Antimicrobial activity and synergism of some substituted flavonoids

Natural and synthetic substituted chalcones, flavones and flavanones were tested for antibacterial activity. In order to determine synergism, new combinations of substituted flavonoids against Staphylococcus aureus, Escherichia coli and Enterobacter aerogenes were assayed. The results allow us to establish relationships between antimicrobial effect of the compounds and membrane structures of these microorganisms. When flavonoid combinations were employed a stronger effect was found against E. coli than against S. aureus. This fact is due to the existence of porins in the outer membrane of G(-)-bacteria. The compound that acts as enhancer acts by blocking the charges of amino acids in the porins and thus facilitates the passage of the other compound by diffusion into the bacterial cell.     

A fluorescence quenching test for the detection of flavonoid transformation

A novel fluorescence quenching test for the detection of flavonoid degradation by microorganisms was developed. The test is based on the ability of the flavonoids to quench the fluorescence of 1,6-diphenyl-1,3,5-hexatriene (DPH). Several members of the anthocyanidins, flavones, isoflavones, flavonols, flavanones, dihydroflavanones, chalcones, dihydrochalcones and catechins were tested with regard to their quenching properties. The anthocyanidins were the most potent quenchers of DPH fluorescence, while the flavanones, dihydroflavanones and dihydrochalcones, quenched the fluorescence only weakly. The catechins had no visible impact on DPH fluorescence. The developed test allows a quick and easy differentiation between flavonoid-degrading and flavonoid-non-degrading bacteria. The investigation of individual reactions of flavonoid transformation with the developed test system is also possible.     

Antiproliferative activity of flavonoids on several cancer cell lines.

Twenty-seven Citrus flavonoids were examined for their antiproliferative activities against several tumor and normal human cell lines. As a result, 7 flavonoids were judged to be active against the tumor cell lines, while they had weak antiproliferative activity against the normal human cell lines. The rank order of potency was luteolin, natsudaidain, quercetin, tangeretin, eriodictyol, nobiletin, and 3,3',4',5,6,7,8-heptamethoxyflavone. The structure-activity relationship established from comparison among these flavones and flavanones showed that the ortho-catechol moiety in ring B and a C2-C3 double bond were important for the antiproliferative activity. As to polymethoxylated flavones, C-3 hydroxyl and C-8 methoxyl groups were essential for high activity.     

The Structure and Distribution of the Flavonoids in Plants

6 -C₃-C₆ skeleton, have been found in plants, and are divided into several classes, i.e., anthocyanins, flavones, flavonols, flavanones, dihydroflavonols, chalcones, aurones, flavan and proanthocyanidins, isoflavonoids, biflavonoids, etc. In this review, the chemical structures of the reported flavonoid classes are introduced and their distribution in nature are described. Additionally, some recent chemotaxonomical examples using the flavonoids are also given. Received 1 June 2000/ Accepted in revised form 1 July 2000     

Structural requirements of flavonoids for inhibition of protein glycation and radical scavenging activities

To clarify the structural requirements of flavonoids for formation of advanced glycation end-products (AGEs), various flavonoids were examined. The results suggested the following structural requirements of flavonoids for the inhibition of AGEs formation: (1) as the hydroxyl groups at the 3′-, 4′-, 5-, and 7-positions increased in number, the inhibitory activities became stronger; (2) the activities of flavones were stronger than those of corresponding flavonols, flavanones, and isoflavones; (3) methylation or glucosylation of the 4′-hydroxyl group of flavones, flavonols, and flavanones reduced activity; (4) methylation or glycosylation of the 3-hydroxyl group of flavonols tended to increase activity; (5) glycosylation of the 7-hydroxyl group of flavones and isoflavones reduced activity. In addition, various flavonoids with strong AGEs formation inhibitory activity tended to exhibit strong scavenging activity for 1,1-diphenyl-2-picrylhydrazyl and superoxide anion radicals, with several exceptions.     

