Efficient Synthesis and Antioxidant Evaluation of 2‐Aryl‐3‐(Pyrimidin‐2‐yl)‐Thiazolidinones

In the present study, we reported the efficient synthesis of 11 3‐(pyrimidin‐2‐yl)‐thiazolidinones in good yields using molecular sieve as the desiccant agent. In addition, we have evaluated the antioxidant capacity of the synthesized compounds by the 2,2‐diphenyl‐2‐picrylhydrazyl hydrate (DPPH?) and the 2,2‐azinobis(3‐ethylbenzothiazoline‐6‐sulfonic acid) diammonium salt (ABTS^+?) radicals scavenging assay. Six compounds showed antioxidant activity towards DPPH? (EC₅₀ between 16.13 and 49.94 µg/mL) and also demonstrated excellent activity regarding ABTS^+? (TEAC: 10.32–53.52). These results showed that compounds 3‐(pyrimidin‐2‐yl)‐thiazolidinones may be easily synthesized by a less expensive procedure and could be a good starting point to the development of new antioxidant compounds. © 2013 Wiley Periodicals, Inc. J BiochemMol Toxicol 27:445‐450, 2013; View this article online at wileyonlinelibrary.com . DOI 10.1002/jbt.21506     

Novel 3‐Oxo‐ and 3,24‐Dinor‐2,4‐secooleanane‐Type Triterpenes from Terminalia ivorensis A. Chev.

Two new oleanane‐type triterpenes named ivorengenin A (=3‐oxo‐2α,19α,24‐trihydroxyolean‐12‐en‐28‐oic acid; 1 ) and ivorengenin B (=4‐oxo‐19α‐hydroxy‐3,24‐dinor‐2,4‐secoolean‐12‐ene‐2,28‐dioic acid; 2 ), together with five known compounds, arjungenin, arjunic acid, betulinic acid, sericic acid, and oleanolic acid, were isolated from the barks of Terminalia ivorensis A. Chev . (Combretaceae). Their structures were established on the basis of 1D‐ and 2D‐NMR data, and mass spectrometry. A biogenetic pathway to the formation of these compounds from sericic acid, isolated as the major compound from this plant, was proposed. The antioxidant activities of different compounds were investigated by means of the 2,2‐azinobis(3‐ethylbenzothiazoline‐6‐sulfonic acid) (ABTS) and 1,1‐diphenyl‐2‐picrylhydrazyl (DPPH) assays, and IC₅₀ values were calculated and compared with Trolox activity. Antiproliferative activities of the isolated compounds were also evaluated against MDA‐MB‐231, PC3, HCT116, and T98G human cancer cell lines, against which the compounds showed significant cytotoxic activities.     

An Alternative Standard for Trolox‐Equivalent Antioxidant‐Capacity Estimation Based on Thiol Antioxidants. Comparative 2,2′‐Azinobis[3‐ethylbenzothiazoline‐6‐sulfonic Acid] Decolorization and Rotational Viscometry Study Regarding Hyaluronan Degradation

Comparison of the effectiveness of antioxidant activity of three thiol compounds, D ‐penicillamine, reduced L ‐glutathione, and 1,4‐dithioerythritol, expressed as a radical‐scavenging capacity based on the two independent methods, namely a decolorization 2,2′‐azinobis[3‐ethylbenzothiazoline‐6‐sulfonic acid] assay and a rotational viscometry, is reported. Particular concern was focused on the testing of potential free‐radical scavenging effects of thiols against hyaluronan degradation, induced by hydroxyl radicals. A promising, solvent‐independent, antioxidative function of 1,4‐dithioerythritol, comparable to that of a standard compound, Trolox^®, was confirmed by the 2,2′‐azinobis[3‐ethylbenzothiazoline‐6‐sulfonic acid] assay. The new potential antioxidant 1,4‐dithioerythritol exhibited very good solubility in a variety of solvents (e.g., H₂O, EtOH, and DMSO) and could be widely accepted and used as an effective antioxidant standard instead of a routinely used Trolox^® on 2,2′‐azinobis[3‐ethylbenzothiazoline‐6‐sulfonic acid] assay.     

Phytochemical Analysis and in vitro Free‐Radical‐Scavenging Activities of the Essential Oils from Leaf and Fruit of Melaleuca leucadendra L.

