Biosynthesis cinnamic acid

Fig. 3. Cinnamate biosynthesis from phenylalanine (8) to cinnamic acid (9) or from tyrosine (10) to coumaric acid (11). Coumarylquinic acid (12) is also...

The earliest references to cinnamic acid, cinnamaldehyde, and cinnamyl alcohol are associated with thek isolation and identification as odor-producing constituents in a variety of botanical extracts. It is now generally accepted that the aromatic amino acid L-phenylalanine [63-91-2] a primary end product of the Shikimic Acid Pathway, is the precursor for the biosynthesis of these phenylpropanoids in higher plants (1,2). 

El-Basyouni, S.Z., A. C. Neish, andG. H. N. Towers The Phenolic Acids in Wlxeat III. Insoluble Derivatives of Phenolic Cinnamic Acids as Natural Intermediates in Lignin Biosynthesis. Phytochem. 3, 627—640 (1964). 

A different approach to investigate active lignification during resistance reactions is provided by the determination of enzyme activities involved in lignin biosynthesis. Resistant plants are expected to be more strongly activated during or immediately preceding the resistance reaction compared to susceptible plants. Thus, phenylalanine ammonia-lyase (PAL) (43-45), cinnamic acid 4-hydroxylase (46), O-methyltransferases (44), and... 

Tiburzy (22,31) obtained similar results by application of the PAL inhibitor aminooxyacetic acid (AOA). However, AOA does not specifically inhibit PAL (99), and PAL is not only involved in lignin biosynthesis (100). Thus, AOA and the related inhibitor aminooxyphenyl propionic acid (AOPP) (101,102) inhibit the biosynthesis of lignin (103,104), anthocyanins (105), other flavonoids (106), and conjugates of cinnamic acids (107) via PAL, as well as ethylene (108-110) via a pyridoxal phosphate dependent enzyme (110,111). In view of the possible function of phenolic compounds as phytoalexins (21,112,113) and the well documented role of ethylene in some resistance reactions (114-116), the above cited experiments with AOA (22,... 

For the biosynthesis of vanillin, several other enzymes are of interest. First of all, phenylalanine ammonia lyase (PAL) this enzyme converts phenylalanine into the cinnamic acid type of compounds, the first intermediates in the vanillin biosynthesis after the primary metabolism. PAL activity could be detected in green beans, but after scalding this activity is lost. The chain shortening enzyme (CSE), responsible for the conversion of a C Cs compound into a C6Ci compound, was found to be localised in the cytosol of cells of the placental tri-chomes in the green beans [23]. 

The biosynthesis of coumarins begins with traw5 -4-cinnamic acid, which is oxidized to ort/io-coumaric acid (2-hydroxy cinnamic acid) followed by formation of the glucoside. This glucoside isomerizes to the corresponding cA-compound, which finally through ring closure forms... 

Fig. (2). Proposed pathways of SA and 4HBA biosynthesis. Enzymatic steps for which the enzymes have been identified include PAL, CA4H (cinnamic acid 4-hydroxylase), and BA2H (benzoic acid 2-hydroxylase). Taken from Smith-Becker et al., 1998, [55].

The biosynthesis of gallic acid (3.47) has been under investigation for more than 50 years. Different biosynthetic routes have been proposed, as depicted in Figure 3-6 (/) direct biosynthesis from an intermediate of the shikimate pathway, (2) biosynthesis via phenylalanine (3.27), cinnamic acid (3.29), />coumaric acid (3.30), caffeic acid (3.32), and 3,4, 5-trihydroxycinnamic acid (3.44), or (3) biosynthesis via caffeic acid (3.32) and protocatechuic acid (3.45). The possibility that different pathways co-existed in different species or even within one species was also considered. 

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. 