Structural requirements of flavonoids for nitric oxide production inhibitory activity and mechanism of action

To clarify the structure-activity relationships of flavonoids for nitric oxide (NO) production inhibitory activity, we examined the inhibitory effects of 73 flavonoids on NO production in lipopolysaccharide-activated mouse peritoneal macrophages. Among those flavonoids, apigenin (IC(50)=7.7 microM), diosmetin (8.9 microM), and tetra-O-methylluteolin (2.4 microM), and hexa-O-methylmyricetin (7.4 microM) were found to show potent inhibitory activity, and the results suggested the following structural requirements of flavonoids: (1) the activities of flavones were stronger than those of corresponding flavonols; (2) the glycoside moiety reduced the activity; (3) the activities of flavones were stronger than those of corresponding flavanones; (4) the flavones and flavonols having the 4'-hydroxyl group showed stronger activities than those lacking the hydroxyl group at the B ring and having the 3',4'-dihydroxyl group; (5) the flavonols having the 3',4'-dihydroxyl group (catechol type) showed stronger activities than those having the 3',4',5'-trihydroxyl group (pyrogallol type); (6) the 5-hydroxyl group tended to enhance the activity; (7) methylation of the 3-, 5-, or 4'-hydroxyl group enhanced the activity; (8) the activities of isoflavones were weaker than those of corresponding flavones; (9) methylation of the 3-hydroxyl group reduced the cytotoxicity. In addition, potent NO production inhibitors were found to inhibit induction of inducible nitric oxide synthase (iNOS) without iNOS enzymatic inhibitory activity.     

Lipophilic exudates of Pteridaceae - chemistry and chemotaxonomy

A number of fern species, belonging to several genera of Pteridaceae, exhibit a more or less conspicuous farinose wax, which is mostly located on the lower leaf surface. Production of these waxes is often correlated with the presence of glandular trichomes. Particularly during the past two decades, a series of publications appeared on the chemical composition of these exudates. The major components were found to be flavonoids (chalcones, dihydrochalcones, flavanones, dihydroflavonols, flavones, flavonols), some of them with a complex substitution pattern, including esters and C-methyl derivatives, and even bisflavonoids. Diterpenoids and triterpenoids can also occur in such exudates. It is the purpose of this paper to survey the chemical composition of Pteridaceae exudates and their occurrence within the genera of the family. The chemotaxonomic significance of the flavonoid aglycones at the generic, specific and populational level is briefly discussed.     

Flavonoids: structural requirements for antiproliferative activity on breast cancer cells

Several classes of flavonoids (flavones, flavanones, 2′-hydroxychalcones and flavan-4-ols) having a variety of substituents on A ring were investigated for their antiproliferative activity against MCF-7 human breast cancer cells. Structure–activity relationships of these compounds were discussed. 2′-hydroxychalcones and methoxylated flavanones were found to be potent inhibitors of MCF-7 cells growth whereas flavones and flavan-4-ols appeared to be weak inhibitory agents except 7,8-dihydroxyflavone.     

Inhibition of wheat embryo calcium-dependent protein kinase and avian myosin light chain kinase by flavonoids and related compounds.

Avian myosin light chain kinase (MLCK) is inhibited by a range of plant-derived flavonoids. Maximal inhibition requires 2,3-unsaturation and polyhydroxylation of two of the three flavonoid rings. Phosphorylation of a synthetic myosin light chain-related peptide by wheat embryo Ca(2+)-dependent protein kinase (CDPK) is also inhibited by a range of flavonoids but phosphorylation of histone preparation III-S by wheat CDPK is not inhibited by flavonoids. The structural requirements for inhibition of wheat CDPK by flavonoids are more stringent than for inhibition of avian MLCK. Potent flavonoid inhibitors of wheat CDPK are unsaturated in 2,3 position, have hydroxyl groups in positions 3' and 4' and an additional hydroxyl in the chromone ring. Flavonoid glycosylation or methylation can abolish inhibition. A number of other naturally occurring plant phenolics including chalcones and gossypol also inhibit avian MLCK and wheat CDPK. Gossypol binds to calmodulin, abolishing Ca(2+)-dependent enhancement of dansyl-calmodulin fluorescence.     

Flavonoids as chemosystematic markers in the tribe Cichorieae of the Asteraceae

This review summarizes reports on flavonoids from the Cichorieae (Lactuceae) tribe of the Asteraceae family. A total of 135 different compounds have been reported from 354 taxa belonging to 299 species, including many cultivars of common vegetables like chicory and lettuce. The reported compounds encompass flavanones (11 compounds), flavanonols (2 compounds), flavones (72 compounds), flavonols (35 compounds), anthocyanidins (9 compounds), isoflavonoids (2 compounds), chalcones (3 compounds), and an aurone. So far only 43 of the approximately 100 currently recognized genera of the tribe Cichorieae have been investigated for the occurrence of flavonoids. The distribution of the various classes of flavonoids is analyzed with regards to data from the current molecular-based reassessment of the systematics of the tribe.     

