AFM-30a hydrochloride is a potent protein arginine deiminase 2 (PAD2) inhibitor and has excellent PAD2-selectivity. AFM-30a hydrochloride binds to PAD2 with an EC50 value of 9.5 μM. AFM-30a hydrochloride also inhibits H3 citrullination with an EC50 value of 0.4 μM. AFM-30a hydrochloride can be used for the research of certain cancers and a variety of autoimmune diseases including rheumatoid arthritis (RA), multiple sclerosis, lupus, and ulcerative colitis.