Caffeic acid, oxidation

Arakawa, R. Yamaguchi, M. Hotta, H. Osakai, T. Kimoto, T. Product analysis of caffeic acid oxidation by on-line electrochemistry/electrospray ionization mass spectrometry. J. Am. Soc. Mass. Spectrom. 2004,15,1228-1236. 

As alkaloids contain a nitrogen atom, they react mostly alkahne and are able to form soluble salts in aqueous environments. In plants, however, they can occur in the free state, as a salt, or as an N-oxide, and accumulate in the plant vacuole as a reservoir or often coupled to phenoUc acids Uke chloro-genic acid or caffeic acid [2]. 

The presence of tocopherols,114 as well as caffeic acid,108 accounts for the remarkable stability of green coffee bean oils toward oxidation. In coffee beans from different origins, a-tocopherol concentrations are in the range 89 to 188 pg/kg and (p + y)-tocopherol concentrations are in the range 252 to 530 pg/kg.114 Since p- and y-tocopherols have better antioxidant properties than a-tocopherol,114 it is not surprising to see coffee oil patented as an antioxidant material.115117... 

An extract from Lactuca indica showed significant free radical scavenging activity, and protected phixl74 supercoiled DNA against strand cleavage and reduced oxidative stress in human promyelocytic leukemia HL-60 cells. On account of protocatechulic acid, methyl p-hydroxybenzoate, caffeic acid, 3,5-dicaffeoylquinic acid, luteolin 7-O-fT glucopyranoside, and quercetin 3-0-(3-g 1 ucopyranoside are the major antioxidative constituents (111). 

Wang et al. (62) reported the oxidative polymerization of a mixture of phenolic compounds in aqueous solution containing mont-morillonlte, illite, and kaolinite, each of which had been mixed with quartz in a 3 7 ratio, and by quartz alone. The mixture of phenolic compounds contained gallic acid, pyrogallol, protocatechuic acid, caffeic acid, orcinol, ferulic acid, p-coumaric acid, syringic acid, vanillic acid, and p-hydroxybenzoic acid. The oxidative... 

Mason (30) and Pierpoint (31) have described the involvement of o-diphenols in plants and how they contribute to abnormal plant pigmentation. o-Diphenols are oxidized to o-quinones by enzymes of the phenolase complex (o-diphenol O2 oxidoreductase, E.C. 1.10.3.1) and by peroxidase (E.C. 1.11.1.7). o-Quinones react with amino acids, proteins, amines and thiol groups of proteins to polymerize and from reddish-brown pigments. Concentrations of caffeic acid are doubled in both bean (8) and peanut... 

Hapiot, P. et al.. Oxidation of caffeic acid and related hydroxycinnamic acids. J. Electroanal. Chem. 405, 169, 1996. 

Fulcrand, H. et al.. Characterization of compounds obtained by chemical oxidation of caffeic acid in acidic conditions. Phytochemistry 35, 499, 1994. 

Cadmium ehloride (see Cadmium and cadmium compounds) Cadmium oxide (see Cadmium and cadmium compounds) Cadmium sulfate (see Cadmium and cadmium compounds) Cadmium sulfide (see Cadmium and cadmium compounds) Caffeic acid Caffeine... 

The oxidation of DOPA and adrenaline to dopachrome and adrenochrome, respectively, by a horse radish peroxidase-H202 system has been reported by Herzmann.29,30 The oxidation process was activated by trace quantities of caffeic acid, its esters, and related compounds.30 Ascorbic acid inhibited the oxidation of adrenaline by this enzyme in the initial stages of the reaction, but later had a stimulatory effect.30... 

Within the body tissues the changes of caffeic acid are methylation of the hydroxyl group in the 3 position, p-oxidation of side chain and conjugation with glycine or glucuronic acid. 