Flavonoid distribution in Pyracantha coccinea plants at different growth phases

Flavonoid composition during the ontogenetic cycle was examined in Pyracantha coccinea. The flavonoid profiles of plants at different ages showed marked differences in aerial and hypogeal parts. In the vegetative phase there are flavonoids (flavanones, flavones, and flavonols) only in the aerial parts and they appear gradually during the plant life. These secondary metabolites are detectable in the roots exclusively in the reproductive phase.     

蜂胶中的黄酮类化合物

黄酮类化合物是蜂胶中最重要的组成成分和生物活性物质.本文对国内外从蜂胶中鉴定出的黄酮类化合物进行了分类总结,给出每种成分的中英文名称及化学名称,以避免同物异名或同名异物现象的出现.本文共列出黄酮类化合物135种,其中黄酮及黄酮醇类化合物46种,二氢黄酮及二氢黄酮醇类36种,异黄酮类11种,查耳酮和二氢查耳酮类17种,以及最近几年从蜂胶中鉴定出的新黄酮类似物25种.     

Metabolomics reveals abundant flavonoids in edible insect Antheraea pernyi

The natural flavonoids in foods of plant origin have been well-characterized due to their beneficial biological properties. However, the information regarding the flavonoid compounds in edible insects remains severely limited. In the present study, we used a metabolomics approach to identify the flavonoid compounds in the Chinese oak silkworm, Antheraea pernyi Guérin-Méneville (Lepidoptera: Saturniidae), an traditional edible insect. Our study identified over 200 flavonoid metabolites in the larval midgut of A. pernyi with LC-ESI-MS/MS system. These flavonoid metabolites come from eight subclasses, including flavones (1 0 3), flavonols (34), flavonoids (28), flavanones (20), polyphenols (19), isoflavones (9), anthocyanins (9), and proanthocyanidins (4). The relative content of the flavones is the most abundant, with a value of 36.74% of the total. The top five flavonoid components in A. pernyi are hyperoside, isoquercitroside, tricin 7-O-hexoside, hesperetin 5-O-glucoside and protocatechuic acid, accounting for 51.17% of the total flavonoids. Hyperoside is the most abundant flavonoid compound (18.07% of the total) in A. pernyi. Our findings indicated targeted metabolomics is a useful approach to identify flavonoids in edible insects which contain abundant flavonoids than we already knew.     

Flavone synthase II (CYP93B16) from soybean (Glycine max L.)

Flavonoids are a very diverse group of plant secondary metabolites with a wide array of activities in plants, as well as in nutrition and health. All flavonoids are derived from a limited number of flavanone intermediates, which serve as substrates for a variety of enzyme activities, enabling the generation of diversity in flavonoid structures. Flavonoids can be characteristic metabolites, like isoflavonoids for legumes. Others, like flavones, occur in nearly all plants. Interestingly, there exist two fundamentally different enzymatic systems able to directly generate flavones from flavanones, flavone synthase (FNS) I and II. We describe an inducible flavone synthase activity from soybean (Glycine max) cell cultures, generating 7,4′-dihydroxyflavone (DHF), which we classified as FNS II. The corresponding full-length cDNA (CYP93B16) was isolated using known FNS II sequences from other plants. Functional expression in yeast allowed the detailed biochemical characterization of the catalytic activity of FNS II. A direct conversion of flavanones such as liquiritigenin, naringenin, and eriodictyol into the corresponding flavones DHF, apigenin and luteolin, respectively, was demonstrated. The enzymatic reaction of FNS II was stereoselective, favouring the (S)- over the (R)-enantiomer. Phylogenetic analyses of the subfamily of plant CYP93B enzymes indicate the evolution of a gene encoding a flavone synthase which originally catalyzed the direct conversion of flavanones into flavones, via early gene duplication into a less efficient enzyme with an altered catalytic mechanism. Ultimately, this allowed the evolution of the legume-specific isoflavonoid synthase activity.     

