Biotransformation of pungent constituents from ginger (Zingiber officinale Roscoe) by Colletotrichum gloeosporioides yields oxidative ortho���ortho coupling products

This work investigated the biotransformation of ginger constituents (zingerone, [6]-shogaol, [6]-gingerol, and methyl-[6]-gingerol) by the pathogenic fungus Colletotrichum gloeosporioides. Experiments were carried out with and without deuterium-labelled compounds. The product metabolites were analyzed by liquid chromatography coupled to tandem mass spectrometry and liquid chromatography solid phase extraction-nuclear magnetic resonance. Substrates supplied to the fungus were incorporated into metabolic pathways mostly by oxidation reactions, including aromatic carbon���carbon coupling. Zingerone and [6]-gingerol biotransformation products included biphenol dimers. A biodegradation pathway for biphenol formation was proposed based on the presence of the intermediate 4-(2-hydroxyethyl)-2-methoxyphenol, commonly identified from [6]-gingerol and [6]-shogaol biodegradation. This intermediate likely originates from a Baeyer���Villiger reaction followed by hydrolysis. The C���C coupling of molecules could result in phenolic oxidative ortho���ortho coupling, suggesting that biphenol dimers are products of C. gloeosporioides laccase catalysis.