The phytochemical profile of Melaleuca leucadendra L. leaf and fruit oils from Cuba was investigated by GC and GC/MS. Forty‐one and sixty‐four volatile compounds were identified and quantified, accounting for 99.2 and 99.5% of the leaf‐oil and fruit‐oil total composition, respectively. The main components were 1,8‐cineol (43.0%), viridiflorol (24.2%), α‐terpineol (7.0%), α‐pinene (5.3%), and limonene (4.8%) in the leaf oil, and viridiflorol (47.6%), globulol (5.8%), guaiol (5.3%), and α‐pinene (4.5%) in the fruit oil. The antioxidant capacity of these essential oils was determined by three different in vitro assays (2,2‐diphenyl‐1‐picrylhydrazyl (DPPH) radical, thiobarbituric acid reactive species (TBARS), and 2,2′‐Azinobis(3‐ethylbenzothiazoline‐6‐sulfonic acid) (ABTS) radical cation), and significant activities were evidenced for all of them.     

Comparison of in vitro antioxidant and antiradical activities of L-tyrosine and L-Dopa

Summary. Phenolic compounds are interesting because of their antioxidant properties. In the present study, the antioxidant properties of L-tyrosine as a monophenolic and L-Dopa as a diphenolic amino acid were investigated by using different antioxidant assays: (i) 1,1-diphenyl-2-picryl-hydrazyl free radical (DPPH^•) scavenging; (ii) 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) radical cation decolorization assay; (iii) total antioxidant activity by ferric thiocyanate method; (iv) ferric ions (Fe³⁺) reducing power; (v) superoxide anion radical (O₂ ^•−) scavenging; (vi) hydrogen peroxide (H₂O₂) scavenging, and (vii) ferrous ions (Fe²⁺) chelating activities. Butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), α-tocopherol and trolox, a water-soluble analogue of tocopherol, were used as the reference antioxidant compounds. At the same concentration (20 μg/mL), L-tyrosine and L-Dopa showed 30.6 and 67.9% inhibition of lipid peroxidation of linoleic acid emulsion, respectively. On the other hand, BHA, BHT, α-tocopherol and trolox indicated inhibitions of 74.4, 71.2, 54.7 and 20.1% on the peroxidation of linoleic acid emulsion, respectively, at the above-mentioned concentration. In addition, L-tyrosine and L-Dopa had an effect on DPPH radical scavenging, ABTS radical scavenging, superoxide anion radical scavenging, H₂O₂ scavenging, total ferric ions reducing power and metal chelating on ferrous ions activities.     

Evaluation of antioxidant activity of <Emphasis Type="Italic">Melothria maderaspatana in vitro</Emphasis>

In this study, an aqueous extract of leaves from Melothria maderaspatana was tested for in vitro antioxidant activity. Free radical scavenging assays, such as hydroxyl radical, hydrogen peroxide, superoxide anion radical and 2,2-diphenyl-1-picryl hydrazyl (DPPH), 2,2’-azinobis-(3-ethyl-enzothiazoline-6-sulfonic acid) (ABTS) radical scavenging, and reducing power assay, were studied. The extract effectively scavenged hydroxyl radical, hydrogen peroxide and superoxide anion radicals. It also scavenged DPPH and ABTS radicals. Furthermore, it was found to have reducing power. All concentrations of leaf extract exhibited free radical scavenging and antioxidant power, and the preventive effects were in a dose-dependent manner. The antioxidant activities of the above were compared to standard antioxidants such as butylated hydroxytoluene (BHT), ascorbic acid, and α-tocopherol. The results obtained in the present study indicate that the M. maderaspatana extract could be considered a potential source of natural antioxidant.     

Sulphonamides incorporating 1,3,5-triazine structural motifs show antioxidant,acetylcholinesterase, butyrylcholinesterase,and tyrosinase inhibitory profile

Abstract

A series of 16 novel benzenesulfonamides incorporating 1,3,5-triazine moieties substituted with aromatic amines, dimethylamine, morpholine and piperidine were investigated. These compounds were assayed for antioxidant properties by using 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging assay, 2,2`-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid (ABTS) radical decolarisation assay and metal chelating methods. They were also investigated as inhibitors of acetylcholinesterase (AChE), butyrylcholinesterase (BChE) and tyrosinase, which are associated with several diseases such as Alzheimer, Parkinson and pigmentation disorders. These benzenesulfonamides showed moderate DPPH radical scavenging and metal chelating activity, and low ABTS cation radical scavenging activity. Compounds 2?b, 3d and 3?h showed inhibitory potency against AChE with % inhibition values of >90. BChE was also effectively inhibited by most of the synthesised compounds with >90% inhibition potency. Tyrosinase was less inhibited by these compounds.     

