4- Hydroxycinnamate, from cinnamate

Phenylpropanoids are biologically synthesized from phenylalanine as described above. Among them, cinnamic acid is synthesized directly from phenylalanine by phenylalanine ammonia-liase (PAL), and p-hydroxycinnamic acid p-coumaric acid) is synthesized from cinnamic acid by cinnamic acid 4-hydroxylase (C4H, an enzyme in the cytochrome P-450 family).The phenylpropanoid metabolic pathway is important for plants to synthesize lignin, and some phenylpropanoids are seen at junctions of cell wall polysaccharides such as hemicellulose and pectin. 

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. 

Further support for the intermolecular route is provided by the isolation of the substituted trans-cinnamic acid, the normal Perkin product. This arises through elimination of carboxylic acid from the fully acylated species (393) rather than cyclization. For example, a considerable amount of 2-acetoxy-3-methoxycinnamic acid is formed from 3-methoxysalicylaldehyde, perhaps as a result of steric interference with cyclization so allowing the intermolecular process to predominate (39JPR(152)23). It should be noted that trans- 2-hydroxycinnamic acids do not cyclize under normal Perkin conditions, though the cis isomer does so quite readily. Isomerization of the trans acid has been effected by treatment with a trace of iodine in acetic anhydride or by UV irradiation. 

In vitro cell free microsomes (from pea seedlings and 4-T-Cinnamic acid 3-T-4-Hydroxycinnamic acid 85-90 107... 

Precursors. Both hydroxycinnamic acids and 4-vinylphenols can lead to the formation of hydroxyphenyl-pyranoanthocyanins. The main hydroxycinnamic acids present in wines are p-coumaric, caffeic, ferulic and sinapic acids. 4-Vinylphenol and 4-vinylguaiacol are volatile phenols associated with off flavors in wine (Eti6vant 1981) and arise from the decarboxylation of p-coumaric and ferulic acid, respectively, via the yeast cinnamate decarboxylase (CD) (Chatonnet et al. 1993). 

Fig. 5. Hammett plot for the reaction of "OH radical with cinnamate derivatives (1) OT-hydroxycinnamate, (2) -hydroxycinnamate, (3) w-methoxycinnamate, (4) p-methoxycinnamate, (5) w-chlorocinnamate, (6) p-chlorocinnamate, (7) OT-nitrocinnamate, and (8) p-nitrocinnamate pH 7, Dose/pulse 15 Gy. [Taken from P. Yadav, Ph.D. Thesis, University of Pune, 2006.]...

The use of certain pectolytic enzyme preparations to facilitate the extraction or clarification of white must may lead to an increase in the vinyl-phenol content of white wines and a deterioration of their aromatic qualities (Chatonnet et al 1992a Dugelay etal., 1993 Barbe, 1995). Indeed, certain industrial pectinases, made from Aspergillus niger cultures, have a cinnamyl esterase (CE) activity. This enzyme catalyzes the hydrolysis of tartrate esters of hydroxycinnamic acids in must during the pre-fermentation phase (Figure 8.7). Feruhc and j9-coumaric acids are then converted into vinyl-phenols during alcohohc fermentation due to the cinnamate decarboxylase activity of Saccharomyces cerevisiae. 

Norwood et al. (1980) chlorinated a considerable number of phenolic acids of both benzoic and cinnamic acid types and looked for haloform production. Concentrations were from 0.5-6 mM and approximately a twofold excess of chlorine was added. For most of the acids tested, except those with 1,3-dihydroxy (resorcinol-type) substituents, chloroform yields were low (0-4 7o) except in the case of 3-methoxy-4-hydroxycinnamic acid (ferulic acid, 10), where about an 11% yield was... 

Kaneko et al. [79] have prepared hyperbranched structures from the copolymerization of 4-hydroxycinnamic acid with 3,4-dihydroxy cinnamic acid i.e. monomers bearing some resemblance to lignin structural units). These... 

It is believed that these compounds, characteristic of Brettanomyces and Dekkera, result from decarboxylation of hydroxycinnamic acids, yielding vinyl phenol intermediates and subsequent reduction to produce the ethyl analog (Steinke and Paulson, 1964). As seen in Fig. 3-3 initial decarboxylation is mediated by cinnamate decarboxylase, whereas the reduction step utilizes a vinyl phenol reductase. 

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