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PubMed2004

Structural and spectroscopic study of 5,7-dihydroxy-flavone and its complex with aluminum.

The structure, stability and molar absorptivity of the complex formed between AlCl(3) and 5,7-dihydroxy-flavone in methanol were investigated using UV-Vis spectroscopy and the AM1 method. The molar ratio method and Job's method of continuous variation were applied to ascertain the stoichiometric composition of the complex in methanol at constant ionic strength. A 1:2 complex was indicated by both methods. The molar absorptivity and stability constant of the complex were determined using a simple and accurate procedure that requires solutions having the ligand and metal ion in the stoichiometric proportion. The high stability constant demonstrates that the complexation reaction is total. The structure of this complex, obtained by the quantum semi-empirical AM1 method, indicates that two classes of metal-ligand interactions are involved in the formation of the metal complex: (a) two simple covalent bonds between the aluminum atom and the oxygen atoms of o-hydroxyl groups of 5,7-dihydroxy-flavone; (b) two stronger Coulombic interactions between the aluminum atom and the carbonyl oxygen atoms of the ligand.

Aluminum↗
PubMed2003

Synthesis, X-ray crystal structure and biological properties of acetylenic flavone derivatives.

The reactions of iodoflavone with 3-methyl-3-hydroxybut-1-yne and 3-methylbut-3-en-2-yne are described and the antimicrobial and cytotoxic activities of the obtained compounds have been tested. The molecular structures of 6-(3-hydroxy-3-methylbut-1-ynyl)-flavone (1a) and 6-(3-methylbut-3-en-1-ynyl) flavone (1b) have been determined by X-ray crystallography. The planar configuration of the two compounds has been attributed to intramolecular hydrogen bond interactions. In 1a, the presence of the hydroxyl group determines a dimeric arrangement of the molecules. In both compounds in the crystal state, molecular stacking has been observed.

Acetylene↗
PubMed1979

Quantitation of polymethoxylated flavones in orange juice by high-performance liquid chromatography.

A quantitative high-performance liquid chromatographic (HPLC) procedure for the determination of the five major polymethoxylated flavones (PMFs) in orange juice has been developed. It employs a unique ternary solvent system with coupled UV-fluorescence detection. The dual detectors were employed to determine the presence of interfering substances and served as a cross check on quantitation. Stop flow UV and fluorescence scanning was used to identify peaks and determine the presence of impurities. Although all five citrus PMFs fluoresce, some HPLC fluorescence peaks were too small to be of much practical use. All five citrus PMFs could be quantitated satisfactorily with the fixed wavelength UV (313 nm) detector. The HPLC procedure has been used to evaluate each step in the preparation. The optimum extracting solvent was selected and one time consuming step was eliminated, as it was found to be unnecessary. HPLC values for nobiletin and sinensetin are in good agreement with the thin-layer chromatographic (TLC) values in the literature. HPLC values for the other three flavones were considerably lower than those reported in the literature. The HPLC procedure is considerably faster than the TLC procedure with equal or superior precision and accuracy.

Beverages↗
PubMed1996

Separation of naphthalene and flavone derivatives by micellar electrokinetic chromatography with double- and triple-chain surfactants.

Three surfactants, p-bis(2-dodecyloxymethyl-3-oxa-6-sodiosulfonatohexyloxy)benz ene (BDSB) having two sulfonate groups and two lipophilic chains, disodium 10-dodecanoyl-5,15-bis(dodecyloxymethyl)-10-aza-4,7,13,16-tetra oxa-1,19-nonadecanedisulfonate (DDBTN) having two sulfonate groups and three lipophilic chains and disodium 4,11-bis(dodecyloxymethyl)-3,6,9,12-tetraoxa-1,14-tetrade canedionate (DBTT) having two carboxylate groups and two lipophilic chains, were used in micellar electrokinetic chromatography (MEKC). Eight naphthalene derivatives were baseline separated at 10 mM BDSB or 5 mM DBTT, and five flavone derivatives at 5 mM BDSB, DDBTN or DBTT. The elution order of the naphthalene derivatives in MEKC with BDSB was identical with that with DDBTN. However, this elution order was different from that found with DBTT. In the case of the flavone derivatives, BDSB, DDBTN and DBTT produced the identical elution order. These double- and triple-chain surfactants exhibited different selectivity when compared with widely used sodium dodecyl sulfate.

