Cross-coupling of hydroxycinnamyl aldehydes into lignins

[GRAPHICS] Pathways for hydroxycinnamyl aldehyde incorporation into lignins are reveal ed by examining transgenic plants deficient in cinnamyl alcohol dehydrogena se, the enzyme that converts hydroxycinnamyl aldehydes to the hydroxycinnam yl alcohol lignin monomers. In such plants the aldehydes incorporate into l ignins via radical coupling reactions. As diagnostically revealed by long-r ange C-13-H-1 correlative NMR, sinapyl aldehyde (3,5-dimethoxy 4-hydroxy-ci nnamaldehyde) 8-O-4-cross-couples with both gualacyl (3-methoxy-4-hydroxyph enyl-propanoid) and syringyl (3,5-dimethoxy-4-hydroxyphenyl-propanoid) unit s, whereas coniferyl aldehyde cross-couples only with syringyl units.