Cinnamic acids with caffeic acid

Figure 6.8 UV spectra of standard chlorogenic acid (a) trans-cinnamic acid (b) cafFeic acid (c) p-coumaric acid (d) and femlic acid (e). The spectra of peaks 1 (chlorogenic acid) (f), peak 2 (chlorogenic acid isomer) (g), and peak 3 (caffeic acid) (h) were determined with HPLC fractions isolated from extracts of Superior potato peel.

Tracer studies with labeled phenylalanine and with tyrosine have shown that these are specifically incorporated. Intermediates in this biosynthesis are tryamine, cinnamic acid, p-coumaric acid, and caffeic acid 11). 

All findings up to now indicate that all other coumarins are formed in the same way from the corresponding substituted cinnamic acid, p-Coumaric acid furnishes umbelliferone, caffeic acid aesculetin and ferulic acid scopoletin (Fig. 99). Thus, our reaction scheme (Fig. 98) is generally valid, the appropriate ring substituents have simply to be inserted. The mode of biosynthesis provides us with an explanation of the fact that the most important cinnamic acids and coumarins exhibit the same pattern of substitution. 

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. 

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). 

Figure 6.6 HPLC chromatogram of the extract from Superior potato flesh (a) and of the same extract spiked with standards (b). Identification p.1, chlorogenic acid p.2, chlorogenic acid isomer p.3, caffeic acid p.4, p-coumaric acid p.5, ferulic acid p.6, t-cinnamic acid. Column, Inertsil ODS-3 V (5 p.m, 4.0 X 250 mm) flow rate, l.OmL/min column temperatures, 20°C mobile phase, acetonitrile 0.5% formic acid (gradient mode) detector, UV at 280 nm.

After oral administration of caffeic acid to rats, small amounts of vanillic acid and vanilloylglycine are excreted. The conversion of p-hydroxycinnamic acid into /7-hydroxybenzoic acid is found in rat liver mitochondria [18], Studies with /7-hydroxy[U-14C]cinnamic acid have showed that 14C02 is released during reaction, indicating that reaction probably followed the p-oxidation type reactions, the two carbon being first removed as acetyl-CoA, and then oxidized to C02. It is assumed that conversion of ferulic acid formed by methylation of caffeic acid into vanillic acid occurs in rat liver mitochondria. 

A pure culture of the organism was inoculated into a basal medium with the addition of 0.025% caffeic acid. After 7 days incubation at 25°C under conditions of reduced oxygen tension, the caffeic acid was completely metabolized. Metabolites of caffeic acid are identified as dihydrocaffeic acid and ethyl catechol, respectively. In the 1960s, it has been reported that a constitutive enzyme present in strains of Aerobacter decarboxylates caffeic acid to 4-vinylcatechol nonoxidatively [20], Several cinnamic acids have been tested and the decarboxylation product from /7-coumaric acid has been identified as 4-vinylphenol. Thus, the bacterial enzyme activity requires a relatively unhindered 4-hydroxy group on the aromatic ring and an acrylic acid side chain. 

Figure S.21 Resulting chromatogram at the optimum conditions predicted by figure S.20. pH = S.8 concentration of n-octylamine = 3.2 mM. ODS column mobile phase methanol-water (20/80) with 0.010 M acetate buffer. Solutes E = phenylethylamine, P = phenylalanine, V = vanillic acid, C = trans caffeic acid, M = trans p-coumaric acid, F = trans ferulic acid, A = phenylacetic acid, H = hydrocinnamic acid and N = trans cinnamic acid. Figure taken from ref. [559]. Reprinted with permission. 

Phenylpropanoids have an aromatic ring with a three-carbon substituent. Caffeic acid (308) and eugenol (309) are known examples of this class of compounds. Phenylpropanoids are formed via the shikimic acid biosynthetic pathway via phenylalanine or tyrosine with cinnamic acid as an important intermediate. Phenylpropanoids are a diverse group of secondary plant compounds and include the flavonoids (plant-derived dyes), lignin, coumarins, and many small phenolic molecules. They are known to act as feeding deterrents, contributing bitter or astringent properties to plants such as lemons and tea. 

It should be emphasized that a complex of substances is generally involved when allelopathic interferences occur, often with each below a threshold level for impact. This is illustrated by the combinations of phenolic acids found in decomposing crop residues (25-27) and from soils (28-34). In allelopathic situations which implicate phenolic acids, soil quantities of ferulic, p-coumaric, and caffeic acids have ranged from below 10 to above 1,000 ppm for each compound (11,35). The lower end of this spectrum is below a concentration required for an effect in current bioassays. However, additive and synergistic effects have been documented for combinations of cinnamic acids (35), benzoic acids (36), benzoic and cinnamic acids (37), and p-hydroxybenzaldehyde with coumarin (38). Each of the allelochemicals in these tests was not equally toxic, but they contributed incrementally to inhibition of germination and growth. Whereas combinations of many allelochemicals have not been determined, it appears that both additive and synergistic interactions are extremely important under field conditions. 

A number of putrescine derivatives have been detected in nature for which one or two cinnamic acid analogs with amide linkages are known 4-coumaroylputrescine (2), di-4-coumaroylputrescine (3), feruloylpu-trescine (4) (subaphylline), diferuloylputrescine (5), caffeoylputrescine (6) (paucine), dicaffeoylputrescine (7), sinapoylputrescine (8), and disinapoyl-putrescine (9). Paucine, one of the first diaminoalkane alkaloids known since 1894 as a component of the seed of Pentaclethra macrophylla, was hydrolyzed (40% KOH - H20) to give putrescine and caffeic acid. Structure 6 was deduced (37) from this data together with spectroscopic data, especially mass spectra. Another derivative of putrescine, subaphylline (4), first isolated from Salsola subaphylla, was shown to be the monoferuloyl derivative of putrescine by hydrolysis (30% K0H-H20) (38). The structure elucidation of the other derivatives of putrescine (2, 3, 5, 7-9) mentioned before was undertaken in a manner similar to that of 4 and 6. Several compounds were synthesized and compared to the natural products and are summarized in Table II of Section V. 

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. 

There is a growing interest in naturally occurring phenolic compounds that display biological antioxidant properties such as -hydroxycinnamic acid, ferulic zcid, caffeic acid/ and curcumin which are ubiquitous in plant food. It has been demonstrated that the interaction of the oxidizing OH adduct of DNA, poly-A and poly-G with hydrox-ycinnamic acid derivatives proceed via electron transfer. Cinnamic acid derivatives have been shown to be able to scavenge superoxide, peroxyl, and hydroxyl radicals. 

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