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At least 343 records · Page 19Linked to original sources
PubMed2002

Cytotoxic flavonoids from the stem bark of Lonchocarpus aff. fluvialis.

Activity-guided fractionation of a chloroform-soluble extract of Lonchocarpus aff. fluvialis stem bark using a human epidermoid (KB) tumour cell line as a monitor afforded five rotenoids, one pterocarpan, one chalcone, three flavanones, one flavone and one triterpenoid. All of the compounds isolated proved to be of previously known structure. Among them, the rotenoids (-)-sumatrol and (+/-)-villosinol, the dibenzoylmethane derivative (+)-3,4-methylenedioxy-2'-methoxy-[2",3":4',3']-furanodibenzoylmethane, and the flavanones (-)-isoglabrachromene and (-)-candidone have been shown to exhibit significant cytotoxic activity against human cancer cells for the first time. This is the first report of the chemical constituents of this species, and the profile of compounds obtained was in accordance with the established chemosystematic patterns of species in the tribe Tephrosieae (Leguminosae, Papilionoideae).

Antineoplastic Agents, Phytogenic↗
PubMed2005

Liquid chromatography/electrospray ionization mass spectrometry for the characterization of twenty-three flavonoids in the extract of Dalbergia odorifera.

A method incorporating high-performance liquid chromatography (HPLC) with electrospray ionization and tandem mass spectrometry, with parallel analysis by HPLC with UV detection using a diode-array detector, was developed for the qualitative characterization of flavonoids in D. odorifera. Twenty-three flavonoids, including six isoflavones, six neoflavones, four isoflavanones, three flavanones, two chalcones, one isoflavanonol and one pterocarpan, were unambiguously identified by comparing their retention times, UV and MS spectra with those of authentic compounds. Furthermore, the collision-induced dissociations of the [M-H]- ions were studied to clarify the MS behavior of the different types of flavonoids. In negative ion ESI-MS all the flavonoids yielded prominent [M-H]- ions in the first order mass spectra. Fragments involving losses of CH3*, H2O, CO, C2H2O, and CO2 were observed in the MS/MS spectra. Each of the seven types of flavonoid showed characteristic MS/MS fragmentation patterns. The isoflavanones, flavanones and chalcones were observed to undergo retro-Diels-Alder fragmentations. The spectra of almost all the neoflavonoids unexpectedly exhibited only [M-H-CH3]-* radical anions as base peaks without any further fragmentation. Substitution positions also remarkably influenced the fragmentation behavior, which could assist in distinction among the flavonoid isomers. The fragmentation rules deduced here could aid in the characterization of other flavonoids of these types.

Chromatography, Liquid↗
PubMed2001

Purification and antigenicity of flavone synthase I from irradiated parsley cells.

Flavone synthase I, a soluble 2-oxoglutarate-dependent dioxygenase catalyzing the oxidation of flavanones to flavones in several Apiaceae species, was induced in parsley cell cultures by continuous irradiation with ultraviolet/blue light for 20 h. The enzyme was extracted from these cells and purified by a revised purification protocol including the fractionation on hydroxyapatite, Fractogel EMD DEAE, and Mono Q anion exchangers, which resulted in an apparently homogeneous flavone synthase at approximately 10-fold higher yield as compared to the previous report. The homogeneous enzyme was employed to raise an antiserum in rabbit for partial immunological characterization. The specificity of the polyclonal antibodies was demonstrated by immunotitration and Western blotting of the crude ammonium sulfate-fractionated enzyme as well as of the enzyme at various stages of the purification. High titer cross-reactivity was observed toward flavone synthase I, showing two bands in the crude extract corresponding to molecular weights of 44 and 41 kDa, respectively, while only the 41 kDa was detected on further purification. The polyclonal antiserum did not cross-react with recombinantly expressed flavanone 3beta-hydroxylase from Petunia hybrida or flavonol synthase from Citrus unshiu, two related 2-oxoglutarate-dependent dioxygenases involved in the flavonoid pathway.

Antibody Specificity↗
PubMed2000

Antibacterial activity of flavonoids against methicillin-resistant Staphylococcus aureus strains.

