Mechanism of Oxidative Ring‐Closure as Part of the Hygromycin Biosynthesis Step by a Nonheme Iron Dioxygenase

Abstract

AbstractNonheme iron dioxygenases catalyze vital reactions for biosystems including the biosynthesis of antibiotics. One such enzyme, namely the hygromycin biosynthesis enzyme (HygX), performs an oxidative ring‐closure reaction to form an ortho−ester product, which is a relevant reaction step for drug synthesis and biotechnology. To understand the selective reaction mechanism of oxidative ring‐closure to form ortho−ester products in HygX, we investigated its catalytic reaction mechanism leading to various products. Large active site cluster models were set‐up and various pathways for substrate activation have been calculated. The work identifies a high‐valent iron(IV)‐oxo species in the quintet spin state as the active oxidant that selectively abstracts a proton of an alcohol group of the substrate, which is followed by a hydrogen atom abstraction from a tertiary C−H group and rapid electron transfer. The latter‐formed biradical intermediate rearranges to form the desaturated ring‐closed product. The calculations show that an active site Lys residue donates positive charge to the metal−oxo group and guides the reaction to a chemoselective desaturation pathway.