Electrophoresis, Capillary↗
PubMed1998

Quantitative analysis of flavonols, flavones, and flavanones in fruits, vegetables and beverages by high-performance liquid chromatography with photo-diode array and mass spectrometric detection.

A high-performance liquid chromatographic (HPLC) separation method with photo-diode array (PDA) and mass spectrometric (MS) detection was developed to determine and quantify flavonols, flavones, and flavanones in fruits, vegetables and beverages. The compounds were analysed as aglycones, obtained after acid hydrolysis of freeze-dried food material. Identification was based on retention time, UV and mass spectra by comparison with commercial standards, and the UV peak areas were used for quantitation of the flavonoid contents. Examples of HPLC-MS, analyses of orange pulp, tomato, and apple are presented. The method has been used to screen foods on the Danish market, and the contents of flavones, flavonols, and flavanones were measured.

Beverages↗
PubMed2001

Acylated flavone C-glycosides from Cucumis sativus.

Leaves of Cucumis sativus plants treated with silicon and infected with Sphaerotheca fuliginea yielded five new acylated flavone C-glycosides identified as isovitexin 2"-O-(6"'-(E)-p-coumaroyl)glucoside (6), isovitexin 2"-O-(6"'-(E)-p-coumaroyl)glucoside-4'-O-glucoside (7), isovitexin 2"-O-(6"'-(E)-feruloyl)glucoside-4'-O-glucoside (11), isoscoparin 2"-O-(6"'-(E)-p-coumaroyl)glucoside (9), and isoscoparin 2"-O-(6"'-(E)-feruloyl)glucoside-4'-O-glucoside (12). The known flavone-glycosides isovitexin (1), saponarin (2), saponarin 4'-O-glucoside (3), vicenin-2 (4), apigenin 7-O-(6"-O-p-coumaroylglucoside) (5), isovitexin 2"-O-(6"'-(E)-feruloyl)glucoside (8) and isoscoparin 2"-O-(6"'-(E)-feruloyl)glucoside (10), were also identified in this plant material.

Acylation↗
PubMed2002

Flavones from Andrographis viscosula.

Two new 2'-oxygenated flavones, 5,7,2'-trimethoxyflavone (1). and 5,7,2',4',6'-pentamethoxyflavone (2). were isolated from the whole plant of Andrographis viscosula along with three known flavones, echioidinin (3). 5,2',6'-trihydroxy-7-methoxyflavone (4). and echioidin (5). The structures of these compounds were elucidated on the basis of 1D and 2D NMR spectral studies.

Andrographis↗
PubMed2003

A "flavone-polysaccharide" redefined as a mixture of 6-methoxyluteolin penta- and hexa-O-glycosides.

The incomplete structure proposed in 1972 for a unique "flavone-polysaccharide" compound, MF-1, from the liverwort Monoclea forsteri, has been re-examined. Rather than the proposed 8-methoxyluteolin structure with polysaccharides attached to the 7- and 4'-hydroxyls, MF-1 has been shown to be primarily a mixture of penta- and hexa-O-glycosides of 6-methoxyluteolin, which are accompanied by their luteolin analogues. MS and NMR evidence is marshalled to define the structure of MF-la as 6-methoxyluteolin 7-O-[2-O-alpha-rhamnosyl-3-O-alpha-arabinosyl-beta-glucuronide]-4'-O-[2-O-alpha-rhamnosyl-3-O-beta-xylosyl-beta-glucuronide], and MF-1b as 6-methoxyluteolin 7-O-[2-O-alpha-rhamnosyl-beta-glucuronide]-4'-O-[2-O-alpha-rhamnosyl-3-O-beta-xylosyl-beta-glucuronide]. This report is the first to provide substantive evidence for the existence of flavone penta- and hexa-O-glycosides in nature. The newly defined structure(s) for MF-1 more closely align M. forsteri with the only other species in the order Monocleales, M. gottschei.

