Primary ferulic

The plant cell wall contains different types of polysaccharides, proteins (structural glycoproteins and enzymes), lignin and water, as well as some inorganic components (1, 14-16). The plant cell suspensions, however, grow as a population of cells with a primary cell wall(17). The main components of these walls are cellulose-free polysaccharides and pectic polysaccharides in particular, which constitute 1/3 of their dry weight. (18). Some fragments, e g. methanol, acetic, ferulic and p-cumaric acids, are connected with the pectic polysaccharides by ester bonds with the carboxylic and hydroxylic groups. 

Einhellig and Rasmussen (17) reported that In addition to ferulic and p-coumaric acids, vanillic acid reduced chlorophyll content of soybean leaves but did not affect chlorophyll In grain sorghum fSorghum bicolor (L.) Moench.]. It Is not known whether these reported mechanisms are primary or secondary events In the Inhibition of plant growth by allelochemlcals. 

Some monocot, primary cell-wall polysaccharides may be cross-linked by esters of ferulic acid (4-hydroxy-3-methoxycinnamic acid). There is evidence for the existence of such cross-links in monocot tissues containing secondary walls, including Italia ryegrass stem276 and wheat endosperm.277 Ferulic acid is also present in barley cell-wall,278 and it has been reported that treatment with base releases ferulic acid from the cell walls of several Graminae,276 supporting the idea that ferulic acid is bound to the wall as an ester. However, ferulic acid has not, so far, been reported to be present specifically in primary cell-walls in either monocots or dicots. 

There is evidence684,685,685 for the attachment of phenolic components (ferulic and coumaric acids) both to / -(l— 4)-linked D-galactose and a-(l— 3)-linked L-arabinose in the primary cell-wall, suggesting feruloylation-coumaroylation of pectic neutral side-chains. Earlier papers686-688 had also suggested the attachment of these phenolic compounds to primary-wall polysaccharides which remained uncharacterized. 

In order to eluddate the mechanism of the further transformations of the primary lignin decomposition products including the cleavage reactions, we synthesized some of the important primary products labelled with Cu and introduced these into the cultures of fungi or enzymes. Thus, it could be shown, for example, that the breakdown of the side chain of ferulic acid occurs at the double bond vanillic acid is found. During polymerization in the presence of phenoloxidases, in the case of carboxyl-labelled ferulic acid, about 60% of the activity is split off as Cli02. The polymers labelled in the 2 and 3 position in the side chain or in the methoxyl group contain the whole applied activity. 

Phenolic acids, and especially ferulic acid, which is abundantly present in cereals, is found esterified to the polysaccharides present in primary and secondary cell walls of plants. Ferulic acid is the major phenolic acid occurring in the cell walls of monocotyledons and appears as cis and the more abundant trans isomers (reviewed in [Klepacka and Forna, 2006]). Ferulic acid is found in wheat, maize, rye, barley [Sun et al., 2001], oats, spinach, sugar beet, and water chesnuts [Clifford, 1999], generally esterified, and rarely as free form, such as in barley [Yu et al., 2001]. It is esterified in primary cell walls to arabinoxylans (Fig. 2.4) in the aleurone layer and pericarp [Clifford, 1999], as in spinach [Fry, 1982] or in wheat bran [Smith and Hartley, 1983], Ferulic acid can also be found esterified to other hydroxycinnamic acids such as in Mongolian medicinal plants where it is found as feruloylpodospermic acid, which is... 

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... 

Ferulic acid (XIX) is found ester-linked to polysaccharides in the primary cell walls of Graminaceae, which include cereals and grasses [95]. Ferulic acid is an effective scavenger of free radicals [96] and can also protect low density lipoprotein against met-myoglobin-induced oxidative damage... 

The electrooxidations of allyl- and propenyl-phenols may follow even more different pathways leading to a rich diversity of products. At a carbon anode in methanol-lithium perchlorate, ferulic acid formed the tricyclic diacid (306 c/. Section 2.9.5), in a concentration-dependent process probably involving [4 + 2] dimerization of the primary oxidation product, the dienone acetal (307). 

Grabber, J. H., Ralph, J., and Hatfield, R. D. (2002) Model smdies of ferulate-coniferyl alcohol cross-product formation in primary maize walls Imphcations for lignification in grasses. J. Agr. Food Chem. 50(21), 6008-6016. 

