Aminofutalosine Synthase: Evidence for Captodative and Aryl Radical Intermediates Using β-Scission and S_RN1 Trapping Reactions

Abstract

Aminofutalosine synthase (MqnE) is a radical SAM enzyme involved in the menaquinone biosynthetic pathway. In this communication, we propose a novel mechanism for this reaction involving the addition of the adenosyl radical to the substrate double bond to form a captodative radical followed by rearrangement and decarboxylation to form an aryl radical anion which is then oxidized by the [4Fe–4S] +2 cluster. Consistent with this proposal, we describe the trapping of the captodative radical and the aryl radical anion using radical triggered C–Br fragmentation reactions. We also describe the trapping of the captodative radical by replacing the vinylic carboxylic acid with an amide.