Flavonoids↗
PubMed1998

Flavone aglycones in glandular hairs of Origanum x intercedens.

On the leaf surfaces of Origanum x intercedens numerous peltate glandular hairs producing essential oil occur. Although all glandular hairs have the same anatomical and developmental pattern, they differ in the appearance of the contents of the subcuticular space. Thus, in many hairs the subcuticular space is homogeneously filled with essential oil, whereas in others, within the mass of the oil numerous droplets constituting another phase exist. These droplets were tested for the presence of flavone aglycones. From the chloroform extract of glandular hairs, the free flavone aglycones thymusin(5,6,4'-trihydroxy-7,8-dimethoxyflavone), 5,6,4'-trihydroxy-7,3'-dimethoxyflavone, thymonin (5,6,4'-trihydroxy-7,8,3'-trimethoxyflavone), cirsimaritin (5,4'-dihydroxy-6,7-dimethoxyflavone), and genkwanin (5,4'-dihydroxy-7-methoxyflavone) have been isolated and identified by spectral methods.

Journal Article↗
PubMed2001

Artoindonesianins G-I, three new isoprenylated flavones from Artocarpus lanceifolius.

Three new isoprenylated flavones, artoindonesianins G-I (1-3), together with the two known flavones artelastofuran (4) and artelasticin (5), have been isolated from the heartwood of Artocarpus lanceifoliu. The structures of the new compounds were determined on the basis of spectroscopic data. Compounds 1-3 and 5 showed strong cytotoxicity against P-388 cells.

Flavonoids↗
PubMed2000

Evidence for protective and antioxidant properties of rutin, a natural flavone, against ethanol induced gastric lesions.

This study was designed to determine the ulcer-protecting effects of rutin, a natural flavone, against gastric lesions induced by 50% ethanol, the experimental model related to lesion pathogenesis with production of reactive species. The possible involvement of sulphydryl compounds (SH), neutrophil infiltration, and the capacity of this flavone to restrain the oxidative process produced in the gastric tissue were also investigated. The levels of thiobarbituric acid (TBA, as index of lipid peroxidation), the myeloperoxidase activity (MPO, as a marker of neutrophil infiltration), the content of mucosal sulphydryls (SH) groups and the activity of glutathione peroxidase (GSH-Px, an important antioxidant enzyme) were determined. Pretreatment with the highest dose of rutin (200 mg/kg), 120 min before 50% ethanol, resulted in the most effective necrosis prevention. TBA reactive substances in the gastric mucosa, were increased by ethanol injury, and this increase was inhibited by the administration of 200 mg/kg of rutin. However, the flavonoid was not able to modify the ethanol-induced neutrophil infiltrate expressed as myeloperoxidase activity. Exposure of the gastric mucosa to 50% ethanol induced a significant diminution in gastric non-protein SH content; this parameter also was not modified by the treatment with rutin. GSH-Px activity decreased in the gastric mucosa after ethanol-treatment. In contrast, rutin at all tested doses induced a significant increase in this enzymatic activity, higher than in control group. These results suggest that the gastroprotective effect of rutin in this experimental model appears through an anti-lipoperoxidant effect, and also by enhancement of the anti-oxidant enzymatic (GSH-Px) activity.

Animals↗
PubMed1999

Redox regulation of tumor cell toxicity by flavones from Lethedon tannaensis.

