nephroprotective and hepatoprotective effects, little attention has been paid toward the investigation of phytochemical constituents of this plant. In the current study, phytochemical analysis of isolates from L. asiatica led to the identification of 24 compounds, including a novel phenolic glucoside, seven triterpenoids, eight flavonoids, two phenolic glycosides, four diglycosidic compounds, and two miscellaneous compounds. The phytochemical structures of the isolates from L. asiatica were elucidated using spectroscopic analyses including 1D- and 2D-NMR and ESI-Q-TOF-MS. The presence of triterpenoids and flavonoids supports the evidence for anthelmintic and antioxidative effects of L. asiatica.
... The presence of these free-OH groups could be linked to higher antioxidant activity of the compound compared to other derivatives with more methoxylated groups. Methylation of free-OH groups in flavonoids substantially reduces the antioxidant activity of the compounds (Op de Beck et al., 2003 ). In line with this observation, compound 2 with 3- OMe and 6-OMe and also compound 3 with 3-OMe, 4'-OMe and 6-OMe did not inhibit 50% of DPPH free radical hence their EC 50 was higher than the highest concentration tested. ...
... In line with this observation, compound 2 with 3- OMe and 6-OMe and also compound 3 with 3-OMe, 4'-OMe and 6-OMe did not inhibit 50% of DPPH free radical hence their EC 50 was higher than the highest concentration tested. The weak activity exhibited by these compounds could be linked to the methylation of some of their phenolic-OH groups (Martini et al., 2004; Op de Beck et al., 2003). At the highest concentration (200 µM) tested, compounds 2 and 3 had 19.06 and 8.23% antioxidant activities respectively. ...
... All its -OH groups are free and this significantly enhances its antioxidant activity. This observation is in agreement with the earlier structural activity study (Op de Beck et al., 2003; Rice-Evans et al., 1996; Saskia et al., 1996). The effect of 6-OMe on activity is not clear. ...
Fractionation of dichloromethane and acetone fractions obtained by serial extraction from the leaf powder of Dodonaea viscosa Jacq. var. angustifolia (Sapindaceae) resulted in the isolation of four kaempferol methyl ethers. The compounds were identified by spectral data (1H NMR, 13C NMR and MS) as: 3, 5, 7-trihydroxy-4'-methoxyflavone (1); 5, 7, 4'-trihydroxy-3, 6-dimethoxyflavone (2); 5, 7-dihydroxy-3, 6, 4'-trimethoxyflavone (santin) (3); and 5-hydroxy -3, 7, 4'-trimethoxyflavone (4) together with 3,4',5,7-tetrahydroxy flavone (kaempferol) (5). Antioxidant potential of the compounds was evaluated using a DPPH spectrophotometric assay, while antibacterial activity was determined using a serial dilution microplate technique. The isolates demonstrated varying degrees of antioxidant and antibacterial activities. Of all the compounds
investigated, compounds 1 and 5 demonstrated some antioxidant activity (EC50=75.49±1.76 μM and 35.06±0.85 respectively) but lower than Lascorbic acid (EC50=13.55±0.28 μM) used as a standard antioxidant agent. The minimum inhibitory concentration (MIC) of isolated compounds
against Staphylococcus aureus, Enterococcus faecalis, Escherichia coli and Pseudomonas aeruginosa varied from 16 μg/ml to more than 250 μg/ml. Some structure activity relationships could be established for these compounds.
... Given the great amount of distribution of sulfated flavonoids in plants that grow in aquatic habitats, the sulfation of flavonoids seems to represent an ecological adaptation. [22][23][24][25][26][27][28] On the other hand, sulfated flavonoids seem to have an important role in copigmentation; due to their increased water solubility, they form stable molecular complexes with polyphenolic pigments, such as anthocyanins, thus contributing to a strong intensification of the natural coloration. 29 These photochemical properties could be of value in bioimaging techniques; for instant, several sulfated coumarins are already in use as substrates for fluorometric assays. ...
... The nature, number, and position of the conjugated groups of the circulating metabolites are not always assigned; the position of the sulfate is however of great significance to establish the ability of sulfated conjugates to retain-or not-some degree of activity as can be inferred from Table VI data. In the last decade, several sulfated flavonoids were tested for their ability to trap 2,2diphenyl-1-picrylhydrazyl (DPPH), 24,29,46,99 to bind metal ions (Al 3+ , Fe 2+ , Fe 3+ ), 29,96,134 to inhibit xanthine oxidase, 118,144 and lipoxygenase, 144 and for their resistance against copperinduced lipid peroxidation 118,142,143,147 (Table VI). ...
... The overall results obtained with DPPH assay were in agreement with the well-known flavonoids structure-antioxidant activity relationships, namely the importance of the orthodihydroxy (catechol) moiety in the B-ring, and both 3-and 5-hydroxyl groups: when the 3, 3 , and/or 4 hydroxyl groups were sulfated, the activity significantly decreased (compounds 1, 3, 67, and 68, Section 1.1 in Table VI). 24 Monosulfation of quercetin in 7-position (compound 2) did not decrease the antioxidant activity, showing that hydroxyl at C-7 was not important for the antioxidant activity (Section 1.1 in Table VI). 29 Also the DPPH-antioxidant activity of two 3 -monosulfated flavonoids glycosides 71 and 72 was shown to be lower than the corresponding activity of nonsulfated flavonoid glycosides (Section 1.3 in Table VI). ...
Nature uses sulfation of endogenous and exogenous molecules mainly to avoid potential toxicity. The growing importance of natural sulfated molecules, as modulators of a number of physiological and pathological processes, has inspired the synthesis of non-natural sulfated scaffolds. Until the 1990s, the synthesis of sulfated small molecules was almost restricted to derivatives of flavonoids and aimed mainly at structure elucidation and plant biosynthesis studies. Currently, the synthesis of this type of compounds concerns structurally diverse scaffolds and is aimed at the development of potential drugs and/or exploitation of the biological effects of sulfated metabolites. Some important hit compounds are emerging from sulfated flavonoids and other polyphenols mainly as anticoagulant and antiviral agents. When compared with polymeric macromolecules such as heparins, sulfated small molecules could be of value in therapeutics due to their hydrophobic nature that can contribute to improve the bioavailability. This review highlights the synthetic approaches that were applied to obtain monosulfated or polysulfated phenolic small molecules and compiles the diverse biological activities already reported for this type of derivatives. Toxicity and pharmacokinetic parameters of this emerging class of derivatives will also be considered, emphasizing their value for therapeutic applications.
... There is a strong interest in understanding the antioxidant and anti-inflammatory potential of sulphated flavonoids because this is one of the main metabolites found in human blood after administration of aglycones. [48][49][50]. Usually, flavonoids with a catechol moiety (ortho-dihydroxy) in rings A or B, with a double bond at C2-C3 are COX-2 inhibitors. Pascual-Teresa et al. (2004) showed that quercetin 3 -sulphate downregulates COX-2 expression in human lymphocytes in a dose-dependent way [51]. ...
... The study compared quercetin vs. quercetin 3 -sulphate and quercetin 3,3 -disulphate. The assay showed that when the hydroxyl groups are substituted by a sulphate, the antioxidant activity failed dramatically [48]. ...
The great diversity of enzymatic reactions in plant secondary metabolism allows the continuous discovery of new natural compounds and derivatives. Flavonoids, for example, can be found as aglycone or as several sorts of glycosylated, acetylated, methylated, and sulphated derivatives. This review focuses on sulphated flavonoids, an uncommon group of flavonoid derivatives found in some plant families. This work presents a compilation of sulphated flavonoids and their natural sources reported in the literature. Biosynthetic aspects and biological activities have also been reviewed, showing that these particular kinds of natural compounds play an interesting role in plant metabolism, as well as being potential candidates for the development of new drugs.
... From the mass spectroscopy studies, it was concluded that most probably the conjugation positions for quercetin are at the 5-and 7-hydroxyl groups, and therefore the antioxidant activity of quercetin COOH OH metabolites would not be significantly modified, thus contributing to the antioxidant potential of plasma. In contrast, studies (Op of Beck et al., 2003) concerning the antioxidant effect on free radicals scavenging by flavonoids from Leea guineense concluded that the hydroxyl group substitution by sulfate leads to a dramatically failure in the antioxidant activity (quercetin vs quercetin 3'-O-sulfate (26) and quercetin 3,3'-O-disulfate (27)) (Op of Beck et al., 2003). To know whether or not quercetin acts as an in vivo antioxidant after metabolic conversion, the oxidative susceptibility of plasma obtained from rats after intra-gastric administration of quercetin showed more resistance against copper sulfate-induced lipid peroxidation than the control plasma. ...
