Activating Metalloenzymes By Electricity: Bioelectrocatalytic Aerobic Oxidation in the Synthesis of Islatravir

Abstract

Electrochemistry is a green and sustainable technique that has been widely applied in bioanalysis, organic synthesis and energy conversion. Despite the huge potential for green and selective synthesis, bioelectrochemistry is uncommon in synthetic organic applications. The recently disclosed fully biocatalytic cascade synthesis of the HIV drug islatravir represents a groundbreaking approach to pharmaceutical manufacturing. The first step in the synthesis is the biocatalytic desymmetrizing oxidation of ethynyl glycerol to (R)-ethynyl glyceraldehyde. This oxidation process requires 3 redox enzymes: Cu-dependent galactose oxidase (GOase) together with two auxiliary enzymes: catalase and horseradish peroxidase (HRP). While elegant, this three-enzyme system introduced a significant cost and protein burden. GOase is critical to achieving enantioselectivity, while HRP is proposed to facilitate generation of catalytically active intermediate through modification of the oxidation state of the GOase active site. Thus we sought electrochemical strategies to achieve enzyme activation and replace HRP. Here we disclose the development of bioelectrocatalytic aerobic oxidation of alcohols under mild conditions, using a water-soluble ferrocene derivative as the electrocatalyst. Mechanistic insights into the electrochemical activation of GOase were gathered by interrogating the enzyme redox properties and the electron transfer rates between GOase and the electrochemically generated oxidants.