Scope: Inhibiting human neutrophil elastase (HNE) is a promising strategy for treating inflammatory lung diseases,such as H1N1 and SARS virus infections.The use of sivelestat, the only clinically registered synthesized HNE inhibitor, is largely limited by its risk of organ toxicity because it irreversibly inhibits HNE.Therefore, potent reversible HNE inhibitors are promising alternatives to sivelestat.