Fig. 1
Wheat straw lignin model. The most abundant substructures are included, attempting to fairly represent the relative abundances of each moiety, based on literature [14,15,16,17,18,19]. H: p-hydroxyphenyl unit; G: guaiacyl unit; S: syringyl unit; A: β-O-4′alkyl-aryl ether; A′: β-O-4′alkyl-aryl-ether γ-acylated; Aox: β-O-4′alkyl-aryl-ether Cα-oxidized; B: phenylcoumaran; C: resinol; D: dibenzodioxocin; E: α,β-diarylether; F: spirodienone; I: cinnamyl alcohol (or aldehyde); T: tricin; pCA: p-coumarate; FA: ferulate (R = H or arabinose). Note that γ-acylation here is only shown on β-O-4 linkages, while in fact any free γ-OH can by acylated. For simplicity only monomeric 8-O-4′ linked FA is shown, though many other ferulate and diferulate linkages are known to exist. For more detailed structures, see Fig. 5