Antioxidant profile of dihydroxy- and trihydroxyphenolic acids-A structure–activity relationship study

Eight structurally similar dihydroxy and trihydroxyphenolic acids (protocatechuic acid, 3,4-dihydroxyphenylacetic acid, hydrocaffeic acid, caffeic acid, gallic acid, 3,4,5-trihydroxyphenylacetic acid, 3-(3,4,5-trihydroxyphenyl)propanoic acid and 3-(3,4,5-trihydroxyphenyl)propenoic acid) were examined for their total antioxidant capacity (TAC). Furthermore, their ability to scavenge peroxyl radicals, generated by AAPH in liposomes, was determined. The antioxidant/pro-oxidant activity of the compounds was screened using the 2′-deoxyguanosine assay. All compounds behave as radical scavengers, with 3,4,5-trihydroxyphenylacetic acid being the most potent. Nevertheless, in the lipid peroxidation assay an inverse ranking order was observed, 3,4-dihydroxyphenylacetic acid being the most effective compound. All the dihydroxylated compounds showed a pro-oxidant behaviour leading to an increase of 50% in 8-OH-dG induction. From the structure–antioxidant activity relationship studies performed it may be concluded that the number of phenolic groups and the type of the alkyl spacer between the carboxylic acid and the aromatic ring strongly influence the antioxidant activity.     

Metabolism of myricetin and related compounds in the rat. Metabolite formation in vivo and by the intestinal microflora in vitro

1. The metabolism of a group of polyphenols related in structure to myricetin (3,5,7,3',4',5'-hexahydroxyflavone), including myricetin, myricitrin, 3,4,5-trihydroxyphenylacetic acid, delphinidin, robinetin, tricetin, tricin, malvin and 5,7-dihydroxy-3',4',5'-trimethoxyflavone, has been studied both in vivo after oral administration to the rat and in vitro in cultures of micro-organisms derived from the intestine of the rat. 2. It was shown that the rat intestinal microflora are able to degrade compounds of this group to the ring-fission products observed in urine after oral administration of the specific flavonoid. 3. All flavones and flavonols possessing free 5- and 7-hydroxyl groups in the A ring and a free 4'-hydroxyl group in the B ring gave rise to ring-fission products that included 3',5'-dihydroxyphenylacyl derivatives. 4. The metabolites 3,5-dihydroxyphenylacetic acid, 3-hydroxyphenylacetic acid, 3,5-dihydroxyphenylpropionic acid and 3-hydroxyphenylpropionic acid were isolated and identified by chromatographic and spectral methods. 5. On anaerobic incubation in a thioglycollate medium it was shown that intestinal micro-organisms can effect cleavage of glycosidic bonds, ring fission of certain flavonoid molecules showing 3',4',5'-trihydroxyphenyl substitution and dehydroxylation of certain flavonoid metabolites. 6. The urinary excretion of the metabolites 3,5-dihydroxyphenylacetic acid and 3-hydroxyphenylacetic acid was completely abolished when neomycin-treated rats were used.     

Phytochemicals from the aerial parts of Ligularia thomsonii and their radical scavenging activity

Phytochemical investigation of the aerial parts of Ligularia thomsonii has led to the isolation of three new phenylpropanoid glucosides ligularoside I (1), ligularoside II (2) and ligularoside III (3) along with nine known compounds; cinnamic acid (4), 3-phenylpropanoic acid (5), 3,4,5-trihydroxybenzoic acid (6), 4-hydroxybenzoic acid (7), p-coumaric acid (8), caffeic acid (9), 3,4-dihydroxybenzoic acid (10), kaempferol 3-O-β-d-glucopyranoside (11) and 3,5-di-O-caffeoylquinic acid (12), hitherto unreported from L. thomsonii. Their chemical structures were elucidated by spectroscopic analysis and chemical transformation. All these compounds were tested for antioxidant activity using the 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging assay. Among them, compounds 9, 10 and 12 showed significant antioxidant activity against DPPH radicals with IC₅₀ of 19.6, 23.3 and 8.9 μm, respectively.     