An experimental and theoretical study was performed on the anti-staphylococcal activity of 18 natural and synthetic flavonoids against methicillin-resistant Staphylococcus aureus strains. The analysed flavonoids belong to three well-differentiated structural patterns: chalcones, flavanones and flavones. The quantitative analysis of the anti-staphylococcal activity of the compounds was carried out by determining their percent inhibition degree. The hierarchical cluster analysis method was used to analyse the anti-MRSA activity of the compounds. With this methodology, the flavonoids were classified into four groups according to their anti-staphylococcal activity (high, sufficient, intermediate and low). The carbonylic region is of importance because it is part of the bioactive region inducing anti-MRSA activity in the flavonoid molecules. The introduction of OH groups in positions 2' of chalcones and 5 of flavanones (or flavones) increases flavonoid activity, while the OCH(3)groups produce the reverse effect. Using the experimental anti-MRSA activity data of flavonoids and six quantum chemical parameters calculated by means of the AM1 semiempirical molecular orbital method, a very good quantitative structure-activity relationship was obtained (confidence range: 95%; significance level for tests: 0.05; correlation coefficient=0.9842). The selected parameters explain 96.86% of the percent inhibition degree. The obtained relation is consistent with the conclusions formulated in this paper and serves as a theoretical support for some of them. Finally, it is concluded that the flavonoids chalcone, 2'(OH)-chalcone, 2',4'(OH)(2)-chalcone and 2',4(OH)(2)-chalcone might constitute promising therapeutic agents against infections with methicillin-resistant S. aureus strains.

Animals↗
PubMed1995

Heterogenous effects of natural flavonoids on monooxygenase activities in human and rat liver microsomes.

The in vitro effects of nine flavonoids on different monooxygenase activities from human and rat liver were investigated. Flavonoids belonging to different chemical classes [flavones (chrysin, tangeretin, flavone, 5,6-benzoflavone, 7,8-benzoflavone), flavonols (quercetin), and flavanones (pinocembrin, eriodictyol, flavanone)] were chosen. Ethoxyresorufin O-deethylase (EROD) and benzyloxyresorufin O-debenzylase (BROD) were selected as marker activities of P450 isoenzymes involved in carcinogen activation. Human EROD activity was inhibited by all flavonoids. Flavonoids without hydroxyl groups were more effective than those with hydroxyl groups. Flavonoids with an unsaturated flavone nucleus were more inhibitory than the corresponding saturated analogues. Similar structure-activity relationships were found in microsomes from methylcholanthrene-treated rats. The effects of flavonoids on human BROD activity were quite different from those observed on EROD activity. Nonhydroxylated flavones were effective activators. Hydroxylated flavonoids showed a biphasic effect, being activators at low concentrations and inhibitors at higher concentrations. The effects of flavonoids on BROD activity were rather similar in man and control rats.

Adult↗
PubMed1978

Pigment synthesis in maize aleurone from precursors fed to anthocyanin mutants.

Aleurone tissue of c2 Pr, C2 pr, or c2 pr genotypes can utilize either of two flavanones (naringenin, homoeriodictyol) or a flavanonol (dihydroquercetin) to synthesize anthocyanin. The anthocyanins formed have substitution patterns corresponding to those of the precursors, but c2 Pr tissue can hydroxylate the 4'-OH precursor at the 3' position. The results presented suggest that C2 acts before the flavanone step and that the hydroxylation gene (Pr) can act after C2.

Anthocyanins↗
PubMed2006

Antioxidant activity with flavonoidal constituents from Aerva persica.

A new flavanone Persinol (1) and the new flavanone glucosides persinosides A (2) and B (3), along with known flavonoids (4 and 5) have been isolated from the ethyl acetate soluble fraction of the whole plants of Aerva persica. Their structures were elucidated on the basis of extensive analysis of nuclear magnetic resonance (1D and 2D-NMR) spectral data. All of them showed profound antioxidative activities by DPPH and cytochrome-c-reduction assays using the HL-60 cell culture system.

Amaranthaceae↗
PubMed2005

In vitro free radical and ONOO- scavengers from Sophora flavescens.

