P-hydroxycinnamic acid

Quideau, S. Incorporation of p-hydroxycinnamic acids into lignins via oxidative coupling. Ph.D. Thesis, University of Wisconsin—Madison, USA, University Microfilms International 9428350, 1994. 1994. 

Coumarins and isocoumarins appear to be of varied origins. Simple coumarins, such as umbelliferone, are formed by the shikimic acid pathway in which hydroxylation of p-hydroxycinnamic acid occurs. Other coumarins, for example alternariol (690), are derived from a polyketide unit, as are a number of chromanones, chromones, pyranones and isocoumarins (B-78MI22400). The biosynthesis of 5-hydroxy-2-methylchromone has been shown to involve the chromanone (60JCS654). However, isocoumarins are also derived from the mixed acetate-shikimate route, through initial cyclization of the polyketide and subsequent lactonization. 

After oral administration of caffeic acid to rats, small amounts of vanillic acid and vanilloylglycine are excreted. The conversion of p-hydroxycinnamic acid into /7-hydroxybenzoic acid is found in rat liver mitochondria [18], Studies with /7-hydroxy[U-14C]cinnamic acid have showed that 14C02 is released during reaction, indicating that reaction probably followed the p-oxidation type reactions, the two carbon being first removed as acetyl-CoA, and then oxidized to C02. It is assumed that conversion of ferulic acid formed by methylation of caffeic acid into vanillic acid occurs in rat liver mitochondria. 

Demethoxyabresoline (67) was obtained as a noncrystalline solid. Spectroscopic investigation revealed the presence of a phenolic OH, a 1-phenyl-quinolizidine system, and a trans-cinnamyl group. The stereochemistry at C-l, C-3, and C-5 was the same as in abresoline. The molecular formula C25H29N05 was established by mass spectrometry. The presence of fragment ions at m/e 259 (M —164) and 258 was characteristic of p-hydroxy-cinnamyl esters of the phenylquinolizidol (63a). The assigned structure 68 was confirmed by basic hydrolysis to 63a and p-hydroxycinnamic acid as well as by catalytic hydrogenation to a known dihydro derivative (52). 

In the lactonic alkaloid molecule one can find three synthons pelle-tierine, a 4-methoxybenzaldehyde derivative, and p-hydroxycinnamic acid. In all published syntheses of lactonic Lythraceae alkaloids they are the building blocks. 

The phenolic acids of interest here [caffeic acid (3,4-dihydroxycinnamic acid), ferulic acid (4-hydroxy-3-methoxycinnamic acid), p-coumaric acid (p-hydroxycinnamic acid), protocatechuic acid (3,4-dihydroxybenzoic acid), sinapic acid (3,5-dimethoxy-4-hydroxyxinnamic acid), p-hydroxybenzoic acid, syringic acid (4-hydroxy-3,5-methoxybenzoic acid), and vanillic acid (4-hydroxy-3-methoxybenzoic acid)] (Fig. 3.1) all have been identified as potential allelopathic agents.8,32,34 The primary allelopathic effects of these phenolic acids on plant processes are phytotoxic (i.e., inhibitory) they reduce hydraulic conductivity and net nutrient uptake by roots.1 Reduced rates of photosynthesis and carbon allocation to roots, increased abscisic acid levels, and reduced rates of transpiration and leaf expansion appear to be secondary effects. Most of these effects, however, are readily reversible once phenolic acids have been depleted from the rhizosphere and rhizoplane.4,6 Finally, soil solution concentrations of... 

Peak 3 (Fig. 6.4.3) corresponds to p-hydroxybenzoic acid which is mainly ester-linked in poplar lignins. Although no study using appropriate model compounds has been made, it may be assumed that the thioacidolysis reagent is able to cleave, to a minor extent, benzoic and p-hydroxycinnamic ester linkages, as manifested by the recovery of benzoic and p-hydroxycinnamic acids from... 

The flavonoids, which comprise the largest group of these natural products, are derived from a mixed acetate-shikimate pathway. A shikimate-derived C6-C3 unit combines with a six-carbon polyketide chain to provide the open-chain precursor (685) of the group. The derivation of p-hydroxycinnamic acid (p-coumaric acid), the C6-C3 component, from shikimic acid proceeds through chorismic acid, prephenic acid and phenylalanine. 

SYNS p-COUMARIC ACID p-CUMARIC ACID p-HYDROXYCINNAMIC ACID 4-HYDROXYCINNAMIC ACID 4 -HYDROXYCINNAMIC ACID p-HYDROXY-PHENYLACRYLIC ACID P-(4-HYDROXYPHENYL)-ACRYLIC ACID 3-(4-HYDROXYPHENYL)-2-PROP-ENOIC ACID... 

HYDROXYCINNAMIC ACID see CNU825 p-HYDROXYCINNAMIC ACID see CNU825 4 -HYDROXYCINNAMIC ACID see CNU825... 

C9H7N03S 5-isoquinolinesulfonic acid 27655-40-9 25.00 1.3837 2 16223 C9H803 p-hydroxycinnamic acid, predominantly trans 501-98-4 25.00 1.2467 2... 

Lunarine (26), one of the typical neolignans, is biosynthesized by the ortho-para radical coupling between two molecules of p-hydroxycinnamic acid. In this connection, oxidative coupling reactions of 4-substituted phenols have been extensively stndied using thallium trifluoroacetate (TTFA), potassium ferricyanide (K3[Fe(CN)g]) and other reagents. p-Cresol (27) was also electrolyzed at a controlled potential (+0.25 V vi. SCE) in a basic medium to afford Pummerer s ketone 28 in 74% yield. The snggested mechanism is given in Scheme 4. 

Castellan et al. [171] have recently suggested that dityrosine protein residues or p-hydroxycinnamic acid are possible candidates for the fluorphores in pure cellulose. Other recent studies [172,173] have shown that typical cellulose processing conditions (e.g., hot alkali) can induce the formation of small amounts of aromatic structures from reducing end groups or hemicelluloses. However, many of the structures identified in these studies are quinones, which are at best weakly fluorescent. 

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