Coniferyl ferulate

Grabber, J. H., Hatfield, R. D., Lu, F, and Ralph, J. (2008) Coniferyl ferulate incorporation into lignin enhances the alkaline delignification and enzymatic degradation of maize cell walls. Biomacromolecules 9(9), 2510-2516. 

It has been suggested that metabolites resulting from detoxification of plant compounds such as ferulic acid, a detoxification by-product of coniferyl benzoate and analogous compounds, may interfere with reproduction. However, experiments have shown that coniferyl benzoate in the diet of Japanese quail [Coturnix coturnix) had no hormonal effects. Rather, costs of detoxication and reduced nutrient utilization deter wild birds such as ruffed grouse, Bonasa umbel-lus, from feeding (Jakubas etal, 1993). 

Attachment of Hydroxycinnamic Acids to Structural Cell Wall Polymers. Peroxidase mediation may also result in binding the hydroxycinnamic acids to the plant cell wall polymers (66,67). For example, it was reported that peroxidases isolated from the cell walls of Pinus elliottii catalyze the formation of alkali-stable linkages between [2-14C] ferulic acid 1 and pine cell walls (66). Presumably this is a consequence of free-radical coupling of the phenoxy radical species (from ferulic acid 1) with other free-radical moieties on the lignin polymer. There is some additional indirect support for this hypothesis, since we have established that E-ferulic acid 1 is a good substrate for horseradish peroxidase with an apparent Km (77 /tM), which is approximately one fifth of that for E-coniferyl alcohol (400 /iM) (unpublished data). 

The only stem materials examined were from the Setaria anceps and Digitaria decumbens grasses. The major substituted cyclobutane dimers in these walls appeared, from the mass spectral data, to be mixed dimers of ferulic acid and coniferyl alcohol (FA-ConAlc type). Further examination of the aromatics of stems is required but if such dimers are present then they may well be involved in the biosynthesis of lignin (41,42). 

Figure 2. 13C NMR solid state difference spectra of (a) L. leucocephala and (b) T. aestivum (24) root tissue previously administered [1-13C] ferulic acid 5a. Fig. 2c shows the difference spectrum of a DHP polymer, derived from [1-13C] coniferyl alcohol 2a (29). CP/MAS spectra were obtained at 50 MHz on a Varian XL-200 Spectrophotometer equipped with a Doty Scientific MAS Probe. SSB = spinning side band.

Incorporation of [3-13C] Ferulic Acid 5c. Figs. 4a and 4b show the results obtained following uptake of [3-13C] ferulic acid 5c to L. leucocephala and T. aestivum L., respectively the spectrum shown in Fig. 4c corresponds to a synthetic DHP polymer from [2-13C] coniferyl alcohol 2c. 

The bioconversion of eugenol and ferulic acid to vanillin was first characterised in Pseudomonas fluorescens (Scheme 26.4) [36, 37]. However, an enzyme of the pathway, vanillin NAD+ oxidoreductase, catalysed the removal of vanillin from the medium through the formation of vanillic acid [38]. Deletion of the oxidoreductase was, however, only partially successful, largely because vanillin is also the substrate of coniferyl aldehyde dehydrogenase, an enzyme of the eugenol degradative pathway present in Pseudomonas sp. [39]. 

Other monolignols formed during the dehydrogenation of coniferyl alcohol are conifer aldehyde (VII), trans- and m-ferulic acid (XV, XVI), vanillin (traces), and vanillic acid (traces). 

Coniferaldehyde (3.76) can undergo several fates, some of which can ultimately lead to the same end product. It can be reduced to coniferyl alcohol (3.79) by the enzyme cinnamyl alcohol dehydrogenase (CAD). Alternatively, the enzyme coniferyl aldehyde/coniferyl alcohol 5-hydroxylase (C5H), also known by its less accurate name ferulic acid 5-hydroxylase (F5H Humphreys et al., 1999) can catalyze the hydroxylation of C5 to result in 5-hydroxyconiferyl aldehyde (3.77). C5H is also able to form 5-hydroxyconiferyl alcohol (3.80) from coniferyl alcohol (3.79). This enzyme was initially identified as F5H, after analysis of the Arabidopsis ferulic acid hydroxylase 1 (fahl) mutant, which was isolated in a mutant screen based on reduced levels of the UV-fluorescent sinapoyl esters (Section 13 Chappie et al., 1992). The FAH1 gene was cloned using a T-DNA tagged mutant allele (Meyer et al., 1996), which revealed that the... 

Fig. 4-2. Simplified reaction route illustrating the formation of lignin precursors. 1, 5-Dehydroquinic acid 2, shikimic acid 3, phenylpyruvic acid 4, phenylalanine 5, cinnamic acid 6, ferulic acid (Ri=H and R2=OCH3), sinapic acid (R,= R2=OCH3), and p-coumaric acid (R1=R2 = H) 7, coniferyl alcohol (Ri = H and R2=OCH3), sinapyl alcohol (Rj = R2=OCH3), and p-coumaryl alcohol (R =R2=H) 8, the corresponding glucosides of 7.

Figure 3.1 Structures of principal low molecular weight phenols in wine (1) pyrocatechol (2) resorcinol (3) hydroquinone (4) phloroglucinol (5) vanillin (6) p-hydroxybenzaldehyde (7) syringic aldehyde (8) coniferyl aldehyde (9) sinap-inaidehyde (10) gentisic acid (11) gallic acid (12) vanillic acid (13) salicylic acid (14) syringic acid (15) caffeic acid (16) ferulic acid (17) p-coumaric acid (18) hydrox-ycinnamoyltartaric acids (R = H, OH, OCH3)...

Syringyl Lignin Pathways Two key enzymes (beyond the coniferyl alcohol pathway) are required for the production of sinapyl alcohol, which is the essential monolignol for production of syringyl units in lignins. Ferulate 5-hydroxylase, FH5, now perhaps more appropriately called CAld-5H to reflect coniferaldehyde as the preferred substrate [347,348], effects the 5-hydroxylation. Caffeate 0-methyltransferase,... 

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