Synthesis, stereochemical assignments, and biological activities of homoisoflavonoids

A series of four naturally occurring homoisoflavonoids and eight analogs have been synthesized starting from an appropriately substituted phenol through chroman-4-one, in four steps. The products were assigned as E-isomers based on NMR spectroscopic data. The E-isomers were converted into Z-isomers by photoisomerization. The E- and Z-isomers showed distinct chemical shifts and the differences between (E) and (Z)-homoisoflavonoids in the proton NMR spectra afford a useful method for ascertaining the stereochemistry. The antioxidant activity of homoisoflavonoids was determined by superoxide (NBT) and DPPH free radical scavenging methods. The analog 7-hydroxy-3-[(3,4,5-trihydroxyphenyl)methylene]chroman-4-one displayed excellent activity followed by sappanone A in both the methods and were several times potent than the commercial antioxidants like BHA, BHT, etc. These compounds were evaluated in vitro for their inhibitory activities against 5-lipoxygenase (5-LOX) enzyme. The analog 7-hydroxy-3-[(N,N-dimethylaminophenyl)methylene]chroman-4-one was found to possess potent inhibitory activity and was comparable to that of the standard, nordihydroguiaretic acid. These results suggest that these homoisoflavonoids, with their potent antioxidant and 5-LOX inhibitory activities, may have useful applications as antioxidants and lead compounds for asthma and inflammatory diseases.     

New antioxidant mixture for long term stability of serotonin, dopamine and their metabolites in automated microbore liquid chromatography with dual electrochemical detection

An automated microbore liquid chromatographic assay with dual electrochemical detection is described for the determination of serotonin, dopamine and their metabolites, 5-hydroxyindoleacetic acid, 3,4-dihydroxyphenylacetic acid and homovanillic acid. Due to the chemical instability of the compounds, the addition of an antioxidant is required for automated analysis over a long period of time (e.g., 20 h). Therefore, the time stability of these substances was tested with different antioxidants. The stability for serotonin and 5-hydroxyindoleacetic acid was poor in acidic medium containing Na₂EDTA but could greatly be improved by the addition of

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-cysteine and ascorbic acid. Using this assay, the neurotransmitters and their metabolites could easily be determined in microdialysates obtained from different rat brain areas.     

Alkyl esters of hydroxycinnamic acids with improved antioxidant activity and lipophilicity protect PC12 cells against oxidative stress

Hydroxycinnamic acids (HCAs) are phenolic compounds present in dietary plants, which possess considerable antioxidant activity. In order to increase the lipophilicity of HCAs, with the aim of improving their cellular absorption and expansion of their use in lipophilic media, methyl, ethyl, propyl and butyl esters of caffeic acid and ferulic acid have been synthesized. All caffeate esters had a slightly lower DPPH IC(50) (13.5-14.5 μM) and higher ferric reducing antioxidant power (FRAP) values (1490-1588 mM quercetin/mole [mMQ/mole]) compared to caffeic acid (16.6 μM and 1398 mMQ/mole, respectively) in antioxidant assays. In contrast, ferulate esters were less active in DPPH (56.3-74.7 μM) and FRAP assays (193-262 mMQ/mole) compared to ferulic acid (44.6 μM and 324 mMQ/mole, respectively). Redox properties of HCAs were in line with their antioxidant capacities, so that compounds with higher antioxidant activities had lower oxidation potentials. Measurement of partition coefficients disclosed the higher lipophilicity of the esters compared to parent compounds. All esters of caffeic acid significantly inhibited hydrogen peroxide-induced neuronal PC12 cell death assessed by MTT assay at 5 and 25 μM. However, caffeic acid, ferulic acid and ferulate esters were not able to protect the cells. In conclusion, these findings suggest that alkyl esterification of some HCAs augments their antioxidant properties as well as their lipophilicity and as a consequence, improves their cell protective activity against oxidative stress. These compounds could have useful applications in conditions where oxidative stress plays a pathogenic role.     

