Hydroxycinnamic acids Sinapic acid

The MALDI-TOF technique was first developed for the analysis of large biomolecules (Karas and others 1987). This technique presents some interesting characteristics. Of these, the high speed of analysis and the sensitivity of the technique have been pointed out as important advantages compared with other methods. In MALDI the samples are cocrystallized with a matrix that is usually composed of organic compounds, such as 3,5-dimethoxy-4-hydroxycinnamic acid (sinapic acid), 2, 4, 6 -trihydroxyacetophenone, a-cyano-4-hydroxycinnamic acid (alpha-cyano or alpha-matrix), and 2,5-dihydroxybenzoic acid (DHB). After the cocrystallization, the laser is fired and the matrix absorbs energy and allows a soft ionization of the samples. Afterward the ions are analyzed by a TOF mass spectrometer. 

As discussed in Section 7, the general phenylpropanoid pathway originally included the biosynthesis of the hydroxycinnamic acids caffeic acid (3.32), femlic acid (3.33), 5-hydroxyferulic acid (3.34), and sinapic acid (3.35) from />coumaric acid (3.30), as well as the corresponding CoA-esters... 

Phenolic acids Hydroxycinnamic acids Caffeic acid Chlorogenic acid Ferulic acid Sinapic acid Caftaric acids Neochlorogenic acid p-Coumaric acid Blackberry, raspberry, strawberry, blackcurrant, blueberry, cranberry, pear, sweet cherry, apple, orange, grapefruit, lemon, and peach [8]... 

These are CgC3 compounds, made up of a benzene ring with a three-carbon side chain. The most important are the hydroxycinnamic acids caffeic acid, p-coumaric acid, ferulic acid and sinapic acid. They can be derived from different stages of the shikimic acid pathway. These acids are of much benefit therapeutically and are non-toxic. They may also occur as glycosides. 

Advances in analytical procedures resulted in several reports on anthocyanins acy-lated with hydroxycinnamic acids (p-coumaric, caffeic, ferulic, sinapic, and 3,5-dihydroxycinnamic acids), hydroxybenzoic acids (p-hydroxybenzoic and gallic acids), and aliphatic acids (malonic, acetic, malic, oxalic, succinic and tartaric acids). However, not all of them were found in anthocyanins isolated from foods. Among the 44 fruits listed in Table 4.3.1, 15 presented acylated anthocyanins as did 12 of 13 vegetables shown in Table 4.3.3 and 2 of the 9 grains cited in Table 4.3.4. On the other hand, acylated anthocyanins were found in all grapes from Vitis species, although at different abundance levels, as can be seen in Table 4.3.2. A higher... 

Among the hydroxycinnamic acids, anthocyanins acylated with sinapic acid are not widespread in foods they have been isolated only in black carrots " and red cabbages." Anthocyanins that are acylated with p-hydroxybenzoic acid were only found in black carrots " and sweet potatoes. This acyl group was located within the 6 position of a glucoside moiety. 

Takahama, U. Oniki, T. Effects of ascorbate on the oxidation of derivatives of hydroxycinnamic acid and the mechanism of oxidation of sinapic acid by cell wall-bound peroxidases. Plant Cell Physiol. 1994, 35, 593-600. 

Hydroxycinnamic acids are common in the majority of plant species and certain fruits and vegetables (e.g. plums and artichoke) and cereal brans (e.g. whole grains) are a good source (Clifford, 1999). They occur less often as the free acids (e.g. /9-coumaric, caffeic, ferulic, sinapic) but usually occur as... 

The most common hydroxycinnamic acid derivatives are p-coumaric (4-hydroxy-cinnamic), caffeic (3,4-dyhydroxycinnamic), ferulic (4-hydroxy-3-methoxycinnamic), and sinapic (4-hydroxy-3,5-dimethoxycinnamic) acids, which frequently occur in foods as simple esters with quinic acid or glucose (Mattila and Kumpulainen 2002). 

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. 

Polyphenolics are classified into three important groups phenolic acids, flavonoids, and tannins. Phenolic acids include hydroxyben-zoic (C6-Ci), hydroxyphenylacetic (C6-C2), and hydroxycinnamic (C6-C3) acids (Figure 11.2.3 also see Figure 11.3.3). Hydroxycinnamic acids are most widely distributed in plant tissues. The important hydroxycinnamic acids are p-coumaric, caffeic, ferulic, and sinapic... 