Activity-guided fractionation of the CH2Cl2-soluble fraction of the roots of Sophora flavescens furnished five 1,1-diphenyl-2-picrylhydrazyl (DPPH) free radical scavengers: trans-hexadecyl ferulic acid (1), cis-octadecyl ferulic acid (2), trans-hexadecyl sinapic acid (3), (-)-4-hydroxy-3-methoxy-(6aR,11aR)-8,9-methylenedioxypterocarpan (4) and desmethylanhydroicaritin (8), along with nine known inactive compounds: (-)-maackiain (5), xanthohumol (6), formononetin (7), (2S)-2'-methoxykurarinone (9), (2S)-3beta,7,4'-trihydroxy-5-methoxy-8-(gamma,gamma-dimethylallyl)-flavanone (10), (2S)-7,4'-dihydroxy-5-methoxy-8-(gamma,gamma-dimethylallyl)-flavanone (11), umbelliferone (12), kuraridin (13), and trifolirhizin (14). Compounds 1-4 and 8 exhibited DPPH free radical scavenging effects at IC50 values of 33.01 +/- 0.20, 57.06 +/- 0.16, 39.84 +/- 0.36, 35.83 +/- 0.47, and 18.11 +/- 0.04 microM, respectively. L-Ascorbic acid, when used as a positive control, exhibited an IC50 value of 7.39 +/- 0.01 microM. Compounds 1-4 and 8 also appeared to exert significant scavenging effects on authentic ONOO-, with IC50 values of 5.76 +/- 1.19, 15.06 +/- 1.64, 8.17 +/- 4.97, 1.95 +/- 0.29, and 4.06 +/- 2.41 microM, respectively. Penicillamine (IC50 = 2.36 +/- 0.79 microM) was used as a positive control. In addition, compounds 2, 4, 6, 8, and 10 were isolated from this plant for the first time.

Free Radical Scavengers↗
PubMed2004

Flavonoids from Spatholobus suberectus.

Two pterocarpans [(6aR,11aR)-maackiain, (6aR,11aR)-medicarpin], one flavanone [(2S)-7-hydroxy-6-methoxy-flavanone], one isoflavan (sativan) and two isoflavones (pseudobaptigenin, genistein) were isolated from the Spatholobus suberectus (Leguminosae). Their chemical structures were determined by comparison of their spectroscopic parameters of CD, EIMS, 1D-NMR and 2D-NMR with those reported in the literatures. All of these compounds are reported for the first time from this plant through the present study.

Chemistry, Pharmaceutical↗
PubMed2005

Combinatorial biosynthesis of flavones and flavonols in Escherichia coli.

(2S)-Flavanones (naringenin and pinocembrin) are key intermediates in the flavonoid biosynthetic pathway in plants. Recombinant Escherichia coli cells containing four genes for a phenylalanine ammonia-lyase, cinnamate/coumarate:CoA ligase, chalcone synthase, and chalcone isomerase, in addition to the acetyl-CoA carboxylase, have been established for efficient production of (2S)-naringenin from tyrosine and (2S)-pinocembrin from phenylalanine. Further introduction of the flavone synthase I gene from Petroselinum crispum under the control of the T7 promoter and the synthetic ribosome-binding sequence in pACYCDuet-1 caused the E. coli cells to produce flavones: apigenin (13 mg/l) from tyrosine and chrysin (9.4 mg/l) from phenylalanine. Introduction into the E. coli cells of the flavanone 3beta-hydroxylase and flavonol synthase genes from the plant Citrus species led to production of flavonols: kaempferol (15.1 mg/l) from tyrosine and galangin (1.1 mg/l) from phenylalanine. The combinatorial biosynthesis of the flavones and flavonols in E. coli is promising for the construction of a library of various flavonoid compounds and un-natural flavonoids in bacteria.

Citrus↗
PubMed2005

Differential combinatorial interactions of cis-acting elements recognized by R2R3-MYB, BZIP, and BHLH factors control light-responsive and tissue-specific activation of phenylpropanoid biosynthesis genes.

Chalcone synthase (CHS), chalcone flavanone isomerase (CFI), flavanone 3-hydroxylase (F3H) and flavonol synthase (FLS) catalyze successive steps in the biosynthetic pathway leading to the production of flavonols. We show that in Arabidopsis thaliana all four corresponding genes are coordinately expressed in response to light, and are spatially coexpressed in siliques, flowers and leaves. Light regulatory units (LRUs) sufficient for light responsiveness were identified in all four promoters. Each unit consists of two necessary elements, namely a MYB-recognition element (MRE) and an ACGT-containing element (ACE). C1 and Sn, a R2R3-MYB and a BHLH factor, respectively, known to control tissue specific anthocyanin biosynthesis in Z. mays, were together able to activate the AtCHS promoter. This activation of the CHS promoter required an intact MRE and a newly identified sequence designated R response element (RREAtCHS) containing the BHLH factor consensus binding site CANNTG. The RRE was dispensable for light responsiveness, and the ACE was not necessary for activation by C1/Sn. These data suggest that a BHLH and a R2R3-MYB factor cooperate in directing tissue-specific production of flavonoids, while an ACE-binding factor, potentially a BZIP, and a R2R3-MYB factor work together in conferring light responsiveness.

