Cinnamic acids gallic acid from

The biosynthesis of gallic acid (3.47) has been under investigation for more than 50 years. Different biosynthetic routes have been proposed, as depicted in Figure 3-6 (/) direct biosynthesis from an intermediate of the shikimate pathway, (2) biosynthesis via phenylalanine (3.27), cinnamic acid (3.29), />coumaric acid (3.30), caffeic acid (3.32), and 3,4, 5-trihydroxycinnamic acid (3.44), or (3) biosynthesis via caffeic acid (3.32) and protocatechuic acid (3.45). The possibility that different pathways co-existed in different species or even within one species was also considered. 

The concentration of phenolic acids can vary from 0.01 to 10 ppm (Anklam, 1998). The dominant acids are gallic acid and p-coumaric acid, followed by the caffeic, ferulic, ellagic, chlorogenic, syringic, vanillic, cinnamic, and p-hydroxybenzoic acids (Baltrusaityte et al., 2007 Bertoncelj et al., 2007 Estevinho et al., 2008). The high concentrations of benzoic, phenylacetic, mandelic, and (S-fenil lactic acids (Anklam, 1998) can be used in the identification of heather honey. 

The olive mesocarp contains a number of phenolic and polyphenolic compounds and their esters, small amounts of which are present in olive oil (35, 43, 44). These include monohydroxy- and dihydroxy-phenylethanol, including tyrosol and other phenols and a series of carboxy-phenols, including caffeic, o-coumaric, p-coumaric, cinnamic, ferulic, gallic, p-hydroxybenzoic, protocatechuic, sinapic, syringic, and vanillic acids. Benzoic and cinnamic acids are produced by hydrolysis of flavonoids. The hydroxyphenyl-ethanols arise from hydrolysis of oleoeuropein. Their esters are responsible for the bitterness and pepperlike sensation occasionally dominant in the taste of olive oils. 

From the cinnamic acids or phenyl propanoids described above, / -oxidation and truncation of side chains yields a variety of benzoic or simple phenolic acids [28], Rao et al., [22] identified gallic acid (18), gentisic acid (19), protocatechuic acid (20), />-hydroxybenzoic acid (21), oc-resorcyclic acid (22), vanillic acid (23) and salicylic acid (24) in C. arietinum and showed that overall, leaf content of all phenolic compounds was much greater than in roots and stem. They postulated that the production of these compounds may enhance the activity of indole acetic acid oxidase or may express antimicrobial properties when leached into the soil. However, Singh et al. [24] showed that the production of both 18 and 24 by C. arietinum was induced when treated by the culture filtrate of Sclerotium rolfsii along with the phenyl propanoids 14, 15 and 17 mentioned above. 

Benzoic and cinnamic acid derivatives and flavonoids are the two most distributed phenolics within plants. Polyphenolic units are biosynthesized via shikimate pathway, resulting in cinnamic acids C -C phenylpropanoid building block that also contributes to other plant phenolics backbones such as those from flavonoids (Q-Ca-Ce), anthocyanidins (C6-C3-C6), and coumarins (C6-C3). Stilbeneoids (C6-C2-C6) and benzoic acid derivatives (Cfi-Ci) such as gallic and ellagic acids are also synthesized through this metabolic pathway (Fig. 1). 

It is of interest that fungi synthesize gallic acid in this way in contrast to other organisms which form this compound either from dehydroshikimic acid (D 8) or cinnamic acid derivatives (D 22.2.5). 

Against this backcloth it is perhaps not surprising to learn, that, despite its distinctive position in the overall patterns of plant phenol metabolism, ambiguity still surrounds the biosynthesis of gallic acid. Several pathways have been proposed. Zenk formulated a conventional pathway (Fig. 7, a) from L-phenylalanine to 3,4,5-trihydroxy-cinnamic acid followed by 6-oxidation to give gallic acid. 

Phenolic compounds are widely distributed in plant parts from the roots to the seeds and include phenolic acids, flavo-noids and tannins. The tannins may reduce protein digestibility (Ford and Hewitt, 1979) and perhaps the bioavailability of other nutrients. The flavonoids have been reported to have a number of nutritional and pharmacological activities (Kuhnau, 1976). Phenolic acids include benzoic and cinnamic acid derivatives. The benzoic acid derivatives include p-hydroxy-benzoic, protochate-chuic, vanillic, gallic and syringic acids. The cinnamic acids, p-coumaric, caffeic, ferulic and sinapic are found in most oilseeds used to prepare protein concentrates and frequently occur in the form of esters with quinic acid or sugars. Chlorogenic acid for example is an ester of caffeic acid and quinic acid and is found in several isomeric and derivatized forms. 

Phenolic acids and coumarins Two families of phenolic acids are widely distributed in plants - a range of substituted benzoic (Cg-Ci) acid derivatives and those derived from cinnamic (C -C ) acid. Both types of phenolic acids usually occur in conjugated or esterified form. The simpler types of benzoic acid derivatives include p-hydroxybenzoic, protocatechuic, vannilic, gallic and syringic acids, and the o-hydroxy salicylic and gentisic acids (Fig. 1). The cinnamic acids p-coumaric, caffeic, ferulic, and sinapic, are found in most oilseeds and occur frequently in the form of esters with quinic acid or sugars (Fig. 1). Chlorogenic... 

The amino acid phenylalanine is derived from gallic acid, being this compound biosynthesized in the shikimic acid metabolic route. Most of the phenolic compounds from higher plants are also derived from this amino acid, formed in the phenylpropanoid metabolic route, in the cell cytoplasm, being various enzymes involved in this metabolism. Phenylalanine ammonia lyase interacts with phenylalanine forming cinnamic acid, that is, hydrolyzed by citmamate-4-hydroxylase, rendering p-coumaric acid. Different hydroxylations and/or methoxylations, of this... 

New layers have been studied and introduced for the separation of 30 organic acids. For example, phenoxyacetic acid herbicide was separated from cinnamic, citric, gallic, maleic, oxalic acid, etc., on a calcium sulfate layer containing /r-dimethyl-aminobenzaldehyde and developed with distilled water (87) (Table 7). 

Further, phenolic phytochemicals can be targeted for antimicrobial applications. Many phenolic containing Ifuit and herbal products have shown to possess antimicrobial activity agdimsi Listeria monocytogenes (Chung etal. 1990 Hao et al. 1998 Puupponen-Pimia etal. 2001 Sa-gun et al. 2006). Recent research with purified compoimds from natural products has shown that phenolic phytochemicals such as cinnamic acid, cinnamaldehydes, coumarins, capsaicin, and tannins have anti-7/. pylori activity (Bae et al. 1999, 1998 Jones et al. 1997) when caffeic and gallic acid have Staphylococcus aureus inhibitory activity (Kwon etal. 2007). 

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