... From the mass spectroscopy studies, it was concluded that most probably the conjugation positions for quercetin are at the 5-and 7-hydroxyl groups, and therefore the antioxidant activity of quercetin COOH OH metabolites would not be significantly modified, thus contributing to the antioxidant potential of plasma. In contrast, studies (Op of Beck et al., 2003) concerning the antioxidant effect on free radicals scavenging by flavonoids from Leea guineense concluded that the hydroxyl group substitution by sulfate leads to a dramatically failure in the antioxidant activity (quercetin vs quercetin 3'-O-sulfate (26) and quercetin 3,3'-O-disulfate (27)) (Op of Beck et al., 2003). To know whether or not quercetin acts as an in vivo antioxidant after metabolic conversion, the oxidative susceptibility of plasma obtained from rats after intra-gastric administration of quercetin showed more resistance against copper sulfate-induced lipid peroxidation than the control plasma. ...
ABSTRA ABSTRA ABSTRA ABSTRA ABSTRACT CT CT CT CT Though flavonoids are one of the most abundant groups of secondary plant metabolites, the interest in sulfated flavonoids has only increased in the last years due to their hydrophilic nature and their relevant biological activities. More than one hundred and fifty sulfated flavonoids from plants and sea grass were reported so far, mostly within the flavonol and flavone subclasses. As sulfate groups are present in many bioactive macromolecules, the flavonoid sulfates and other small molecules are being investigated for their biological activities. The purpose of this chapter is to describe the natural occurrence and biological activities of sulfated flavonoids and other sulfated small molecules showing their value for therapeutic application especially as anticoagulant and antiviral agents. Aspects related to biosynthesis and some pharmacokinetic studies of sulfated flavonoids will also be considered.
... Falodun et al. (2007) have shown that the aqueous leaf extract has anti-inflammatory activity in the carrageenan-induced rat paw oedema test model. Phytochemical evaluation of the woods and leaves revealed volatile constituents including terpenoids (Op de Beck et al., 2000) and hydrophilic flavonoids namely quercetin-3′-sulphate-3-O-α-L-rhamnopyranoside, quercetin-3,3′-disulphate and quercetin-3,3′,4′-trisulphate, together with kaempferol, quercetin, quercitrin, mearnsitrin, gallic acid and ethyl gallate (Op de Beck et al., 2003). These flavonoids were found to have free radical scavenging activity when evaluated in the DPPH assay (Op de Beck et al., 2003). ...
... Phytochemical evaluation of the woods and leaves revealed volatile constituents including terpenoids (Op de Beck et al., 2000) and hydrophilic flavonoids namely quercetin-3′-sulphate-3-O-α-L-rhamnopyranoside, quercetin-3,3′-disulphate and quercetin-3,3′,4′-trisulphate, together with kaempferol, quercetin, quercitrin, mearnsitrin, gallic acid and ethyl gallate (Op de Beck et al., 2003). These flavonoids were found to have free radical scavenging activity when evaluated in the DPPH assay (Op de Beck et al., 2003). Our search has revealed that there are no scientific reports available in established literature to support the effectiveness of the plant in the treatment of pain and epilepsy. ...
Leea guineensis G. Don (Family: Leeaceae) is an evergreen shrub or small tree used in Ghanaian traditional medicine to treat various ailments including epileptic fits and pain. However, little scientific evidence exists to support its use. The present study examined the anti-nociceptive, anti-anxiety and anticonvulsant effects of the aqueous leaf extract of L. guineensis (LGE) in murine models of pain (formalin test), anxiety (elevated plus-maze and light/dark box tests) and convulsion (pentylenetetrazole-, picrotoxin-and maximal electroshock-induced seizures tests). LGE (30 to 300 mg/kg, p.o.) and the positive control morphine (3 to 10 mg/kg, i.p.) exerted profound dose-dependent anti-nociceptive activity in both phases of the formalin test. LGE (30 to 300 mg/kg, p.o.) also showed anxiolytic effects similar to diazepam (0.1 to 1.0 mg/kg, i.p.) but contrary to pentylenetetrazole (3 to 30 mg/kg, i.p.). LGE increased the frequency and duration of open arm exploration while decreasing the protected forms of stretch-attend postures and head-dips in the elevated plus-maze. It also decreased the emergence latency of mice into the lit compartment of the light/dark box and increased the amount of time spent there. LGE (30 to 300 mg/kg, p.o) also exhibited significant anticonvulsant activity by protecting mice against pentylenetetrazole-, picrotoxin-and maximal electroshock-induced seizures. At all the doses used, LGE produced no motor deficits in mice. Together, the results suggest that the extract has anti-nociceptive, anxiolytic and anticonvulsant properties which support its traditional use.
... The occurrence of 5 in the seagrass Zostera marina [19] was previously reported. It was determined that the replacement of hydroxyl with sulfate group on the flavone skeleton drastically decreased antioxidant properties [54]. In contrast, our findings depicted that the sulfated flavones were found to be most active in inhibiting α-glucosidase compared to non-sulfated ones. ...
... The crude ethanol extract, along with hexane, ethyl acetate, and aqueous fractions of ethanol extract obtained from the leaf of L. indica have been demonstrated to display antioxidant activity through DPPH radical scavenging, superoxide radical scavenging, and reducing power assays 60 . In-vitro studies of different fractions L. macrophylla leaf have also shown strong free radical scavenging ability due to the presence of phenolics 34,61,62 . In an experimental study, administration of the L. macrophylla root to the STZ-induced diabetes animals has been shown to upregulate the expression profile of genes responsible for antioxidant enzymes suggesting the pancreas protecting effect of the plant that is mediated through an antioxidant dependent event 44 . ...
The genus Leea distributed majorly in tropical and subtropical regions of Asia, Africa, and Madagascar, belongs to the family Leeaceae. It comprises 36 species that are used worldwide for different medicinal purposes. In this decade, research interests in the genus Leea have grown in the fields of systematics, phylogenetic studies, analytical chemistry, identification and isolation of active metabolites, pharmacology, and phytochemistry. A wide range of phytochemicals with a variety of pharmacological activities were found to be possessed by different species of the Leea family, flavonoids, phenolics, triterpenoids, and tannins being the major ones. Different plant parts are claimed to be used for the treatment of human and animal ailments. Unlike members of Vitaceae, Leeaceae members (Leea species) do not form tendrils and include erect herbs, shrubs and trees but have shared features such as raphides, minute droplets of plant sap called pearl glands, phloem plastids, common corolla-stamen primordia, as well as similar wood and testa anatomy similar to Vitaceae family. This review reveals new insights on the genus Leea and the potential use of species in the genus as medicinal plants, with Leea indica and Leea macrophylla being the most important species, whose roots, leaves, and whole plants possess various pharmacological actions as they are rich in flavonoids, triterpenoids, and tannins.
... −2 ) comparable to those of surface-associated bromophycolides in the red seaweed Callophycus serratus 29 . Interestingly, the antioxidant and cytotoxic capacity of desulfated flavonoids is enhanced compared to their sulfated counterparts 20,46,47 . Thus, sulfate conjugation may not be directly involved in the bioactivity of these secondary metabolites but rather play a physiological function, for instance to facilitate metabolite cellular and/or long-distance transport within the plant 48,49 . ...
Plants rely on both mechanical and chemical defence mechanisms to protect their surfaces against microorganisms. The recently completed genome of the eelgrass Zostera marina, a marine angiosperm with fundamental importance for coastal ecosystems, showed that its re-adaptation from land to the sea has led to the loss of essential genes (for chemical communication and defence) and structural features (stomata and thick cuticle) that are typical of terrestrial plants. This study was designed to understand the molecular nature of surface protection and fouling-control strategy of eelgrass against marine epiphytic yeasts. Different surface extraction methods and comparative metabolomics by tandem mass spectrometry (LC-MS/MS) were used for targeted and untargeted identification of the metabolite profiles of the leaf surface and the whole tissue extracts. Desorption electrospray ionization-imaging mass spectrometry (DESI-IMS) coupled with traditional bioassays revealed, for the first time, the unique spatial distribution of the eelgrass surface-associated phenolics and fatty acids, as well as their differential bioactivity against the growth and settlement of epiphytic yeasts. This study provides insights into the complex chemical defence system of the eelgrass leaf surface. It suggests that surface-associated metabolites modulate biotic interactions and provide chemical defence and structural protection to eelgrass in its marine environment.
... In addition, it appears that the presence of 3-OH groups in the structures of flavonoids compound (2) and (3) increase significantly the antioxidant activity when compared to that with 3-OMe groups of compound (4). This observation is in accordance with that of Op de Beck et al. [23] and with that of Amic et al., who confirmed that the presence of 3-OH groups significantly enhances antioxidant activity [2]. All the flavonoids isolated from the two plants showed antioxidant activity, but less than the Trolox used as control (EC 50 = 0.106 µg/ml). ...
