Structure-antioxidant activity relationships, QSAR, DFT calculation, and mechanisms of flavones and flavonols (original) (raw)
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Quantum chemical QSAR study of flavones and their radical-scavenging activity
Medicinal Chemistry Research, 2007
Flavonoid antioxidants act as scavengers of free radicals by rapid donation of a hydrogen atom. This quantitative structure-activity relationship (QSAR) study of flavones was carried by using selected quantum chemical descriptors. PM3 calculations performed by MOPAC 2000 associated with Cache pro. Molecular weight, dielectric energy (kcal/mole), total energy (Hartree), heat of formation (kcal/mole), highest unoccupied molecular orbital (HOMO) energy (eV), lowest unoccupied molecular orbital (LUMO) energy (eV), log P, molar refractivity (MR), hardness (g), softness (S), chemical potential (l), electrophilicity index (x), etc. were tested as descriptors, and various QSAR models were constructed. The best-fit model (r 2 CV ¼ 0:92; r 2 ¼ 0:96) involved heat of formation, log P, MR, and molecular weight. The overall study indicates that steric bulk and solvation are mainly responsible for the radical scavenging activity of flavones.
Flavonoid antioxidants: chemistry, metabolism and structure-activity relationships
The Journal of Nutritional Biochemistry, 2002
Flavonoids are a class of secondary plant phenolics with significant antioxidant and chelating properties. In the human diet, they are most concentrated in fruits, vegetables, wines, teas and cocoa. Their cardioprotective effects stem from the ability to inhibit lipid peroxidation, chelate redox-active metals, and attenuate other processes involving reactive oxygen species. Flavonoids occur in foods primarily as glycosides and polymers that are degraded to variable extents in the digestive tract. Although metabolism of these compounds remains elusive, enteric absorption occurs sufficiently to reduce plasma indices of oxidant status. The propensity of a flavonoid to inhibit free-radical mediated events is governed by its chemical structure. Since these compounds are based on the flavan nucleus, the number, positions, and types of substitutions influence radical scavenging and chelating activity. The diversity and multiple mechanisms of flavonoid action, together with the numerous methods of initiation, detection and measurement of oxidative processes in vitro and in vivo offer plausible explanations for existing discrepancies in structure-activity relationships. Despite some inconsistent lines of evidence, several structureactivity relationships are well established in vitro. Multiple hydroxyl groups confer upon the molecule substantial antioxidant, chelating and prooxidant activity. Methoxy groups introduce unfavorable steric effects and increase lipophilicity and membrane partitioning. A double bond and carbonyl function in the heterocycle or polymerization of the nuclear structure increases activity by affording a more stable flavonoid radical through conjugation and electron delocalization. Further investigation of the metabolism of these phytochemicals is justified to extend structure-activity relationships (SAR) to preventive and therapeutic nutritional strategies. .
Structure-Radical Scavenging Activity Relationships of Flavonoids
Croatica Chemica Acta
The relationship between the structural characteristics of 29 flavonoids and their antiradical activity was studied. The obtained results suggest that the free radical scavenger potential of these polyphenolic compounds closely depends on the particular substitution pattern of free hydroxyl groups on the flavonoid skeleton. The possible mechanism of action of flavonoids lacking B ring OHs as free radical scavengers has been proposed.
Structure–property studies on the antioxidant activity of flavonoids present in diet
Free Radical Biology and Medicine, 2005
The screening of natural flavonoids for their bioactivity as antioxidants is usually carried out by determinination of their profile as chainbreaking antioxidants, by the evaluation of their direct free radical-scavenging activity as hydrogen-or electron-donating compounds. Since this may not be the only mechanism underlying the antioxidant activity it is important to check the ability of these compounds to act as chelators of transition metal ions. Accordingly, in the present study the acidity constants of catechin and taxifolin, as well as the formation constants of the corresponding copper (II) complexes, were investigated by potentiometry and/or spectrophotometry. Moreover, a detailed quantitative examination of the coordination species formed is presented. In addition, the partition coefficients of both catechin and taxifolin in a biomimetic system (micelles) were determined, since these properties may also contribute to the antioxidant behavior of this type of compound. The log P values determined depend on the electrostatic interactions of the compounds with the differently charged micelles (the highest values were obtained for zwitterionic and cationic micelles). The prooxidant behavior of the compounds was assessed through the oxidation of 2V-deoxyguanosine, induced by a Fenton reaction, catalyzed by copper. The data obtained reveal that the flavonoids under study did not present prooxidant activity, in this particular system. The results obtained are evidence of a clear difference among the pK a , the complexation properties, and the lipophilicity of the flavonoids studied, which can partially explain their distinct antioxidant activity. The most stable geometries of the free compounds were determined by theoretical (ab initio) methods, in order to properly account for the electron correlation effects which occur in these systems, thus allowing a better interpretation of the experimental data.
