Inhibition of human leukocyte elastase (HLE) by N-substituted peptidyl trifluoromethyl ketones

Article abstract of DOI:10.1021/jm00082a005

A series of tripeptides possessing trifluoromethyl or aryl ketone residues at P₁ were prepared and evaluated both in vitro and in vivo as potential inhibitors of human leukocyte elastase (HLE). Tripeptides containing non naturally occurring N-substituted glycine residues at the P₂-position have been demonstrated to be potent in vitro inhibitors of HLE, with IC₅₀ values in the submicromolar range. Sterically demanding substituents on the P₂- nitrogen have no detrimental effect on in vitro potency. The inhibition process presumably acts via hemiketal formation with the active site Ser¹⁹⁵ of HLE, and is facilitated by the strongly electron withdrawing trifluoromethyl functionality. Deletion of the amino acid at the P₃-subsite region affords inactive compounds. Valine is the preferred residue at the P₁-position, whereas the corresponding glycine, alanine, α,α- dimethylglycine, or phenylalanine analogues are all inactive. The compounds described herein all confer a high degree of in vitro specificity when tested against representative cysteine, aspartyl, metallo, and other serine proteases. One of the most potent in vitro inhibitors is (3RS)-N-[4[[[(4- chlorophenyl)sulfonyl]amino]carbonyl]phenyl]oxomethyl]-L-valyl-N-(2,3- dihydro-1H-inden-2-yl)glycine N-[3-(1,1,1-trifluoro-4-methyl-2- oxopentyl)amide (20i; BI-RA-260) (IC₅₀ = 0.084 μM). Compound 20i was also tested in hamsters in an elastase-induced pulmonary hemorrhage (EPH) model. In this model, intratracheal (it.) administration of 20i, 5 min prior to HLE challenge, effectively inhibited hemorrhage in a dose-dependent manner with an ED₅₀ of 4.8 μg. The inhibitor 20i, 20 μg administered it. 24, 48, and 72 h prior to HLE challenge, exhibits significant inhibition against hemorrhage at all time points (97%, 64% and 49%, respectively). In a 21-day chronic model of emphysema in hamsters, 200 μg of HLE administered it. caused an elastase-induced emphysema in the lungs which can be quantitated histologically utilizing image analysis. In this assay, 20i significantly inhibited pulmonary lesions associated with septal destruction and increased alveolar spaces, when dosed at 20 μg it. 5 min prior to challenge with HLE.