The aim of the present work was to evaluate the antioxidant activity of extracts and four flavonoids that had been isolated from the aerial parts of Bunium alpinum Waldst. et Kit. (Apiaceae) and Tamarix gallica L. (Tamaricaceae). In this work, the four flavonoids were first extracted via various solvents, then purified through column chromatography (CC) and thin layer chromatography (TLC). The four compounds were subsequently identified by spectroscopic methods, including: UV, mass spectrum ¹H NMR and ¹³C NMR. The EtOAc extract of Bunium alpinum Waldst. et Kit yielded quercetin-3-O-β-glucoside (3’,4’,5,7-Tetrahydroxyflavone-3-β-D-glucopyranoside) (1), while the EtOAc and n-BuOH extracts of Tamarix gallica L. afforded 3,5,3’-trihydroxy-7,4’-dimethoxyflavone (2), 3,5,7-trihydroxy-4’-methoxyflavone (3) and 5-hydroxy-3,7,4’-trimethoxyflavone (4). The antioxidant activity of the extracts and the flavonoids were then evaluated through DPPH free radical-scavenging assay. Of all studied extracts, the n-Butanol extract of Bunium alpinum (EC50 = 1.84 μg/ml) showed the best antioxidant activity against (DPPH). In contrast, the isolates demonstrated varying degrees of antioxidant activity: compound (1) was the more active (EC50 = 0.28 μg/ml), followed by compound (3) and (2) (EC50 = 0.309μg/ml, EC50 = 0.406 μg/ml, respectively), compound (4) showed the lowest activity. All the isolated flavonoids exhibited antioxidant activity, but this was lower than the control (Trolox). In conclusion, due to the presence of flavonoids in their ariel parts, the studied plants could be natural sources of several important antioxidant agents
... been reported from other species of genus Leea (L. guineense) (Mariotte et al., 2003). HPTLC is as an acquiescent and commonly used technique for qualitative and quantitative analysis of chemical markers in herbal raw materials. ...
A sensitive and reliable high performance thin layer chromatography method has been developed for the simultaneous estimation of quercetin and gallic acid in Leea indica (Burm. f.) Merr., Vitaceae. Ethyl acetate extract prepared from hydrolysed aqueous alcoholic extract (70%) was applied on silica gel G 60 F254 plate. The plate was developed using toluene-ethyl acetate-formic acid, 5:4:1 (v/v/v) as a mobile phase and detection and quantification were performed by densitometric scanning at 254 nm. The system was found to give well resolved bands for quercetin (Rf 0.63) and gallic acid (Rf 0.45) from other constituents present in the extract of L. indica. The correlation coefficient was found to be 0.991 and 0.999 with RSD, 0.97–1.23% and 0.1–1.13% for quercetin and gallic acid respectively in the developed method. The accuracy of the method was confirmed by conducting recovery studies at different levels using the standard addition method. The average recovery of quercetin and gallic acid was found close to 99% suggesting the accurateness of the method. The proposed validated HPTLC method offers a new, sensitive, specific and precise gauge for quantification of quercetin and gallic acid in L. indica.
... Furthermore, methylation of 3-OH position in kaempferol derivatives further reduced the antioxidant activities as exhibited by 3 with an oxygenation pattern similar to 2 except for the methylation of the hydroxyl group at 3-position. The weak activity exhibited by the flavonoid aglycones could be linked to the methylation of some of their phenolic-OH groups [49]. The more the reduction in the hydroxyl moieties of the compound, the lesser the anti-oxidant activities. ...
Phytochemical investigation of surface exudates of the leaves of Gardenia ternifolia resulted to characterization of four flavonoids; 3,5,3′-trihydroxy-7,4′-dimethoxyflavone (1), 5,7-trihydroxy-4′-methoxyflavone (2), 5,7-dihydroxy-3,4′-dimethoxyflavone (3), 5,4′-dihydroxy-7-methoxyflavanone (4) and two tritepenoids; β-sitosterol (6) and stigmasterol (7). Compound 1 exhibited the highest antioxidant activity with IC 50 = 40.3± 1.55 μΜ. The rest of the flavonoids showed minimal activities with IC 50 values of 75.5±1.75, 89±0.22, 94±0.11 μΜ for 2-4, respectively. The antioxidant activities of 1 was substantially lower than the standard, quercetin (IC 50 = 20.1±1.34 M). Methoxylation of quercetin at 7 and 4′-position in 1 substantially reduced antioxidant potential. Lack of oxygenation at 3′ position, as observed for kaempferol derivatives was responsible for further reduction in the radical scavenging potential as observed for 2 and 3. Furthermore, methylation of 3-OH position in kaempferol derivatives further reduced the antioxidant activities as exhibited by 3 with an oxygenation pattern similar to 2 except for the methylation at 3-position. The results of this study are consistent with previous findings that revealed that flavonols, exhibited better anti-oxidant activities as compared to 3-methoxyflavones. Acetylation of 3 at the 5 and 7 positions resulting to 3,4′dimethoxy-5,7-diacetylflavone (5), substantially reduced the activity of this compound. The triterpenoids exhibited were inactive as expected.
... The activity of 3,5,4´-trihydroxy-7-methoxyflavone (2) and kaempferol (1) were comparable at all concentrations. Flavonols exhibited appreciably good anti-oxidant activities compared to the 3methoxyflavones, indicating the importance of the hydroxyl group at C-3 consistent with studies by Harborne, (1983) and Rice-Evans et al. 1996and Saskia et al. 1996, Op de Beck et al. 2003, Teffo et al. 2010). The diterpenoids tested; 2β-hydroxyhardwickiic acid (12), and dodonic acid (13) showed no radical scavenging activity (RSA) at 50 µM as expected. ...
Dodonaea angustifolia L.f is a medicinal plant used in the Kenyan traditional system of medicine to cure human diseases. The secondary metabolites present in the surface exudates, showed phytochemical diversity of this plant from different geographical conditions in Kenya. There was great geographical variability in the composition of the surface exudates in D. angustifolia populations as reflected in the antiplasmodial and radical scavenging activities (RSA) of this substance from the Ngong forest, Nairobi and Taita hills, Voi populations. Most of the compounds from the exudates of D. angustifolia and Senecio roseiflorus showed moderate anti-plasmodial activities against chloroquine sensitive (D6) and resistant (W2) strains of P. falciparum with IC 50 values ranging between 3.2 and 23.6 µg/ml. Of the pure compounds tested flavonols ca kaempferol (1) and rhamnocitrin (2) exhibited radical scavenging activities (RSA) comparable to the standard, quercetin (3) at 50 µM. These studies showed that flavonoids exhibited both antiplasmodial and RSA although there was no direct relationship between these activities. This is elaborated in 5,4´-dihydroxy-7-methoxyflavanone (4), exhibiting good antiplasmodial activities but minimal % RSA. The structure-activity relationship of the active flavonoids showed that flavonols had appreciable RSA activities as compared to 3-methoxy flavones from the surface exudates.
... In fact, the sulfated compounds have enhanced hydrophilicity, which may contribute to easier excretion, as it yields passage through the cell membrane more difficult . The interest in these sulfated conjugates arises from the biological activities observed before, like antioxidants or anticoagulants (Op de Beck et al. 2003;Guglielmone et al. 2005). ...
Small quantities of reactive species of oxygen and nitrogen are produced in physiological processes occurring in all organisms. However, when they are formed in excess or when the antioxidant defence system is depleted, homeostasis is disrupted favouring pro-oxidants. Loss of oxidative status has been linked to several diseases. Thus, antioxidants compounds may assist the prevention and therapeutics of diseases in which oxidative phenomena are involved, e.g. cancer, chronic inflammatory disease, cardiovascular disorders and aging. There are several synthetic compounds with antioxidant properties, although their use has been restricted due to their toxicity. So, there is a growing interest on the search of natural compounds with antioxidant potential, which may exhibit improved tolerability. Natural matrices have proven antioxidant activity, which is due to their chemical composition. These matrices present a wide range of low molecular weight phytochemicals, like alkaloids, carotenoids and organic acids, which constitute the basis of their antioxidant capacity. Phenolic compounds are among those with more interest, because they are largely distributed in nature and can exert their antioxidant activity at several levels. As different natural matrices have distinct compounds contents, with several structures, they offer different protective mechanisms. In this chapter we describe different vegetable matrices, like Catharanthus roseus, Passiflora edulis, Rumex induratus and insect-plant system considerations, involving Pieris brassicae. All refered matrices display antioxidant activity, with special attention being given to their phenolic compounds. Because no single method is able to provide exact information about antioxidant potential, some methods currently used to assess this capacity will be referred.
