Oxidative Ring Contraction by a Multifunctional Dioxygenase Generates the Core Cycloocatadiene in the Biosynthesis of Fungal Dimeric Anhydride Zopfiellin

To elucidate the biosynthesis of a fungicidal dimeric anhydride zopfiellin, the putative biosynthetic gene cluster was identified. We conducted heterologous expression of candidate genes for the synthesis of maleic anhydride and its dimerization and identified the two isomeric dimers with 9-membered rings as products. Notably, α-ketoglutarate-dependent dioxygenase ZopK oxidized one of the dimers, giving the 8-membered ring of zopfiellin. The mechanism of oxidative rearrangement is proposed by analyzing the incorporation of ¹³C-labeled precursors.