Target agnostic photoaffinity labelling by sulfonylhydrazones

Photoaffinity labeling is a widely used methodology for interrogating small molecule‐protein interactions. However, these applications are limited by the few photo‐cross‐linkers that typically modify the affinity and the binding mode of the original ligand. Here, we report the development of new target agnostic photoaffinity warheads, sulfohydrazones that form a reactive carbene upon UV irradiation. Careful optimization of the reaction conditions allowed us to effectively label five different amino acid residues in proteins. Our approach turned biologically relevant hydrazones and sulfohydrazones to intrinsically irreversible covalent binders without structural modifications by photoactivation as demonstrated on monoamine oxidase A (MAO‐A) enzyme and STAT5b (Signal transducer and activator of transcription 5b) transcription factor. Sulfohydrazones are readily accessible by transforming the corresponding carbonyl group of a ligand or a suitable tag that extends the application domain of the method for any ligands exemplified by conditional labelling of the acetylcholine esterase enzyme and the oncogenic mutant of GTP‐ase KRasG12D.