Lysine-Targeted Covalent Inhibitors: Emerging Warheads and Expanding Applications in Medicinal Chemistry

Covalent inhibition has re-emerged as a central strategy in drug discovery, yet most successes have focused on cysteine residues. Expanding covalent design to other nucleophilic amino acids offers new opportunities to overcome resistance, broaden ligandable targets, and modulate protein function beyond enzyme active sites. Among these, lysine is an attractive target due to its high abundance, structural diversity, and roles in catalysis and protein-protein interactions (PPIs). This Perspective advances recent insights into lysine-directed covalent chemistry, highlighting electrophilic warheads with tunable reactivity and selectivity, including activated esters, benzaldehyde derivatives, 2-formylphenylboronic acid, sulfur(VI) fluorides, and photoactivatable scaffolds. Representative applications in kinase inhibition, transthyretin stabilization, and PPI modulation illustrate the breadth of this approach. Emerging directions integrating reversible covalency and targeted degradation further underscore the potential of lysine covalency for next-generation covalent drug discovery. Challenges associated with lysine targeting, including achieving selectivity and minimizing off-target reactivity, are also briefly discussed.