Metabolism of a phenylcoumaran substructure lignin model compound in ligninolytic cultures of Phanerochaete chrysosporium

Abstract

The degradation of the phenylcoumaran substructure model compound methyl dehydrodiconiferyl alcohol by the white-rot wood decay fungus Phanerochaete chrysosporium was investigated using culture conditions optimized for lignin oxidation. Initial attack was in the cinnamyl alcohol side chain, which was oxidized to a glycerol structure. This was subsequently converted by loss of the two terminal carbon atoms, Cβ′ and Cγ′, to yield a Cα′-aldehyde structure, which was further oxidized to the Cα′-acid compound. The next detected intermediate, a phenylcoumarone, was produced by double bond formation between Cα and Cβ, and oxidation of the Cγ-alcohol to an aldehyde group. Further oxidation of Cγ to an acid yielded the next intermediate. The final identified degradation product was veratric acid. No products from the 5-substituted aromatic ring, and no phenolic products, were found. The initial glycerol-containing intermediate was a mixture of the threo and erythro forms, and no optical activity could be found, suggesting that its formation might have involved nonstereospecific Cα′-Cβ′ epoxidation followed by non-enzymatic hydrolysis of the epoxide.