Coniferyl aldehyde

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]. 

The acid condensation reaction of the aromatic and phenolic units is a typical reaction of lignin. The presence of acids results in resonance stabilized carbonium ion structures formed in the lignin macromolecule. These car-bonium ion structures react further, e.g., with unsubstituted positions in the lignin macromolecule. Thus, thermal treatment of powdered wood in acidic conditions causes condensation, the coniferyl aldehyde and coniferyl alcohol groups being especially reactive. In addition, other inter- and/or intramolecular condensations may occur. 

Figure 3-9. Biosynthesis of monolignols. The enzymes involved in this pathway are ( ) hydroxycinnamoyl-CoA shikimate/quinate hydroxy-cinnamoyl transferase, (b) p-coumaroyl-CoA 3 -hydroxylase (E.C. 1.14.14.1), (c) caffeoyl-CoA O-methy 1 Iranslerasc (E.C. 2.1.1.104), (d) cinnamoyl-CoA reductase (E.C. 1.2.1.44) (e) cinnamyl alcohol dehydrogenase (E.C. 1.1.1.195), (f) coniferyl aldehyde/coniferyl alcohol 5-hydroxylase (E.C. 1.14.13), (g) coniferaldehyde/coniferyl alcohol O-methyltransferase (E.C. 2.1.1.68).

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... 

Treatment of lignin with acid as is the situation, for example, in acidolysis (Chap. 6.1) gives rise to stilbene and phenylcoumarone structures (Adler et al. 1966). Stilbenes similar to those identified in acid sulfite pulping liquors have been detected in the steam hydrolyzate of aspen wood (Bardet et al. 1985), and a coniferyl aldehyde structure was formed when a yS-aryl ether-type lignin model compound was heated with slightly acidified water (Kratzl et al. 1959). 

Kratzl K, Kisser W, Gratzl J, Silbernagel H (1959) 2 Guaiacyl ether of guaiacylglycerol and its conversion to coniferyl aldehyde and other arylpropane derivatives Monatsh Chem 90 771-782... 

As shown in Table 7.4.1, 4-O-isopropylconiferyl aldehyde (18) and 2-(2-methoxyphenoxy)-l-(3,4-dimethoxyphenyl)-3-hydroxy-l-propanone (20) have Aer maxima at 342 and 310 nm with corresponding Aer values of 19800 and 9400 mol 1 cm-1, respectively, at the reduction time of 100 min (see Table 7.4.1 for Aer values and Fig. 7.4.2 for structures of model compounds). In addition, compound (18) has a Aer value of 2020tmol em 1 at 310nm, while compound (20) has a Aer value of 10500 mol-1 cm 1 at 342nm (Adler and Marton 1959). Thus, the quantities of etherified coniferyl aldehyde-type (2) and etherified l-(guaiacyl)-l-propanone-type (JT) structures in lignin can be estimated by simultaneously solving Eqs. (9) and (10) ... 

Monolignol units usually maintain their trans-double bond in the side chain. During heartwood formation in gymnosperms, however, this double bond is reduced by phenylpropenal double bond reductases (PPDBR). The enzyme from Pinus taeda accepted dehydrodiconiferyl and coniferyl aldehydes but not the respective alcohols and NADPH as substrates (Kasahara et at, 2006). The structure of a very similar alkenal double bond reductase from Arabidopsis was studied (Youn et at, 2006b). 

Higuchi, T. (2003) Coniferyl aldehyde 5-hydroxylase, a possible key enzyme in an-giosperm syringyl lignin biosynthesis. Proc. ]pn. Acad. B, 79, 227-36. 

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)...

Pauly synthesized coniferyl aldehyde (11) by condensing (9), the methoxymethyl ether of vanillin, with acetaldehyde under carefully defined conditions of alkalinity. 

Colchicine, 920 s-Collidine, 155, 194, 617 Congressane, 1209 Coniferyl aldehyde, 134 Copper, decarboxylation catalyst, 157-158, 975... 

H Hirashima and M Sumimoto. Fundamental Properties of Mechanical Pulp Lignins. II. Behaviors of Coniferyl Aldehyde Type Structures in Pulp Lignin. J. Japan Wood Res. Soc. 33 31 1, 1987. 

Higuchi, T., Ito, T., Umezawa, T., Hibino, T., and Shibata, D. (1994) Red-brown color of lignified tissues of transgenic plants with antisense CAD gene Wine-red lignin from coniferyl aldehyde. J. Biotechnol 37(2), 151-158. 

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