Flavones

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Matthias Beller - One of the best experts on this subject based on the ideXlab platform.

Li Li - One of the best experts on this subject based on the ideXlab platform.

  • studies on the Flavones using liquid chromatography electrospray ionization tandem mass spectrometry
    Journal of Chromatography A, 2004
    Co-Authors: Wei Wu, Li Li
    Abstract:

    Fragmentation pathways of nine flavone compounds have been studied by using electrospray ionization multi-stage tandem mass spectrometry (ESI-MSn). Analyzing the product ion spectra of flavonoids and aglycones, we observed some diagnostic neutral losses, such as *CH3, H2O, residue of glucose and gluconic acid, which are very useful for the identification of the functional groups in the structures. Furthermore, specific retro Diels-Alder (RDA) fragments for Flavones with different hydroxyl substitution have also been discussed. The information is helpful for the rapid identification of the location site of hydroxyl substitution on Flavones. Fragmentation pathways of C-glycosidic flavonoid have also been discussed using ESI-MSn, demonstrating ions [M-H-60](-), [M-H-90](-), [M-H-120](-) are characteristic ions of C-glycosidic flavonoid. According to the fragmentation mechanism of mass spectrometry and HPLC-MS data, the structures of seven Flavones in Scutellaria baicalensis Georgi have been identified on-line without time-consuming isolation. The HPLC-ESI-MSn method for analyzing constituents in the Scutellaria baicalensis Georgi has been established.

Stefan Martens - One of the best experts on this subject based on the ideXlab platform.

  • Flavones and flavone synthases
    Phytochemistry, 2005
    Co-Authors: Stefan Martens, Axel Mithofer
    Abstract:

    Abstract Within the secondary metabolite class of flavonoids which consist of more than 9000 known structures, Flavones define one of the largest subgroups. Their natural distribution is demonstrated for almost all plant tissues. Various flavone aglyca and their O- or C-glycosides have been described in the literature. The diverse functions of Flavones in plants as well as their various roles in the interaction with other organisms offer many potential applications, not only in plant breeding but also in ecology, agriculture and human nutrition and pharmacology. In this context, the antioxidative activity of Flavones, their use in cancer prevention and treatment as well as the prevention of coronary heart disease should be emphasized. The therapeutic potential of Flavones makes these compounds valuable targets for drug design, including recombinant DNA approaches. The biosynthesis of Flavones in plants was found to be catalyzed by two completely different flavone synthase proteins (FNS), a unique feature within the flavonoids. The first, FNS I, a soluble dioxygenase, was only described for members of the Apiaceae family so far. The second, FNS II, a membrane bound cytochrome P450 enzyme, has been found in all other flavone accumulating tissues. This phenomenon is particularly of interest from the evolutionary point of view concerning the flavone biosynthesis and functions in plants. Recently, FNS I and FNS II genes have been cloned from a number of plant species. This now enables detailed biochemical and molecular characterizations and also the development of direct metabolic engineering strategies for modifications of flavone synthesis in plants to improve their nutritional and/or biopharmaceutical value.

  • molecular evolution of flavonoid dioxygenases in the family apiaceae
    Phytochemistry, 2005
    Co-Authors: Yvonne Helen Gebhardt, Simone Witte, Richard Lukacin, Gert Forkmann, Ulrich Matern, Stefan Martens
    Abstract:

    Plant species of the family Apiaceae are known to accumulate flavonoids mainly in the form of Flavones and flavonols. Three 2-oxoglutarate-dependent dioxygenases, flavone synthase or flavanone 3 β-hydroxylase and flavonol synthase are involved in the biosynthesis of these secondary metabolites. The corresponding genes were cloned recently from parsley (Petroselinum crispum) leaves. Flavone synthase I appears to be confined to the Apiaceae, and the unique occurrence as well as its high sequence similarity to flavanone 3β-hydroxylase laid the basis for evolutionary studies. In order to examine the relationship of these two enzymes throughout the Apiaceae, RT-PCR based cloning and functional identification of flavone synthases I or flavanone 3β-hydroxylases were accomplished from Ammi majus, Anethum graveolens, Apium graveolens, Pimpinella anisum, Conium maculatum and Daucus carota, yielding three additional synthase and three additional hydroxylase cDNAs. Molecular and phylogenetic analyses of these sequences were compatible with the phylogeny based on morphological characteristics and suggested that flavone synthase I most likely resulted from gene duplication of flavanone 3β-hydroxylase, and functional diversification at some point during the development of the apiaceae subfamilies. Furthermore, the genomic sequences from Petroselinum crispum and Daucus carota revealed two introns in each of the synthases and a lack of introns in the hydroxylases. These results might be explained by intron losses from the hydroxylases occurring at a later stage of evolution.