Gas chromatographic method for the simultaneous determination of dopamine and norepinephrine metabolites

A new gas chromatographic method, using only flame ionization detection which can determine nanogram quantities of homovanillic acid, 3,4-dihydroxyphenylacetic acid, 3-methoxy-4-hydroxyphenylethyleneglycol and 3,4-dihydroxyphenylethyleneglycol in the same reaction, is described. These compounds are treated with diazoethane and n-butylboronic acid. Homovanillic acid and 3,4-dihydroxyphenylacetic acid are converted to their ethyl esters while 3-methoxy-4-hydroxyphenylethyleneglycol and 3,4-dihydroxyphenylethyleneglycol from cyclic boronates and are thus assayed. This method is quantitative, highly specific and sensitive. It has been applied to the analysis of these compounds in urine.     

Edible Myrciaria vexator fruits: bioactive phenolics for potential COPD therapy

The edible fruits of Myrciaria vexator McVaugh (Myrtaceae), from northern South America, are eaten in certain locales, either fresh or processed into jellies and drinks. Activity-guided fractionation of M. vexator resulted in identification of ellagic acid (1), cyanidin-3-O-glucoside (2), delphinidin-3-O-glucoside (3), 2-O-(3,4-dihydroxybenzoyl)-2,4,6-trihydroxyphenylacetic acid (4), and jaboticabin (5), and latter two compounds are being reported for the first time in this species. Ellagic acid was further examined, and found to inhibit cigarette smoke extract induced MMP-1 expression in vitro, and may be of significance in the treatment of chronic obstructive pulmonary (COPD). Other compounds identified for the first time from M. vexator include cyanidin-3-O-galactoside (6), cyanidin-3-O-arabinoside (7), cyanidin-3-O-rutionoside (8), petunidin (9), peonidin-3-O-galactoside (10) malvidin (11), hyperoside (12), querecetin-3-O-glucoside (13), and guajaverin (14), methyl protocatechuate (15), and protocatechuic acid (16).     

Simultaneous determination of catecholamines and unconjugated 3,4-dihydroxyphenylacetic acid in brain tissue by ion-pairing reverse-phase high-performance liquid chromatography with electrochemical detection

A rapid, sensitive method was developed for the simultaneous assay of catecholamines and 3,4-dihydroxyphenylacetic acid in rat brain tissue. The method is simple, involving only tissue disruption, adsorption of the catechols onto alumina, desorption, and injection into a reverse-phase high-performance liquid chromatography system. Selectivity and high sensitivity are obtained using electrochemical detection. The addition of 3,4-dihydroxyphenylacetic acid determination to assays for catecholamines allows one to observe effects of pharmacological maniqulations on in vivo monoamine oxidase activity and/or turnover of dopamine as well as effects on catecholamine concentrations.     

一株白粉寄生菌的酚类代谢产物

从得自鼎湖山自然保护区的一株白粉寄生菌(Ampelomyces sp.)SC0307固体发酵物中分离得到7个酚类化合物.通过波谱分析,分别鉴定为2,5-二羟基苯甲醇(1)、对羟基苯甲酸(2)、2,5-二羟基苯甲酸(3)、3,4-二羟基苯甲酸(4)、苯乙酸(5)、3,4-二甲氧基肉桂酸(6)、3,4,5-三甲氧基肉佳酸(7).7个化合物均为从白粉寄生菌属真菌中首次分离获得.     

Synthesis,Biological Evaluation and in Silico Studies of 3-Hydroxy-N-(2-(substituted phenyl)-4-oxothiazolidin-3-yl)-2-napthamide Derivatives

