Inhibition of neurotoxic esterase in vitro by novel carbamates.

Carbamyl sulfonate (CS) compounds are a novel class of carbamates derived from amino acid methyl esters. They have the general structure RCH(COOCH3)NH(CO)SO-3K+, where R is the sidechain of the parent amino acid. These compounds were developed as active site-directed inhibitors of human leukocyte elastase (HLE). The purpose of this study was to characterize the inhibition of hen brain neurotoxic esterase (neuropathy target esterase, NTE), horse serum butyrylcholinesterase (BuChE), and bovine erythrocyte acetylcholinesterase (AChE) by CS analogs derived from the methyl esters of L-ala, D-norval, L-norval, L-phe, L-val, L-norleu, D-met, and L-met. Bimolecular rate constants of inhibition (ki) for NTE ranged from 0.571 for L-ala-CS to 17.7 mM-1 min-1 for L-norleu-CS (10-min I50 values of 123 and 3.92 microM, respectively). Potency against NTE increased with chain length for straight-chain R-groups of L-CS compounds. Unlike HLE, NTE was only weakly stereoselective for CS compound enantiomers. The L-isomers were weaker inhibitors of BuChE than NTE (10-min I50 range of 742 to 35.6 microM). In contrast to the L-enantiomers, the I50 plots of D-met-CS and D-norval-CS were not linear for BuChE, suggesting a possible stereospecific mechanistic shift for inhibition of this enzyme, AChE was not effectively inhibited by any of the CS compounds (I50 values > 750 microM). The specificity and charged nature of CS compounds give these unusual NTE inhibitors potential advantages for mechanistic studies of organophosphorus compound-induced delayed neurotoxicity (OPIDN) and its protection or potentiation.

Synthesis, kinetics, and structural studies of a photolabile caged isocitrate: a catalytic trigger for isocitrate dehydrogenase.

A biologically inactive photolabile derivative of isocitrate has been synthesized and characterized. The caged isocitrate is photolyzed to isocitrate with a rate constant of 234 s-1, a half-life of 3 ms, and a quantum yield of 0.3 at pH = 6.4. Caged isocitrate (1-(2-nitrophenyl)ethyl 1-hydroxy-1,2-dicarboxy-3- propanecarboxylate) was synthesized in a straightforward synthetic manner starting with racemic isocitric acid lactone. Laser pulse photolysis at a wavelength of 355 nm was used to determine the rate of photolysis and the quantum yield and to quantify the amount of energy needed for quantitative conversion of the caged isocitrate to free isocitrate. Enzymatic conversion of the liberated isocitrate to alpha-ketoglutarate was achieved in solution as well as in wild-type and mutant isocitrate dehydrogenase (IDH) protein crystals. The X-ray crystal structures of wild-type IDH soaked with photolabile caged isocitrate and Mg2+ and void of nicotinamide adenine dinucleotide phosphate were solved at 2.5 A resolution before and after photolysis and compared by difference mapping against previously determined enzyme structures. Prior to photolysis the enzyme active site contains a low occupancy of bound free Mg2+ in the metal binding site but no observable bound isocitrate, whereas after photolysis the enzyme is complexed to liberated isocitrate and Mg2+ with binding interactions identical to those of previously determined substrate complexes. Single-crystal spectroscopy of the crystals after flash photolysis in the presence of substrates shows production of bound enzyme-substrate complexes and reduced nicotinamide adenine dinucleotide phosphate induced by the photolytic event.

Design, synthesis and biological evaluation of succinimide derivatives as potential mechanism-based inhibitors of human leukocyte elastase, cathepsin G and proteinase 3.

Structure-activity relationship study and in vitro biochemical studies with human leukocyte elastase, cathepsin G and proteinase 3 were conducted using a series of succinimide derivatives.

Derivatives of 3-alkyl-N-hydroxysuccinimide: probing the effect of structure on bioactivity toward human leukocyte elastase.

A structure-activity relationship study was conducted in order to probe the nature of the interaction between some 3-alkyl-N-hydroxysuccinimide derivatives and human leukocyte elastase. The structural features in substituent X (structure I) that lead to the manifestation and optimization of inhibitory activity have been examined. The data suggest that the presence of an alkyl or aryl(sulfonyloxy) group in the active compounds may serve a triple purpose, namely, it functions as a good leaving group as dictated by the established mechanism of action of this class of compounds, secondly, it may enhance binding by assuming a favorable spatial orientation and, thirdly, it may increase the chemical reactivity of the carbonyl carbon in the bioactive compounds.

