Alcohol lignin from cinnamyl

Ralph, J., Hatfield, R. D., Piquemal, J., Yahiaoui, N., Pean, M., Lapierre, C., Boudet, A. M., 1998, NMR characterization of altered lignins extracted from tobacco plants down-regulated for lignification enzymes cinnamyl alcohol dehydrogenase and cinnamyl-CoA reductase, Proc. Natl. Acad. Sci. USA 95 12803-12808. 

Lignin Complex molecules that constitute part of the insoluble dietary fiber. It is formed from cinnamyl alcohols that form the phenylpropaue units by a complex polymerization process. Lignin is viewed as a three-dimensional molecule formed by the aromatic hydroxyphenyl, guaiacyl, and springyl moieties. It is the main structural component of plant tissues. It is highly resistant to enzymes and chemical degradation. 

Thioacidolysis allows the distinction between products derived from lignin and products derived from />coumaric and ferulic acids, and the distinction between products derived from cinnamaldehydes and cinnamyl alcohols. Recent improvements have made it possible to estimate the fraction of free phenolic groups in uncondensed lignin (see Section 1.3.1), and to depolymerize the dimers, so that they can be included in the analysis of the lignin composition. 

The reductive sequence from an appropriate cinnamic acid to the corresponding cinnamyl alcohol is not restricted to lignin and lignan biosynthesis, and is utilized for the production of various phenylpropene derivatives. Thus cinnamaldehyde (Figure 4.23) is the principal component in the... 

The activity of cinnamyl alcohol dehydrogenase (CAD EC 1.1.1.195) was already described in the 1970s and was mainly investigated with respect to lignin biosynthesis (see Petersen et al, 1999, for further information). It catalyses the reduction of cinnamaldehydes to cinnamyl alcohols with the help of NADPH the reaction is readily reversible (Fig. 4.7). From a functional point of view, CAD activity is involved in developmental lignification and in the formation of defence compounds. Several reviews have treated the involvement of this enzyme in lignin monomer formation (Boudet et al, 1998,... 

Lignins are anchored to the cell wall polysaccharides in several ways. One of the most common mechanisms is the nucleophilic addition of hydroxyl groups of polysaccharides to the quinone methide structure (XXXI) resulting from the P->(9-4 coupling mode of two cinnamyl alcohol radicals (Scheme XIII). 

Different types of end-groups are shown in Figure 7.7. End-groups of the cinnamyl alcohol (47) and cinnamaldehyde (48) types have been detected in both isolated lignins and lignins in wood. Quantitative analysis of MWL from spruce wood by H NMR spectroscopy suggests the presence of about 1% units of type 47 [40] and... 

Lignins. Lignins are amorphous, cross-linked phenolic polymers that occur uniquely in vascular plants and comprise 20-30% of most wood. Lignins isolated from wood are polydisperse, with molecular weights in the range of thousands to hundreds of thousands (4). Lignins are produced almost exclusively from three cinnamyl alcohols, whose structures are shown in Chart I. These structural units have propylphenyl carbon skeletons and differ... 

A different approach to the analysis of 3-0-4 structures involves a two-step procedure with acetyl bromide treatment followed by a reductive cleavage of the 3-ether substituent as depicted in Rg. 9.11 [59, 60]. The reaction can be applied to isolated lignins, as well as on cell wall material, and results in the formation of acetylated cinnamyl alcohols which can be readily quantified by gas chromatography. The yield of the major compounds originating from G-, H-and S-units seems, however, to be inferior to the corresponding values obtained from thioacidolysis [20,60,76]. 

Additional support for the theory of lignin formation by dehydrogenation of Cg. C3 cinnamyl alcohol precursors is often derived from the widespread occurrence of dimers of the Cg. C3 carbon skeleton, joined by the -carbon atoms in the side chains, in woods and wood exudates. This group of natural products— lignans—has long been recognised and has stimulated a considerable research interest - Typical members of this class are for example (—)-guaiaretic acid (86) and (+)-pinoresinol (87), the... 

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