On the antioxidant properties of three synthetic flavonols (original) (raw)

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. .

Flavonoids as superoxide scavengers and antioxidants

Free Radical Biology and Medicine, 1990

The superoxide anions scavenging activity and antioxidation of seven flavonoids-quercetin, rutin, morin, acacetin, hispidulin, hesperidin, and naringin-were studied. The superoxide anions were generated in a phenazin methosulphate-NADH system and were assayed by reduction of nitroblue tetrazolium. The scavenging activity ranked: rutin was the strongest, and quercetin and naringin the second, while morin and hispidulin were very weak. The concentration values yielding 50% inhibition of lipid peroxidation in mouse liver homogenate were in order of 10-6 M for quercetin, rutin, and morin; and of 10-5 M for acacetin and hispidulin, while naringin and hesperidin had no antioxidative action. In comparison with the antioxidative and scavenging activities of flavonoids, there are no correlations.

Antioxidant and Antiradical Activities of Flavonoids

Journal of Agricultural and Food Chemistry, 2001

The relationship between the structure of 42 flavonoids and their antioxidant and antiradical activities was elucidated by heat-induced oxidation in a-carotene and linoleic acid system and by the 1,1-diphenyl-2-picrylhydrazyl decoloration test. From seven structurally divergent groups of flavonoids, only flavonols with a free hydroxyl group at the C-3 position of the flavonoid skeleton showed high inhibitory activity to-carotene oxidation. Antiradical activity depended on the presence of a flavonol structure or free hydroxyl group at the C-4′ position. The effect of the 4′-hydroxyl was strongly modified by other structural features, such as the presence of free hydroxyls at C-3 and/or C-3′ and a C2-C3 double bond.

Structureactivity relationship of flavonoids with superoxide scavenging activity

Biological Trace Element Research, 1995

The superoxide scavenging activities of 12 flavonoids were measured. The superoxide anions were generated by a hypoxanthine-xanthine oxidase system and measured by the nitrite method. The results showed that the scavenging ability enhanced with an increasing number of hydroxyl groups in rings B. Substitution at C3 position with a hydroxyl group increased the activity. Compared to a methoxyl group or a glycoside in this position, a free hydroxyl group showed the highest activity. A saturated C2−C3 bond showed a higher activity than a unsaturated bond. The absence of a carbonyl group at C4 position increased the activity.

Comparative Study of the Antioxidative Potential of Common Natural Flavonoids and Isoflavonoids

Korean Journal of Microbiology and Biotechnology, 2013

Oxygen (O 2 ) gets reduced to oxygen-derived free radicals such as superoxide, hydrogen peroxide, hydroxyl, and nitric oxide radicals during the normal physiological and metabolic processes in the human body . These reactive oxygen species (ROS) generate oxidative stress in the body [9] which affects cell proteins, lipids and carbohydrates, leading to a number of physiological disorders, cancer, cardiovascular disorders, and neurological disorders, and is involved in the process of aging . Many plants often contain substantial amounts of antioxidants such as vitamin C and E, carotenoids, flavonoids and tannins to neutralize excess ROS. These natural compounds can therefore be utilized to scavenge those free radicals from the human body. Antioxidants are widely used as food additives to provide protection against oxidative degradation of foods. Since ancient times, spices added to different types of food to improve flavors have also been recognized for their antioxidant capacities . In order to prolong the storage stability of foods, synthetic antioxidants such as butylated hydroxytoluene and butylated hydroxyanisole are used for industrial processing. However, these compounds are inappropriate for chronic human consumption.