Radical scavenging activity of dicaffeoyloxycyclohexanes: contribution of an intramolecular interaction of two caffeoyl residues

Six regio- and stereoisomers of dicaffeoyloxycyclohexanes and 2,4-di-O-caffeoyl-1,6-anhydro-beta-D-glucose were synthesized as model compounds of dicaffeoylquinic acids, and their radical scavenging activity was evaluated by DPPH (2,2-diphenyl-1-picrylhydrazyl) and ABTS (2,2'-azinobis(3-ethylbenzthiazoline-6-sulfonic acid) diammonium salt) radical scavenging tests. Both DPPH and ABTS radical scavenging reactions of these compounds consisted of two different steps. In the first step, catechol moieties of the caffeoyl residues were rapidly converted to o-quinone structures and no significant difference in the reactivity was observed among the tested compounds. In the second step, however, the rate of the reaction increased as the intramolecular distance of the two caffeoyl residues decreased. A novel intramolecular coupling product, which could scavenge additional radicals, was isolated from the reaction mixture of trans-1,2-dicaffeoyloxycyclohexane and DPPH radical. The result suggests that the second step of the radical scavenging reaction is arising from an intramolecular interaction between the two caffeoquinone residues to regenerate catechol structures, and that the closer their distance is, the more rapidly they react. The radical scavenging activity of natural dicaffeoylquinic acids in a biological aqueous system might also depend on the positions of caffeoyl ester groups.     

Antioxidant and radical scavenging properties of curcumin

Curcumin (diferuoyl methane) is a phenolic compound and a major component of Curcuma longa L. In the present paper, we determined the antioxidant activity of curcumin by employing various in vitro antioxidant assays such as 1,1-diphenyl-2-picryl-hydrazyl free radical (DPPH*) scavenging, 2,2'-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS) radical scavenging activity, N,N-dimethyl-p-phenylenediamine dihydrochloride (DMPD) radical scavenging activity, total antioxidant activity determination by ferric thiocyanate, total reducing ability determination by the Fe(3+)-Fe(2+) transformation method, superoxide anion radical scavenging by the riboflavin/methionine/illuminate system, hydrogen peroxide scavenging and ferrous ions (Fe(2+)) chelating activities. Curcumin inhibited 97.3% lipid peroxidation of linoleic acid emulsion at 15 microg/mL concentration (20 mM). On the other hand, butylated hydroxyanisole (BHA, 123 mM), butylated hydroxytoluene (BHT, 102 mM), alpha-tocopherol (51 mM) and trolox (90 mM) as standard antioxidants indicated inhibition of 95.4, 99.7, 84.6 and 95.6% on peroxidation of linoleic acid emulsion at 45 microg/mL concentration, respectively. In addition, curcumin had an effective DPPH* scavenging, ABTS*(+) scavenging, DMPD*(+) scavenging, superoxide anion radical scavenging, hydrogen peroxide scavenging, ferric ions (Fe(3+)) reducing power and ferrous ions (Fe(2+)) chelating activities. Also, BHA, BHT, alpha-tocopherol and trolox, were used as the reference antioxidant and radical scavenger compounds. According to the present study, curcumin can be used in the pharmacological and food industry because of these properties.     

