Cinnamate, Hydroxycinnamates and their Derivatives Phenylpropanoids Sensu Latiore

3 Cinnamate, Hydroxycinnamates and their Derivatives (Phenylpropanoids Sensu Latiore) 

Cinnamic acid and Hydroxy cinnamic acids. The biosynthetic sequence cinnamic acid — p-coumaric acid caffeic acid — ferulic acid — 5-hydroxy-ferulic acid - sinapic acid (Eig. 6.3) includes progressive hydroxylation at the 

0- glucosides are common metabolites of higher plants. The carboxylic group of free cinnamic acid and its hydroxy derivatives must be activated via synthesis of coenzyme-A thioesters before any derivatization or modification is possible. The resulting hydroxycinnamoyl-CoA derivatives are central intermediates in the biosynthesis of many phenylpropanoids (Bernards and Lewis 1998). Alternatively, hydroxycinnamate 1-0-acylglucosides (1-0-hydroxycinnamoylglucose) may serve as acyl donor molecules in the biosynthesis of 0-esters (Strack 1997) e.g., 

Hydroxycinnamates as well as their conjugates may act as powerful antioxidants. In edible plants they have received much attention as protecting agents against oxidative deterioration of food. Antioxidant mechanism studies on ferulic acid and its coupling products with linoleate on the molecular level have been conducted recently. A radical scavenging reaction occurred at the 3 -position of the ferulate radical with four types of peroxyl radicals of ethyl linoleate. The produced peroxides subsequently underwent intramolecular rearrangement to afford stable tricyclic peroxides (Masuda et al. 2006). 

Occurrence in the Solanaceae. p-Coumaric acid, caffeic acid, methyl caffeate, and methyl ferulate as well as certain of their 2,3-dihydro derivatives have been identified as constituents of the leaves of Cestrum parqui L Herit. with good phytotoxic activity against different species (D Abrosca et al. 2004). Family-specific phenylpropanoid acids like tropic acid or 2-hydroxytropic acid as acyl moieties of tropane alkaloids are synthesized via phenylalanine - phenylpyruvic acid (l )-3-phenyllactic acid (Fig. 3.14 Table 3.1 (T5-T7-B)]. Tropic acid may occur as a metabolite of, e.g., hyoscyamine, but the free acid is not synthesized as such (for details see Sect. 3.4). 

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