Phenolic acid compounds

Methyl 3,4-dihydroxybenzoate (MDHB) is a phenolic acid compound, reported to have antioxidative and neurotrophic effects. Pretreatment of primary cortical neurons with MDHB suppressed Ap25 35-induced cellular toxicity and increased the level of Bcl-2, decreased the level of Bax, and inhibited the activation of caspase-9 and caspase-3 [570]. 

Creosote bush resin consists of phenolic (e.g., flavonoids and nordihydroguaiaretic acid), neutral (e.g., waxes), basic (e.g., alkaloids), and acidic (e.g., phenolic acids) compounds. The phenolic portion comprises 83-91% of the total resin. Nordihydroguaiaretic acid accounts for 5-10% of the dry weight of the leaves (Leonforte 1986). It is not known whether the health effects associated with creosote bush resin are attributable to the phenolic components. 

A wide variety of stationary phases have been used to separate substituted monocyclic phenols and phenolic acid compounds and their derivates by thin-layer chromatography (TLC). In particular, the composition of phenolic acids and flavonoids in leaves, roots, and fruits of several plants and in natural products has been extensively studied by the two-dimensional TLC by using cellulose or silica gel plates in one direction and silanized silica gel in the second direction. Quantitative determinations of flavonoids components of plant extracts were widely performed. 

Taruscio, T. G., Barney, D. L., Exon, J. Content and profile of flavanoid and phenolic acid compounds in conjunction with the antioxidant capacity for a variety of northwest Vaccinium berries. J. Agric. Food Chem. 52(10), 3169-76,2004. 

Although there are several mechanisms by which respiratory electron transport can be inhibited, the compounds in Figure 5.2 are classed as inhibitory uncouplers. " This activity is not restricted to mitochondrial electron transport as photosystem II (PSII) electron transport and phosphorylation are also affected by dinitrophenols and hydroxybenzonitriles (Refs. 3-5 and Chapter 1). In isolated mitochondrial preparations, lower concentrations of herbicides uncouple oxidative phosphorylation, that is, promote electron transport, without ATP synthesis, whereas higher concentrations inhibit electron transport. Fedtke calculated that uncoupling is 2-10 times more sensitive for a range of phenolic/acidic compounds." A similar difference has also been reported for dinoterb (Figure 5.2), which uncouples oxidative phosphorylation at 0.05-0.15 mM and inhibits respiration at 0.5-1.0mM. ... 

Cannot be used for alcohols, phenols or amines, with all of which it combines. Not advisable for acidic liquids, as ordinary calcium chloride always contains some calcium hydroxide owing to partial hydrolysis during preparation. Usually used for alcohols (see p. 88). Cannot be used for acidic compounds, nor for esters, which it would hydrolyse. 

Diasomethane Method. Diazomethane readily methylates phenolic hydroxy-compounds, primary and secondary amines, and carboxylic acids,... 

Most of the acidic compounds containing only the elements C, H and O are either carboxylic acids or phenols. They are found mainly in Solubility Group III, although the water soluble members are in Solubility Groups I and II. 

Ck)ol the alkaline solution resulting from the distillation of the volatile neutral compounds, make it acid to litmus with dilute sulphuric acid, and add an excess of solid sodium bicarbonate. Extract this bicarbonate solution with two 20 ml. portions of ether remove the ether from the combined ether extracts and identify the residual phenol (or enol). Then acidify the bicarbonate solution cautiously with dilute sulphiu-ic acid if an acidic compound separates, remove it by two extractions with 20 ml. portions of ether if the acidified solution remains clear, distil and collect any water-soluble, volatile acid in the distillate. Characterise the acid as under 2. 

Other Phenolic Compounds. There are several phenolic acids important to tea chemistry. GaUic acid (3) and its quinic acid ester, theogallin (4), have been identified in tea (17,18) and have been detected by hplc (19,20). 

Toxic Reactions of the Skin Irritation is the most common reaction of the skin. Skin irritation is usually a local inflammatory reaction. The most common skin irritants are solvents dehydrating, oxidizing, or reducing compounds and cosmetic compounds. Acids and alkalies are common irritants. Irritation reactions can be divided into acute irritation and corrosion. Necrosis of the surface of the skin is typical for corrosion. Acids and alkalies also cause chemical burns. Phenols, organotin compounds, hydrogen fluoride, and yellow phosphorus may cause serious burns. Phenol also causes local anesthesia, in fact it has been used as a local anesthetic in minor ear operations such as puncture of the tympanous membrane in cases of otitis. ... 