Antioxidant properties of di-tert-butylhydroxylated flavonoids

Epidemiological evidence suggests an inverse relationship between dietary intake of flavonoids and cardiovascular risk. The biological activities of flavonoids are related to their antioxidative effects, but they also can be mutagenic, due to the prooxidant activity of the catechol pattern. To prevent these problems, we synthesized new flavonoids where one or two di-tert-butylhydroxyphenyl (DBHP) groups replaced catechol moiety at position 2 of the benzopyrane heterocycle. Two DBHP moieties can also be arranged in an arylidene structure or one DBHP fixed on a chalcone structure. Position 7 on the flavone and arylidene or position 4 on the chalcone was substituted by H, OCH(3), or OH. New structures were compared with quercetin and BHT in an LDL oxidation system induced by Cu(II) ions. Arylidenes and chalcones had the best activities (ED(50) = 0.86 and 0.21) compared with vitamin E, BHT, and quercetin (ED(50) = 10.0, 7. 4, and 2.3 microM). Activity towards stable free radical 1, 1-diphenyl-2-picryl-hydrazyl (DPPH) was measured by log Z and ECR(50) parameters. Synthesized flavones proved to be poor DPPH radical scavengers, the activity increasing with the number of DBHP units. In contrast, arylidenes and chalcones were stronger DPPH radical scavengers (log Z > 3, 0.3 < ECR(50) < 2.12) than BHT (log Z = 0.75, ECR(50) = 12.56) or quercetin (log Z = 2.76, ECR(50) = 0.43). Unlike quercetin, synthesized compounds neither chelated nor reduced copper, proving that these new flavonoids had no prooxidant activity in vitro.     

Flavonoid 6-hydroxylase from soybean (Glycine max L.), a novel plant P-450 monooxygenase

Cytochrome P-450-dependent hydroxylases are typical enzymes for the modification of basic flavonoid skeletons. We show in this study that CYP71D9 cDNA, previously isolated from elicitor-induced soybean (Glycine max L.) cells, codes for a protein with a novel hydroxylase activity. When heterologously expressed in yeast, this protein bound various flavonoids with high affinity (1.6 to 52 microm) and showed typical type I absorption spectra. These flavonoids were hydroxylated at position 6 of both resorcinol- and phloroglucinol-based A-rings. Flavonoid 6-hydroxylase (CYP71D9) catalyzed the conversion of flavanones more efficiently than flavones. Isoflavones were hardly hydroxylated. As soybean produces isoflavonoid constituents possessing 6,7-dihydroxy substitution patterns on ring A, the biosynthetic relationship of flavonoid 6-hydroxylase to isoflavonoid biosynthesis was investigated. Recombinant 2-hydroxyisoflavanone synthase (CYP93C1v2) efficiently used 6,7,4'-trihydroxyflavanone as substrate. For its structural identification, the chemically labile reaction product was converted to 6,7,4'-trihydroxyisoflavone by acid treatment. The structures of the final reaction products for both enzymes were confirmed by NMR and mass spectrometry. Our results strongly support the conclusion that, in soybean, the 6-hydroxylation of the A-ring occurs before the 1,2-aryl migration of the flavonoid B-ring during isoflavanone formation. This is the first identification of a flavonoid 6-hydroxylase cDNA from any plant species.     

小苍兰花色色素成分及稳定性分析

以小苍兰(Freesia refracta)16个不同花色品种及后代为试验材料,对花瓣色素用特征显色反应和紫外-可见光谱扫描,分析其色素的成分和花色素苷的稳定性.结果表明,小苍兰花色的色素属于类黄酮化合物,含黄酮和花色素苷类物质,可能含有异黄酮,不含黄酮醇、二氢黄酮、二氢黄酮醇、查耳酮和橙酮,其中黄色系品种及后代还含有类胡萝卜素.避光下小苍兰花色素苷的稳定性要强于光照;温度对花瓣色素的稳定性有一定的影响.     

