P-coumaric acid derivatives

The principal phenolic acids in these vegetables are ferulic and p-coumaric acid derivatives, the green parts of chives and leeks containing more than in the white part. In leek, the white tissue contains 6-7 mg ferulic acid per kg f.w., while this compound reaches concentrations of 23-39 mg/kg in the green parts [64]. In the case of chive, p-coumaric acid derivatives reach 21-51 mg/kg and ferulic acid derivatives 32-76 mg/kg. In garlic a different pattern of phenolic metabolite accumulation is observed in skins and internal tissues. The external tissues contain 49-58 mg/kg p-coumaric acid, 27-31 mg/kg ferulic acid and 27-25 mg/kg sinapic acid, whereas the internal tissues only contain 2mg, 6-8 mg and 2 mg/kg, respectively. In addition, the internal tissues contain 12-13 mg/kg p-hydroxybenzoic acid [64]. 

Cell wall fraction and vacuome. Most of the plastid and EE secretions are found finally in the cell wall fractions or in the vacuome. Therefore, the 7 0-methyl-ation of certain p-coumaric acid derivatives such as genkwanin and rhamnocitrin may be correlated to the crossing through the plasmalemma, eind the 4 0-methyl-... 

Cinnamic acid and p-coumaric acid, derived from L-phenyl-alanine, probably occur in all plants and fungi. Their biosynthesis was discussed in Chapter 7. 

Premvardhan, L.L., Buda, F., van der Horst, M.A., Liihrs, D.C., Hellingwerf, K.J., et al. Impact of photon absorption on the electronic properties of p-coumaric acid derivatives of the photoactive yellow protein chromophore. J. Phys. Chem. B 108, 5138-5148 (2004)... 

In this section we present results of the application of the ASEP/MD method to the study of solvent effects on electron transitions in p-coumaric acid derivatives. This system was chosen because it is an example of electron excitations that promote internal rotation around formal double bonds. Internal rotations are characterized by large flows of charge and, consequently, important solvent effects. Furthermore, they are involved in very interesting phenomena, as are dual fluorescence in push-pull chromophores [33-35] or cA-trans photoisomerization reactions [36-38]. An adequate description of the excited states involved in these processes demand state of the art quanmm calculations including both static and dynamic electron correlation contributions. Furthermore, in many cases the solute is stabilized by hydrogen bonds, consequently, it is compulsory to use a microscopic description of the solvent in order to account for specific interactions. In these conditions ASEP/MD becomes a good alternative to other methods and it can help to shed light on these processes [39 2]. 

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. 

Studies by Hudson et al, (2000) have demonstrated the presence of eight polyphenols in rice bran by using high-pressure liquid chromatography. They are protocatechuic acid, p-coumaric acid, ferulic acid, sinapic aci vanillic acid, caffeic acid, which is a methoxycirmamic acid derivative, and tricin. The effect of these polyphenols on cell viability and on the colony-forming ability of human-derived MDA MB 468 and HBL 100 breast cells, colon-derived SW 480 and human colonic epithelial cells was assessed. These authors concluded that rice bran polyphenols have putative cancer chemopreventive properties. 

Simple phenolic compounds include (1) the phenylpropanoids, trans-cinnamic acid, p-coumaric acid and their derivatives (2) the phenylpropanoid lactones called coumarins (Fig. 3.4) and (3) benzoic acid derivatives in which two carbons have been cleaved from the three carbon side chain (Fig. 3.2). More complex molecules are elaborated by additions to these basic carbon skeletons. For example, the addition of quinic acid to caffeic acid produces chlorogenic acid, which accumulates in cut lettuce and contributes to tissue browning (Fig. 3.5). 

Some of the acidic and basic polymers of the cell wall bear phenolic side-chains. The acidic polysaccharides carry ferulic and p-coumaric acid and related cinnamate-derivatives, esterified to specific hydroxy groups... 

Dimeric forms of ferulic and p-coumaric acids also occur in bound form within plant cell walls. The most common of these is didehydroferulic acid 23, which has been isolated from some plants of the Gramineae (53,54) and spinach cell cultures (7). While no such p-coumaric acid 2 derived dimer (i.e., C5-C5 linked) has ever been reported, cell walls of Lolium multiflorum contain another intriguing structural variation, namely 4,4 -dihydroxytruxillic acid 24 (5,55). 

It is well established that cinnamic acid and some substituted cinnamic acids (including frans-p-coumaric acid but not ferulic acid) can be dimerized in vitro by sunlight to truxillic and truxinic acids and their derivatives... 

Theoretically, trans-p-coumaric acid can produce 12 isomers depending on whether head-to-tail (4,4 -dihydroxytruxillic acid) or head-to-head (4,4 -dihydroxytruxinic acid) dimerizations occur with syn or anti and with cis or trans ring junctions (37). Mass spectrometric analysis of the tetra-TMSi derivatives showed that head-to-tail dimers split symmetrically on electron impact, whereas head-to-head dimers fragment asymmetrically (Figures 2 and 3) (33,35,38,39). Thus the tetra-TMSi derivative of 4,4 -dihydroxytruxillic acid has a mass spectrum similar to that of the bis-TMSi derivative of p-coumaric acid (33). 

The flavonoids, which comprise the largest group of these natural products, are derived from a mixed acetate-shikimate pathway. A shikimate-derived C6-C3 unit combines with a six-carbon polyketide chain to provide the open-chain precursor (685) of the group. The derivation of p-hydroxycinnamic add (p-coumaric acid), the C6-C3 component, from shikimic acid proceeds through chorismic acid, prephenic acid and phenylalanine. 

Most HPLC applications used for phenolic analysis simply allow the room temperature to determine the operating temperature of the column, but elevated temperatures of between 30°C and 40°C are often applied for phenolics and derivatives in apples (14), carrots (15), apple juice (6,13), bilberry juice (16), and for cis-trans isomers of caffeic and p-coumaric acids in wines (17). Generally, a change in temperature has only a minor effect on band spacing in reversed-phase HPLC and has essentially no effect in normal-phase separations. Thermostatic control of the column temperature is generally recommended to provide reproducible retention. 

For white wines (85), a similar HPLC condition to that of Betes-Saura et al. (79) was employed with a Nucleosil C)8 column (250 X 4.0-mm ID, 5 /zm) with binary gradient using eluent (A) acidified water (pH 2.65) and eluent (B) 20% A with 80% acetonitrile applied for hydroxy-cinnamate derivatives esters (caffeoyl tartaric, p-coumaroyl tartaric, and feruloyl tartaric acid esters) and free hydroxycinnamic acids (caffeic, ferulic, and p-coumaric acids). 

An HPLC method using a 90-min binary gradient with (a) acidified water, pH 2.4, and (b) acetonitrile on an Adsorbosphere C]8, 3-/zl cartridge (Alltech) was also developed for pheno-lics in barley (127). Seven phenolic compounds, including vanillic acid, p-coumaric acid, ferulic acid, and their derivatives, were separated by HPLC after alkaline hydrolysis in order to evaluate the role of bound phenolic acids in their antioxidant activity in beer. In this method, cis and trans isomers of p-coumaric and ferulic acids are quantified by HPLC, although cls-p-coumaric acid was not well separated from its trans isomer in this analysis. 

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). 

Among the hydroxycinnamic acids, caftaric acid predominates (up to 50% of total hydroxycinnamic acids). Other important substances are the tartaric esters of p-coumaric acid and ferulic acid, and the franx-p-coumaric glucoside (Somers et al. 1987). The concentration levels of hydroxycinnamic acid derivatives in wine depend on many factors like grape variety, growing conditions, climate, etc. It is... 

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