Biocatalytic Cleavage of para-Acetoxy Benzyl Ethers: Application to Protecting Group Chemistry

Abstract

Aryl ethers are ubiquitous protecting groups of alcohols and amines in organic chemistry. This is owed to the simplicity of their appendage to molecules and the robust protection afforded. However, aryl ethers and amines can be challenging to cleave, often requiring harsh and unselective reductive conditions. We report the structure-based engineering of a promiscuous, ether-cleaving vanillyl alcohol oxidase-type biocatalyst for activity on a wide range of para-hydroxy benzyl ethers. Two superior quadruple mutants are identified with improved kinetics and substrate scope. One evolved variant and two predecessors are crystallized, and their structures resolved to 2.8-1.5 Å, revealing a significant increase in the volume and flexibility of the active site cavity. To illustrate the potential usefulness of the engineered biocatalysts, one is later coupled with another biocatalyst in a cascade reaction to catalyze the selective cleavage of an uncommon aryl ether protecting group, para-acyloxy benzyl ethers, in good yield and under mild conditions.