Guaiacyl

Allard A-S, P-A Hynning, M Remberger, AH Neilson (1994) Bioavailability of chlorocatechols in naturally contaminated sediment samples and of chloroguaiacols covalently bound to Cj-guaiacyl residues. Appl Environ Microbiol 60 777-784. 

Akiyama, T. Goto, H. Nawawi, D. S. Syafii, W. Matsumoto, Y. Meshitsuka, G. Erythro/threo ratio of P-O-4-structures as an important structural characteristic of lignin. Part 4 variation in the erythro/threo ratio in softwood and hardwood lignins and its relation to syringyl/guaiacyl ratio. Holzforschung 2005, 59, 276-281. 

Takahama, U. Oxidation of hydroxycinnamic acid and hydroxycinnamyl alcohol derivatives by laccase and peroxidase—interactions among p-hydroxyphenyl, guaiacyl and syringyl groups during the oxidation reactions. Physiol. Plantarum 1995, 93, 61-68. 

It weis found that hardwood lignins yielded both guaiacyl and syringyl units on oxidation, whereas softwood lignins yielded only guaiacyl units. Hibbert and co-workers (20), (21) distinguished perennial plant lignins... 

However, in the light of the results presented herein, this cannot be stated unequivocally, otherwise it would follow that only guaiacyl type compounds would be obtained as softwood lignin degradation products. It has been found that the native lignin from the softwood white Scots pine also yields p-hydroxybenzaldehyde upon oxidation. Thus, it seems that either coniferyl alcohol is not the only lignin progenitor in woody tissues, or that this coniferyl compound is preceded in the process of... 

Fig. 2.2 A. Chemical structure of the three types of lignin monomer units H, p-hydroxyphenyl- G, guaiacyl and S, syringyl. Note the methyl groups (boxed) in the methoxy moieties of the G and S monomers. B. Pie chart showing the proportions of pine xylem ESTs that putatively encode enzymes of Ci metabolism, glycolysis, and the TCA cycle.

Oniki, T. and Takahama, U. (1997). Free radicals produced by the oxidation of compounds containing syringyl and guaiacyl groups. Mokuzai Gakkaishi, 43(6), 493 98. 

It has also been observed that syringyl-type precursors arc transformed in part into guaiacyl-type lignin 78, 90, 91), i.e. a demethoxyla-tion, not merely a dcmcthylation has taken place. It has also been found that sweet almond emulsin hydrolyses syringin only extremely slowly 143) and that pure peroxidase does not oxidize sinapyl alcohol well 71). The metabolism of the sinapyl component of lignin is perhaps not quite as simple as the analogy between its />-coumaryl and conifcryl components suggests. 

Naturally lignins that have been modified by chemical reactions, e.g. condensed or sulfonated by pulping, are far less susceptible to biological decay than natural lignins, because the weak, readily hydrolyzable benzyl aryl ether bonds or the readily oxidisable benzyl alcohols of guaiacyl-glycerol units have been sulfonated or transformed by condensation reactions into strong carbon-carbon bonds. 

For example, yatein and podophyllotoxin are biosynthesized from matairesinol (Fig. 12.4) [11, 13, 49]. This conversion involves 5-hydroxylation of one of the 3-methoxy-4-hydroxylphenyl (guaiacyl) moieties of matairesinol to give rise to 5-hydroxymatairesinol (thujaplicatin) followed by dual methylation at the 4- and 5-hydroxyls, giving rise to a 3,4,5-trialkoxyphenyl moiety (Fig. 12.4) [11, 13,49],... 

Noguchi et al. (8) synthesized precursors of lignin biosynthesis (i.e., coniferyl and sinapyl alcohols) in which the side chain and methoxy groups were doubly labeled by and H, prepared the DHP (synthetic lignin) from them, and treated the DHP with the laccase. These results showed that about 25% of Hs of the a- and -positions were removed in a ratio of one to one, respectively, and that the methoxyl group of a syringyl unit was de-methylated easier than that of a guaiacyl. 

Figure 15. Hypothetical scheme for the transformations experienced by veratrylglycerol-B-guaiacyl ether at the hands of a seemingly extracellular NAD-dependent oxidoreductase system from Poria subacida (90).

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