... [23] Quercetin sulfates were shownt od isplay some lipid peroxidation inhibitory effect [24] anda ntiradical activity (in the 2,2-diphenyl-1-picrylhydrazyl assay). [25] Quercetin 3'-O-sulfate demonstrated not only inhibition of cyclooxygenase-2a ctivity but also reduction of the expression of cyclooxygenase-2 messenger RNA. [26,27] Other interesting biological activities (antimicrobial, anti-inflammatory,a nti-HIV,a ntitumor,e tc.) of various quercetin sulfates and their derivatives were described in ar ecent review. ...
Two types of sulfotransferases, namely recombinant rat liver aryl sulfotransferase AstIV and bacterial aryl sulfotransferase from Desulfitobacterium hafniense, were used for the sulfation of quercetin, its glycosylated derivatives (isoquercitrin and rutin), and dihydroquercetin ((+)-taxifolin). The rat liver enzyme was able to sulfate only quercetin and taxifolin, whereas the quercetin glycosides remained intact. The D. hafniense enzyme sulfated isoquercitrin and rutin selectively at the C-4′ position of the catechol moiety with very good yields. Taxifolin was sulfated at the C-4′ position and a minor amount of the C-3′ isomer was formed. Sulfation of quercetin proceeded preferentially at the C-3′ position, but a lower proportion of the C-4′ isomer was formed as well. A detailed analysis of the kinetics of this reaction is provided and a full structural analysis of all products is presented.
... These compounds were also reported by Mthembu from a phytochemical study of Elephantorrhiza elephantine (Fabaceae) [144]. Gallic acid (101) and methylgallate (102) have also been isolated from other plants growing in Africa, either together or singly and in some of the studies their activities were measured against various diseases [148][149][150][151][152][153][154][155][156][157][158][159][160]. ...
... In another study, Op de Beck et al., (2003) isolated and identified three hydrophilic flavonoids named quercetin-3ˊ-sulphate-3-O-α-L-rhamnopyranoside, quercetin-3,3ˊdisulphate and quercetin-3,3ˊ4ˊ-trisulphate, together with kaemferol, quercitrin, mearnsitrin, gallic acid and ethyl gallate. These flavonoids were found to have free radical scavenging effect which was evaluated in the 2, 2-Diphenyl-1-Picrylhydrazyl (DPPH) assay. ...
... Studies of structure-radical scavenging activity relationship of flavonoids (Rice-Evans et al., 1996;Pietta, 2000) showed the antioxidant activity depends on the number and position of hydroxyl groups in rings A and B as well as 2, 3-double bond, the 4-oxo group in ring C, thus quercetin (Fig. 2) meet all the above characteristic. Our results suggest that the crude EtOAc extract, composed by various flavonoids, are the cause of significant antioxidant activity of this extract and can be a response to both a synergistic effect of these substances and the presence of a specific substance with high antioxidant capacity (Silva and Paiva, 2012), as quercetin that was employed as standard agent in antioxidant studies (Beck et al., 2003). ...
Hymenaea stigonocarpa, is an endemic tree from the Brazilian cerrado (savannah) and popularly known as jatobá-do-cerrado. The wood of this species is resistant to biodegradation and is used in naval and civil construction. Cuttings from heartwood of this species showed resistance to fungi and termites. In this paper, we report the antitermitic and antioxidant activities of H. stigonocarpa heartwood ethyl acetate extract and its main flavonoids constituents, hultenin (1), taxifolin (2), quercetin (3) and 7-methoxycathequin (4). The structure elucidation of the isolated flavonoids was performed by spectroscopic methods. The ethyl acetate extract possesses highest antitermitic and antioxidant activity when compared with isolated flavonoids.
... These compounds were also reported by Mthembu from a phytochemical study of Elephantorrhiza elephantine (Fabaceae) [144]. Gallic acid (101) and methylgallate (102) have also been isolated from other plants growing in Africa, either together or singly and in some of the studies their activities were measured against various diseases [148][149][150][151][152][153][154][155][156][157][158][159][160]. ...
Cancer is known to be the second most common disease-related cause of death among humans. In drug discovery programs anti-cancer chemotherapy remains quite challenging due to resistant issues. Plants used in traditional medicine are known to contribute significantly within a large proportion of the African population. A survey of the literature has led to the identification of ~400 compounds from African medicinal plants, which have shown anti-cancer, anti-proliferation, anti-tumor and/or cytotoxic activities, tested by in vitro and in vivo assays (from mildly active to very active), mainly alkaloids, terpenoids, flavonoids, coumarins, phenolics, polyacetylates, xanthones, quinones, steroids and lignans. The first part of this review series focuses on xanthones, quinones, steroids, coumarins, phenolics and other classes compounds which were not discussed in part I.
... From these observations it is not clear whether the reduction in activity of compounds 4 and 5 with reference to quercetin which exhibited an activity of 6.0 AE 0.2 mg/mL (19.9 mM) was due to the additional oxygenation at C-8 in ring A or methoxylation of the C-3, C-5 0 and C-7 hydroxyl groups. However, previous studies have shown that methylation of the 3-OH in flavanols substantially reduced antioxidant activities compared to methylation of the hydroxyl groups at the 5-OH, 7-OH, 4 0 -OH and 3 0 -OH of quercetin (Op de Beck et al., 2003;Teffo et al., 2010). The flavones 2, lacking a free hydroxyl group at C-4 0 and the flavanone (6) lacking oxygenation at 3 0 position exhibited substantially lower antioxidant activity with IC 50 values of 8.79 AE 0.3 (24.4 mM and 8.54 AE 0.3 mg/mL (28.3 mM), respectively. ...
Three novel compounds; two polymethoxylated flavonoids, 5,7,4′-trihydroxy-3,8,3′,5′-tetramethoxyflavone (1), 5,7,3′-trihydroxy-3,8,4′,5′-trimethoxyflavone (2), and a clerodane diterpenoid; 8-acetoxyisochiliolide lactone (3) were characterized from the leaf exudates of Microglossa pyrifolia. In addition, three known polymethoxylated flavonoids including; 5,7,4′-trihydroxy-3,8,3′-trimethoxyflavone (4), 5,3′4′-trihydroxy-3,7,8-trimethoxyflavone (5), 5,3′4′-trihydroxy-7-methoxyflavanone (6) and a clerodane diterpenoid; 7,8-epoxyisocholiolide lactone (7) were identified. Their structures were determined on the basis of spectroscopic evidence. All the compounds did not exhibit antiplasmodial and antimicrobial activities at 47.6 μg/mL and were not cytotoxic at 5 μg/mL. Compound 6 exhibited modest antileishmanial activity with IC50 value of 13.13 μg/mL with 5 and 7 showing activities with IC50 values of 31.13 and 38.00 μg/mL, respectively, therefore inactive. The flavonoids (quercetin derivatives, 4 and 5) showed similar antioxidant activities, using 2,2-diphenylpicrylhydrazyl (DPPH) assay, with IC50 values of 6.2 ± 0.3 μg/mL for 4 (17.3 μM) and 5 (17.8 μM) respectively. These activities were comparable to that of the standard quercetin (IC50 value of 6.0 ± 0.2 μg/mL (19.9 μM)), irrespective of methylation of the characteristic hydroxyl groups expected to be responsible for activity and additional substitution at C-8 in ring A of the flavonoid ring. These studies revealed that the presence of an hydroxyl group at C-4′ positions and oxygenation at C-3 in flavone skeleton, appears to be necessary for good antioxidant activities as encountered in compounds 1, 4 and 5. Substantial reduction in antioxidant activity was shown by methoxylation of the 4′-OH as observed in compound 2 with an IC50 value of 8.79 ± 0.3 μg/mL (24.4 μM).
... Nevertheless, dietary polyphenols undergo extensive conjugation, namely sulfation and the in vitro antioxidant activity evaluation may not be reflected in vivo. A reflex of this phenomenon is the investigation in the last decade of several sulfated metabolites of dietary polyphenols for their antioxidant properties, namely for their ability to trap 2,2-diphenyl-1-picrylhydrazyl (DPPH) (Alluis and Dangles, 2001;de Beck et al., 2003;Rimbach et al., 2004;Yang et al., 2003) to bind metal ions (Al 3+ , Fe 2+ , Fe 3+ ) (Alluis and Dangles, 2001;Ruefer et al., 2005;Wessel et al., 2005), to inhibit xanthine oxidase (Day et al., 2000;Yagi et al., 1994) and lipoxygenase (Day et al., 2000) and for their resistance against copper-induced lipid peroxidation (Janisch et al., 2004;Manach et al., 1998;Morand et al., 1998;Yagi et al., 1994). Although the majority of sulfated derivatives presented lower antioxidant potencies than their respective nonsulfated analogues, some examples of higher antioxidant potencies could be noted (Correia-da-Silva et al., 2014). ...
