Diethenyl Sulfoximine (DESI) as an Irreversible Lysine‐Targeting Warhead Enables the Design of Covalent Allosteric EGFR Inhibitor

Targeting lysine residues with covalent inhibitors is challenging due to their abundance in the proteome and the protonation of lysine's ε‐amino group, which diminishes its reactivity. This study introduces diethenyl sulfoximine (DESI) as a novel bio‐orthogonal aminophilic electrophile which can react with lysine via double conjugate addition to form a cyclic adduct. The second addition promotes the entire and efficient electrophilic attack by the ε‐amino of lysine on the ethenyl groups. DESI exhibits superior aqueous stability, overcoming the hydrolysis issue encountered by most reported lysine‐targeting covalent agents. Incorporation of DESI in the allosteric pocket binder EAI045 of oncoprotein epidermal growth factor receptor (EGFR) yields compound 4, which specifically reacts to the catalytic lysine (Lys745). Compound 4 showed potent inhibition of EGFR‐driven cell proliferation with IC50 values of 0.789 µM and 1.22 µM in engineered BaF3‐EGFRL858R/T790M/C797S and NCI‐H1975 cells, respectively, overcoming EAI045's limitation of lack in cellular potency as a single agent. Tyrosine kinases panel profiling confirmed selectivity toward mutant EGFR while sparing the wild type with minimal off‐targets. These findings highlight DESI's potential as a versatile strategy for targeting lysine residues irreversibly, offering solutions to overcome drug resistance in cancer therapy and advance next‐generation precision medicines.