Title: NMR analysis of lignins in CAD-deficient plants. Part 1, Incorporation of hydroxycinnamaldehydes and hydroxybenzaldehydes into lignins
Author: Kim, Hoon; Ralph, John; Lu, Fachuang; Ralph, Sally A.; Boudett, Alain-M.; MacKay, John J.; Sederoff, Ronald R.; Ito, Takashi; Kawai, Shingo; Ohashi, Hideo; Higuchi, Takayoshi;
Source: Organic and biomolecular chemistry. Vol. 1 (2003): pages 268-281
Publication Series: Miscellaneous Publication
Description: Peroxidase/H2O2-mediated radical coupling of 4-hydroxycinnamaldehydes produces 8–O–4-, 8–5-, and 8–8-coupled dehydrodimers as has been documented earlier, as well as the 5-5-coupled dehydrodimer. The 8–5- dehydrodimer is however produced kinetically in its cyclic phenylcoumaran form at neutral pH. Synthetic polymers produced from mixtures of hydroxycinnamaldehydes and normal monolignols provide the next level of complexity. Spectral data from dimers oligomers and synthetic polymers have allowed a more substantive assignment of aldehyde components in lignins isolated from a CAD-deficient pine mutant and an antisense-CAD-downregulated transgenic tobacco. CAD-deficient pine lignin shows enhanced levels of the typical benzaldehyde and cinnamaldehyde end-groups, along with evidence for two types of 8–O–4-coupled coniferaldehyde units. The CAD-downregulated tobacco also has higher levels of hydroxycinnamaldehyde and hydroxybenzaldehyde (mainly syringaldehyde) incorporation, but the analogous two types of 8–O–4-coupled products are the dominant features. 8–8-Coupled units are also clearly evident. There is clear evidence for coupling of hydroxycinnamaldehydes to each other and then incorporation into the lignin, as well as for the incorporation of hydroxycinnamaldehyde monomers into the growing lignin polymer. Coniferaldehyde and sinapaldehyde (as well as vanillin and syringaldehyde) co-polynerize with the traditional monolignols into lignins and do so at enhanced levels when CAD-deficiency has an impact on the normal monolignol production. The implication is that, particularly in angiosperms the aldehydes behave like the traditional monolignols and should probably be regarded as authentic lignin monomers in normal and CAD-deficient plants.
Keywords: Oligomers, dimers, lignin, nuclear magnetic resonance spectroscopy, aldehydes, coniferaldehyde, cinnamyl alcohol dehydrogenase, hydroxycinnamaldehydes, hydroxybenzaldehydes
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Kim, Hoon; Ralph, John; Lu, Fachuang; Ralph, Sally A.; Boudett, Alain-M.; MacKay, John J.; Sederoff, Ronald R.; Ito, Takashi; Kawai, Shingo; Ohashi, Hideo; Higuchi, Takayoshi 2003. NMR analysis of lignins in CAD-deficient plants. Part 1, Incorporation of hydroxycinnamaldehydes and hydroxybenzaldehydes into lignins. Organic and biomolecular chemistry. Vol. 1 (2003): pages 268-281
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