Engineered enzymes for enantioselective nucleophilic aromatic substitutions

Nucleophilic aromatic substitutions (S Ar) are amongst the most widely used processes in the pharmaceutical and agrochemical industries , allowing convergent assembly of complex molecules through C-C and C-X (X = O, N, S) bond formation. S Ar reactions are typically carried out using forcing conditions, involving polar aprotic solvents, stoichiometric bases and elevated temperatures, which do not allow for control over reaction selectivity. Despite the importance of S Ar chemistry, there are only a handful of selective catalytic methods reported that rely on small organic hydrogen-bonding or phase-transfer catalysts . Here we establish a biocatalytic approach to stereoselective S Ar chemistry by uncovering promiscuous S Ar activity in a designed enzyme featuring an activated arginine . This activity was optimized over successive rounds of directed evolution to afford an engineered biocatalyst, S Ar1.3, that is 160-fold more efficient than the parent and promotes the coupling of electron-deficient arenes with carbon nucleophiles with near-perfect stereocontrol (>99% e.e.). S Ar1.3 can operate at a rate of 0.15 s , perform >4000 turnovers and can accept a broad range of electrophilic and nucleophilic coupling partners, including those that allow construction of challenging 1,1-diaryl quaternary stereocentres. Biochemical, structural and computational studies provide insights into the catalytic mechanism of S Ar1.3, including the emergence of a halide binding pocket shaped by key catalytic residues Arg124 and Asp125. This study brings a landmark synthetic reaction into the realm of biocatalysis to provide an efficient and versatile platform for catalytic S Ar chemistry.