Coniferyl alcohol, biosynthesis

Savidge, R. A. Forster, H. Coniferyl alcohol metabolism in conifers—II. Coniferyl alcohol and dihydroconiferyl alcohol biosynthesis. Phytochemistry 2001, 57, 1095-1103. 

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. 

Figure 49 The precursors of lignin biosynthesis, p-coumaryl alcohol (I), coniferyl alcohol (II) and sinapyl alcohol (III). [65]...

On the other hand, biosynthetic pathways that do not involve the conversion from coniferyl alcohol to matairesinol have been proposed for lignans composed of two syringyl (3,5-dimethoxy-4-hydroxyphenyl) groups (+)-syringaresinol formation in Liriodendron tulipifera [50] and (H-)-lyoniresinol biosynthesis in Lyonia ovalifolia var. elliptica [51]. Enantioselective coupling of two sinapyl alcohol units was proposed for the selective formation of (H-)-syringaresinol [50], On the other hand, a non-enantioselective dimerization of sinapyl alcohol was proposed for (+)-lyoniresinol biosynthesis and the enantioselectivity in the biosynthesis was ascribed... 

The only stem materials examined were from the Setaria anceps and Digitaria decumbens grasses. The major substituted cyclobutane dimers in these walls appeared, from the mass spectral data, to be mixed dimers of ferulic acid and coniferyl alcohol (FA-ConAlc type). Further examination of the aromatics of stems is required but if such dimers are present then they may well be involved in the biosynthesis of lignin (41,42). 

From a physiological standpoint, molecular and biochemical studies have suggested that ozone stimulates phenolic metabolism and the biosynthesis of lignin or other substances partly derived from coniferyl alcohol [89]. Lignification of mesophyll cell walls might confer some protection against oxidation, and thus be a defence response against ozone [90]. 

The substitution of the phenyl ring necessary for the biosynthesis of coniferyl alcohol (3.79) and sinapyl alcohol (3.81) begins with the hydroxylation of C3. This is a conversion that requires the formation of the ester of /5-coumaroyl-CoA with D-quinate (3.73) or shikimate (3.74) catalyzed by the enzyme hydroxycinnamoyl-CoA shikimate/quinate hydroxy-cinnamoyl transferase (HCT Hoffmann et al., 2003). The hydroxylation of this ester intermediate is catalyzed by the enzyme /i-coumarovl-Co A 3 -hydroxylase (C3 H Schoch et al., 2001 Franke et al., 2002a,b). The resulting shikimate or quinate ester (3.75 3.76) is subsequently hydrolyzed by the same HCT, resulting in caffeoyl-CoA (3.36). 

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).

Irradiation of 2,2-dimethyl chromene through Pyrex using a 550-W Hanovia lamp initiates a retro 4 + 2 reaction to form the extended quinone methide 4, which reacts with methanol to form a pair of methyl ethers (Scheme 6A).18 Flash photolysis of coniferyl alcohol 5 generates the quinone methide 6 (Scheme 6B) by elimination of hydroxide ion from the excited-state reaction intermediate.19 The kinetics for the thermal reactions of 6 in water were characterized,20 but not the reaction products. These were assumed to be the starting alcohol 5 from 1,8-addition of water to 6 and the benzylic alcohol from 1,6-addition of water (Scheme 6). A second quinone methide has been proposed to form as a central intermediate in the biosynthesis of several neolignans,21a and chemical synthesis of neolignans has been achieved... 

Katayama, T., Suzuki, T., Lourith, N. and Kurita, Y. (2005) Biosynthesis and stereochemistry of lignans and neolignans Stereoselective cross coupling of coniferyl alcohol and sinapyl alcohol in broad-leaved trees. Kami Parupu Kenkyu Happyokai Koen Yoshishu, 72, 84 9. 

Fig. 1 Precursors of lignin biosynthesis. (A) / -Coumaryl alcohol (4-hydroxyl-phenyl propane) (B) coniferyl alcohol (guaiacyl) and (C) sinapyl alcohol (syringyl).

Little is known about the tissue and subcellular compartmentation of lignan biosynthesis in Podophyllum. In vitro cultured cells of P. emodi are capable of synthesizing podophyllotoxin from coniferyl alcohol, implying... 

Most lignans are obtained optically active and, presumably, enantiomerically pure. However, the phenolic coupling processes catalysed by H2C>2-dependent peroxidases, Ch-requiring laccases or phenol oxidases yield racemic products. A protein without an active centre has been isolated that in presence of an oxidase produces stereoselective bimolecular phenoxy radical coupling reactions in in vitro lignan biosynthesis. Its mechanism of action is presumed to involve capture of -coniferyl alcohol-derived free radical intermediates [34],... 

The principle pathways of lignan biosynthesis in Forsythia have been elucidated from studies using labelled precursors and cell free extracts. The sequence from coniferyl alcohol (9) to (+)-pinoresinol (10), (+)-lariciresinol (11), (-)-secoisolariciresinol (12) and (-)-matairesinol (13) is now clearly established (scheme 1) [30-33]. Lewis et al. have shown that (+)-pinoresinol (10) is formed via direct stereoselective coupling of the two coniferyl alcohol molecules, a process which requires the complimentary action of a specific protein and an auxiliary oxidase or peroxidase [34,35]. (+)-Lariciresinol (11) and (-)-secoisolariciresinol (12) are then formed by consecutive enantiospecific reduction [36], and (-)-secoisolariciresinol is further metabolised into (-)-matairesinol (13) via enantiospecific dehydrogenation, and into (-)-arctigenin (14) via regioselective 0-methylation [37]. 

Biosynthesis L. is formed from coniferyl alcohol (or syringaaldehyde) under the action of laccase (phenol dehydrase). L. is degraded in the soil by the lignases of bacteria and fungi to humic acids. 

In 1956, Karl Freudenberg at the University of Fleidel-berg had already succeeded in using an enzyme (phe-nol-oxidoreductase) from button mushrooms (Agaricus bisporus) to simulate the oligomerisation of coniferyl alcohol and thereby the biosynthesis of lignin. [141]... 

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