Being thrombosis a complex process involving multiple pathways, drugs acting simultaneously as antioxidants and anticoagulants would be of value to prevent and treat this pathology. We have recently discovered a new class of sulfated polyphenols derivatives which exhibited both in vitro and in vivo antithrombotic activity. That these derivatives showed water solubility and no putative toxicity was observed in vivo for the investigated compounds. Herein, the antioxidant potential of these polyphenolic derivatives was investigated by the DPPH and peroxyl radical scavenging activity assays and by the copper ion-chelating ability assay. The results showed that the persulfate of chlorogenic acid (7) was the most promising derivative, displaying antioxidant activity both by the DPPH and the peroxyl radical scavenging assays. Additionally, this compound was able to chelate Cu2+ ions. The gathered information provided a model for the future design of dual anticoagulant-antioxidant agents.
... Of the isolated compounds, kaempferol (3) and quercetrin (4) 3-OH and a keto group in position 4 (Op de Beck et al., 2003 andSaskia et al., 1996). Only quercetrin (4) fulfilled these entire requirements and as expected had the highest activity 13 comparable to L-ascorbic acid. ...
Species of the family Combretaceae are used extensively in traditional medicine against inflammation and infections, and although antibacterial activity has been reported in non-polar extracts, further rationale for the widespread use of the Combretaceae is expected to exist. Methanol extracts of leaves of ten different Combretum species were evaluated for antioxidant activity by spraying TLC chromatograms of each leaf extract with 2, 2-diphenyl-1-picrylhydrazyl (DPPH). Compounds with antioxidant activity were detected by bleaching of the purple DPPH colour. Leaf extracts of Combretum apiculatum subsp. apiculatum had the most antioxidant compounds. This species was consequently selected for phytochemical investigation. A DPPH assay-directed fractionation of the leaf extracts of C. apiculatum led to the isolation of four antioxidant compounds from the ethyl acetate and butanol soluble fractions. The structures of the compounds were determined by spectroscopic analyses (1 H-NMR, 13 C-NMR and MS) and identified as: cardamonin (1), pinocembrin (2), quercetrin (3) and 2 kaempferol (4). In a quantitative antioxidant assay, the more polar fractions (ethyl acetate and butanol) obtained by solvent-solvent fractionation had the highest antioxidant activity among the solvent fractions obtained from C. apiculatum, with EC 50 values of 3.91 ± 0.02 and 2.44 ± 0.02 µg/mL respectively. Of the four isolated compounds, quercetrin (4) and kaempferol (3) had the strongest antioxidant activity, with EC 50 values of 11.81 ± 85 and 47.36 ± 0.03 µM respectively. Cardamonin (1) and pinocembrin (2) did not demonstrate strong activity. L-ascorbic acid was used as standard antioxidant agent (EC 50 = 13.37 ± 0.20 µM or 2.35 µg/mL). The cytotoxicity of cardamonin and pinocembrin was evaluated on Vero kidney cells using the MTT (3-(4, 5-dimethylthiazol)-2,5-diphenyl tetrazolium bromide) assay with berberine as positive control. At concentrations higher than 50 µg/ml of cardamonin or pinocembrin, the cells were not viable. Cardamonin was more toxic (LC 50 = 1.97 µg/ml) than pinocembrin (LC 50 = 29.47 µg/ml) and even the positive control, berberine (LC 50 = 12.35 µg/ml).
... Compound 3, quercetin-3-O-glucoside, had higher activity than L-ascorbic acid and compound 2, kaempferol-3-O-glucoside had the least antioxidant activity (Table 1).μ Conditions for effective radical scavenging activity in flavonoids as demonstrated by structure activity relationship studies include the presence of catechol groups (3´-OH and 4´-OH) on ring B, the 3-OH group in combination with a C2 C3 double bond and keto group in position 4 [22][23]. These structural units strengthen the antioxidant activity exhibited by increasing the stability of the flavonoid radical after donating phenolic hydrogen. ...
A 1, 1-diphenyl-2-picrylhydrazyl (DPPH) activity-guided fractionation procedure was used to isolate the antioxidant constituents of a 50% ethanol dried leaf extract of Bauhinia tomentosa. Four flavonol glycosides: kaempferol-7-O-rhamnoside (1), kaempferol-3-O-glucoside (2), quercetin-3-O-glucoside (3) and quercetin-3-Orutinoside (4) were isolated by accelerated gradient chromatography (AGC) and Sephadex LH-20 column chromatography. Compounds 1-3 are reported for the first time from this species. The structures of the compounds were established by spectroscopic methods (1H NMR, 13C NMR and MS). A DPPH spectrophotometric assay was employed to evaluate the antioxidant activity of the isolated compounds. Compound 3 had higher antioxidant activity than L-ascorbic acid while 1 and 4 similar
and 2 lower activities. Compounds 2-4 were non-cytotoxic, but kaempferol-7-O-rhamnoside (compound 1) displayed slight cytotoxicity to bovine dermal cells (LC50 = 116.58 μg/ml) in the tetrazolium (MTT) based assay
... These structural units fortify the antioxidant activity by increasing the stability of the flavonoids radical after donating phenolic hydrogen. The higher antioxidant activity of compound 2 compared to compound 1 could be due to the presence of free hydroxyl group in position 3 as both compounds have catechol group (3` and 4` di-OH) on ring B. It has been demonstrated that substitution of 3-OH reduces activity, (Op de Beck, 2003). ...
Bauhinia monandra (Kurz), traditionally use in the treatment of diabetes with established significant anti-diabetic activity was investigated for its antioxidant constituents since the activity demonstrated can be linked to the presence of antioxidant compounds. Bioassay directed fractionation of the ethyl acetate soluble leaves extract has led to isolation of two active compounds identified as: Quercetin-3-O-rutinoside (1) and Quercetin (2). The molecular structures elucidations of both compounds were carried out using spectroscopic studies (1H NMR, 13C NMR and MS). These compounds are reported from this species for the first time. A DPPH spectrophotometric assay was used to evaluate the antioxidant potential of the compounds. Compound2 had higher antioxidant activity while Compound 1 had lower activity than L-ascorbic acid which was used as standard.
... Hence, this study aimed to develop an optimized HPLC method for the separation of caffeic, ferulic, vanillic, ellagic, gallic, benzoic, cinnamic and hydrocinnamic acids. Their choice was focused either on their relatively close structure and their well-known antimutagenic, antibacterial, antioxidant and anti-inflammatory activities (Rukkumani et al., 2004;Friedman et al., 2003;Op de Beck et al., 2003;Privadiarsin et al., 2002;Fernandez et al., 1998;Kaur et al., 1997;Fernandez et al., 1996;Garcia and Marhuenda, 1985;Wood et al., 1982). The selection of optimal HPLC operating conditions is rather difficult and complex for multi-component mixtures due to the high degree of process variable interaction. ...
Experimental design methodology was used to optimize the HPLC separation of various relevant phenolic acids from an artificial mixture. The effect of four characteristic factors of the HPLC procedure on the Chromatographic Response Function was investigated by a Central Composite Face-Centred Design and Multi Linear Regression fitting. The eight phenolic acids were successfully separated. The optimal HPLC setting condition was applied to rapid screening of free phenolic acids from Striga hermonthica (Del.) Benth. (Scrophulariaceae), Guiera senegalensis J. F. Gmel (Combretaceae) and unifloral honey from Acacia sp. (Mimosaceae). None of reference phenolic acid was identified in S. hermonthica extract when some of them were detected in G. senegalensis and honey extracts. This work is considered as a first step for a largest phenolic acids screening from various preparations used in Burkina Faso folk medicine to justify some of their properties or potentialities.
There is still a lack of studies evaluating the effect of different methods in processing of herbal tea from Oenanthe javanica. The present study aims to optimize the processing methods for the optimal recovery of antioxidant in the herbal tea. The aerial part of this plant was processed according to the standard manufacturing procedure to produce unfermented, partially-fermented and fully-fermented teas. The highest Ferric Reducing Antioxidant Potential (FRAP) and 1,1-diphenyl-2-picryhydrazyl (DPPH) scavenging activities were indicated by the infusion of unfermented tea with EC50 values of 94.99 ± 0.32 μg/mL and 244.28 ± 11.72 μg/mL, respectively. The aerial part was subjected to steaming for seven different time durations and two rolling conditions. The maximum extraction recovery of total antioxidant (on the basis of FRAP analysis) was achieved from the machine rolled sample that was steamed for 60 min. The FRAP activity (EC50 67.00 ± 0.16 μg/mL) was correlated with the highest total phenolic content (TPC) (10.98 ± 0.41 μg GAE/mg tea), total flavonoid content (TFC) (8.12 ± 0.20 μg QE/mg tea) and persicarin content (96.59 ± 5.32 μg persicarin/mg tea) with r values ranging from -0.627 to -0.817 (p < 0.05). Thus, the findings have highlighted the optimization of steaming and rolling conditions are important procedures to produce herbal tea with high antioxidant ingredients.