In the present study, a series of 3-hydroxy-N-(2-(substituted phenyl)-4-oxothiazolidin-3-yl)-2-napthamide derivatives were synthesized, characterized and evaluated for theirin vitroactivity, i. e., antimicrobial, antioxidant and anti-inflammatory. The target compounds were synthesized by condensation reaction of 3-hydroxy-2-naphthoic acid hydrazide with substituted benzaldehydes which were subjected to cyclization reaction with thioglycolic acid and ZnCl₂ to get target compounds. The synthesized 3-hydroxy-N-(2-(substituted phenyl)-4-oxothiazolidin-3-yl)-2-napthamide derivatives were examined for their antimicrobial activity and 3-hydroxy-N-(4-oxo-2-(3,4,5-trimethoxyphenyl)thiazolidin-3-yl)-2-naphthamide ( S20 ) exhibited the highest antimicrobial potential. The N′-(2,3-dichlorobenzylidene)-3-hydroxy-2-naphthohydrazide ( S5 ) displayed good antifungal potential against Rhizopus oryzae, whereas N′-(2,3-dichlorobenzylidene)-3-hydroxy-2-naphthohydrazide ( S20 ) showed the highest antioxidant potential and N-(2-(2,6-dichlorophenyl)-4-oxothiazolidin-3-yl)-3-hydroxy-2-naphthamide ( S16 ) displayed the highest anti-inflammatory activity. The results of molecular docking studies revealed that existence of hydrogen bonding and hydrophobic interactions with their respective proteins. In silico ADMET studies were carried out by Molinspiration, Pre-ADMET and OSIRIS property explorer to predict the pharmacokinetic behaviour of synthesized 3-hydroxy-N-(2-(substituted phenyl)-4-oxothiazolidin-3-yl)-2-napthamide derivatives.     

Antioxidant Properties of the Major Polyphenolic Compounds in Broccoli

We have examined the antioxidant activity of the major phenolic compounds in Broccoli: two flavonol glycosides (quercetin 3-O-sophoroside and kaemp-ferol 3-O-sophoroside) and four hydroxycinnamic acid esters (1,2'-disinapoyl-2-feruloyl gentiobiose, 1-sinapoyl-2-feruloyl gentiobiose, 1,2,2'-trisinapoyl gentiobiose and 1,2-disinapoyl gentiobiose). The Trolox C equivalent antioxidant capacity (TEAC) and inhibition of iron/ascorbate-induced lipid per-oxidation of phosphatidyl choline vesicles were measured. In the aqueous phase TEAC assay, the two flavonol glycosides were less active than their respective aglycones. TEAC values for the hydroxycinnamic acid esters were less than the sum of their constituent hydroxycinnamic acids on a molar basis. Quercetin 3-O-sophoroside was a potent inhibitor of lipid peroxidation, in contrast to kaempferol 3-O-sophoroside. The hydroxycinnamic acid esters were highly effective at preventing lipid damage with the exception of 1,2,2'-trisinapoyl gentiobiose. The six compounds analysed herein demonstrate the antioxidant activity of the major phenolics in broccoli and indicate the effect on antioxidant activity of sugar substitutions in the phenolic B ring.     

Antioxidant activity of pine bark constituents

A modified in vitro lipid peroxidation inhibition assay was used to guide the fractionation and the isolation of antioxidative principles of Fnnish pine bark extract. This approach yielded 3,4-dihydroxybenzoic acid (protocatechuic acid) and taxifolin-3-O-beta-glucopyranoside as major antioxidative compounds from the plant material. The structural elucidation of these compounds was undertaken with the help of HPLC-DAD and HPLC-ESI-MS analyses. Their IC50 values, in comparison to trolox (6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid), were: trolox (1.78 +/- 0.56 microM) < protocatechuic acid (5.77 +/- 1.63 microM) < taxifolin-3-O-beta-glucopyranoside (16.30 +/- 1.98 microM). The method for the determination of antioxidant activity proved reproducible and quick for routine analyses with 96 well plates.     

DPPH radical scavenging reaction of hydroxy- and methoxychalcones

The DPPH radical scavenging activity of 2',4',6'-trihydroxy- and 2'-hydroxy-4',6'-dimethoxychalcones carrying a 2,3- and 3,4-dihydroxylated, and 3,4,5-trihydroxylated B-ring was evaluated in alcoholic and non-alcoholic solvents. All test compounds scavenged more than two equivalent of radicals by a possible conversion to the corresponding B-ring quinones and in most cases subsequently underwent cyclization to aurones and flavanones, these being identified in the reaction solutions by an in situ NMR analysis. Interestingly, the reaction between 2',3,4-trihydroxy-4',6'-dimethoxychalcone and the DPPH radical was significantly affected by the solvent used, which might be accounted for by the difference in readiness for cyclization to an aurone.     