Structural requirements of flavonoids for inhibition of antigen-Induced degranulation,TNF-alpha and IL-4 production from RBL-2H3 cells

To clarify the structure-activity relationships of flavonoids for antiallergic activity, the inhibitory effects of various flavonoids on the release of beta-hexosaminidase, as a marker of degranulation of RBL-2H3 cells, were examined. Among them, luteolin (IC(50)=3.0 microM), diosmetin (2.1 microM), and fisetin (3.0 microM) were found to show potent inhibitory activity, and the results suggested the following structural requirements of flavonoids: (1) the 2-3 double bond of flavones and flavonols is essential for the activity; (2) the 3- or 7-glycoside moiety reduced the activity; (3) as the hydroxyl groups at the 3'-, 4'-, 5-, 6-, and 7-positions increased in number, the inhibitory activities become stronger; (4) the flavonols with a pyrogallol type moiety (the 3',4',5'-trihydroxyl groups) at the B ring exhibited less activity than those with a phenol type moiety (the 4'-hydroxyl group) or catechol type moiety (the 3',4'-dihydroxyl groups) at the B ring; (5) the activities of flavones were stronger than those of flavonols; and (6) methylation of flavonols at the 3-position reduced the activity. However, (7) several flavones and flavonols with the 4'- and/or 7-methoxyl groups did not obey rules (3), (4), and (5). In addition, several flavonoids, that is apigenin, luteolin, diosmetin, fisetin, and quercetin, inhibited the antigen-IgE-mediated TNF-alpha and IL-4 production from RBL-2H3 cells, both of which participate in the late phase of type I allergic reactions.     

FLAVONOID EVOLUTION IN ROBINSONIA (COMPOSITAE) OF THE JUAN FERNANDEZ ISLANDS

Leaf flavonoids were isolated and identified from 54 populations representing all seven species of Robinsonia, a genus of dioecious rosette trees endemic to the Juan Fernandez Islands. Fourteen compounds were detected consisting of flavonols, flavones, flavanones and dihydroflavonols. The distribution of these compounds in Robinsonia largely corresponds to specific and sectional limits based on morphological data. The morphologically similar species, R. gayana and R. thurifera, have identical flavonol profiles (derivatives of quercetin). Likewise, the closely related R. evenia and R. masafuerae are unique in the genus by possessing flavones. The inclusion of Rhetinodendron (i.e., R. berteroi) in Robinsonia is supported by its strong flavonoid similarity with species in two other sections of the genus. The morphologically diverse section Eleutherolepis exhibits the greatest flavonoid variation of any section, and only here are found flavones, flavanones and dihydroflavonols. The direction of flavonoid evolution in Robinsonia is hypothesized to be from fewer to more classes of compounds. Biosynthetic considerations suggest that this gain in compounds is due both to a gain of an additional enzymatic step and to the sequestering of precursors. This interpretation of direction of flavonoid evolution is in agreement with several lines of evidence including the flavonoid chemistry of the hypothesized outgroup (i.e., species of Senecio on mainland Chile), the ages of the two islands, and morphological trends.     

Chalcones and flavonoids as anti-tuberculosis agents

A series of flavonoids, chalcones and chalcone-like compounds were evaluated for inhibitory activity against Mycobacterium tuberculosis H37Rv. Among them, eight compounds exhibited >90% inhibition on the growth of the bacteria at a concentration of 12.5 microg/mL. Chalcones 1-(2-hydroxyphenyl)-3-(3-chlorophenyl)-2-propen-1-one (22) and 1-(2-hydroxyphenyl)-3-(3-iodophenyl)-2-propen-1-one (37) demonstrated 90 and 92% inhibition, respectively. Chalcone-like compounds (heterocyclic ring-substituted 2-propen-1-one) 1-(4-fluorophenyl)-3-(pyridin-3-yl)-2-propen-1-one (48), 1-(3-hydroxyphenyl)-3-(phenanthren-9-yl)-2-propen-1-one (49), 1-(pyridin-3-yl)-3-(phenanthen-9-yl)-2-propen-1-one (50) and 1-(furan-2-yl)-3-phenyl-2-propen-1-one (51) exhibited 98, 97, 96 and 96% inhibition, respectively. The actual minimum inhibitory concentrations (MIC), defined as the lowest concentration inhibiting 99% of the inoculum, for 22, 37, 48, 49, 50 and 51 were 20.3, 31.5, 48.3, >35.7, 6.8 and 19.2, respectively. A hydrophobic substituent on one aromatic ring, and a hydrogen-bonding group on the other aromatic ring resulted in increased anti-TB activity of the chalcones and chalcone-like compounds. Flavones and flavanones are more geometrically constrained than the corresponding chalcone analogues. The decreased activity of the flavones with respect to the chalcones may be due to the confinement of the terminal aromatic rings to the same plane.