A sensitive and reliable high-performance thin-layer chromatography (HPTLC) method has been developed to simultaneously estimate quercetin and gallic acid in Annona reticulata L. The methanolic extract of the leaf of A. reticulata L. was performed to detect standard marker compounds like quercetin and gallic acid by the automatic TLC applicator. The plate was developed using toluene‒ethyl acetate‒formic acid (9:10:1.6, V/V) as the mobile phase, and detection was performed by densitometric scanning at 254 nm. The system was found to give well-resolved bands for quercetin (standard) at RF = 0.71 and gallic acid (standard) at RF = 0.63 from other constituents present in the leaf extract of A. reticulata L. The spectral analysis of standard gallic acid and sample in the HPTLC study confirmed the presence of gallic acid in the plant extract. The average recovery of quercetin and gallic acid was found close to 99%, suggesting the accurateness of the method. The proposed validated HPTLC method offers a new, sensitive, specific method for the quantification of quercetin and gallic acid in A. reticulata L. The presence of the phytochemicals like quercetin and gallic acid in the leaves of A. reticulata L. supports the view that the leaves could be a potential source of natural antioxidant, anti-inflammatory, and antidiabetic drugs.
Much of the beneficial action of fruits and vegetables are attributed to flavonoids, a class of natural compounds with polyphenolic structure. To date, the anticancer action of different flavonoids is well known as these plant secondary metabolites can exert a wide range of biological effects, including antioxidant, antiinflammatory, antiproliferative, antiinvasive, and antimetastatic responses, in various cancer cells in vitro. However, in vivo conditions in human organisms, flavonoids undergo an extensive metabolism in the intestine and the liver with formation and entering the systemic circulation of different glucuronidated, methylated and sulfated derivatives. Only a small portion of aglycones detected in the blood further indicates a high rate of conjugation. However, rather little is known about the bioactivities of flavonoid conjugates, with the sulfates being still the least studied. At the same time, it can be expected that substitution of the important hydroxyl moieties by sulfate groups in flavonoid backbone might lead to substantial alterations in biological activities of these phytochemicals. Therefore, the focus of this chapter is on the sulfated flavonoid metabolites: their formation, structure and different anticancer properties.
The ability of Leea philippinensis, an endemic tree in the Philippines, as in vitro free radical scavenger was investigated. Soxhlet extraction using solvents in increasing order of polarity (hexane<chloroform<ethyl acetate<acetone<methanol) yielded acetone and methanol extracts with the highest Total Phenolic Content (TPC) and Total Flavonoid Content (TFC). These crude extracts were further separated using silica gel column chromatography with eluents hexane, hexane:acetone (1:1), acetone, acetone:methanol (1:1) and methanol. Fractions with the most TFC and TPC exhibited concentration-dependent activity with an IC50 value range of 0.10 - 0.29, 0.17 - 0.80, 0.29 - 0.84 and 3.40 - 9.75 mg/mL, respectively, against DPPH, hydroxyl, nitric oxide and hydrogen peroxide inhibition assays. In addition, these fractions demonstrated reducing power by transforming the Fe3+ to Fe2+. Infrared spectra of fractions at 4000-500 cm-1 using FTIR revealed presence of phenolic group.
Background: Danae racemosa (L.) Moench (Ruscus racemosa L., Asparagaceae) is an erect, muchbranched evergreen shrub, native in the mountains from Syria to Iran, commonly used for its decorative green foliage in fresh flower arrangements. Despite its importance, far too little attention has been paid to gather detailed documentations of chemical constituent present in extract of D. racemosa. Methods: In this study, leaves of D. racemosa were collected from north of Iran, next, extracted via maceration followed by partitioning through solvents of different polarity. The qualitative-quantitative chemical composition of the extract was determined using high-performance liquid chromatography. Results: Two major flavonoids, quercetin and kaempferol, were separated whilst their identities were confirmed by UV-visible, shift reagents and 1H-NMR spectroscopy.
Many of nowadays diseases are due to the oxidative stress resulting from imbalance between formation and neutralization of free radicals. Intake of dietary antioxidants is therefore crucial to maintain good health. As the safety of synthetic antioxidants has raised several questions the search for natural efficient antioxidants from chemicals produced by plants has gained increased popularity in recent years. Quercetin is an abundant dietary flavonoid with well-known radical scavenging properties being often used as a reference compound in many antioxidant tests. Its reaction with 1,1-diphenyl-2-picrylhydrazyl (artificial DPPH radical) is rapid and stoichiometric; however the published inhibitory constants vary in a very wide range, from 95 nM to 226 μM. The analysis indicates the dependence of antiradical capacity of quercetin on the composition of solvent systems where the reactions are performed and also on the surrounding temperature showing somewhat higher scavenging ability at body temperature compared to room conditions. At the same time, this activity is generally independent on the initial DPPH concentration. These data highlight the importance to consider the reaction environment and conditions when predicting the redox behavior of quercetin in a certain cellular context. Moreover, due to the changes in cellular environment accompanying with different pathogeneses the redox action of polyphenols can essentially vary leading even to the situations where the well-known antioxidant quercetin may reveal prooxidant properties.
Leea, sometimes treated as the monogeneric family Leeaceae, is sister to the rest of the grape family, Vitaceae, but its systematics is poorly known. Phylogenetic relationships in Leea were reconstructed with parsimony and Bayesian methods using nuclear ribosomal sequences to assess species circumscriptions, morphological evolution and biogeography. The internal transcribed spacer secondary structure model for Leea facilitated homology assessments during sequence alignment. Nine morphological characters were mapped onto the phylogenetic tree. Four major clades in Leea were supported, with L. asiatica s.l. (=clade I) as the earliest diverging clade and having plesiomorphic free stamens. Clade II, which includes the prickle-bearing species, is sister to clade III, which includes species with comparatively large flowers. Clade IV, sister to clade II + III, was resolved into four subclades. Each subclade included accessions of L. indica and L. guineensis intermixed with six other morpho-logically distinct species, showing the polyphyly of these two species as currently circumscribed. Flower colour, previously used to characterize species, was shown to be unreliable for species identification. Dating analyses estimated that Leea originated in Indochina in the Late Cretaceous (65–86.19 Mya, 95% highest posterior density). The members of the major clades later spread to India, Africa, Madagascar, South-East (SE) Asia and tropical Australasia. Major species diversification occurred in the Neogene, when dynamic environmental and geological changes in SE Asia presented new ecological niches.
Phytochemical investigation of the roots of Leea thorelii led to the isolation of nine compounds. Their structures were determined from spectroscopic data as bergenin (1), 11-O-acetyl bergenin (2), 11-O-(4'-O-methylgalloyl) bergenin (3), 3,5-dihydroxy-4-methoxybenzoic acid (4), ( - )-epicatechin (5), 4″-O-methyl-( - )-epicatechin gallate (6), ( - )-epicatechin gallate (7), microminutinin (8) and stigmasterol. Compounds 1-8 are reported for the first time from this plant, and this is also the first report of the presence of 1, 3, 4, 6 and 8 in the Vitaceae family.
Over the last decade, much research has focused on the potential health benefits of antioxidants and indeed many synthetic and natural compounds have been evaluated for their antioxidant profile. However, in several studies only a limited number of assays, often poorly validated, are used and the techniques available frequently lack specificity. These limitations may incorrectly influence the results. This review will therefore focus on several pitfalls that may emerge in vitro and in vivo antioxidant research. First, different in vitro techniques to determine antioxidant potential are discussed, including radical scavenging assays and fingerprinting methods. As a rule, a panel of different assays is indispensable to characterize and establish in vitro antioxidant activity. Furthermore, as problems of absorption, distribution, metabolism and excretion are only accounted for by in vivo studies, the need for in vivo antioxidant research is pointed out. Several methods to characterize the in vivo activity of antioxidants, including major drawbacks and pitfalls of some assays, have been discussed. The availability of both a representative “oxidative stress” animal model and a battery of well-validated assays to assess the broad diversity of oxidative damage and antioxidative defence parameters, are crucial for antioxidant research in vivo.
This review reports the occurrence of flavonoids in subtribe Centaureinae of Asteraceae family. It extensively covers the literature up to 2010 and collects all available (13) C-NMR data.
