Automated Solid Phase Synthesis of Stapled Oligopeptides as Covalent <scp>PAD4</scp> Inhibitors

ABSTRACT We demonstrate our results with the synthesis of inhibitors of Protein Arginine Deaminase 4 (PAD4), a key regulator of neutrophil elastase extracellular traps (NETs), as potential therapeutics for chronic obstructive pulmonary disease (COPD). Furthermore, we report an automated method for solid phase synthesis of macrocyclic stapled peptides with chloroacetamidine guanidine mimetic function as PAD4 inhibitors. This approach utilizes the 2,4,6‐trimethylbenzenesulfenyl protective group for cysteine, followed by reaction with various halogen derivatives upon deprotection under mild conditions. Furthermore, derivatization of the amino group with ethyl chloroacetamidate hydrochloride after its deprotection, performed on solid phase, offers a new, efficient method for rapid and robust synthesis of stapled peptide derivatives. This process notably reduces time, energy, and solvent use compared to traditional in‐solution methods.