High affinity and selective human neutrophil elastase 1 (HNE1) inhibitor (Ki = 12 nM). Exhibits >100-fold less activity at other related proteases including trypsin, pancreatic elastase, collagenase and murine macrophage elastase. Inhibits HNE-induced lung hemorrhaging and suppresses leukocyte levels in an in vivo model of COPD. Orally active. Purity 98%. MW (observed): 452.51