The purpose of the present work has been to seek a correlation of potential predictive value, demonstrating redox control of cytotoxicity toward human nasopharynx carcinoma (KB) cells by seven 5-hydroxy-7-methoxyflavones, together with two glycoside derivatives, all extracted from Lethedon tannaensis. In this approach, redox control is characterized by a physicochemical parameter expressing quantitatively the relative electron-donating power of the flavones, this parameter being the second order rate constant, kdelta, for quenching of singlet oxygen O2 (1deltag). This rate constant kdelta is usually related to the ability of a given molecule D to donate an electron and, thus, with the reduction potential E of the couple (D*+/D). Our results show that the flavone toxicity is linearly correlated with ease of oxidation: the higher the rate constant of reaction with singlet oxygen, the easier the oxidation, the less positive or more negative the reduction potential ((D*+/D), the higher the cytotoxicity. The results suggest new screening strategies to identify and improve potential antitumor drugs.

Antineoplastic Agents, Phytogenic↗
PubMed2001

Molecular modeling and QSAR analysis of the interaction of flavone derivatives with the benzodiazepine binding site of the GABA(A) receptor complex.

A large number of structurally different classes of ligands, many of them sharing the main characteristics of the benzodiazepine (BDZ) nucleus, are active in the modulation of anxiety, sedation, convulsion, myorelaxation, hypnotic and amnesic states in mammals. These compounds have high affinity for the benzodiazepine binding site (BDZ-bs) of the GABA(A) receptor complex. Since 1989 onwards our laboratories established that some natural flavonoids were ligands for the BDZ-bs which exhibit medium to high affinity in vitro and anxiolytic activity in vivo. Further research resulted in the production of synthetic flavonoid derivatives with increased biochemical and pharmacological activities. The currently accepted receptor/pharmacophore model of the BDZ-bs (Zhang, W.; Koeler, K. F.; Zhang, P.; Cook, J. M. Drug Des. Dev. 1995, 12, 193) accounts for the general requirements that should be met by this receptor for ligand recognition. In this paper we present a model pharmacophore which defines the characteristics for a ligand to be able to interact and bind to a flavone site, in the GABA(A) receptor. closely related to the BDZ-bs. A model of a flavone binding site has already been described (Dekermendjian, K.; Kahnberg, P.; Witt, M. R.; Sterner, O.; Nielsen, M.; Liljerfors, T. J. Med. Chem. 1999, 42, 4343). However, this alternative model is based only on graphic superposition techniques using as template a non-BDZ agonist. In this investigation all the natural and synthetic flavonoids found to be ligands for the BDZ-bs have been compared with the classical BDZ diazepam. A QSAR regression analysis of the parameters that describe the interaction demonstrates the relevance of the electronic effects for the ligand binding, and shows that they are associated with the negatively charged oxygen atom of the carbonyl group of the flavonoids and with the nature of the substituent in position 3'.

Animals↗
PubMed2001

An experimental and theoretical study of excited-state dipole moments of some flavones using an efficient solvatochromic method based on the solvent polarity parameter, E(N)(T).

The electronic absorption and fluorescence spectra of some biologically active natural flavones have been recorded at room temperature (298 K) in solvents of different polarities. The effects of the solvents upon the spectral properties are discussed. Difference in fluorescence intensity of flavones has been explained on the basis of intersystem crossing and degree of non-planarity calculated theoretically using Austin Model 1 (AM1) method. Excited-state dipole moments have been determined using the solvatochromic method based on the microscopic solvent polarity parameter, E(N)(T). A reasonable agreement has been observed between experimental and AM1 calculated dipole moment changes. Our results are found to be quite reliable in view of the fact that the correlation of the solvatochromic Stokes shifts with microscopic solvent polarity parameter, E(N)(T) is superior to that obtained using bulk solvent polarity functions for all the systems studied here.

Flavonoids↗
PubMed2001

Kinetics method for the quantitation of anthocyanidins, flavonols, and flavones in foods.

Flavonoids are important dietary constituents owing to their health-promoting properties. As a result, simplified analytic techniques are required for the population of databases with food values so that associations between dietary intake and disease risk/incidence can be established. The current research provides a simplified sample preparation procedure for the accurate estimation of food anthocyanidins, flavones, and flavonols as aglycons. Traditionally, flavonoid aglycons have been formed by acidic hydrolysis. However, some flavonoid aglycons are slowly degraded by acid. A procedure has been developed whereby anthocyanidins and flavonols are deglycosylated with HCl in 50% aqueous methanol and the resulting aglycons subsequently quantified by application of pseudo-first-order kinetics to their degradation. Flavones are also deglycosolated under similar conditions but, at appropriate temperatures, their aglycons are stable in acid, so kinetics were not required for the quantitation of this subclass of flavonoids. Catechins and flavanones were rapidly degraded under the hydrolytic conditions used in these studies.

