Coniferyl alcohol, enzymatic dehydrogenation

According to a widely accepted concept, lignin [8068-00-6] may be defined as an amorphous, polyphenoHc material arising from enzymatic dehydrogenative polymerization of three phenylpropanoid monomers, namely, coniferyl alcohol [485-35-5] (2), sinapyl alcohol [537-35-7] (3), and /)-coumaryl alcohol (1). 

Recent work by Atalla(H) supports the idea that lignin is at least a semi-ordered substance in wood with the plane of the aromatic ring parallel to the cell wall surface. Woody plants synthesize lignin from trans-coniferyl alcohol (pines), trans-sinapyl alcohol 2 (deciduous), and trans-4-coumaryl alcohol 3 by free radical crosslinking initiated by enzymatic dehydrogenation(l2). Structures of these alcohols are given in Figure 1. 

Meanwhile, Freudenberg (17) was the first person who demonstrated the formation of an addition compound from a quinonemethide and sucrose during enzymatic dehydrogenation of coniferyl alcohol in a concentrated sucrose solution. Thereafter, Tanaka (18) observed the formation of a benzyl ester between the quinonemethide of a dilignol and a uronic... 

Freudenberg realized the importance of investigating this possibility. In 1937 he found that dehydrogenation of coniferyl alcohol with ferric chloride seemed to proceed in a way comparable with that of isoeugenol, and in 1943 he started his studies on the enzymatic dehydrogenation of coniferyl alcohol. It would not be possible here to give even a brief survey of the outstanding work which he has done since then. 

Figure 2.10. The structure of lignin (Adler, 1977). (a) Building units of lignin, (b) Enzymatic dehydrogenation of coniferyl alcohol results in a number of resonance-stabilized phenoxyl radicals. Subsequent polymerization creates the variety of linkages between phenylpropane units that is characteristic of lignin, (c) Common substmctures and their proportions, as found in Picea abies and Betula verrucosa milled wood lignins. The proportion of individual bond types is noted beside each substructure for softwoods (S/w) and hardwoods (H/w).

VI. Investigations on an Enzymatic Dehydrogenation Polymerisate of Coniferyl Alcohol (Freudenberg s DHP). Svensk Papperstidn. 59 363-371, 1956. 

R Kondo, T Sako, T limori, H Imamura. Formation of glycosidic lignin-carbohydrate complex in the enzymatic dehydrogenative polymerization of coniferyl alcohol. Mokuzai Gakkaishi 36 332-338, 1990. 

Pauley, Feuerstein, Ber. 60, 1031 (1927). HydrolysU by emulsin yields coniferyl alcohol and D-glucose, Yields lignin dike material by enzymatic dehydrogenation and polymerization Freudenberg er al.t Ber. 85, 641 (1952) Freu-denberg Rasenack, Ber. 86 756 (1953),... 

In the purest sense, lignin is a complex racemic consisting from aromatic heteropolymers produced by free radical coupling reactions initiated by enzymatic dehydrogenation of the three primary precursors, the hydroxycinnamyl alcohol monomers differing in their degree of methoxylation trans-4-coumaryl alcohol [3-(4-hydroxyphenyl)-2-propenol)], trans-coniferyl alcohol [3-(4-hydroxy-3-methoxyphenyl)-2-propenol)] and trans-sinapyl alcohols [3-(4-hydroxy-3,5-dime-thoxyphenyl)-2-propenol)] (Fig. 8.4). 

The quinone methide is not very stable, and quickly adds another molecule of coniferyl alcohol onto the quinone group. The higher molecular weight polymerizate is then obtained by renewed enzymatic dehydrogenation. Through reactions of this kind and a profusion of others the structure... 

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