Overcoming challenges in the synthesis of a lignin-carbohydrate complex (LCC) model: Mitsunobu versus Appel product

Abstract

Arabinoxylan ferulate representing a macromolecular LCC model valid for annual plants is synthesized under Mitsunobu conditions. The content of ferulic acid ester is tuned by the reaction conditions achieving degree of substitution values from 0.09 to 0.45. Utilization of the chloride-free solvent N-methyl-2-pyrrolidone allows the design of pure Mitsunobu products without occurrence of deoxychloro moieties arising from Appel type reaction. 2D NMR experiments reveal nature-identical structure of ferulate moieties present at position 5 of the arabinose side chain. Enzymatic dehydrogenation polymerization of coniferyl alcohol on ferulate anchor groups under homogeneous conditions lead to beta -O-4, beta -5, and Hibbert ketone structures identified by Py-GC-MS. The results are valuable to study structure-property relationships within the formation of natural and non-native lignins.Graphical abstract