Coniferyl aldehyde/alcohol

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... 

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). 

From coniferin by hydrolysis with emulsin. From ferula aldehyde (coniferyl aldehyde) by the action of fermenting yeast Small amounts of coniferyl alcohol are found in brandy from beet molasses. 

The experimental studies on the phenolic lignin model compounds (4-propyl-guaiacol, eugenol, isoeugenol, coniferyl alcohol, coniferyl aldehyde and 4-allyl-2,6-dimethoxyphenol) demonstrated that these compounds had more active antioxidants activity than the commercial inhibitor (2,6-di-tert-butyl-4-methyl-phenol) BHT during peroxidation of styrene in chlorobenzene initiated by... 

Hanninen, X, Kontturi, E., and Vuorinen, X. (2011) Distribution of lignin and its coniferyl alcohol and coniferyl aldehyde groups in Picea ahies and Pinus sylvestris as observed by Raman imaging. Phytochemistry, 72 (14-15), 1889-1895. 

Coniferyl alcohol Coniferyl aldehyde Benzyl alcohol dehydrogenase Lact. plantamm... 

Foumand, D. Cathala, B. Lapierre, C. Initial steps of the peroxidase-catalyzed polymerization of coniferyl alcohol and/or sinapyl aldehyde capillary zone electrophoresis study of pH effect. Phytochemistry 2003, 62, 139-146. 

Dimeric aldehydes analogous to (II) and (VI) have in fact been isolated from incubates of coniferyl alcohol with laccase (58). There are only 3% such aldehydic groups in lignin 4) [cf. Unit 10 in Fig. 9] but these suffice to give a intense red color with phloroglucinol and concentrated hydrochloric acid, the conventional Wiesner test for lignin. 

Lignin has a complex structure that varies with the source, growing conditions, etc. This complex and varied structure is typical of many plant-derived macromolecules. Lignin is generally considered as being formed from three different phenylpropanoid alcohols— coniferyl, coumaryl, and sinapyl alcohols, which are synthesized from phenylalanine via various cinnamic acid derivatives and commercially is sometimes treated as being composed of a Cg repeat unit where the superstructure contains aromatic and aliphatic alcohols and ethers, and aliphatic aldehydes and vinyl units. 

To determine the reasons for this, DHP s were prepared from a mixture of [ring-2-3H] p-coumaryl alcohol and [or-14C] coniferyl alcohol in the presence of carbohydrates by the procedure described above (35). The LCC fraction so obtained was subjected to combustion, and the exact p-hydroxyphenylpropane guaiacylpropane ratio was determined from the activity of 3H20 and 14C02 released (Figure 2). A portion of the same LCC fraction was also oxidized with nitrobenzene and alkali, and the resulting liberated aromatic aldehydes were then analyzed by HPLC. Results are shown in Table V. 

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). 

Dehydrodiconiferaldehyde (XVIII) 25) is an unsaturated aldehyde corresponding to XVII and is formed partly by condensation of free radicals derived from coniferyl alcohol and coniferaldehyde. 

---