This TDR/WHO project was carried out from 2003 to 2005 in an 0.1-ha biodiversity plot in the Altos de Campana National Park to discover novel active antiparasitic and larvicidal compounds in Panamanian plants. One-hundred-fifty organic plant extracts representing 43 families, 73 genera, and 93 species were tested in a panel of antimalarial (Plasmodium falciparum. W2, chloroquine resistant), antileishmanial (Leishmania mexicana. amastigotes), antitrypanosomal (Trypanosoma cruzi. trypomastigotes), and larvicidal (Aedes aegypti.) screens. Of these 150 plant extracts, two (1.3%) (Talisia nervosa. and Topobea parasitica.) showed significant antimalarial activity (IC50 values < 10 µg/ml), two (1.3%) (Cestrum megalophyllum. and Zanthoxylum acuminatum.) weak antileishmanial activity (IC50 values ranging from 10 to 20 µg/ml), one (0.6%) (Zanthoxylum acuminatum.) weak antitrypanosomal activity (IC50 values ranging from 10 to 20 µg/ml), and one (0.6%) (Piper fimbriulatum.) larvicidal activity (LC100 values < 30 µg/ml). Ethyl gallate (1) and methyl gallate (2) were isolated from stems of Talisia nervosa. by bioassay-guided fractionation. Both (1) and (2) showed weak in vitro. antiplasmodial activity against P. falciparum. (IC50 35.3 µM and IC50 38.0 µM, respectively), but both compounds were less active than chloroquine (IC50 0.088 µM). Moreover, compounds (1) (IC50 33.1 µM) and (2) (IC50 33.6 µM) showed weakly antileishmanial activity (miltefosine: IC50 0.5 µM), but they were not cytotoxic to Vero mammalian cells.
A new megastigmane diglycoside, leeaoside, was isolated along with four known compounds; benzyl O-α-l-rhamnopyranosyl-(1→6)-β-d-glucopyranoside, quercetin 3-O-α-l-rhamnopyranoside, myricetin 3-O-α-l-rhamnopyranoside and citroside A from the leaves of Leea thorelli. The structure determinations were based on physical data and spectroscopic evidence.
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Phytochemical investigations of Calotropis procera leaves have led to the isolation of two new compounds: quercetagetin-6-methyl ether 3-O-β-D- ⁴ C 1 -galacturonopyranoside () and (E)-3-(4-methoxyphenyl-2-O-β-D- ⁴ C 1 -glucopyranoside)-methyl propenoate ( 4 ), along with eleven known metabolites: nine flavonol and two cinnamic acid derivatives. All metabolites were isolated for the first time from the genus Calotropis, except for 1 isolated previously from Calotropis gigantea. The structures were determined by spectroscopic methods (UV, ESI-MS, ¹ H, ¹³ C NMR, ¹ H- ¹ H COSY, HSQC, and HMBC). The radical scavenging activity of the aqueous methanol extract and compounds 8 - 13 was measured by the 1,1-diphenyl- 2-picrylhydrazyl (DPPH) method. Cytotoxic screening of the same compounds was carried out on brine shrimps as well
A 1,1-diphenyl-2-picrylhydrazyl (DPPH)-activity-directed fractionation was used to target antioxidant constituents of the ethyl acetate fraction obtained from a 20% aqueous methanol crude extract of Croton zambesicus leaf. Repeated column chromatography of the fraction on silica gel and Sephadex LH-20 led to the isolation of a new natural product, identified as quercetin-3-O-β-6″(p-coumaroyl) glucopyranoside-3'-methyl ether, helichrysoside-3'-methyl ether (1), along with kaempferol-3-O-β-6″(p-coumaroyl) glucopyranoside, tiliroside (2) and apigenin-6-C-glucoside, isovitexin (3) as the antioxidant constituents. The structures of the isolated compounds were elucidated using spectroscopic techniques, namely NMR (1D and 2D) and mass spectrometry. Compounds 1 and 2 are reported from this species for the first time. In the qualitative antioxidant assay, the three isolated compounds instantly bleached the DPPH (0.2% MeOH) purple colour indicating antioxidant activity. In the quantitative antioxidant assay, all the isolated compounds demonstrated weak antioxidant activity compared to quercetin and rutin used as positive control antioxidant agents. The compounds displayed little to no cytotoxicity against Vero cells in an in vitro assay. The presence of these antioxidant compounds in the leaf extract of C. zambesicus could provide a rationale for the ethnomedicinal use of the plant in the management of oxidative-stress-related diseases in folk medicine.
Diabetes is one of the most prevalent chronic diseases throughout the world. The majority of its complications arise from vascular-related inflammation apparently initiated by endothelial cell injury. One cause of this injury has been attributed to hyperglycaemia-induced reactive oxygen species. Consequently, current drug developmental strategy has targeted specific inflammatory and oxidative stress pathways for the prevention of diabetic vascular complications. Herbal medicines have traditionally been used for the treatment of diabetes and its complications. In fact, current pre-clinical and clinical studies have demonstrated that many of them exhibit potent anti-inflammatory and anti-oxidative properties, and have also identified the active phytochemicals responsible for their activities. The present review summarises the latest research on the molecular mechanisms of diabetic vascular complications, and evaluates the level of scientific evidence for common herbal medicines and their bioactive phytochemicals. These agents have been shown to be effective through various mechanisms, particularly the NF-κB signalling pathways. Overall, herbal medicines and nutraceuticals, as well as their bioactive components, which exhibit anti-inflammatory and anti-oxidative properties, provide a promising approach for the prevention and treatment of diabetic complications.
The ethyl acetate extract of Piliostigma reticulatum leaves was investigated for its antioxidant constituents. Isolated secondary metabolites of the leaves extract include: 2-O-( p -hydroxyphenyl)-5-hydroxy-6-C-methyl-7-methoxychromone (piliostigmin) 1, 6-C- methylkaempferol- 3-methyl ether 2, quercetin 3, quercetrin (quercetin-3-O-rhamnose) 4, and Isoquercetrin (quercetin-3-O-glucoside) 5. These compounds were evaluated for their antioxidant potentials. A rapid test for antioxidants using DPPH (1,1-dipheny-2-picryhydrazyl) TLC screening, demonstrated considerable radical scavenging activity for all the compounds. The DPPH spectrophotometric method was employed for quantitative determination of radical scavenging activity. The activity was expressed as EC<sub>50</sub> value, which ranges between 4.68�0.03 and 50.76�1.71 for the flavonoids constituent.
The aim of the present study is to evaluate and compare the antioxidant potential of the leaves extracts of Annona senegalensis (Annonaceae) of Togo versus the one of Burkina Faso. To this end, aqueous methanol and ethyl acetate extracts by splitting and by steeping were achieved and the determination of total polyphenols of which flavonoids was carried out. A survey of the antioxidant activity using the DPPH methods was performed. The content in total polyphenol (3.47 ± 0.03%) and flavonoid (2.33 ± 0.17%) of 70% (v/v) aqueous methanol extract of the specimen from Togo was significantly higher than the one from Burkina (2.66 ± 0.08 and 1.64 ± 0.04%, respectively) (p<0.00001 for total polyphenol; p<0.05 for total flavonoid), whereas, the amount of total flavonoid in the ethyl acetate extract of the species from Burkina (40.38%) was triplicated. For the two types of extracts, the species of Burkina Faso showed an improved antioxidant activity than the one of Togo (IC<sub>50 </sub>= 8.51 and 21.08 μg mL<sup>-1</sup> versus 12.46 and 29.22 μg mL<sup>-1</sup>, respectively) (p<0.05). These free radicals inhibition activity of the extracts may be due at least to polyphenolic flavonoids identified by means of HPLC assay performed in the preliminary study. These flavonoids were rutin and isoquercetrin as flavanols (specimen from Togo) of which are added epicatechin and catechin derivatives (flavanols) in the specimen from Burkina. The traditional use of plant leaves may imply in part this activity against the free radicals.
Changes in the phenolics composition of Pieris brassicae larvae fasted for distinct periods (1, 2, 4, 6, and 8 h) and their excrements and of Brassica oleracea L. var. costata DC leaves were determined by high-pressure liquid chromatography/UV-photo diode array detector/mass spectrometry-electrospray ionization. This is the first report following phenolics' metabolism by P. brassicae through time. The results evidence that P. brassicae sequesters and metabolizes the phenolic compounds from the host plant. In a general way, deacylation was the main metabolic reaction that took place, but deglycosylation and sulfate conjugation reactions also occur. Additionally, several kaempferol derivatives containing rhamnose, which is not common in Brassica, were found in the host plant. Attending to the bioactivities recognized for the type of identified compounds, the different materials may constitute an interesting source of bioactive compounds, namely, of highly glycosylated and acylated kaempferol and quercetin derivatives, constituting an economic advantage for producers who have great losses caused by this pest. In addition, a deeper understanding of phenolics metabolism in insects was pursued.