Anthocyanins↗
PubMed2001

Phenols in citrus peel byproducts. Concentrations of hydroxycinnamates and polymethoxylated flavones in citrus peel molasses.

In addition to the main flavanone glycosides (i.e., hesperidin and naringin) in citrus peel, polymethoxylated flavones and numerous hydroxycinnamates also occur and are major phenolic constituents of the molasses byproduct generated from fruit processing. Although a small number of the hydroxycinnamates in citrus occur as amides, most occur as esters and are susceptible to alkaline hydrolysis. This susceptibility to alkaline hydrolysis was used in measuring the concentrations of hydroxycinnamates in citrus peel molasses. The highest concentrations of hydroxycinnamates occurred in molasses of orange [C. sinensis (L.) Osbeck] and tangerine (C. reticulata Blanco.) compared to grapefruit (C. paradisi Macf.) and lemon [C. limon (L.) Burm.]. Concentrations of two phenolic glucosides, phlorin (phloroglucinol-beta-O-glucoside) and coniferin (coniferyl alcohol-4-beta-O-glucoside), were also measured. Measurements of the polymethoxylated flavones in molasses from several tangerine and orange varieties showed that these compounds occurred in the highest amounts in Dancy tangerine, whereas samples from two other tangerine molasses contained significantly lower levels, similar to those in the molasses samples from late- and early/mid-season oranges.

Chromatography, High Pressure Liquid↗
PubMed1992

Flavones. 3. Synthesis, biological activities, and conformational analysis of isoflavone derivatives and related compounds.

A series of 2-alkylisoflavone derivatives 1 was prepared with the intent to study the importance of the phenyl group (at the 3-position) of the isoflavone in imparting antihypertensive activity and the substitution effects at the 2-position of isoflavone. With the exception of the 2-isopropyl analog, the antihypertensive activity of these compounds appears to have a slow onset and long duration. None of the analogs appears better than the corresponding flavone (3) and 3-phenylflavone (2) analogs. An unsuccessful attempt to correlate the relationship between antihypertensive activity and the calculated torsional angle of C2-C3-C1'-C2' is discussed. Antiinflammatory activities of these compounds along with 7-(oxypropylamine)flavones were also evaluated and found to be not very potent. The antiinflammatory activity appears to be sensitive to steric effects of the alkyl group on the nitrogen and of substituents at the 2-position of the isoflavones, while the hydroxyl group of the propanolamine side chain is not essential.

Animals↗
PubMed2002

Refinement and evaluation of a pharmacophore model for flavone derivatives binding to the benzodiazepine site of the GABA(A) receptor.

To further develop and evaluate a pharmacophore model previously proposed by Cook and co-workers (Drug Des. Discovery 1995, 12, 193-248) for ligands binding to the benzodiazepine site of the GABA(A) receptor, 40 new flavone derivatives have been synthesized and their affinities for the benzodiazepine site have been determined. Two new regions of steric repulsive interactions between ligand and receptor have been characterized, and the receptor region in the vicinity of 6- and 3'-substituents has been mapped out. 2'-Hydroxy substitution is shown to give a significant increase in affinity, which is interpreted in terms of a novel hydrogen bond interaction with the previously proposed hydrogen bond-accepting site A2. On the basis of the results of these studies and the refined pharmacophore model, 5'-bromo-2'-hydroxy-6-methylflavone, the highest affinity flavone derivative reported so far (K(i) = 0.9 nM), was successfully designed. A comparison of the pharmacophore model with a recently proposed alternative model (Marder; et al. Bioorg. Med. Chem., 2001, 9, 323-335) has been made.

Animals↗