Biocatalytic Regioselective C‐Formylation of Resorcinol Derivatives

Although aromatic formylation reactions are highly valuable from a synthetic perspective, a biocatalytic version has not yet been reported. Here, the cofactor-independent multimeric three-component acyltransferase from Chromobacterium sphagni (CsATase) was identified to enable the nonnatural promiscuous regioselective C-formylation of polyphenolic substrates, especially resorcinol derivatives, and thus extending the reaction scope of acyltransferases. Formylation of 4- and 5-substituted resorcinol derivatives gave access to regioselectively mono-formylated products with up to 99% conversion and up to 74% isolated yield. Formylation of phloroglucinol led to the di-formylated product with 99% conversion, outperforming chemical methods. Structural analysis of CsATase by X-ray crystallography provided insights into its active site.