Phenylpropanoids vanillin

Validation of the role of femloyl-CoA in the synthesis of the vanillin precursor will be detection of the appropriate intermediates and/or enzyme activities in placental extracts that could account for the production of the predicted levels of capsaicinoids. The presence of low levels of monolignol intermediates could be explained by lignin biosynthesis. An alternate route from phenylalanine to vanillin has been considered by some investigators Orlova et al. [68] demonstrated the role of the benzenoid pathway in petunia flowers for the biosynthesis of phenylpropanoid/benzenoid volatiles. 

Funk C, Brodelius P (1992) Phenylpropanoid metabolism in suspension cultures of Vanilla planifolia Andr. IV Induction of vanillinic acid formation. Plant Physiol 99 256-262 Funk C, Brodelius P (1994) Vanilla planifolia Andrews in vitro biosynthesis of vanillin and other phenylpropanoids derivatives. In Bajaj YPS (ed) Biotechnology in agriculture and forestry. Medicinal and aromatic plants VI, vol 26. Springer, Berlin Heidelberg New York, pp 377-402... 

In summary, of the alternatives available for introducing a pathway of vanillin production de novo, or for enhancing vanillin production in Vanilla, HCHL presents the most attractive option of generating vanillin from a phenylpropanoid precursor (feruloyl-CoA) naturally present in plants (Whetten and Sederoff, 1995). 

Fig. 4-1. Examples of classical methods indicating a phenylpropanoid structure of lignin. (A) Permanganate oxidation (methylated spruce lignin) affords veratric acid (3,4-dimethoxybenzoic acid) (1) in a yield of 8% and minor amounts of isohemipinic (4,5-dimethoxyisophtalic acid) (2) and dehydrodiveratric (3) acids. The formation of isohemipinic acid supports the occurrence of condensed structures (e.g., /3-5 or y-5). (B) Nitrobenzene oxidation of softwoods in alkali results in the formation of vanillin (4-hydroxy-3-methoxybenzaldehyde) (4) (about 25% of lignin). Oxidation of hardwoods and grasses results, respectively, in syringaldehyde (3,5-dimethoxy-4-hydroxybenzaldehyde) (5) and p-hydroxybenzaldehyde (6). (C) Hydrogenolysis yields pro-pylcyclohexane derivatives (7). (D) Ethanolysis yields so-called Hibbert ketones (8,9,10, and 11).

It is also common to find compoimds of phenylpropanoid origin that have had the three-carbon side chain cleaved. As a result, phenylmethane derivatives, such as vanillin, are also common in plants. 

Similar results have been obtained in a study of the biogenesis of vanillin (105) in Vanilla planifolia and a similar direct breakdown of the phenylpropanoid precursor ferulic acid (13) was proposed. The mechanism of breakdown of the cinnamic acids to Cg.Ci compounds has most reasonably been formulated by Zenk as a i -oxidation involving the removal of acetate (or more probably acetyl co-enzyme A) from the side chain of the phenylpropanoid substrate. A scheme based on these ideas is shown in Figure 5.11. 

Others. Solvent extracts of allspice have shown potent in vitro antioxidant activity and antimutagenic activity/ Radical scavenging activity was found from various constituents of the berries including gallic acid, galloylglu-cosides, phenylpropanoids, eugenol, and vanillin. A fluid extract of the berries has shown in vitro antibacterial and antifungal activities. ... 

Many phenolic compounds other than phenylpropanoids can be obtained from plants catechol, guaiacol, syringic acid, syringaldehyde, gallic acid, vanillin, and vanillic acid are obtained from plants. These phenolic compounds have become candidates for monomers used in the polymer industry. They undergo oxidative polymerization and serve as monomers for phenol-formaldehyde type resins, and some compounds having a hydroxyl group and a carboxylic acid serve as monomers for polycondensation. 

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