Fig. 2. Monolignol (1) and lignin (2) radicals can undergo ß-O-4 coupling to form quinone methide intermediates (3). These intermediates are stabilized by the addition of nucleophiles (Nu), such as water, uronic acids, or neutral sugars to form structures (4), which are substituted with -hydroxyl groups or cross-linked to the cell wall matrix by benzyl -ester or benzyl -ether linkages.