Quinone Methides in Lignification

John Ralph1 2 3, Paul F. Schatz3, Fachuang Lu1, Hoon Kim1, 

1 Department of Biochemistry and Great Lakes Bioenergy Research Center, University of Wisconsin, Madison, WI, USA 

Quinone Methides, Edited by Steven E. Rokita Copyright 2009 John Wiley Sons, Inc., Publication. 

This chapter does not purport to be a comprehensive review of quinone methides in lignification. It covers aspects of quinone methide chemistry that our laboratory has been involved in over the past 30 years and is therefore heavily weighted toward our own studies and those with which we have interacted. 

2 QUINONE METHIDES FROM RADICAL COUPLING IN LIGNIFICATION 

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Quinone methides play an important role in lignification. They are produced directly, as intermediates, when lignin monomers, be they hydroxycinnamyl alcohols, hydroxy-cinnamaldehydes, or hydroxycinnamates, couple or cross-couple at their 8- positions. A variety of postcoupling quinone methide rearomatization reactions leads to an array of structures in the complex lignin polymer (Fig. 12.2). 

However, the quinone methide (V) allows of a much wider scope of variation. Not only will water (dissociation constant = lO- ) add onto (V) under the normal conditions of lignification via the ionic mechanism shown in Fig. 5, but coniferyl alcohol itself or other phenolic lignin intermediates (dissociation constants of phenols 10" ) will add... 

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