Cinnamic acids sinapic

Recent scientific investigations of natural polyphenols have demonstrated their powerful antioxidant property (Niki et al, 1995). Several classes of polyphenols have been chemically identified. Some of these are grape polyphenols, tea polyphenols, soy polyphenols, oligomeric proanthocyanidines (OPA) and other natural polyphenols of the flavone class. Rice bran polyphenols are different from the above in that they are p-hydroxy cinnamic acid derivatives such as p-coumaric acid, ferulic acid and p-sinapic acid. Tricin, a flavone derivative, has also been isolated from rice bran. 

Hydroxy cinnamic acids are included in the phenylpropanoid group (C6-C3). They are formed with an aromatic ring and a three-carbon chain. There are four basic structures the coumaric acids, caffeic acids, ferulic acids, and sinapic acids. In nature, they are usually associated with other compounds such as chlorogenic acid, which is the link between caffeic acid and quinic acid. 

A series of subsequent reactions after PAL first introduces a hydroxyl at the 4-position of the ring of cinnamic acid to form p- or 4-coumaric acid (i.e., 4-hydroxycinnamic acid). Addition of a second hydroxyl at the 3-position yields caffeic acid, whereas O-methylation of this hydroxyl group produces ferulic acid (see Fig. 3.3). Two additional enzymatic reactions are necessary to produce sinapic acid. These hy-drocinnamic acids are not found in significant amounts in plant tissue because they are rapidly converted to coenzyme A esters, or glucose esters. These activated intermediates form an important branch point because they can participate in a wide range of subsequent reactions. 

Landete and others (2009) reported that Lactobacillus plantarum have the ability to metabolize phenolic compounds found in olive products (such as oleuropein, hydroxytyrosol, and tyrosol, as well as vanillic, p-hydroxybenzoic, sinapic, syringic, protocatechuic, and cinnamic acids). For example, oleuropein was metabolized mainly to hydroxytyrosol, whereas protocatechuic acid was decarboxylated to catechol by the enzymatic actions. 

The most common cinnamic acids are caffeic (3,4-dihydroxycinnamic acid), ferulic (3-methoxy-4-hydroxy), sinapic (3,5-dimethoxy-4-hydroxy) and p-coumaric (4-hydroxy) acid, Table 4 [13]. 

There are six common cinnamic acids, which have a C6 - C3 skeleton. All plants probably contain at least three of them. Shown below are cinnamic, acid (1.12), / -coumanc acid (1.13), caffeic acid (1.14), ferulic acid (1.15), 5-hydroxyferulic acid (1.16), and sinapic acid (1.17). 

The branch pathway of lignin biosynthesis is shown in Fig. 2. The first steps are shared with the general phenylpropanoid pathway. Cinnamic acid is transformed by hydroxylation and methylation to produce acids with different substitutions on the aromatic ring. The 4-coumaric, ferulic and sinapic acids are then esterified by hydroxycinnamate CoA ligase to produce cinnamyl-CoAs, which are reduced by cinnamyl-CoA reductase (CCR) to produce the three aldehydes. These in turn are reduced by CAD to the three cinnamyl alcohols which are then polymerised into lignins. 

Fig. 4-2. Simplified reaction route illustrating the formation of lignin precursors. 1, 5-Dehydroquinic acid 2, shikimic acid 3, phenylpyruvic acid 4, phenylalanine 5, cinnamic acid 6, ferulic acid (Ri=H and R2=OCH3), sinapic acid (R,= R2=OCH3), and p-coumaric acid (R1=R2 = H) 7, coniferyl alcohol (Ri = H and R2=OCH3), sinapyl alcohol (Rj = R2=OCH3), and p-coumaryl alcohol (R =R2=H) 8, the corresponding glucosides of 7.

Spermidines substituted with cinnamic acid derivatives seem to be widely distributed in the plant kingdom. Cinnamic acid (alkaloid maytenine), caffeic acid (caffeoylspermidine, dicaffeoylspermidine), 4-coumaric acid (coumaroylspermidine, dicoumaroylspermidine, tricoumaroylspermidine), ferulic acid (feruloylspermidine, diferuloylspermidine), and sinapic acid (sinapoylspermidine, disinapoylspermidine) are known as aromatic amide substituents of spermidine. Occurrence, structure elucidation, and syntheses are summarized in Section V. 

Cinnamic acid and its derivatives found in plants originate from the aromatic amino acids L-phenylalanine and L-tyrosine by the elimination of ammonia. Some common natural cinnamic acid derivatives include -coumaric acid, caffeic acid, femlic acid, and sinapic acid. 

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. 