After oral administration of caffeic acid to rats, small amounts of vanillic acid and vanilloylglycine are excreted. The conversion of p-hydroxycinnamic acid into /7-hydroxybenzoic acid is found in rat liver mitochondria [18], Studies with /7-hydroxy[U-14C]cinnamic acid have showed that 14C02 is released during reaction, indicating that reaction probably followed the p-oxidation type reactions, the two carbon being first removed as acetyl-CoA, and then oxidized to C02. It is assumed that conversion of ferulic acid formed by methylation of caffeic acid into vanillic acid occurs in rat liver mitochondria. 

According to the theory of free radical oxidation, antioxidizing activities of chlorogenic acids are stipulated by their participation in reaction with free radicals. Chlorogenic and caffeic acids have high stoichiometric numbers and reactivity with peroxyl radicals as compared with trolox, the water-soluble analogue of tocopherol [48]. Considering... 

A free radical scavenger will come to possess an unpaired electron once it has contributed an electron to neutralize a free radical. Paradoxically, the free radical scavenger becomes a free radical. When chlorogenic acids neutralize a free radical they become phenoxyl radicals. However, products of chlorogenic and caffeic acids formed by reaction with free radicals are rapidly broken down further to products that are not able to generate any free radicals. This is the beneficial nature of antioxidants, because other antioxidants are not necessary for the reduction of one-electron oxidation products of these compounds [39],... 

Despite the abundance of biological data demonstrating antioxidant activities of chlorogenic acids, the controversy whether these compounds are potent antioxidants or pro-oxidants, remains. The pro-oxidant characteristics of chlorogenic and caffeic acids have been suggested in the several papers [44, 52, 117-121],... 

The above-described observations indicate that chlorogenic and caffeic acids switch from anti- to pro-oxidant activity, depending on their concentration, on the presence of free transition metal ions, or on their... 

Also, the phenolic compounds in olives have a strong influence on the flavor of the oil and seem to be responsible for the high oxidation resistance of olive oil. The phenolic content in the flesh of olive fruits ranges between 1% and 3%, w/w, (66) oleuropein, vanillic, caffeic, p-coumaric acid, rutin, luteolin-7-glucoside, heterosidic ester of caffeic acid, and hydroxytyrosol (verbascoside) have been identified in olive fruits. 

In conclusion, phenolic-rich fractions of oats possess an antioxidant capacity that can be assessed quantitatively through their ability to inhibit LDL oxidation and protein oxidation. The greatest degree of antioxidant capacity was associated with compounds extracted with methanol from the aleurone. The identification of the oat constituents from these fractions should be investigated, although candidate compounds include caffeic acid, ferulic acid, and avenanthramides. These compounds may be bioavailable and contribute to the health effects associated with dietary antioxidants and oats. 

The kinetics of the oxidation of adenosine and caffeic acid by r-butoxyl radicals has been studied by the photolysis of /-BuOOH in the presence of r-BuOH. The rates and the quantum yields of oxidation of caffeic acid by r-BuO" radicals have been determined in the absence and presence of various concentrations of adenosine. An increase in the concentration of adenosine has been found to decrease the rate of oxidation of caffeic acid, suggesting that adenosine and caffeic acid compete for r-BuO radicals. It has been suggested that caffeic acid not only protects adenosine from r-BuO radicals but also repairs adenosine radicals formed by the reaction of r-BuO radicals.219... 

In the presence of bulky groups, such as in 3,5-di-ferf-butylquinone, the quinone is stable and can be isolated, but in most cases, it easily undergoes other reactions, such as Michael addition by nucleophiles present in solution, including the catechol itself. On the other hand, in some cases, the substrate oxidation can be driven to selected products [44], as in the synthesis of neurotrophic americanol A and isoamericanol by HRP-catalyzed oxidative coupling of caffeic acid [45] (Fig. 6.3b). 

Matsumoto K, Takahashi H, Miyake Y, Fukuyama Y (1999) Convenient syntheses of neurotrophic americanol A and isoamericanol A by HRP catalyzed oxidative coupling of caffeic acid. Tetrahedron Lett 40 3185-3186... 

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