Proceedings of the National Academy of Sciences, India Section B: Biological Sciences, 2015
The recent advances in the field of computational data production and analyses have made it easier to formulate the relationship involved between physiological properties of chemical compounds and their structures. Flavonoids are one such group of plant products that are known for exhibiting strong anti-oxidant properties owing to their radical scavenging nature. These properties establish them as important anti-cancer compounds along with being anti-bacterial, antifungal, anti-viral and anti-allergic molecules. This study aims at establishing a quantitative structure activity relationship between flavonoid structure and their anti-oxidant property. A number of molecular descriptors were calculated namely, SdsCHE-index, MMFF_2, MMFF_6, chi1, XcompDipole, T_O_O_6, MMFF_5, ?vePotentialSurfaceArea, and MMFF_29 which were chosen to build the model to elucidate crucial structural features that enhance or decrease this property. A statistically robust QSAR model was obtained with an r 2 value of 0.8765, cross validation coefficient, q 2 value of 0.7189 and pred_r 2 value of 0.5795, well above the threshold. The selected descriptors and their contribution to the regression model indicate towards the respective properties that they denote. A decrease in positively charged surface area, a high dipole moment, high number of aromatic carbon atom distribution signifies the importance of unsaturated rings, and hydroxyl groups etc. enhance the anti-oxidant activity. Thus, the present study and thus induce understanding of the structural properties of flavonoids that influence their physiological properties.
On the antioxidant properties of three synthetic flavonols
Die Pharmazie, 2007
The antioxidant properties of a series of synthetic and natural flavonoids towards the oxygenated species superoxide radical anion (O 2 .-) enzimatically generated, were evaluated. 7-Hydroxyflavonol, 7,3 0-dihydroxyflavonol and 3 0-hydroxyflavonol were synthesised, with a systematic variation of the OH substitution on positions C3, C7, C3 0 and C4 0 , and their respective antioxidative abilities compared to those of the already characterised natural flavonoids quercetin, kaempferol and rutin. The efficiency of O 2 .-deactivation by the flavonoids does not correlate with their respective determined oxidation potentials, suggesting that the pure one-electron-transfer-mechanism of O 2 .-quenching could not be the main scavenging process involved. Experimental evidence demonstrated that the possible inhibition of the O 2 .-generator enzymatic system by the flavonoids must be disregarded as a possible indirect cause for the inhibition of the oxidative species. One possible mechanism for the inhibition of O 2 .-, highly dependent on the substitution pattern of the flavonoid, may be the generation of hydroperoxides or dioxetanes as oxidation products, as already postulated for other biologically relevant compounds. The simultaneous OH-substitution on positions C3 and C7 of the flavonoid skeleton plays a definitive role in the enhancement of the O 2 .-inhibitory effect. The replacement of OH by a O-rutinosyl group on position C7 suppresses at all that effect, whereas the absence of an OH group in position 7 significantly reduces the antioxidative power. Finally, the presence of OH groups on positions 3 0 and 4 0 does not produce any determinant effect in the antioxidative behaviour of the flavonoids.
Antioxidant properties of hydroxy-flavones
Free Radical Biology and Medicine, 1996
The antioxidant properties of 24 hydroxy-flavones were evaluated. Results show that 2',3 ',4'-OH substitution on the B ring plays a crucial role in radical scavenger activity in the DPPH assay and in the inhibitory effect on pereoxydation of tissue lipids in the MDA test. The formation of stable radicals for this type of compounds has been studied by ESR. In addition, it has been found that 7-hydroxy-flavones are potent competitive inhibitors of xanthine oxidase. It is proposed that the C-7 OH of flavones may take the place of the C-2 or C-6 OH of xanthine in the active site of the enzyme. A C-4' OH or C-4' OMe substitution on the 7-hydroxy flavones is not favourable to a fit in the active site. The 2',3 ',4'-trihydroxy-flavones inhibited XO by another process, which remains to be determined. In summary, this study provides evidence that hydroxy-flavones exhibit interesting antioxidant properties expressed either by the capacity to scavenge free radicals (for 2',3 ',4'-trihydroxy-flavones) or to competitively inhibit xanthine oxidase (for 7-hydroxy-flavones). These compounds may be drug candidates for treating pathologies related to free radical oxidation.
SAR and QSAR of the Antioxidant Activity of Flavonoids
Current Medicinal Chemistry, 2007
Flavonoids are a group of naturally occurring phytochemicals abundantly present in fruits, vegetables, and beverages such as wine and tea. In the past two decades, flavonoids have gained enormous interest because of their beneficial health effects such as anti-inflammatory, cardio-protective and anticancer activities. These findings have contributed to the dramatic increase in the consumption and use of dietary supplements containing high concentrations of plant flavonoids. The pharmacological effect of flavonoids is mainly due to their antioxidant activity and their inhibition of certain enzymes. In spite of abundant data, structural requirements and mechanisms underlying these effects have not been fully understood. This review presents the current knowledge about structure-activity relationships (SARs) and quantitative structure-activity relationships (QSARs) of the antioxidant activity of flavonoids. SAR and QSAR can provide useful tools for revealing the nature of flavonoid antioxidant action. They may also help in the design of new and efficient flavonoids, which could be used as potential therapeutic agents.
Structure–antioxidant activity relationships of flavonoids isolated from different plant species
Food Chemistry, 2005
Anti-DPPH radical effect as well as anti-peroxide activity of o-hydroxyl, o-methoxy, and alkyl ester derivatives of p-hydroxybenzoic acid in a bulk fish oil system and its O/W emulsion were investigated. Electronic phenomena, intra-and/or intermolecular hydrogen bonds, interfacial properties, and chemical reaction of the solvent molecules with phenolic compounds were considered to be mainly involved in the antiradical activities observed. Antioxidant activity of the phenolic acids derivatives as a function of these factors was variously affected by the environmental conditions which may occur in practice.