Protection of Flavonoids Against Lipid Peroxidation: The Structure Activity Relationship Revisited

Free Radical Research, 2014

The inhibition of the lipid peroxidation, induced by iron and ascorbate in rat liver microsomes, by phenols and flavones was studied. The activity of phenol was enhanced by electron donating substituents, denoted by the Hammett sigma (s ). The concentration of the substituted phenols giving 50% inhibition (IC 50 ) of lipid peroxidation gave a good correlation with the s of the substituent ðlnð1=IC 50 Þ ¼ 28:92s þ 5:80 ðR ¼ 0:94; p , 0:05ÞÞ: In flavones two pharmacophores for the protection against lipid peroxidation were pinpointed: (i) a catechol moiety as ring B and (ii) an OH-group at the 3 position with electron donating groups at the 5 and/or 7 position in the AC-ring. An example of a flavone with the latter pharmacophore is galangin (3,5,7-trihydroxyflavone) where the reactivity of the 3-OH-group is enhanced by the electron donating effect of the 5-and 7-OH-groups. This is comparable to the effect of electron donating substituents on the activity of phenol.

Antioxidant properties of flavonoids

Abstrak Flavonoids, metabolit sekunder terbanyak yang bersumber dari tanaman, telah lama dimanfaatkan sebagai obat tradisional dan secara ilmiah juga telah terbukti memiliki efek farmakologi. Senyawa ini juga memiliki beragam manfaat terhadap kesehatan sehingga sangat berpotensi sebagai bahan baku untuk pengembangan obat baru. Penelitian terbaru memaparkan pemanfaatan flavonoids sebagai antioksidan untuk penyakit akibat radikal bebas. Sari pustaka ini menyoroti peran flavonoid sebagai anti oksidan. Abstract Flavonoids represent a remarkable group of plant secondary metabolites and have long been used as traditional medicines with scientifically proven pharmacological benefits. They serve vast-ranging medicinal activities that may lead drug discovery with novel and potential therapeutic evidence. Latest research magnifies primarily functional activity of flavonoids as antioxidant against oxidative stress. This review enlightens the prospective role of flavonoids as antioxidant.

Vasorelaxant and Antioxidant Activity of Flavonols and Flavones: Structure-Activity Relationships

Journal of Cardiovascular Pharmacology, 2005

We investigated the structure-activity relationships regarding vascular and antioxidant activity of a range of synthetic flavonols and flavones with 3 or fewer hydroxyl (OH) or methoxyl substitutions. The relaxant responses and ability of the flavones/flavonols to inhibit phenylephrine (PE)-and Ca 2+ -induced contraction was determined in rat isolated thoracic aorta. The ability of these compounds to reduce the level of superoxide and preserve endotheliumdependent relaxation in the presence of oxidative stress was also examined. Four compounds impaired contraction to PE or Ca 2+ , in the potency order 3#-hydroxyflavonol . 3#,4#-dihydroxyflavonol . 7,4#-dihydroxyflavonol . 3#,4#-dihydroxyflavone. Flavonol, 3#,4#dimethoxyflavonol, and flavone were significantly less active. The flavonoids caused concentration-dependent reductions in superoxide produced by rat aorta in the presence of NADPH. The most active compounds, 3#,4#-dihydroxyflavonol and 7,4#-dihydroxyflavonol, preserved endothelium-dependent relaxation in the presence of oxidative stress caused by pyrogallol or xanthine/xanthine oxidase. The results indicate that the catechol group is not critical for vascular relaxant or antioxidant activity, but rather, the important determinants for higher vascular and antioxidant activity of these compounds are the presence of a C 3 OH group and the total number of OH substituents, respectively. These results have allowed the identification of the structural characteristics that promote vascular and antioxidant activity of flavonols, which may lead to the development of agents useful in treatment of cardiovascular disease.

Antioxidant activity of flavonoids: Efficiency of singlet oxygen (< sup> 1 Δ< sub> g) quenching

… of Photochemistry and …, 1993

Flavonoids, polyphenolic pigments widely present in plants, have been reported to act as scavengers of various oxidizing species. However, most often an overall antioxidant effect was measured. In this paper we report the results of a systematic study of the reactivity of 13 selected flavonoids (from the flavonol, flavone, flavanone and flavane families) with singlet oxygen ('O,('A&) in order to establish a structure-activity relationship. The rate constants of the chemical reaction of these flavonoids with '0,(/c,) and their rate constants of '02 physical quenching (k,) have been determined by kinetic measurements and near-IR singlet oxygen luminescence.