An Alternative Cascade for the Selective Methylation of Catechols and Tetrahydroisoquinolines by O‐Methyltransferases

Methyltransferases are gaining traction as a method to achieve greener and regioselective methylations of a wide array of substrates. In this work, a halide methyltransferase biomethylation cascade was successfully adapted with the incorporation of a methionine adenosyltransferase to generate the S ‐adenosyl‐L‐methionine (SAM) methylation cofactor in situ from less costly ATP and L‐methionine, instead of directly adding SAM to start the cascade. Furthermore, this cascade was applied to achieve novel catechol and tetrahydroisoquinoline methylations with the O ‐methyltransferases Rn COMT, Mx SafC and Np N4OMT with high conversions and regioselectivities. In addition, the cascade was successfully trialled with the less toxic methyl group donor, methyl tosylate.