Sinapyl alcohol polymerization

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). 

Lignin polymerization is a natural process initiated by the enzymatic oxidation of hydroxycinnamyl alcohols such as /)-coumaryl (CM), coniferyl (CF), and sinapyl alcohols (SN), which are known as monolignols (Scheme 2.20).60... 

Tobimatsu, Y. Takano, T. Kamitakahara, H. Nakatsubo, F. Azide ion as a quinone methide scavenger in the horseradish peroxidase catalyzed polymerization of sinapyl alcohol. J. WoodSci. 2008, 54, 87-89. 

Since the oxidative polymerization of phenols is the industrial process used to produce poly(phenyleneoxide)s (Scheme 4), the application of polymer catalysts may well be of interest. Furthermore, enzymic, oxidative polymerization of phenols is an important pathway in biosynthesis. For example, black pigment of animal kingdom "melanin" is the polymeric product of 2,6-dihydroxyindole which is the oxidative product of tyrosine, catalyzed by copper enzyme "tyrosinase". In plants "lignin" is the natural polymer of phenols, such as coniferyl alcohol 2 and sinapyl alcohol 3. Tyrosinase contains four Cu ions in cataly-tically active site which are considered to act cooperatively. These Cu ions are presumed to be surrounded by the non-polar apoprotein, and their reactivities in substitution and redox reactions are controlled by the environmental protein. 

Lignin, a phenolic polymer, is also incorporated into the wall during the secondary-thickening phase. This component permeates the spaces between the plant cells, thereby strengthening the tissue. Lignification is a result of enzymic dehydrogenation and subsequent polymerization of coumaryl, coniferyl, and sinapyl alcohols, the relative proportions of which differ in the lignins from different plants.23-28... 

After polymerization the different lignin subunits are referred to as / -hyrdoxyphcnyl (H), guaiacyl (G), and syringyl (S) residues, depending on whether they originated from />coumaryl alcohol, coniferyl alcohol, or sinapyl alcohol, respectively. 

Yoshida, S. (1994) Effect of hemicelluloses on dehydrogenative polymerization of sinapyl alcohol B. Formation of (l-y linkage in the presence of pectin. Mokuzai Gakkaishi 40(9), 966-973. 

Tanahashi, M., and Hignchi, T. (1990) Effect of the hydrophobic regions of hemiceUn-loses on dehydrogenative polymerization of sinapyl alcohol. Mokuzai Gakkaishi 36(5), 424-428. 

---