Thyroid peroxidase (TPO), the key enzyme in thyroid hormone biosynthesis, is inhibited by dietary flavonoids; thus, a high consumption of plants containing inhibitory flavonoids may affect thyroid function and lead to hypothyroidism. In this work, TPO inhibition by the aqueous partition of Myrcia uniflora and its isolated compounds has been evaluated. The aqueous partition of the methanolic extract of M. uniflora is able to inhibit TPO activity in vitro. Two known flavonoids were isolated and characterized by mass spectrometry and (1)H NMR from plant extracts: mearnsitrin and myricitrin. The degree of TPO inhibition produced by the aqueous solution of the flavonoids was very high, with a 50% inhibition of the original TPO activity (IC(50)) obtained at 1.97 microM mearnsitrin and at 2.88 microM myricitrin. These results suggest that the indiscriminated consumption of M. uniflora pharmaceutical products allied to the nutritional deficiency of iodine might contribute to the development of hypothyroidism and goiter.
The potential antihypertensive activity of Brazilian plants was evaluated in vitro by its ability to inhibit the angiotensin-converting enzyme (ACE). Forty-four plants belonging to 30 families were investigated. Plants were selected based on their popular use as antihypertensive and/or diuretics. The following plants presented significant ACE inhibition rates: Calophyllum brasiliense, Combretum fruticosum, Leea rubra, Phoenix roebelinii and Terminalia catappa. (c) 2007 Elsevier B.V. All rights reserved.
The antioxidant activity of the crude extract and solvent fractions obtained from the leaves of Bauhinia galpinii was evaluated in terms of capacity to scavenge 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radicals. The crude extract and the more polar solvent fractions (ethyl acetate and butanol) showed considerable antioxidant activity. The antioxidant potential of the extracts, expressed as EC50, ranged between 28.85 +/- 1.28 microg mL(-1)and 118.16 +/- 6.41 microg mL(-1). L-Ascorbic acid was used as a standard (EC50 = 19.79 +/- 0.14 microM). Bioassay guided fractionation of the two active solvent fractions led to the isolation of three flavonoid glycosides, identified as: quercetin-3-O-galactopyranoside (1), myricetin-3-O-galactopyranoside (2), and 2''-O-rhamnosylvitexin (3). These compounds are reported for the first time from this species. The structures of the compounds were determined on the basis of spectral studies (1H NMR, 13C NMR and MS). Their antioxidant potential was evaluated using a DPPH spectrophotometric assay. Compound 2 had higher and 3 had lower antioxidant activity than L-ascorbic acid. No cytotoxic effects were displayed by compounds 1 and 3, but compound 2 was cytotoxic to Vero cells (LC50 = 74.68 microg mL(-1)) and bovine dermis cells (LC50 = 30.69 microg mL(-1)).
A number of flavonoid 3', 4'-disulfates were synthesized from the corresponding 4'-sulfate esters, using sulfur trioxide-trimethylamine complex. Desulfation of the sulfate esters using aryl sulfatase demonstrated that the rate of hydrolysis of the 3'-sulfate group was slower than either the 7- or 4' groups, thus allowing the specific synthesis of flavonol 3, 3'-disulfates. The effects of ori/io-disulfation on the 13CNMR spectra of flavonoids, and the regative FAB-MS spectra of diand trisulfated flavonoids are discussed.
Introducing an oceanic, volcanic and tropical island, leads us to its plant and human inhabitants. Tisaneurs are the pillars of its popular and traditional medicine. Their high average age does not necessarily endanger the tisanerie of tomorrow. The chemical analyses made for every species lead us from empirism to a firts stage of rationality
A new natural product was isolated together with known flavonoids from the leaves of Leea guinensis (Leeaceae). It was characterized as quercetrin 3-O-α-l-rhamnopyranoside-3′-sulphate by means of spectroscopic analysis, especially 2D NMR experiments.
Three hydrophilic flavonoids were isolated and identified from leaves of Polygonum hydropiper as quercetin 3-sulphate, isorhamnetin 3,7-disulphate and tamarixetin 3-glucoside-7-sulphate. The structures were established by chemical and spectral evidence, and their antioxidative activity and effect on the generation of superoxide anion evaluated.
Quercetin 3,4′-disulphate and an equimolar mixture of two novel flavonol sulphates, quercetin 3,3′-disulphate and patuletin 3,3′-disulphate, were isolated from the butanolic extract of the leaves of Flaveria chloraefolia. Purification of these components was carried out by gel filtration, and their structures elucidated by UV, IR, 1H and 13C NMR spectroscopy, as well as FAB-MS. The effect of 3′- and 4′-sulphation on the 13C NMR spectra of flavonols is discussed.
The UV spectra of 31 naturally occurring and synthetic flavonoid sulphates were analysed in the presence of hydrochloric acid and aryl-sulphatase reagents. After the addition of HCl, the spectra of sulphated flavones showed a bathochromic shift of about 8 nm when a 3′-sulphate group was present, while bathochromic shifts of 15 to 25 nm and 35 nm were indicative of 4′-mono- and 3′,4′-disulphation, respectively. Similarly, in the flavonol series, bathochromic shifts of 15 to 20 nm were indicative of sulphation in position 3; 25 nm, of 3,3′-; 30 to 40 nm, of 3,4′-; and 48 to 53 nm, of 3,3′,4′-sulphation. The aryl-sulphatase shift was found useful in the diagnosis of flavonol 3,3′-, 3,4′-disulphates and 3,3′,4′-trisulphates, which exhibited bathochromic shifts after treatment of 7 to 10, 17 to 22, and 30 to 65 nm, respectively.
The leaves of Acacia mearnsii have been found to contain, in addition to four previously identified compounds (myricitrin, quercitrin, (+)-catechin and (+)-gallocatechin), a new flavonol glycoside for which the name mearnsitrin is proposed and the 3-glucosides of myricetin and quercetin.
METHODS for measuring antioxidants and appraising antioxidant activity appear to be of two general types. If the chemical nature of the antioxidant is known, one may strive for a test specific for the compound or group of interest; for example, the nitroprusside test for sulphydryl groups. Alternatively one may observe the inhibition of some natural oxidative process such as the β-oxidation of fats, as a function of the added antioxidant.
The increasing knowledge of various aspects of flavonoid sulphates calls for an update of previous reviews. This article describes the recent advances in their structural variation and distribution patterns in plants. The methods used in their photochemical analysis and structural determination are outlined. Furthermore, the recently developed chemical and enzymatic methods for the synthesis of specifically sulphated flavonoids are reviewed, and two hitherto unreported, position-specific flavonol sulphotransferases are described.
Extracts from the four plant species Atuna racemosa Raf. ssp. racemosa, Syzygium corynocarpum (A. Gray) C. Muell., Syzygium malaccense (L.) Merr. & Perry and Vantanea peruviana Macbr., traditionally used for inflammatory conditions, were fractionated using a cyclooxygenase-1 catalysed prostaglandin biosynthesis in vitro assay. The flavan-3-ol derivatives (+)-catechin, (+)-gallocatechin, 4'-O-Me-ent-gallocatechin, ouratea-catechin and ouratea-proanthocynidin A were isolated as active principles. The IC50 values ranged from 3.3 microM to 138 microM whilst indomethacin under the same test conditions had an IC50 value of 1.1 microM. The flavonol rhamnosides mearnsitrin, myricitrin and quercitrin were also isolated. When further tested for inhibitory effect on cyclooxygenase-2 catalysed prostaglandin biosynthesis, the five flavan-3-ol derivatives exhibited from equal to weaker inhibitory potencies, as compared to their cyclooxygenase-1 inhibitory effects. The flavonol rhamnosides were inactive towards both enzymes.
Flavonoids are phenolic substances isolated from a wide range of vascular plants, with over 8000 individual compounds known. They act in plants as antioxidants, antimicrobials, photoreceptors, visual attractors, feeding repellants, and for light screening. Many studies have suggested that flavonoids exhibit biological activities, including antiallergenic, antiviral, antiinflammatory, and vasodilating actions. However, most interest has been devoted to the antioxidant activity of flavonoids, which is due to their ability to reduce free radical formation and to scavenge free radicals. The capacity of flavonoids to act as antioxidants in vitro has been the subject of several studies in the past years, and important structure-activity relationships of the antioxidant activity have been established. The antioxidant efficacy of flavonoids in vivo is less documented, presumably because of the limited knowledge on their uptake in humans. Most ingested flavonoids are extensively degraded to various phenolic acids, some of which still possess a radical-scavenging ability. Both the absorbed flavonoids and their metabolites may display an in vivo antioxidant activity, which is evidenced experimentally by the increase of the plasma antioxidant status, the sparing effect on vitamin E of erythrocyte membranes and low-density lipoproteins, and the preservation of erythrocyte membrane polyunsaturated fatty acids. This review presents the current knowledge on structural aspects and in vitro antioxidant capacity of most common flavonoids as well as in vivo antioxidant activity and effects on endogenous antioxidants.
Taxonomy of the Vitaceae -A chemical approach
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