Synthesis and in-vitro evaluation of novel low molecular weight thiocarbamates as inhibitors of human leukocyte elastase

A series of novel low molecular weight thiocarbamate esters (1e-6e) were sy nthesized and evaluated as inhibitors of human leukocyte elastase (HLE). Th e thiocarbamate esters studied consist of a substituted primary or secondar y aliphatic or aromatic amine and a 1-phenyl-1H-tetrazole-5-thiol (Table 1) . The HLE catalyzed hydrolysis of N-methoxysuccinyl- L-Ala-LAla-L-Pro-L-Val -p-nitroanilide substrate was utilized as the measure of inhibition. N-n-bu tyl, 1-phenyl-1H-tetrazole- 5-thiocarbamate (1e) exhibited the highest inhi bitory activity (k(obs)/[1] = 2.1 x 10(5) M-1 min(-1)) and N-allyl, 1-pheny l-2H-tetrazole-5-thiocarbamate (2e) (K-obs/[I]] = 6.1 x 10(4) M-2 . min(-1) ) exhibited the second highest inhibitory activity of all the thiocarbamate s. The aromatic N-phenyl, 1-phenyl-1H-tetrazole-5-thiocarbamate (4e) showed the lowest inhibitory activity (K-obs/[I] = 1.9 x 10(2) M-1 (.) min(-1)) a mong the N-monosubstituted derivatives, similar to that of N-ethyl-N-n-buty l, 1-phenyl-1H-tetrazole-5-thiocarbamate (5e) (K-obs/[I] = 1.8 x 10(2) M-1 (.) min(-1)). The N-isopropyl, 1-phenyl-1H-tetrazole-5-thiocarbamate (3e) ( K-obs/[I] = 3.3 x 10(3) M (1) (.) min(-1)) was about 10 fold more active th an (4e) and N, N-diisopropyl, 1-phenyl-1H-tetrazole- Ei-thiocarbamate (6e) showed no inhibitory activity against HLE. In the present work less than 3% of HLE specific activity was regained after 24 hours incubation with each of the tested N-monosubstituted thiocarbamates (1e-4e). The time-dependent inhibition of HLE by the thiocarbamate compounds (1e-5e) seems to involve t he interaction and possible chemical modification of one enzyme residue. St raight chain nonpolar aliphatic substituents on the nitrogen of the thiocar bamate functionality may be essential for high inhibitory activity. As the degree of substitution (branching) on the nitrogen of the thiocarbamate fun ctionality increases the inhibitory activity of the compounds decreases. Th e time-dependent inhibition of HLE and the slow deacylation rates by the N- monosubstituted thiocarbamates are consistent with irreversible inhibition.