In vitro antioxidant activity of silymarin

Silymarin, a known standardized extract obtained from seeds of Silybum marianum is widely used in treatment of several diseases of varying origin. In the present paper, we clarified the antioxidant activity of silymarin by employing various in vitro antioxidant assay such as 1,1-diphenyl-2-picryl-hydrazyl free radical (DPPH(.)) scavenging, 2,2'-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS) radical scavenging activity, total antioxidant activity determination by ferric thiocyanate, total reducing ability determination by Fe3+ - Fe2+ transformation method and Cuprac assay, superoxide anion radical scavenging by riboflavin/methionine/illuminate system, hydrogen peroxide scavenging and ferrous ions (Fe2+) chelating activities. Silymarin inhibited 82.7% lipid peroxidation of linoleic acid emulsion at 30 microg/mL concentration; butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), alpha-tocopherol and trolox indicated inhibition of 83.3, 82.1, 68.1 and 81.3% on peroxidation of linoleic acid emulsion at the same concentration, respectively. In addition, silymarin had an effective DPPH(.) scavenging, ABTS(.)+ scavenging, superoxide anion radical scavenging, hydrogen peroxide scavenging, ferric ions (Fe3+) reducing power by Fe3+-Fe2+ transformation, cupric ions (Cu2+) reducing ability by Cuprac method, and ferrous ions (Fe2+) chelating activities. Also, BHA, BHT, alpha-tocopherol and trolox, were used as the reference antioxidant and radical scavenger compounds. Moreover, this study, which clarifies antioxidant mechanism of silymarin, brings new information on the antioxidant properties of silymarin. According to the present study, silymarin had effective in vitro antioxidant and radical scavenging activity. It could be used in the pharmacological and food industry because of its antioxidant properties.     

Synthesis and antioxidant activities of novel 4-Schiff base-7-benzyloxy-coumarin derivatives

4-Schiff base-7-benzyloxy-coumarins 5a(1)-5h(2) and its derivative 6 were designed and synthesized based on the 7-benzyloxy-coumarin structure as novel antioxidants. The in vitro antioxidant activities screening revealed that 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activities of compounds 5b(1), 5d(1), 5f(1), 5f(2), 5g(1) and 5g(2), and 2,2'-azinobis-(3-ethylbenzthiazoline-6-sulfonate) cation (ABTS(+)) radical scavenging activities of compounds 5a(1), 5b(1), 5c(1), 5c(2), 5d(1), 5e(1), 5e(2), 5f(2), 5g(1), 5g(2) and 5h(1) were better than that of the commercial antioxidant butylated hydroxytoluene (BHT), while the superoxide anion radical scavenging activities of 5a(2) and 5g(2) were stronger than that of the commercial antioxidant butylated hydroxyanisole (BHA), and the hydroxyl radical scavenging activity of 5e(1) was much better than that of the common antioxidant ascorbic acid.     

Antioxidant activity of some polyphenol constituents of the medicinal plant Phyllanthus amarus Linn

Phyllanthus amarus Linn is a widely distributed tropical medicinal plant highly valued for its therapeutic properties. The antioxidant activity of some of its principal constituents, namely amariin, 1-galloyl-2,3-dehydrohexahydroxydiphenyl (DHHDP)-glucose, repandusinic acid, geraniin, corilagin, phyllanthusiin D, rutin and quercetin 3-O-glucoside were examined for their ability to scavenge free radicals in a range of systems including 2,2-diphenyl-2-picrylhydrazyl (DPPH), 2,2-azobis-3-ethylbenzthiazoline-6-sulfonic acid (ABTS)/ferrylmyoglobin, ferric reducing antioxidant power (FRAP) and pulse radiolysis. In addition, their ability to protect rat liver mitochondria against oxidative damage was determined by measuring the ROO* radical induced damage to proteins and lipids and *OH radical induced damage to plasmid DNA. The compounds showed significant antioxidant activities with differing efficacy depending on the assays employed. Amariin, repandusinic acid and phyllanthusiin D showed higher antioxidant activity among the ellagitannins and were comparable to the flavonoids, rutin and quercetin 3-O-glucoside.     

Synthesis of dimeric phenol derivatives and determination of in vitro antioxidant and radical scavenging activities

In this study, di(2,6-dimethylphenol) (Di-DMP), di(2,6-diisopropylphenol) (Di-DIP, dipropofol) and di(2,6-di-t-butylphenol) (Di-DTP) were synthesized by the reaction of monomeric phenol derivatives with catalytic CuCl(OH). TMEDA and Na2S2O4. Their antioxidant capacity and radical scavenging activity were examined using different in vitro methodologies such as 1,1-diphenyl-2-picryl-hydrazyl (DPPH*) free radical scavenging, 2,2'-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS) radical scavenging activity, total antioxidant activity by ferric thiocyanate, total reducing power by potassium ferricyanide reduction method, superoxide anion radical scavenging, hydrogen peroxide scavenging and ferrous ions chelating activities.     