Acyltransferases↗
PubMed1990

Purification and characterization of flavone synthase I, a 2-oxoglutarate-dependent desaturase.

Soluble flavone synthase I from illuminated parsley cells was purified to near homogeneity by a six-step procedure. A molecular mass of 48 +/- 2 kDa was determined by gel permeation chromatography and denaturing polyacrylamide gel electrophoresis. A single protein with an isoelectric point at pH 4.8 +/- 0.1 was detected on isoelectric focusing gels, which catalyzed the overall conversion of 2S-flavanones into the corresponding flavones in the presence of molecular oxygen, 2-oxoglutarate, ferrous ion, and ascorbate. Apparent Michaelis constants for 2S-naringenin, 2S-eriodictyol, and 2-oxoglutarate were determined as 5, 8, and 16 microM, respectively. (+)-Dihydrokaempferol and 2R-naringenin were not accepted as substrates. The enzyme was strongly inhibited by Cu2+ and Zn2+. Potent competitive inhibition with respect to 2-oxoglutarate was observed with 2,4-pyridinedicarboxylate (Ki = 1.8 microM). With crude extracts as well as with the purified enzyme neither the hypothetical intermediate 2-hydroxyflavanone nor a dehydratase activity capable of converting the chemically synthesized compound to flavone could be observed. Moreover, the introduction of the double bond into the substrate naringenin was not altered by addition of chemically synthesized 2-hydroxynaringenin into the reaction mixture. Therefore, 2-hydroxyflavanones are apparently not freely dissociable intermediates in the biosynthesis of flavones in parsley and are not capable of entering the active site of the enzyme to compete with the flavanone. It is postulated that flavone synthase I catalyzes double-bond formation by direct abstraction of vicinal hydrogen atoms at C-2 and C-3 of the substrate. Thus, flavone synthase I is a member of a novel subgroup within the 2-oxoglutarate-dependent dioxygenases that can be referred to as 2-oxoglutarate-dependent desaturases.

Carbon Radioisotopes↗
PubMed1988

Flavonoids as inhibitors of rat liver monooxygenase activities.

Flavanone and six hydroxylated derivatives, and cianidanol and eight ethers and esters thereof, were investigated as inhibitors of cytochrome P-450 mediated reactions in rat liver microsomes. The IC50 values towards aminopyrine N-demethylation varied over a 20-fold range and were shown to depend on the pattern of hydroxylation (flavanone derivatives) and on lipophilicity (cianidanol derivatives). In the latter case, a bilinear relationship exists, the optimal log P being 2.92. Using selected compounds, IC50, Km and Vmax values were determined for aminopyrine N-demethylation, biphenyl 4-hydroxylation, and biphenyl 2-hydroxylation. Depending on the inhibitor and on the activity examined, non-competitive, competitive, or mixed inhibition was seen. Interaction with cytochrome P-450 was also studied spectrally and was always found to result in a modified type II difference spectrum (ligand binding). A dual binding mode is postulated, involving electrostatic and lipophilic interactions.

Aminopyrine N-Demethylase↗
PubMed1989

Modifying role of dietary factors on the mutagenicity of aflatoxin B1: in vitro effect of plant flavonoids.

Eighteen flavonoids have been tested for their ability to inhibit the mutagenicity of aflatoxin B1 (AFB1) towards strains TA100 and TA98 of Salmonella typhimurium provided with a rat liver activation system. These flavonoids belong to 5 different groups: flavone, isoflavone, flavanone, flavanol and flavonol, and many individual members are natural products present in edible portions of a variety of food plants. Several flavonoids exhibited significant inhibitory ability in both strains. Flavonols in general are more active in this regard, while flavanones show a strain-specific response. The flavanol group of compounds did not display any activity. Among the most effective flavonoids are kaempferol, morin, fisetin, biochanin A and the glycoside rutin, all of which exhibit a dose-dependent inhibition pattern. Kaempferol and rutin, in particular, show exceptional activity inasmuch as, on a molar basis, only a 10-fold excess dose of each can inhibit the mutagenic activity of AFB1 in strain TA98 by 50%. The action of flavonoids is possibly mediated through interaction with microsomal activating enzymes. Previous evidence from this laboratory about their inhibitory action on DNA-adduct formation and metabolic activation together with the present results suggests that certain flavonoids, notably polyhydroxylated flavonols, may have potential anticarcinogenic activity against AFB1.

