Chemoenzymatic Total Synthesis of a Naturally Occurring (5-5′)/(8′-O-4″) Dehydrotrimer of Ferulic Acid

The cross-linking of plant cell walls by ferulate dehydrodimerization reactions is well established. Recently, a (5-5 ')/(8 '-O-4 '') dehydrotrimer of ferulic acid (A) was isolated from alkali extracts of maize bran. Its structure was elucidated on the basis of an extensive structural analysis (UV, MS, 1D and 2D NMR). This first identified ferulic acid dehydrotrimer has revealed that parietal polysaccharide chains can be more extensively cross-linked than has been previously recognized. To produce the (5-5 ')/(8 '-O-4 '') dehydrotrimer (A) in suf-ficient high-purity quantities and allow the development of analytical methodologies (e.g., LC/GC, immunohistochemistry) to identify and quantify this peculiar trimer in plant extracts or samples, its first total convergent synthesis has been achieved in 10 steps and in 18% yield starting from commercially available vanillin by horseradish peroxidase mediated enzymatic aryl-aryl coupling, aldolization/crotonization, and Wittig olefination reactions as the key steps.