Free radical scavenging abilities of flavonyl‐thiazolidine‐2,4‐dione compounds

Free radical scavenging activity of flavonyl‐thiazolidine‐2,4‐dione compounds has been evaluated using chemiluminescence, electron spin resonance spectroscopy with 5,5‐dimethyl‐1‐pyrroline‐1‐oxide as spin trap and DPPH (2,2′‐diphenyl‐1‐picrylhydrazyl) method. The examined compounds exhibited 28–50% scavenging superoxide anion radical ( ), 16.7–76.7% hydroxyl radical (HO^?) and 9–40% DPPH radical. Compounds containing carbonyl group in their structure can be considered as antioxidants with high relevance and great biological importance. Copyright © 2009 John Wiley & Sons, Ltd.     

Antioxidant activity of L-adrenaline: a structure-activity insight

L-adrenaline belongs to a group of the compounds known as catecholamines, which play an important role in the regulation of physiological process in living organisms. The antioxidant activity and antioxidant mechanism of L-adrenaline was clarified using various in vitro antioxidant assays including 1,1-diphenyl-2-picryl-hydrazyl (DPPH), 2,2'-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS), N,N-dimethyl-p-phenylenediamine (DMPD(+)), and superoxide anion radicals (O(2)(-)) scavenging activity, hydrogen peroxide (H(2)O(2)), total antioxidant activity, ferric ions (Fe(3+)) and cupric ions (Cu(2+)) reducing ability, ferrous ions (Fe(2+)) chelating activity. L-adrenaline inhibited 74.2% lipid peroxidation of a linoleic acid emulsion at 30 microg/mL concentration. On the other hand, butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), alpha-tocopherol and trolox displayed 83.3, 82.1, 68.1 and 81.3% inhibition on the peroxidation of linoleic acid emulsion at the same concentration, respectively. BHA, BHT, alpha-tocopherol and trolox were used as reference antioxidants and radical scavenger compounds. Moreover, this study will bring an innovation for further studies related to antioxidant properties of L-adrenaline. According to present study, L-adrenaline had effective in vitro antioxidant and radical scavenging activity.     

Antioxidant properties of 2-O-beta-D-glucopyranosyl-L-ascorbic acid

The antioxidant activity of a provitamin C agent, 2-O-beta-D-glucopyranosyl-L-ascorbic acid (AA-2betaG), was compared to that of 2-O-alpha-D-glucopyranosyl-L-ascorbic acid (AA-2G) and ascorbic acid (AA) using four in vitro methods, 1,1-diphenyl-picrylhydrazyl (DPPH) radical-scavenging assay, 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) radical cation (ABTS(*+))-scavenging assay, oxygen radical absorbance capacity (ORAC) assay, and 2,2'-azobis(2-amidinopropane) dihydrochloride (AAPH)-induced erythrocyte hemolysis inhibition assay. AA-2betaG slowly and continuously scavenged DPPH radicals and ABTS(*+) in roughly the same reaction profiles as AA-2G, whereas AA quenched these radicals immediately. In the ORAC assay and the hemolysis inhibition assay, AA-2betaG showed similar overall activities to AA-2G and to AA, although the reactivity of AA-2betaG against the peroxyl radical generated in both assays was lower than that of AA-2G and AA. These data indicate that AA-2betaG had roughly the same radical-scavenging properties as AA-2G, and a comprehensive in vitro antioxidant activity of AA-2betaG appeared to be comparable not only to that of AA-2G but also to that of AA.     

Evaluation of in-vitro antioxidant and antibacterial properties of Commelina nudiflora L. extracts prepared by different polar solvents

The study explored on the commonly available weed plant Commelina nudiflora which has potential in-vitro antioxidant and antimicrobial activity. The different polar solvents such as ethanol, chloroform, dichloromethane, hexane and aqueous were used for the soxhlet extraction. The extracts were identified pharmacologically as important bioactive compounds and their potential free radical scavenging activities, and antimicrobial properties were studied. C. nudiflora extracts were monitored on their in-vitro antioxidant ability by DPPH and ABTS radical scavenging assay. Aqueous extract shows significant free radical scavenging activity of 63.4 mg/GAE and 49.10 mg/g in DPPH and ABTS respectively. Furthermore, the aqueous crude extract was used in antibacterial studies, which shows the highest inhibitory activity against Pseudomonas aeruginosa, Escherichia coli and Salmonella typhi. Among all the extracts, aqueous extract of C. nudiflora has significant control over free radical scavenging activity and inhibition of the growth of food pathogenic bacteria. Also, the aqueous extract contains abundance of phenolics and flavonoids higher than other extracts. This study explored weed plant C. nudiflora as a potential source of antioxidant and antibacterial efficacy and identified various therapeutic value bioactive compounds from GC–MS analysis.Abbreviations: ABTS, 2,2′-azinobis-(3-ethylbenzothiazoline-6-sulphonic acid), DPPH, 2,2-diphenyl-1-picrylhydrazyl, GAE, gallic acid equivalent, GC–MS, gas chromatography and mass spectrometry     