Phenolic acids include the benzoic acids (Ce-Ci), e.g., gallic, vanillic, syringic, protocatechuic, p-hydroxy-benzoic acid, as well as cinnamic acids (C6-C3), e.g., caffeic, p-coumaric, ferulic, sinapic acids, and their dep-sides and derivates, e.g., rosmarinic acid and lithospermic acid (Fig. 1). Phenolic acids and flavonoids in plants may occur in the free form, but they are often glycosylated with various sugars, especially glucose. Phenolic acids may also be present in the esterified as well as bound forms. Free phenolic acids are found especially in herbs and spices and, very often, in compounds responsible for antioxidant activity (benzoic and cinnamic acids and some of their derivatives). The bound forms are more common for the fruits, vegetables, and other plant materials. Therefore, in some cases, it is necessary to combine the analysis of their free and bound forms. 

L-Phenylalanine,which is derived via the shikimic acid pathway,is an important precursor for aromatic aroma components. This amino acid can be transformed into phe-nylpyruvate by transamination and by subsequent decarboxylation to 2-phenylacetyl-CoA in an analogous reaction as discussed for leucine and valine. 2-Phenylacetyl-CoA is converted into esters of a variety of alcohols or reduced to 2-phenylethanol and transformed into 2-phenyl-ethyl esters. The end products of phenylalanine catabolism are fumaric acid and acetoacetate which are further metabolized by the TCA-cycle. Phenylalanine ammonia lyase converts the amino acid into cinnamic acid, the key intermediate of phenylpropanoid metabolism. By a series of enzymes (cinnamate-4-hydroxylase, p-coumarate 3-hydroxylase, catechol O-methyltransferase and ferulate 5-hydroxylase) cinnamic acid is transformed into p-couma-ric-, caffeic-, ferulic-, 5-hydroxyferulic- and sinapic acids,which act as precursors for flavor components and are important intermediates in the biosynthesis of fla-vonoides, lignins, etc. Reduction of cinnamic acids to aldehydes and alcohols by cinnamoyl-CoA NADPH-oxido-reductase and cinnamoyl-alcohol-dehydrogenase form important flavor compounds such as cinnamic aldehyde, cin-namyl alcohol and esters. Further reduction of cinnamyl alcohols lead to propenyl- and allylphenols such as... 

Except perhaps for caffeic acid (H.86), these acids were mainly identified after hydrolysis of extracts, which means after degradation of the chlorogenic acids, CGA (See Section 2.1.4). In commercial roasted coffee, Hughes and Thorpe (1987) identified, by comparison with standard compounds, coumaric acid (without specification, probably p-), isoferulic acid (H.88) but surprisingly not ferulic acid (H.87), caffeic acid (H.86) and its dimethyl ether (H.89) as well as sinapic acid (H.90). They used capillary GC for the separation and identification of these phenolic acids and other carboxylic acids. The cinnamic acids are generally linked to quinic acid, but in robusta coffee caffeic and /j-coumaric (H.84) acids have also been identified as derivatives of tryptophan (see Section 2.1.2) (Morishita et al., 1987 Murata et ah, 1995) and... 

Cinnamic acid, 3,5-dimethoxy- sinapic acid 52. Phenol, 5-methyl-2-(l-methylethyl)- thymol... 

The cinnamate decarboxylase (CD) of Saccharomyces cerevisiae is highly specific. These yeasts are incapable of converting benzoic acids into volatile phenols. Only certain acids in the cinnamic series (phenyl-propenoic acids) may be decarboxylated by this microorganism. Among the cinnamic acids in grapes, only ferulic and p-coumaric acids are affected by the CD activity. Caffeic (4,5-dihydroxycinnamic) and sinapic (4-hydroxy-3,5-dimethoxycinnamic) acids are not decarboxylated by S. cerevisiae. Cinnamic acid and... 

Five soluble phenolic acids (free and esterifled), one of which is a hydroxylated derivative of benzoic acid (gallic acid) and four are cinnamic acid derivatives (caffeic, p-coumaric, ferulic, and sinapic acids), have been studied and tentatively identified in ethanolic extracts of hazelnut kernel and hazelnut by-products (Table 13.2) [31]. The order of total phenolic acid concentration was as follows hazelnut hard shell > hazelnut green leafy cover > hazelnut tree leaf > hazelnut skin > hazelnut kernel. Different phenolic acids predominate in each plant part examined. Among the identified phenolic acids, p-conmaric acid was most abundant in hazelnut kernel, hazelnut green leafy cover, and hazelnut tree leaf, whereas gallic acid was most abundant in hazelnut skin and hazelnut hard shell, possibly implying the presence and perhaps the dominance of tannins in the latter samples (Table 13.2). The same number, but different concentration, of phenolic acids have also been reported in hazelnnt kernel and hazelnut green leafy cover [30]. 

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