Anti-virulence factor-IN-3 (Compound 21) is a covalent β-amino sulfone inhibitor of anthrax edema factor (EF), with a Ki of 0.44 μM. It produces an active vinyl sulfone intermediate that forms an irreversible covalent bond with the Lys residue at the EF active site, permanently inhibiting the adenylate cyclase activity of EF. Anti-virulence factor-IN-3 effectively suppresses EF-induced cAMP production, with an EC50 of 0.15 μM, and can be used in the study of anthrax infection.