Plant phenolics, biosynthesis

In plants phenol biosynthesis proceeds by building the aromatic ring from carbohydrate precursors that already contain the required hydroxyl group... 

The shikimate pathway links the metabolism of carbohydrates to the biosynthesis of aromatic natural products via aromatic amino acids. This pathway, which is found only in plants and microorganisms, provides a major route to aromatic and phenolic natural products in plants. To date, over 8,000 phenolic natural products are known, which accounts for about 40% of organic carbon circulating in the biosphere. Although the bulk of plant phenolics are components of cell wall stmctures, many phenolic natural products are known to play functional roles that are essential for the survival of plants. 

Thin layer chromatographic analysis is also highly applicable to the determination of aromatic organic acids.In human organisms, aromatic acids are synthesized as metabolites in intoxication by toluene, xylene, and ethyl benzene. These compounds are easily absorbed through the skin or respiratory system, and are oxidized to aromatic acids. The separation, identification, and quantitative analyses of aromatic acids are also necessary because they appear as semiproducts of the biosynthesis of aromatic amino acids in plants (phenolic acids), and metabolites of numerous toxic substances, drugs, and catecholamines. Polar adsorbents and polar-... 

The combination of a root hair specific EST approach and expression analysis was an effective strategy for isolating candidate polyketide synthases potentially involved in sorgoleone biosynthesis. As a result of these efforts, two novel type III polyketide synthases have been identified that preferentially use long chain acyl Co-A s and are potentially involved in sorgoleone biosynthesis. These candidate polyketide synthases can form pentadecatriene resorcinol, an intermediate in sorgoleone biosynthesis. Furthermore, these efforts may aid in the identification of other polyketide synthases responsible for the biosynthesis of phenolic lipids in other plant species. 

BERNARDS, M.A., RAZEM, F.A., The poly(phenolic) domain of potato suberin a non-lignin cell wall bio-polymer. Phytochemistry, 2001,57,1115-1122. BERNARDS, M.A., Demystifying suberin. Can. J. Botany, 2002, 80,227-240. WHETTEN, R., SEDEROFF, R., Lignin Biosynthesis, Plant Cell, 1995, 7, 1001-1013. 

Biosynthesis. The primary precursors of L. are con-iferyl, sinapyl and p-coumaiyl alcohoi, which are derived from 4-hydroxycinnamic acid. L. from conifers (i. e. from softwood) is derived chiefly from conifeiyl alcohol with variable but small proportions of sinapyl and p-coumaryl alcohol. L. from dicotyledonous an-giosperms (i.e. from hardwood), particularly deciduous trees, is formed chiefly from sinapyl (-44%) and coniferyl (-48 %) alcohol, with about 8 % p-cou-maryl alcohol. L. in grasses is formed from p-coumar-yl (-30%), coniferyl (-50%) and sinapyl (-20%) alcohol. These primary L. precursors are formed from the aromatic amino acids L-phenylalanine and L-tyro-sine by a series of reactions shown (Rg.). The first reaction is catalysed by L-Phenylalanine ammonia-lyase (EC 4.3.1.5) (see) this enzyme is induced by light in a process involving phytochrome, and it is of general importance in the synthesis of plant phenolic compounds from phenylalanine and tyrosine. 

Against this backcloth it is perhaps not surprising to learn, that, despite its distinctive position in the overall patterns of plant phenol metabolism, ambiguity still surrounds the biosynthesis of gallic acid. Several pathways have been proposed. Zenk formulated a conventional pathway (Fig. 7, a) from L-phenylalanine to 3,4,5-trihydroxy-cinnamic acid followed by 6-oxidation to give gallic acid. 

Lattanzio V, Cardinali A, Ruta C, Fortunato IM, Lattanzio VMT, Linsalata V, Cicco N (2009) Relationship of secondary metabolism to growth in oregano (Origanum vulgare L.) shoot cultures under nutritional stress. Environ Exp Bot 65 54-62 Shetty K (2004) Role of proline-linked pentose phosphate pathway in biosynthesis of plant phenolics for functional food and environmental applications a review. Proc Biochem 9 789-803... 

Details about structure, biosynthesis, and classification of phenolics are described in the other chapters in this handbook. Plant phenolics have a distinctive ability to form non-covalent, intermolecular complexes with each other and with both large and small molecules. Recognition of the antioxidant activities of many polyphenols has established correlation with the health benefits by such compounds [34]. This leads to the development of commercial products containing free-radical-scavenging phytochemical mixtures, for example, Pycnogenol (procyanidin extracted from Pinus maritima). Table 82.2 represents a list of polyphenolic compounds used in nutraceuticals and their biologic effects on human health. 

A series for researchers and graduate students whose work is related to plant phenolics and polyphenols, as well as for individuals representing governments and industries with interest in this field. Each volume in this biennial series will focus on several important research topics in plant phenols and polyphenols, including chemistry, biosynthesis, metabolic engineering, ecology, physiology, food, nutrition, and health. 

According to Shetty (2004), the use of phenolic antioxidant phytochemicals for human health and wellness is not surprising. Plant adaptation to biotic and abiotic stresses is possible due to the stimulation of protective secondary metabolite pathways, which results in the biosynthesis of phenolic antioxidants. Therefore, phenolic antioxidants in food-grade plant species should be targeted as promising sources of health-promoting functional ingredients. 

Phenolic compounds are widespread products of secondary metabolism of lichen, and antioxidant activity is most frequently associated with their presence. Lichen phenolics are mainly depsides, depsidones and dibenzofurans, whereas vascular plant phenolics include tannins, lignins and flavonoids. Orsellinic acid is the basic unit in the biosynthesis of hchen phenolics. Lichen phenols are generally secreted by the fungal partner and deposited as crystals on the surface of the ceU wall of the fungal hyphae. Lichen phenols are primarily acetate-polymalonate derived with the exception of pulvinic acid derivates which are synthesised via... 

Rhodes M J C, Wooltorton L S C 1978 The biosynthesis of phenolic compounds in wounded plant storage tissues. In Kahl G (ed) Biochemistry of wounded plant tissue, de Gruyter Berlin, 243-286... 

Cheynier, V., Comte, G., Davies, K. M., Lattanzio, V. Martens, S. (2013). Plant phenolics recent advances on their biosynthesis, genetics, and ecophysiology. Plant Physiology Biochemistry, 72, 1-20. 

Biosynthesis of cinnamaldehyde (VIII) and also phenylalanine (compare biosynthesis of other of eugenol (I) an safrole (VI) originates from plant phenols in 18.1.2.5.1). The following... 

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