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. 

The phenolic acids of interest here [caffeic acid (3,4-dihydroxycinnamic acid), ferulic acid (4-hydroxy-3-methoxycinnamic acid), p-coumaric acid (p-hydroxycinnamic acid), protocatechuic acid (3,4-dihydroxybenzoic acid), sinapic acid (3,5-dimethoxy-4-hydroxyxinnamic acid), p-hydroxybenzoic acid, syringic acid (4-hydroxy-3,5-methoxybenzoic acid), and vanillic acid (4-hydroxy-3-methoxybenzoic acid)] (Fig. 3.1) all have been identified as potential allelopathic agents.8,32,34 The primary allelopathic effects of these phenolic acids on plant processes are phytotoxic (i.e., inhibitory) they reduce hydraulic conductivity and net nutrient uptake by roots.1 Reduced rates of photosynthesis and carbon allocation to roots, increased abscisic acid levels, and reduced rates of transpiration and leaf expansion appear to be secondary effects. Most of these effects, however, are readily reversible once phenolic acids have been depleted from the rhizosphere and rhizoplane.4,6 Finally, soil solution concentrations of... 

Grapes contain several hydroxycinnamic acids, p-coumaric, caffeic, ferulic and sinapic acids, which exist as free acids and esterified with tartaric acid. Saccha-romyces species can take up free acids to produce the corresponding vinyl phenol catalysed by hydroxycinnamate decarboxylase (phenylacrylic acid decarboxylase Padlp) (Fig 8D.11) (Chatonnet et al. 1992b Chatonnet et al. 1993 Edlin et al. 1995). Vinyl phenols are unstable and highly reactive. Dekkera bruxellensis is one of few wine microorganisms that can further reduce vinyl phenols to highly stable ethyl phenols in wine. Vinyl phenols can also react with anthocyanins to form vinyl derivatives, a reaction that is favoured by fermentation yeast having hydroxycinnamate decarboxylase activity (Morata et al. 2006). 

Precursors. Both hydroxycinnamic acids and 4-vinylphenols can lead to the formation of hydroxyphenyl-pyranoanthocyanins. The main hydroxycinnamic acids present in wines are p-coumaric, caffeic, ferulic and sinapic acids. 4-Vinylphenol and 4-vinylguaiacol are volatile phenols associated with off flavors in wine (Eti6vant 1981) and arise from the decarboxylation of p-coumaric and ferulic acid, respectively, via the yeast cinnamate decarboxylase (CD) (Chatonnet et al. 1993). 

Hydroxycinnamic acids possess a C6-C3 skeleton and formally belong to the group of phenylpropanoids. The different compounds present in wine are mainly derived from the hydroxycinnamic acids caffeic acid, p-coumaric acid, ferulic acid, and sinapic acid (Fig. 9C.2). These derivatives can be present in cis- and trans-configured forms, while the trans forms are more stable and therefore more prevalent. In wine HCA are present in low amounts in their free form, while the depside forms, i.e. esters of l-(-i-)-tartaric acid, are predominant. The ubiquitous chlorogenic acids, esters of HCA and quinic acid, cannot be found in wine but are replaced by the tartaric acid esters instead (Ong and Nagel 1978 Singleton et al. 1978 Somers etal. 1987). 

A cross-talk between the two activation pathways of hydroxycinnamic acids by CoA or glucose was shown in an Arabidopsis mutant with hyperfluorescence upon reduction of UDP-glucose sinapate glucosyltransferase acfivify a part of fhe sinapic acid was activated as CoA thioester and directed into flavonoid biosynthesis (Sinlapadech et al, 2007). 

COMT (EC 2.1.1.68) was detected as an enzyme methylating caffeic acid to ferulic acid with the help of SAM and later it was shown that 5-hydroxyferulic acid is also methylated to sinapic acid. Mostly, other substrates will be accepted as well (Roje, 2006). Nowadays, however, there are strong indications that the hydroxycinnamic aldehydes and/or alcohols will be preferentially methylated by COMTs (Parvathi et al, 2001). Kinetic investigations of the... 

In the first category the best known cases are those in which a hydroxycinnamic acid is dimerized oxi< datively to a bisaryldilactone. A range of examples are known.Typical reactions are the oxidation of sinapic acid (273) to the dilactone (274), in 65% yield using oxygen-iron(III) chloride, and in 60%... 

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