A wide vanety of nucleophiles, such as 1-alkylpyrroles, furans, thiophenls [51], phenols [52], anilmes [55, 54], indoles [55], CH-acidic compounds [56, 57], as well as organolithium [56], Gngnard [57, 59], organocadmiura, and organozmc compounds [56], undergo C-hydroxyalkylation with trifluoropynivates to yield derivatives of a-trifluoromethyi a-hydroxy acids. 

Knowledge of the identity of phenolic compounds in food facilitates the analysis and discussion of potential antioxidant effects. Thus studies of phenolic compounds as antioxidants in food should usually by accompanied by the identification and quantification of the phenols. Reversed-phase HPLC combined with UV-VIS or electrochemical detection is the most common method for quantification of individual flavonoids and phenolic acids in foods (Merken and Beecher, 2000 Mattila and Kumpulainen, 2002), whereas HPLC combined with mass spectrometry has been used for identification of phenolic compounds (Justesen et al, 1998). Normal-phase HPLC combined with mass spectrometry has been used to identify monomeric and dimeric proanthocyanidins (Lazarus et al, 1999). Flavonoids are usually quantified as aglycones by HPLC, and samples containing flavonoid glycosides are therefore hydrolysed before analysis (Nuutila et al, 2002). 

Finally, the fact that anthocyanins can reach the brain represents a beginning of an explanation of the purported neuroprotection effects of anthocyanins. Anthocyanins may be eliminated via urinary and biliary excretion routes. " The extent of elimination of anthocyanins via urine is usually very low (< 0.2% intake) in rats and in humans, indicating either a more pronounced elimination via the bile route or extensive metabolism. As mentioned earlier, in the colon, non-absorbed or biliary excreted anthocyanins can be metabolized by the intestinal microflora into simpler break-down compounds such as phenolic acids that may be (re)absorbed and conjugated with glycine, glucuronic acid, or sulfate and also exhibit some biological... 

Phenolic acids and polyphenols are natural plant constituents which impart flavor and textural components to beverages made from these plants. In order to better understand the role of these easily oxidized compounds in the flavor and stability of beverages, it is necessary to determine them at the low concentrations they occur. LCEC has been shown to be quite effective at these trace determinations... 

Endogenous or exogenous aromatic compounds such as phenols and phenolic acids react extremely rapidly with OH radicals to form a mixture of hydroxylated products (Halliwell et /., 1988). Indeed, aromatic hydroxylation serves as an efiective method for evaluating OH radical activity both in vitro (Moorhouse et al., 1985 Grootveld and Halliwell, 1986a) and in vivo (Grootveld and Halliwell, 1986b). 

Some phenolic acids such as ellagic acid can be used as floral markers of heather honey (Cherchi et al., 1994 Ferreres et al., 1996a,b), and the hydroxyciimamates (caffeic, p-coumaric, and ferulic acids) as floral markers of chestnut honey (Cherchi et al., 1994). Pinocembrin, pinobanksin, and chrysin are the characteristic flavonoids of propolis, and these flavo-noid compounds have been found in most European honey samples (Tomas-Barberan et al., 2001). However, for lavender and acacia honeys, no specific phenolic compoimds could be used as suitable floral markers (Tomas-Barberan et al., 2001). Other potential phytochemical markers like abscisic acid may become floral markers in heather honey (Cherchi et al., 1994). Abscisic acid was also detected in rapeseed, lime, and acacia honey samples (Tomas-Barberan et al., 2001). Snow and Manley-Harris (2004) studied antimicrobial activity of phenolics. 

Arcmatic compounds phenols, phenolic acids, cinnamic acid derivatives, coumarins, flavonoids, quinones, and tannins, all of which are aromatic compounds, comprise the largest group of secondary plant products. They are often referred to as "phenolics" and have been identified as allelopathic agents in more instances than all of the other classes of compounds combined 5). 

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