Synthesis and in-vitro Evaluation of Novel Low Molecular Weight Thiocarbamates as Inhibitors of Human Leukocyte Elastase

Abstract

A series of novel low molecular weight thiocarbamate esters (1e-6e) were synthesized and evaluated as inhibitors of human leukocyte elastase (HLE). The thiocarbamate esters studied consist of a substituted primary or secondary aliphatic or aromatic amine and a 1-phenyl-1H-tetrazole-5-thiol (Table I). The HLE catalyzed hydrolysis of N-methoxysuccinyl- L-Ala-L-Ala-L-Pro-L-Val-p-nitroanilide substrate was utilized as the measure of inhibition. N-n-butyl, 1-phenyl-1H-tetrazole-5-thiocarbamate (1e) exhibited the highest inhibitory activity (k_obs/[I] = 2.1 × 10⁵ M⁻¹ · min⁻¹) and N-allyl, 1-phenyl-1H-tetrazole-5-thiocarbamate (2e) (K_obs/[I] = 6.1×10⁴ M⁻¹ · min⁻¹) exhibited the second highest inhibitory activity of all the thiocarbamates. The aromatic N-phenyl, 1-phenyl-1H-tetrazole-5-thiocarbamate (4e) showed the lowest inhibitory activity (K_obs/[I] = 1.9 × 10² M⁻¹ · min⁻¹ among the N-monosubstituted derivatives, similar to that of N-ethyl-N-n-butyl, 1-phenyl-1H-tetrazole-5-thiocarbamate (5e) (K_obs/[I] = 1.8 × 10² M⁻¹ min⁻¹). The N-isopropyl, 1-phenyl-1H-tetrazole-5-thiocarbamate (3e) (K_obs/[I] = 3.3 × 10³ M⁻¹ · min⁻¹) was about 10 fold more active than (4e) and N, N-diisopropyl, 1-phenyl-1H-tetrazole- 5-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 the interaction and possible chemical modification of one enzyme residue. Straight chain nonpolar aliphatic substituents on the nitrogen of the thiocarbamate functionality may be essential for high inhibitory activity. As the degree of substitution (branching) on the nitrogen of the thiocarbamate functionality increases the inhibitory activity of the compounds decreases. The time-dependent inhibition of HLE and the slow deacylation rates by the N-monosubstituted thiocarbamates are consistent with irreversible inhibition.

Key Words:

• Human leukocyte elastase
• Thiocarbamates
• Irreversible inhibition
• HLE