- Polyoxygenated flavonoids from Eugenia edulis
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Leaves of Eugenia edulis contain the new polyoxygenated flavonoid derivatives, gossypetin-3,8-dimethyl ether-5-O-β-glucoside; gossypetin-3,5-dimethyl ether, and myricetin-3,5,3′-trimethyl ether. In addition, ten known polyphenolics were also isolated and identified. All structures were established on the basis of chemical and spectral evidence, including ESI-MS and 13C NMR.
- Hussein, Sahar A.M.,Hashem, Amani N.M.,Seliemb, Mohammed A.,Lindequist, Ulrike,Nawwar, Mahmoud A.M.
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- Three new flavonoids, proanthocyanidin, and accompanying phenolic constituents from Feijoa sellowiana
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Our investigation of phenolic constituents of fruits, flower buds, and leaves of Feijoa sellowiana led to the isolation of twenty-one phenolics including three new gossypetin glycosides 1-3, and also the purification of a proanthocyanidin fraction. A high-performance liquid chromatography method for simultaneous analysis of phenolic constituents was established and then used to investigate the phenolic profiles of the parts of the plant species, to show the presence of characteristic flavonoids and ellagic acid derivatives or ellagitannins in the extracts from fruits, flower buds, and leaves. The branch extract profile also suggested the presence of alkylated ellagic acids as characteristic constituents. Inhibitory effects of feijoa flavonoids on mushroom tyrosinase were seen, although in some cases this may have resulted from direct interaction with the enzyme. Cytotoxic effect of the proanthocyanidin fraction was also shown.
- Aoyama, Hiroe,Sakagami, Hiroshi,Hatano, Tsutomu
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- Preparation of Synthetic and Natural Derivatives of Flavonoids Using Suzuki–Miyaura Cross-Coupling Reaction
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Herein, we report the use of the Suzuki–Miyaura cross-coupling reaction for the preparation of a library of synthetic derivatives of flavonoids for biological activity assays. We have investigated the reactivity of halogenated flavonoids with aryl boronates and with boronyl flavonoids. This reaction was used to prepare new synthetic derivatives of flavonoids substituted at C-8 with aryl, heteroaryl, alkyl, and boronate substituents. The formation of flavonoid boronate enabled a cross-coupling reaction with halogenated flavones yielding biflavonoids connected at C-8. This method was used for the preparation of natural compounds including C-8 prenylated compounds, such as sinoflavonoid NB. Flavonoid boronates were used for the preparation of rare C-8 hy-droxyflavonoids (natural flavonoids gossypetin and hypolaetin). A series of previously unknown derivatives of quercetin and luteolin were prepared and fully characterized.
- Biedermann, David,Cva?ka, Josef,Hurtová, Martina,K?en, Vladimír,Osifová, Zuzana,Valentová, Kate?ina
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- Bioactive constituents from chinese natural medicines. XXXII.1 aminopeptidase N and aldose reductase inhibitors from sinocrassula indica: Structures of sinocrassosides B4, B5, C1, and D1-D3
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From the methanolic extract of the whole plant of Sinocrassula indica (Crassulaceae), six new flavonol glycosides, sinocrassosides B4 (1), B5 (2), C1 (3), D1 (4), D2 (5), and D3 (6), were isolated together with 30 compounds. The structures of 1-6 were elucidated on the basis of chemical and physicochemical evidence. In addition, several constituents were found to show inhibitory effects on aminopeptidase N and aldose reductase.
- Morikawa, Toshio,Xie, Haihui,Wang, Tao,Matsuda, Hisashi,Yoshikawa, Masayuki
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experimental part
p. 1438 - 1444
(2009/10/23)
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- An NADPH and FAD dependent enzyme catalyzes hydroxylation of flavonoids in position 8
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Yellow flavonols contribute to flower pigmentation in Asteraceae. In contrast to common flavonols, they show additional hydroxyl groups in position 6 and/or 8 of the aromatic A-ring in addition to the basic 5,7-hydroxylation pattern. An enzyme introducing a hydroxyl group in position 8 of flavonols and flavones was demonstrated for the first time with enzyme preparations from petals of Chrysanthemum segetum. Flavanones, dihydroflavonols and glucosylated flavonols and flavones were not accepted as substrates. The enzyme was localized in the microsomal fraction and uses NADPH and FAD as cofactors. Experiments with carbon monoxide/blue light and with antibodies specific for cytochrome P450 reductase did not indicate the involvement of a classical cytochrome P450 dependent monooxygenase in the reaction. Thus, the flavonoid 8-hydroxylase represents a novel type of hydroxylating enzyme in the flavonoid pathway. Apart from flavonoid 8-hydroxylase activity, the presence of all enzymes involved in the formation of flavonoid 7-O-glucosides in C. segetum was demonstrated. The pathway leading to 8-hydroxyflavonoids in C. segetum has been derived from enzyme activities and substrate specificities observed.
- Halbwirth, Heidrun,Stich, Karl
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p. 1080 - 1087
(2008/02/10)
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