p-Hydroxyphenylacetic Acid Metabolism in Pseudomonas putida F6

Pseudomonas putida F6 was found to metabolize p-hydroxyphenylacetic acid through 3,4-dihydroxyphenylacetic acid, 3,4-dihydroxymandelic acid, and 3,4-dihydroxybenzaldehyde. Cell extracts of P. putida F6 catalyze the NAD(P)H-independent hydroxylation of p-hydroxyphenylacetic acid to 3,4-dihydroxyphenylacetic acid which is further oxidized to 3,4-dihydroxymandelic acid. Oxidation and decarboxylation of the latter yields 3,4-dihydroxybenzaldehyde. A red-brown color accompanies all of the above enzyme activities and is probably due to the polymerization of quinone-like compounds. 3,4-Dihydroxybenzaldehyde is further metabolized through extradiol ring cleavage.     

Isolation of Natural Naphthoquinones from <Emphasis Type="Italic">Juglans regia</Emphasis> and In Vitro Antioxidant and Cytotoxic Studies of Naphthoquinones and the Synthetic Naphthofuran Derivatives

The naphthoquinones and their derivatives containing hydroxyl group exhibit wide range of pharmacological activities, such as antioxidant, antibacterial, antiviral, anticancer, antimalarial, and antifungal activities. In particular, the antioxidant and anticancer behaviors of these compounds continue to draw attention of researchers. In the present communication, three natural naphthoquinones—juglone, lawsone, and plumbagin—isolated from the chloroform extract of nutshells of Juglans regia Linn. and two 1,4-naphthoquinone derivatives—ethyl-5-hydroxynaphtho[ 1,2-b]furan-3-carboxylate and diethylnaphtho[1,2-b:4,3-b′]difuran-3,4-dicarboxylate—and three 5-hydroxy- 1,4-naphthoquinone derivatives—diethyl-7-hydroxynaphtho[1,2-b:4,3-b']difuran-3,4-dicarboxylate,4-ethoxycarbonyl- 7-hydroxynaphtho[1,2-b:4,3-b']difuran-3-carboxylic acid, and 7-hydroxynaphtho[1,2-b:4,3-b']difuran-3,4- dicarboxylic acid were synthesized and examined for their in vitro antioxidant activity using 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2'-azino-bis-3-ethylbenzthiazoline-6-sulphonic acid (ABTS) bioassays. In addition, the cytotoxicity test using human hepatocellular liver carcinoma cell line (HepG2) was carried out for all the compounds. The 5-hydroxy-1,4-naphthoquinone derivatives displayed almost equivalent scavenging activity in DPPH assay and higher activity in ABTS assay relative to ascorbic acid. On the other hand, naphthoquinones Juglone and Plumbagin showed lesser antioxidant activity, but higher cytotoxic activity than naphthofurans except for diethyl naphtho[1,2-b:4,3-b′]difuran-3,4-dicarboxylate, which showed excellent cytotoxic activity.     

Antioxidant activity of compounds from the medicinal herb Aster tataricus

A number of compounds were isolated from the medicinal plant Aster tataricus including shionone, epifriedelinol, quercetin, kaempferol, scopoletin, emodin, aurantiamide acetate and 1,7-dihydroxy-6-methyl-anthraquinone. The compounds were compared with regard to their ability in inhibiting hemolysis of rat erythrocytes induced by 2'-2' azobis (2-amidinopropane) dihydrochloride, lipid peroxidation using the FeSO(4)-ascorbic acid system, and generation of superoxide radicals using a phenazine methosulfate-nicotinamide adenine dinucleotide system. The effects on the Fe-bleomycin-induced DNA damage reflected pro-oxidant activity. Quercetin and kaempferol were most potent in inhibiting hemolysis, lipid peroxidation and superoxide radical generation. Scopoletin and emodin were similar to quercetin and kaempferol in inhibiting superoxide radical generation and second to them in inhibiting lipid peroxidation. Aurantiamide acetate exhibited some inhibitory activity toward superoxide radical generation. 1,7-dihydroxy-6-methyl-anthraquinone exerted an inhibitory activity only on superoxide radical generation. Shionone and epifriedelinol did not display any antioxidant activity. Quercetin and kaempferol, but not the remaining compounds, exhibited some pro-oxidant activity.     

