Hydroxycinnamic acids, direct

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). 

Megaphones, synthesis of 1250, 1252 Mercaptocalix[4]arenes, synthesis of 1402 [l.l.l.l]Metacyclophane framework 322 [l ]Metacyclophanes 1370 Metalation, directed 677 Metathesis reactions 1432 trarw-3-Methoxy-4-hydroxycinnamic acid, as MALDl matrix 323 Methoxylation 1167... 

The direct reaction between anthocyanins and hydroxycinnamic acids readily explains the formation of anthocyanin-vinylphenol-type adducts in red wines. At the time of writing, this is the only experimentally verified mechanism leading to the development of 4-vinylcatechol and 4-vinylsyringol pigments, as the free vinylphenols have neither been detected in wines nor was it possible to generate these compounds via enzymatic decarboxylation using yeasts commonly applied to red wine fermentation... 

The biosynthetic pathway (Figure 10.5) of polyphenols, including phenolic acids is well known. Phenylalanine formed in plants via the shikimate pathway is a common precursor for most of the phenolic compounds. Forming hydroxycinnamic acids from phenylalanine requires hydroxylation and methylation steps. The formation of hydroxybenzoic acids is simple and they can directly be formed from the corresponding hydroxycinnamic acids with the loss of acetate or with an alternate path stemming from an intermediate in the phenylpropanoid pathway [69,77,78]. 

The phenylpropanoid pathway (Fig. 3.1) is responsible for the production of many natural products that are of interest in the context of plant growth and development, human health, and ecology. For example, flavonoids are necessary for pollen viability in maize and petunia, and have been suggested to play a role in directed auxin transport. Flavonoids and sinapate esters have been found to be important UV-protectants in many species, including Arabidopsis. Furthermore, wall-bound phenolics are thought to impart control over cell wall expansion, and hydroxycinnamic acids are an important structural component of the hydrophobic barrier polymer suberin. Finally, lignin is a phenylpropanoid polymer ubiquitous in higher plants, which is necessary for mechanical support and water transport. " ... 

Direct evidence for the formation of coumarin from shikimate came from the radiotracer experiments of Kosuge and Conn in 1959, and they and others have also demonstrated cinnamic acid and a number of its ring-oxygenated derivatives, well known to originate from shikimate, to be precursors of various coumarins. The committed step in the biosynthesis of coumarins is hydroxylation of the benzene ring ortho to the side-chain of a cinnamic acid. In a few species the substrate is cinnamic acid itself, leading to the formation of coumarin, but for most coumarins, which bear 7-oxygenation, it is known or assumed that p-coumaric (4 -hydroxycinnamic) acid is the substrate, with discrete enzymes involved in the two cases. The product in the latter instance is 7-hydroxycoumarin (umbelliferone) ( 2, Fig. 1), and thus it is this compound rather than coumarin which, from the biosynthetic standpoint, is the parent compound of the vast majority of coumarins. 

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