Hydroxycinnamic esters

Peak 3 (Fig. 6.4.3) corresponds to p-hydroxybenzoic acid which is mainly ester-linked in poplar lignins. Although no study using appropriate model compounds has been made, it may be assumed that the thioacidolysis reagent is able to cleave, to a minor extent, benzoic and p-hydroxycinnamic ester linkages, as manifested by the recovery of benzoic and p-hydroxycinnamic acids from... 

Somers, X, Verette, E., Pocock, K. (1987). Hydroxycinnamate esters of Vitis vinifera Changes during white vinification, and effects of exogenous enzymic hydrolysis. J. Sci. Food Agric., 40, 67-78. 

Isomultiflorenol (157) co-occurs with cucurbitacins in seedlings of Bryonia dioica.41 The derivatives (158) and (159), both of which show diuretic activity in rats, occur in Antidesma menasu (Euphorbiaceae).112 3a-Hydroxymultiflora-7,9(ll)-dien-29-oic acid occurs in the roots of B. dioica as the p-hydroxycinnamate ester.113... 

Jose C. del Rio, Ana Gutierrez, Angel T. Martinez, Identification of intact long-chain p-hydroxycinnamate esters in leaf fibers of abaca (Musa textilis) using gas chromatography/mass mass spectrometry. Rapid Communications in Mass Spectrometry (2004), 18(22), 2691-2696. 

In our definition, CGAs are all hydroxycinnamate esters of (—)-quinic acid. CGAs are ubiquitous in the plant kingdom, produced by nearly all plant species in variable amounts and with variable structures. In a typical human diet, an estimated intake of around 2-3 g of CGAs per human per day is estimated, providing the main motivation for the investigation of CGA chemistry. 

Hydroxycinnamics are the third most abundant group of phenolic compounds in grapes and mainly comprise caffeic, coumaric, ferulic acids, and their corresponding tartaric esters (Fig. 83.2e). The hydroxycinnamic esters are more concentrated (2- to 100-fold) in grape skin than in pulp. Differences in total amount and proportion have been repotted according to grape varieties [32]. 

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. 

In addition to ester-linkages, hydroxycinnamic acids can also be covalently linked to cell wall components via phenyl ether bonds. While this has only been demonstrated for wheat (Triticum aestivum L.) straw lignin... 

Suberin is a composite of polymeric phenylpropanoids and ester-linked long chain fatty acids and alcohols and consists of a hydrophobic layer attached to the cell walls of roots, bark and the vascular system (8,10). The phenylpropanoid portion of suberin purportedly has a lignin-like structure to which both aliphatic domains and hydroxycinnamic acids are esterified. 

As can be seen from Fig 2b, the solid state C-13 nmr spectrum of T. aestivum also shows sets of enhanced resonances at 61 ppm and 169.6-174.9 ppm respectively (24). However, their relative intensities are very different from that observed for L. leucocephala. Indeed, it can immediately be seen that very little reduction of the administered precursor to hydroxymethyl analogues (at 61 ppm) has occurred. On the other hand, the dominant resonances at 169.6 and 174.9 ppm are coincident with bound hydroxycin-namic acids (e.g. ferulic 5a) and its esters (31). Subsequent analysis of its isolated acetal lignin derivative (32) indicated that much of the lignin contained hydroxycinnamate residues (33). 

In our analysis of the chemical structures which are active tur-inducers (41) it was found that the compounds fell into four groups (1) acetophenones and related structures, (2) monolignols, (3) hydroxycinnamic acids and their esters, and (4) chalcone derivatives (Fig. 1). Each compound had either a guaiacyl or a syringyl nucleus, and with the exception of the monolignols, possessed a carbonyl group. Most were of common occurrence in vascular plants. 

Alkaloids 36-41 were isolated from Lupinus luteus L. seedlings. They are considered to be lupinine esters with 4-hydroxycinnamic acids (94-100). The structures of these new alkaloids were elucidated on the basis of H NMR, MS, and chemical and enzymatic transformations. All these alkaloids were obtained from lupinine and hydroxycinnamic acid by two enzymatic systems (96-97) ligase catalyzed formation of the CoA-thioester, and transferase catalyzed lupinine ester formation from the CoA-thioester. 

Okamura, S. and Watanabe, M., Purification and properties of hydroxycinnamic acid ester hydrolase from Aspergillus japonicus. Agric. Biol. Chem. 46, 1839, 1982. 

Price, K.R., Causcelli, F., Colquhoun, I.J., and Rhodes, M.J.C., Hydroxycinnamic acid esters from broccoli florets. Phytochemistry, 45, 1683, 1997. 

Some studies have shown no changes in flavonoid levels in response to UV. Originally, only the flavonoids were thought to serve as UV-screening pigments. It is now clear, however, that other phenolics, such as hydroxycinnamic acids and their esters, are also... 

Proanthocyanidins and Procyanidins - In a classical study Bate-Smith ( ) used the patterns of distribution of the three principal classes of phenolic metabolites, which are found in the leaves of plants, as a basis for classification. The biosynthesis of these phenols - (i) proanthocyanidins (ii) glycosylated flavonols and (iii) hydroxycinnamoyl esters - is believed to be associated with the development in plants of the capacity to synthesise the structural polymer lignin by the diversion from protein synthesis of the amino-acids L-phenylalanine and L-tyro-sine. Vascular plants thus employ one or more of the p-hydroxy-cinnarayl alcohols (2,3, and 4), which are derived by enzymic reduction (NADH) of the coenzyme A esters of the corresponding hydroxycinnamic acids, as precursors to lignin. The same coenzyme A esters also form the points of biosynthetic departure for the three groups of phenolic metabolites (i, ii, iii), Figure 1. 

Some of the pathways of animal and bacterial metabolism of aromatic amino acids also are used in plants. However, quantitatively more important are the reactions of the phenylpropanoid pathway,173-1743 which is initiated by phenylalanine ammonia-lyase (Eq. 14-45).175 As is shown at the top of Fig. 25-8, the initial product from phenylalanine is trails-cinnam-ate. After hydroxylation to 4-hydroxycinnamate (p-coumarate) and conversion to a coenzyme A ester,1753 the resulting p-coumaryl-CoA is converted into mono-, di-, and trihydroxy derivatives including anthocyanins (Box 21-E) and other flavonoid compounds.176 The dihydroxy and trihydroxy methylated products are the starting materials for formation of lignins and for a large series of other plant products, many of which impart characteristic fragrances. Some of these are illustrated in Fig. 25-8. 

The Pechmann reaction is thought to proceed through electrophilic aromatic substitution of the phenol. The resulting /3-hydroxy ester then cyclizes and dehydrates to the coumarin, although of course dehydration may occur earlier in the sequence (Scheme 113). Indeed, the observation that 2-hydroxycinnamic acids readily yield coumarins in sulfuric acid (32JCS1681) renders these compounds or their esters plausible intermediates in the reaction. 

The general phenylpropanoid pathway links the shikimate pathway to the lignin branch pathway. The latter pathway leads to the formation of a series of hydroxycinnamic acids and hydroxycinnamoyl-CoA esters varying in their degrees of hydroxylation and methylation [5]. 

ABSTRACT Chlorogenic acids are polyphenolic compounds that occur ubiquitously in foods of plant origin. They are quinic acid esters of hydroxycinnamic acid. Recently, naturally occurring plant phenolics have attracted considerable attention in relation to their physiological potential. Depending upon the conditions, phenolic compounds can be either beneficial or detrimental to biological processes. 

Chlorogenic acids occur ubiquitously in plants. They are esters of hydroxycinnamic acids with quinic acid. The structures of chlorogenic... 

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