Aflatoxin B1↗
PubMed1996

Effects of flavonoids on rat aortic smooth muscle contractility: structure-activity relationships.

1. Flavonoids produced a concentration-dependent relaxation of the contractile responses induced by noradrenaline, KCl, or phorbol 12-myristate-13-acetate in rat aortic rings. Only the flavonoid with three contiguous hydroxyls in B rings (myricetin), at low concentrations, potentiates the contractions evoked by these agonists. 2. The relaxant effects of flavanone on the noradrenaline-induced contractions were potentiated by isoprenaline and those of morin, chrysin, flavanone, and naringenin by sodium nitroprusside. 3. Several mechanisms are implicated in the vasodilatory effects of flavonoids: inhibition of protein kinase C; inhibition of cyclic nucleotide phosphodiesterases; and/or decreased Ca2+ uptake.

Animals↗
PubMed1990

Vasodilatory active principles of Sophora flavescens root.

Flavanones vexibinol and kurarinone were isolated from an ethyl acetate extract of Sphora flavescens roots and assayed using isolated rabbit and rat thoracic aorta helical strips. These compounds inhibited KCl and norepinephrine maximum contractions in a concentration-dependent manner in the rat but only KCl contractions in the rabbit. Vexibinol and kurarinone weakly inhibited histamine- and serotonin-induced contractions in the rabbit. The results suggest that these flavanones may inhibit Ca2+ influx through a voltage-dependent Ca2+ channel.

Animals↗
PubMed1990

Aromatase inhibition by flavonoids.

Several synthetic flavones were found to inhibit the aromatization of androstenedione to estrone catalyzed by human placental microsomes. Twenty-one compounds were tested and the IC50 of the most active were: flavone, 10 microM; 7-hydroxyflavone, 0.5 microM; 7,4'-dihydroxyflavone, 2.0 microM; flavanone, 8.0 microM; and 4'-hydroxyflavanone, 10 microM. Most of the others had IC50 values ranging from 80 to greater than 200 microM. These findings show that 4'-hydroxylation results in either no change or very little change in IC50 for flavanone, isoflavone and isoflavanone as well as other ring A hydroxylated flavones. Derivatives of flavone with a hydroxyl substituent at position 5, 6 and 7 were also screened. 7-Hydroxyflavone (11) was the most effective competitive inhibitor (IC50 = 0.5 microM) with an apparent Ki value of 0.25 microM. Compound 11 also induced a change in the absorption spectrum of the aromatase cytochrome P-450 which is indicative of substrate displacement. The relative binding affinities of the flavonoid analogs were determined and only ring A adn ring B dihydroxylated analogs were found to bind to the estrogen receptor.

Animals↗
PubMed1996

Effects of flavonoids on aromatase activity, an in vitro study.

In the study, the inhibitory effect of flavonoids, including isoflavonic phytoestrogens, on the ovarian aromatase enzyme complex from the rainbow trout, Oncorhynchus mykiss, was assessed in vitro. Some of the compounds tested on fish were also tested on human placental aromatase activity as a comparison between the two sources of enzyme. It was found that flavone, dl-aminoglutethimide, apigenin, quercetin, 7,4'- dihydroxyflavone, alpha-naphthoflavone and equol were potent inhibitors of the ovarian aromatase activity in rainbow trout. Relative potencies (RP) of these compounds compared to flavone (assigned an effect of 1) were, respectively, 19.0, 8.7, 5.3, 3.7, 3.2 and 0.9. Two other phytoestrogens, namely biochanin A and genistein, slightly inhibited aromatase activity. Finally, 7-hydroxyflavone, formononetin, daidzein, coumestrol, chrysin, flavanone and estradiol-17beta did not inhibit ovarian aromatase activity at doses up to 1000 microM. Experiments on human placental aromatase showed inhibitory effects of dl-aminoglutethimide, flavone, flavanone and equol with RP values of 2.8. 1, 1.5 and 0.4, respectively. These results are in accordance with previous studies. The influence of the experimental procedure on IC50 values and RP is discussed.

Aminoglutethimide↗