The biosynthetic pathway for salicylic acid is not clear. At present, at least two pathways have been proposed. Each branches from phenyl-propanoid biosynthesis after phenylalanine has been converted to trans-cinnamic acid by phenylalanine ammonium lyase (PAL). In one scheme (Pathway 1 Fig. 4), tram-cinnamic acid would be converted to 2-hydroxy cinnamic acid (or 2-coumaric acid) by a cinnamate 2-hydroxylase. This compound could then be converted to salicylic acid via -oxidation possibly through an acetyl coenzyme A (CoA) intermediate. Alternatively, tram-cinnamic acid could be oxidized to benzoic acid and then hydrox-ylated via a postulated o-hydroxylase activity. The details of this pathway, particularly in tobacco and cucumber, deserve further study. 

In either of the proposed pathways, salicylic acid is synthesised from tram-cinnamic acid. This is an intriguing observation and may provide a clue as to how and why the induction of SAR is tightly linked to the formation of a necrotic lesion. When plants react hypersensitively to pathogen attack, many biochemical changes occur, including the induction of phenylpropanoid biosynthesis. In bean, as well as other plants, this induction seems to be at least partly caused by an increase in the synthesis of phenylalanine ammonium lyase and other enzymes involved in the biosynthesis of isoflavonoid phytoalexins, flavonoid pigments and... 

The reductive sequence from an appropriate cinnamic acid to the corresponding cinnamyl alcohol is not restricted to lignin and lignan biosynthesis, and is utilized for the production of various phenylpropene derivatives. Thus cinnamaldehyde (Figure 4.23) is the principal component in the... 

The enc cluster contains four genes (encH, encl, encJ, encP) involved in the biosynthesis of the unusual benzoyl-CoA (185) starter from phenylalanine (186) via a plant-like p-oxidation mechanism (Fig. 32) [208-210]. This pathway is initiated by the unique phenylalanine ammonia-lyase EncP [211], which catalyzes the generation of cinnamic acid (187) from 186. The cinnamate-CoA ligase EncH... 

The second aspect of the biosynthesis of norpluviine which has been studied is the mechanism whereby phenylalanine is incorporated into the C-6-C-1 aromatic unit of the alkaloid. This takes place via cinnamic acid, hydroxylated cinnamic acids, and protocatechualdehyde (389). 

The first studies on the biosynthesis of ephedrine in Ephedra distachya suggested that phenylalanine was incorporated via a C6—C2—N unit (339). When this was reinvestigated more recently, it was found that while C-3 and the aromatic ring of phenylalanine are incorporated, C-2 is not (341, 342). Specific incorporation of C-3 of phenylalanine into norpseudoephedrine in Catha edulis had also been reported (343). Further incorporation experiments showed that [carhaxy/-l4C]benzoate, [7-l4-C]benzaldehyde, and [3-l4C]cinnamic acid are all efficiently incorporated into the a carbon of ephedrine, and the participation of a C6—C, intermediate rather than a C6—C2 unit appears to be well supported (341, 342) (Scheme 4). Studies favor a biosynthetic scheme for ephedrine where C6—C, compounds such as benzoic acid or benzaldehyde react with C2—N compounds or equivalents to give ephedrine. The origin of the C2—N unit is still obscure. Methyl groups for N-methylation were previously shown to be donated from methionine or formate (538). 

Yu et al. (2005) evaluated capsaicin biosynthesis in water-stressed hot pepper fruits. The concentration of capsaicin in the placenta of fruits in the water deficit treatment began to increase rapidly 10 DAF. It reached maximum at 30 DAF and was 3.84-fold higher than in the placenta of control treatment plants. In the pericarp, the concentration of capsaicin reached maximum at 50 DAF and was 4.52-fold higher than in the control treatment. PAL activity was higher in the placenta of fruits in the water deficit treatment than in the fruits of control plants at 50 DAF. At 40 or 50 DAF, cinnamic acid 4-hydroxylase (trans-cinnamate-4-monoox-ygenase) (C4H) activity was higher in plants subjected to the water deficit treatment than in control plants. Capsaicinoid synthase (CS) activity 40 DAF was 1.45- to 1.58-fold higher in fruits in the water deficit treatment than in fruits in the control treatment. 

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