Alternative routes of aromatic catabolism in Pseudomonas acidovorans and Pseudomonas putida: gallic acid as a substrate and inhibitor of dioxygenases.

When 3,4-dihydroxyphenylacetic acid (homoprotocatechuic acid) was added to Pseudomonase acidovorans growing at the expense of succinate, enzymes required for degrading homoprotocatechuate to pyruvate and succinate semialdehyde were strongly induced. These enzymes were effectively absent from cell extracts of the organism grown with 4-hydroxyphenylacetic acid, and this substrate was metabolized by the catabolic enzymes of the homogentisate pathway. Two separate ring-fission dioxygenases for 3,4,5-trihydroxybenzoic acid (gallic acid) were present in cell extracts of Pseudomonas putida when grown with syringic acid, and gallate was degraded by reactions associated with meta fission. One of the two gallate dioxygenases also attacked 3-O-methylgallic acid; the other, which did not, was induced when cells were exposed to gallate. This organism possessed ortho fission enzymes, including protocatechuate 3,4-dioxygenase (EC 1.13.11.3) and cis,cis-carboxymuconate-lactonizing enzyme (EC 5.5.1.2), after induction with 3,4-dihydroxybenzoic acid (protocatechuic acid). Gallate was a substrate for protocatechuate 3,4-dioxygenase, with a Vmax about 3% of that of protocatechuate and with an apparent Km slightly lower. Gallate was a powerful competitive inhibitor of protocatechuate oxidation.     

Oxalic acid stabilizes dopamine, serotonin, and their metabolites in automated liquid chromatography with electrochemical detection

Use of antioxidative agents is required in automated LC assay of microdialysis samples, due to rapid degradation of the monoamine neurotransmitters and their metabolites. Addition of oxalic acid prevented degradation of dopamine, serotonin, 3,4-dihydroxyphenylacetic acid, homovanillic acid and 5-hydroxyindoleacetic acid efficiently: after a 24-h incubation at room temperature the decreases in peak heights were less than 10%. The long-term stability of the analytes, however, was still enhanced when acetic acid and -cysteine were included in the solution. Using this antioxidative solution, the monoamine neurotransmitters and their metabolites could be determined with an automated LC assay even at room temperature.     

Antimutagenicity of mono-, di-, and tricaffeoylquinic acid derivatives isolated from sweetpotato (Ipomoea batatas L.) leaf

The caffeoylquinic acid derivatives, 3-mono-O-caffeoylquinic acid (chlorogenic acid, ChA), 3,4-di-O-caffeoylquinic acid (3,4-diCQA), 3,5-di-O-caffeoylquinic acid (3,5-diCQA), 4,5-di-O-caffeoylquinic acid (4,5-diCQA) and 3,4,5-tri-O-caffeoylquinic acid (3,4,5-triCQA), and caffeic acid (CA) were isolated from the sweetpotato (Ipomoea batatas L.) leaf. We examined the antimutagenicity of these caffeoylquinic acid compounds to promote new uses of the sweetpotato leaf. These caffeoylquinic acid derivatives effectively inhibited the reverse mutation induced by Trp-P-1 on Salmonella typhimurium TA 98. The antimutagenicity of these derivatives was 3,4,5-triCQA > 3,4-diCQA = 3,5-diCQA = 4,5-diCQA > ChA in this order. There was no difference in the antimutagenicity of all dicaffeoylquinic acid derivatives. A comparison of the activities and structures of these compounds suggested that the number of caffeoyl groups bound to quinic acid played a role in the antimutagenicity of the caffeoylquinic acid derivatives. The sweetpotato leaves contained distinctive polyphenolic components with a high content of mono-, di-, and tricaffeoylquinic acid derivatives and could be a source of physiological functions.