In a study of the structure and functions of feruloylated pectins in primary cell walls in spinach, about one feruloyl group was found per sixty sugar residues ( ). Ferulic acid was determined after alkaline hydrolysis by the Folin-Ciocalteu phenol reagent. 

A scheme for the formation of guaiacols from ferulic acid has also been proposed by Manley et al. (1974). The biosynthesis of various phenolic acids from p-coumaric acid (H.84) was studied by Friedrich (1976). Formation pathways for simple phenols in food flavors have been reviewed (Maga, 1978a). The two primary pathways could be the decarboxylation of phenolic carboxylic acids and the thermal degradation of lignin. Secondary pathways include bacterial, fungal, yeast enzymic and glycosidic reactions. 

Figure 3.1 Primary flux of carbon through phenylpropanoid pathway in Arabidopsis. PAL, phenylalanine ammonia-lyase 4CL, 4-(hydroxy)cinnamoyl CoA ligase C4H, cinnamate 4-hydroxylase HCT, hydroxycinnamoyl-CoA shikimate/quinate hydroxycinnamoyltransferase C3 H, /7-coumaroylshikimate 3 -hydroxylase CCoAOMT, caffeoyl CoA O-methyltransferase F5H, ferulate 5-hydroxylase COMT, caffeic acid/5-hydroxyferulic acid o-methyltransferase CCR, cinnamoyl CoA reductase CAD, cinnamyl alcohol dehydrogenase. Not depicted is the HCT catalyzed synthesis of/r-coumaroyl quinate.

Veratraldehyde 3 and veratric acid methyl ester 4 were isolated from vanillic aldehyde 5 and vanillic acid methyl ester 6 in the original reaction mixture. Silica gel chromatography of this reaction mixture was used to isolate small amounts of these primary oxidation products. These compounds had lost two carbon atoms from the origind propenoidic chain. A further component isolated from the methylated mixture was 2-methoxyhomoveratric aldehyde 7, which suggested the presence of 2-hydroxyhomoveratric aldehyde 8 in the oxidation reaction mixture. Its structure was confirmed by independent synthesis. Treatment of the reaction mixture from the catalytic oxidation of E-ferulic acid 1 with 1,3-dithiane followed by methylation formed the thioketal 9, which was also prepared by reaction of veratraldehyde 3 with 1,3-dithiane carbanion 10 followed by methylation. 

Diesters hexadecan-7-yl p-coumarate Ferulic acid esters of Cu-Cjg primary alcohols 0 0 Ri-C-0CHj(CH2) CH2 0 C-R5 Diols C,-C , ... 

Phenolic esters Ferulic acid esters of primary alcohols Cjg to C28 Commonly found in suberin-associated wax... 

Trocino s concept of total utilization of the raw material, Douglas-fir bark, to produce several salable products was good, and earned Bohemia the 1976 Environmental Award from the American Paper Institute and the American Forest Products Institute. Unfortunately a certain amount of solvent losses is inevitable. Thus, efficient solvent extraction and recovery of solvent to obtain the primary product in a 3% yield, based on bark, could only be expected to be cost effective if the product sold in the dollars per kilogram range, such as carnauba wax imported from Brazil or Mexico. Unrefined Douglas-fir wax is soft because of the presence of terpenes, unsaturated fats, etc., and is subject to discolorization by iron salts because of the presence of ferulate esters, which promote the formation of complexes. As in the case of the polyphenolic extractives from redwood and hemlock bark, the product end-use was not sufficiently unique to ultimately justify a price that would support production and operating costs, and generate a reasonable profit. 

Arabinoxylans (Figure 3B) have a backbone composed of 1,4-linked P-D-Xylp residues—some of the Xyl/ residues may be 0-acetylated [7]. Ara/ residues are linked to position C-2 and/or C-3 of the backbone. In primary walls P-d-GIc/jA or 4-0-Me p-D-Glc A residues are also attached to the xylan backbone and these polysaccharides are called glucuronarabinoxylans. The Ara/ side chains of arabi-noxylan and glucuronarabinoxylan may also contain ester-linked phenolic acids such as ferulic acid [9] that are potential sites for cross-linking by oxidative coupling (Figure 3B and C). 

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