  • cloning and expression of flavone synthase ii from gerbera hybrids
    Plant Journal, 1999
    Co-Authors: Stefan Martens, Gert Forkmann
    Abstract:

    Summary In Gerbera hybrids, flavone synthesis is controlled by the locus Fns. The responsible enzyme, flavone synthase II, belongs to the NADPH-dependent cytochrome P450 monooxygenases. From two different chemogenetic defined Gerbera lines with the dominant (fns + ·) or recessive (fns fns) alleles at the locus Fns, a cytochrome P450 fragment (CypDDd7a) was isolated using a differential display technique with upstream primers based on the conserved heme-binding region of cytochrome P450 proteins. The full-length cDNA (CYP93B2) which contained the open-reading frame and part of the CypDDd7a sequence was isolated via 5′-RACE and end-to-end PCR with gene specific primers. Northern blot analysis of total RNA of Gerbera hybrids indicated that the CYP93B2 gene was only transcribed in lines with the dominant allele fns +  and that the transcript levels during flower development are in agreement with the measured enzyme activity of FNS II and flavone accumulation. Microsomes from yeast cells expressing CYP93B2 catalysed the direct formation of [14C]-Flavones from the respective [14C]-flavanones. Thus, CYP93B2 was shown to encode flavone synthase II. This is the first report of the isolation and expression of a functional FNS II cDNA clone from any species. The comparison of amino acid sequences revealed that CYP93B2 had 54% identity with the sequence of CYP93B1, which has recently been reported as a (2S)-flavanone 2-hydroxylase of Glycyrrhiza echinata L.

  • genetic control of flavone synthase ii activity in flowers of gerbera hybrids
    Phytochemistry, 1998
    Co-Authors: Stefan Martens, Gert Forkmann
    Abstract:

    In flower extracts of defined genotypes of Gerbera hybrids an enzyme activity was demonstrated which catalyses the introduction of a double bound between the C atoms 2 and 3 of the flavanones narin- genin and eriodictyol. The products formed were the corresponding Flavones, apigenin and luteolin. Similar to flavone synthases II from other plant species, the enzyme activity of this cytochrome P450-dependent monooxygenase was found to be localized in the microsomal fraction. The reaction required NADPH as cofactor and had a pH-optimum of about 7.5. Flavone synthase II activity was detectable only in flower extracts of genotypes with dominant wild-type alleles at the locus Fns, but not in lines with recessive alleles (fns fns). The results establish for the first time a correlation between a gene and the enzyme activity of fla- vone synthase II. # 1998 Published by Elsevier Science Ltd. All rights reserved

Xiao-feng Wu - One of the best experts on this subject based on the ideXlab platform.

Qing Zhao - One of the best experts on this subject based on the ideXlab platform.

  • two cyp82d enzymes function as flavone hydroxylases in the biosynthesis of root specific 4 deoxyFlavones in scutellaria baicalensis
    Molecular Plant, 2018
    Co-Authors: Qing Zhao, Olesya Levsh, Dongfeng Yang, Jie Li, Lionel Hill, Lei Yang, Yonghong Hu, Jingke Weng
    Abstract:

    Baicalein, wogonin, and their glycosides are major bioactive compounds found in the medicinal plant Scutellaria baicalensis Georgi. These Flavones can induce apoptosis in a variety of cancer cell lines but have no effect on normal cells. Furthermore, they have many additional benefits for human health, such as anti-oxidant, antiviral, and liver-protective properties. Here, we report the isolation and characterization of two CYP450 enzymes, SbCYP82D1.1 and SbCYP82D2, which function as the flavone 6-hydroxylase (F6H) and flavone 8-hydroxylase (F8H), respectively, in S. baicalensis. SbCYP82D1.1 has broad substrate specificity for Flavones such as chrysin and apigenin and is responsible for biosynthesis of baicalein and scutellarein in roots and aerial parts of S. baicalensis, respectively. When the expression of SbCYP82D1.1 is knocked down, baicalin and baicalein levels are reduced significantly while chrysin glycosides accumulate in hairy roots. SbCYP82D2 is an F8H with high substrate specificity, accepting only chrysin as its substrate to produce norwogonin, although minor 6-hydroxylation activity can also be detected. Phylogenetic analysis suggested that SbCYP82D2 might have evolved from SbCYP82D1.1 via gene duplication followed by neofunctionalization, whereby the ancestral F6H activity is partially retained in the derived SbCYP82D2.

  • a specialized flavone biosynthetic pathway has evolved in the medicinal plant scutellaria baicalensis
    Science Advances, 2016
    Co-Authors: Qing Zhao, Lionel Hill, Jingke Weng, Yang Zhang, Gang Wang, Xiaoya Chen, Cathie Martin
    Abstract:

    Wogonin and baicalein are bioactive Flavones in the popular Chinese herbal remedy Huang-Qin (Scutellaria baicalensis Georgi). These specialized Flavones lack a 4′-hydroxyl group on the B ring (4′-deoxyFlavones) and induce apoptosis in a wide spectrum of human tumor cells in vitro and inhibit tumor growth in vivo in different mouse tumor models. Root-specific Flavones (RSFs) from Scutellaria have a variety of reported additional beneficial effects including antioxidant and antiviral properties. We describe the characterization of a new pathway for the synthesis of these compounds, in which pinocembrin (a 4′-deoxyflavanone) serves as a key intermediate. Although two genes encoding flavone synthase II (FNSII) are expressed in the roots of S. baicalensis, FNSII-1 has broad specificity for flavanones as substrates, whereas FNSII-2 is specific for pinocembrin. FNSII-2 is responsible for the synthesis of 4′-deoxyRSFs, such as chrysin and wogonin, wogonoside, baicalein, and baicalin, which are synthesized from chrysin. A gene encoding a cinnamic acid–specific coenzyme A ligase (SbCLL-7), which is highly expressed in roots, is required for the synthesis of RSFs by FNSII-2, as demonstrated by gene silencing. A specific isoform of chalcone synthase (SbCHS-2) that is highly expressed in roots producing RSFs is also required for the synthesis of chrysin. Our studies reveal a recently evolved pathway for biosynthesis of specific, bioactive 4′-deoxyFlavones in the roots of S. baicalensis.

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