6‐Methyl 3‐chromonyl 2,4‐thiazolidinedione/2,4‐imidazolidinedione/2‐thioxo‐imidazolidine‐4‐one compounds: novel scavengers of reactive oxygen species

The benefits of antioxidants on human health are usually ascribed to their potential ability to remove reactive oxygen species providing protection against oxidative stress. In this paper the free radicals scavenging activities of nine 6‐methyl 3‐chromonyl derivatives (CMs) were evaluated for the first time by the chemiluminescence, electron paramagnetic resonance, spin trapping and 2,2‐diphenyl‐1‐picrylhydrazyl (DPPH^?) methods. The total antioxidant capacity was also measured using a ferric‐ferrozine reagent. Compounds having a hydrogen atom at the N3‐position of the β‐ring were effective in quenching CL resulted from the KO₂/18‐crown‐6‐ether system (a source of superoxide anion radical, ) in a dose‐dependent manner over the range of 0.05–1 mmol/L [IC₅₀ ranged from 0.353 (0.04) to 0.668 (0.05) mmol/L]. The examined compounds exhibited a significant scavenging effect towards hydroxyl radicals (HO^? HO^?), produced by the Fenton reaction, and this ranged from 24.0% to 61.0%, at the concentration of 2.5 mmol/L. Furthermore, the compounds examined were also found to inhibit DPPH^? and this ranged from 51.9% to 97.4% at the same concentration. In addition, the use of the total antioxidant capacity assay confirmed that CM compounds are able to act as reductants. According to the present study, CM compounds showed effective in vitro free radical scavenging activity and may be considered as potential therapeutics to control diseases of oxidative stress‐related etiology. Copyright © 2013 John Wiley & Sons, Ltd.     

Endogenous and dietary indoles: a class of antioxidants and radical scavengers in the ABTS assay

Indoles are very common in the body and diet and participate in many biochemical processes. A total of twenty-nine indoles and analogs were examined for their properties as antioxidants and radical scavengers against 2,2'-Azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) ABTS*+ radical cation. With only a few exceptions, indoles reacted nonspecifically and quenched this radical at physiological pH affording ABTS. Indoleamines like tryptamine, serotonin and methoxytryptamine, neurohormones (melatonin), phytohormones (indoleacetic acid and indolepropionic acid), indoleamino acids like L-tryptophan and derivatives (N-acetyltryptophan, L-abrine, tryptophan ethyl ester), indolealcohols (tryptophol and indole-3-carbinol), short peptides containing tryptophan, and tetrahydro-beta-carboline (pyridoindole) alkaloids like the pineal gland compound pinoline, acted as radical scavengers and antioxidants in an ABTS assay-measuring total antioxidant activity. Their trolox equivalent antioxidant capacity (TEAC) values ranged from 0.66 to 3.9 mM, usually higher than that for Trolox and ascorbic acid (1 mM). The highest antioxidant values were determined for melatonin, 5-hydroxytryptophan, trp-trp and 5-methoxytryptamine. Active indole compounds were consumed during the reaction with ABTS*+ and some tetrahydropyrido indoles (e.g. harmaline and 1-methyl-1,2,3,4-tetrahydro-beta-carboline-3-carboxylic acid ethyl ester) afforded the corresponding fully aromatic beta-carbolines (pyridoindoles), that did not scavenge ABTS*+. Radical scavenger activity of indoles against ABTS*+ was higher at physiological pH than at low pH. These results point out to structural compounds with an indole moiety as a class of radical scavengers and antioxidants. This activity could be of biological significance given the physiological concentrations and body distribution of some indoles.