Hydroxycinnamic alcohols

Syrjanen, K., and Brunow, G. (1998) Oxidative cross couphng of p-hydroxycinnamic alcohols with dimeric arylglycerol b-aryl ether hgnin model compounds The effect of oxidation potentials. J. Chem. Soc., Perkin Trans. 1 (20), 3425-3429. 

Quinone methides play an important role in lignification. They are produced directly, as intermediates, when lignin monomers, be they hydroxycinnamyl alcohols, hydroxy-cinnamaldehydes, or hydroxycinnamates, couple or cross-couple at their 8- positions. A variety of postcoupling quinone methide rearomatization reactions leads to an array of structures in the complex lignin polymer (Fig. 12.2). 

Takahama, U. Oniki T. Shimokawa H. A possible mechanism for the oxidation of sinapyl alcohol hy peroxidase-dependent reactions in the apoplast enhancement of the oxidation hy hydroxycinnamic acids and components of the apoplast. Plant Cell Physiol. 1996, 37, 499-504. 

Takahama, U. Oxidation of hydroxycinnamic acid and hydroxycinnamyl alcohol derivatives by laccase and peroxidase—interactions among p-hydroxyphenyl, guaiacyl and syringyl groups during the oxidation reactions. Physiol. Plantarum 1995, 93, 61-68. 

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. 

Attachment of Hydroxycinnamic Acids to Structural Cell Wall Polymers. Peroxidase mediation may also result in binding the hydroxycinnamic acids to the plant cell wall polymers (66,67). For example, it was reported that peroxidases isolated from the cell walls of Pinus elliottii catalyze the formation of alkali-stable linkages between [2-14C] ferulic acid 1 and pine cell walls (66). Presumably this is a consequence of free-radical coupling of the phenoxy radical species (from ferulic acid 1) with other free-radical moieties on the lignin polymer. There is some additional indirect support for this hypothesis, since we have established that E-ferulic acid 1 is a good substrate for horseradish peroxidase with an apparent Km (77 /tM), which is approximately one fifth of that for E-coniferyl alcohol (400 /iM) (unpublished data). 

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. 

Negishi I, Ozawa T (1996) Determination of hydroxycinnamic acids, hydroxybenzoic acids, hydroxybenzaldehydes, hydroxybenzyl alcohols and their glucsides y high-performance liquid chromatography. J Chromatogr A 756 129-136... 

Taraxacum officinale G. H. Weber ex Wigg. Western Pu Gong Ying (Dandelion) (root) Inulin, essential oils, choline, hydroxycinnamic acids, carotenes, ether oils, monoterpene, oxalic acids, hydrocyanic acids, sesquiterpene glucosides, flavonoids, hydroxybenzoic acid, coumarins, anthocyanidines, anthraquinones, phytosterines, squalene, cerylic alcohol, arabinose, vitamins , , C.88-222-450 Sudorific, stomachic, tonic, a remedy for sores, boils, ulcers, abscesses, snakebites. 

Generally the esters of phenols found naturally are compounds where the phenol contributes the carboxyl group, and another compound contributes the alcoholic hydroxyl group. The hydroxycinnamic acids do not seem to undergo intermolecular condensation, but esters with quinic acid and other acids do occur. For example, chlorogenic acid is an ester of cafifeic acid and quinic acid (3-caffeoylquinic acid 2.24). 

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. 

Several papers report new findings on ubiquinone biosynthesis. A mitochondrial membrane-rich preparation from baker s yeast can convert 4-hydroxybenzoate and isopentenyl pyrophosphate into the ubiquinone precursor 3-all-trans-hexaprenyl-4-hydroxybenzoate (234). Details of the cell-free system are presented. With preformed polyprenyl pyrophosphates, the system catalysed the polyprenylation of several aromatic compounds, e.g. methyl 4-hydroxybenzoate, 4-hydroxybenzaldehyde, 4-hydroxybenzyl alcohol, and 4-hydroxycinnamate. No evidence was obtained for the involvement of 4-hydr-oxybenzoyl-CoA or 4-hydroxybenzoyl-S-protein in the reaction. With shorter-chain prenyl pyrophosphates a shorter prenyl side-chain was introduced, e.g. geranyl and farnesyl pyrophosphates gave products with a 3-diprenyl and 3-triprenyl side-chain respectively. A crude enzyme preparation from E. coli... 

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... 

Carnauba wax consists primarily of a complex mixture of esters of acids and hydroxy acids, mainly aliphatic esters, to-hydroxy esters, p-methoxycinnamic aliphatic esters, and p-hydroxycinnamic aliphatic diesters composed of several chain lengths, in which Ci6 and C32 alcohols are the most prevalent. ... 

Figure 4 Current view of the phenylpropanoid pathway to the monolignols 19-23. 4CL, 4-hydroxycinnamate coenzyme Aligases pC3H , p-coumarate 3-hydroxylase C4H, cinnamate 4-hydroxylase CAD, cinnamyl alcohol dehydrogenases CCOMT, hydroxycinnamoyl CoA O-methyltransferases CCR, cinnamoyl-CoA oxidoreductases COMT, caffeic acid O-methyltransferases F5H , ferulate 5-hydroxylase HCT, hydroxycinnamoyl-CoA shikimate hydroxycinnamoyltransferase HOT, hydroxycinnamoyl-CoA quinate hydroxycinnamoyltransferase PAL, phenylalanine ammonia lyase TAL, tyrosine ammonia lyase.

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