Peroxidase-mediated formation of the fungal polyphenol 3,14'-bihispidinyl

Medicinal fungi, Phellinus linteus and Inonotus xeranticus, produce a cluster of yellow pigment in their fermentation broth that acts as an important element of biological activity. The pigment is composed of diverse polyphenols with a styrylpyrone moiety, mainly hispidin and its dimers, 3,14'-bihispidinyl, hypholomine B, and 1,1- distrylpyrylethan. Although dimeric hispidins were proposed to be biosynthesized from two molecules of monomer via oxidative coupling by ligninolytic enzymes, laccase and peroxidase, the details of this process remain unknown. In this preliminary study, we attempted to achieve enzymatic synthesis of the hispidin dimer from hispidin by using commercially available horseradish peroxidase (HRP). Consequently, a hispidin dimer, 3,14'-bihispidinyl, was synthesized, whereas the other dimers, hypholomine B and 1,1-distrylpyrylethan, were not produced. This result suggested that the oxidative coupling at the C-3 and C-14' positions of hispidins was dominant in the process of dimerization by HRP, and indicated that additional catalysts or substrates would be needed to synthesize other hispidin dimers present in the fungal metabolite.