3-(Alkylthio)-N-hydroxysuccinimide derivatives: potent inhibitors of human leukocyte elastase.

A series of 3-(alkylthio)-N-hydroxysuccinimide derivatives was synthesized and their inhibitory activity towards human leukocyte elastase (HLE) was investigated. The interaction of the compounds having a 3-alkylthioether side chain (compounds 1 and 2) with HLE was found to involve rapid acylation of the enzyme, followed by total regain of enzymatic activity within 3 h. Interestingly, compounds 3-8, having an oxidized thioether side chain, were found to be highly effective, time-dependent, irreversible inhibitors of the enzyme. The k(obs)/I values for compounds 3-8 ranged between 890 and 24,000 M-1 s-1. These findings demonstrate that, unlike the physiological inhibitor of HLE (alpha-1-proteinase inhibitor), which is inactivated upon oxidation, low-molecular-weight compounds retain and/or show enhanced inhibitory activity towards HLE upon oxidation of the thioether side chain and lay the groundwork for the development of compounds that embody proteinase inhibitory and antioxidant activity.

Mechanism-based inhibitors of serine proteinases based on the Gabriel-Colman rearrangement.

Neutrophil-derived mediators such as, for example, the serine proteinase elastase, cathepsin G and proteinase 3, play a critical role in inflammatory lung disease. This report describes the design, synthesis and in vitro inhibitory activity of some novel mechanism-based inhibitors of human leukocyte elastase and cathepsin G. The design of the inhibitors is based on the Gabriel-Colman rearrangement. The behavior of the synthesized compounds toward elastase and cathepsin G with respect to inhibitory prowess, mode of interaction, specificity, etc., has been found to be dependent on the recognition and reactivity elements present in each inhibitor.

Human neutrophil proteinase 3: mapping of the substrate binding site using peptidyl thiobenzyl esters.

A series of peptidyl thiobenzyl esters was used to map the active site of human leukocyte proteinase 3. The steady-state kinetics parameters reveal the following features regarding the substrate specificity of proteinase 3 and its putative active site: (a) the preferred P1 residue is a small hydrophobic amino acid such as aminobutyric acid, norvaline, valine or alanine (in decreasing order of preference); (b) the enzyme has an extended active site; and (c) its active site is similar to that of the related serine proteinases leukocyte elastase and leukocyte cathepsin G.

Enantioselective inhibition of human leukocyte elastase.

(RS)-Diethyl-2-benzyl-succinate was resolved using alpha-chymotrypsin. The two enantiomers were then elaborated to yield (S)-(+) and (R)-(-)-3-benzyl-N-[(methyl-sulfonyl)oxy]succinimide and the inhibitory activity of the two enantiomers toward human leukocyte elastase was subsequently determined. The k2/KI values for the R and S isomers were found to be 330 and 1500 M-1 s-1, respectively.

Inhibitors of human neutrophil cathepsin G: structural and biochemical studies.

The interaction of a series of sulfonate and phosphate esters derived from N-hydroxysuccinimide with human leukocyte cathepsin G was investigated. The synthesized compounds were found to be time-dependent inhibitors of the enzyme. The composite interplay of steric and electronic effects leads to the formation of acyl enzymes of variable stability, ultimately resulting in partial or full recovery of enzymatic activity. Compounds acting via phosphorylation of the active site serine inactivated the enzyme rapidly and irreversibly.

Inhibition of human leukocyte elastase by phosphate esters of N-hydroxysuccinimide and its derivatives: direct observation of a phosphorylated enzyme by 31P nuclear magnetic resonance spectroscopy.

A series of phosphate esters derived from N-hydroxysuccinimide and 3-alkyl-N-hydroxysuccinimide have been synthesized and found to be potent time-dependent irreversible inhibitors of human leukocyte elastase (HLE). The observed inhibitory activity in this series of compounds correlated well with the known preference of HLE for substrates with small hydrophobic side chains. Maximum potency was reached when a favorable aromatic interaction involving a phenyl group present in the inhibitor and an aromatic residue located in the vicinity of the S2' subsite was operative. 31P NMR spectroscopy was used to probe the mechanism of action of these compounds. Direct evidence is presented in support of a mechanism involving phosphorylation of the active site serine. These compounds constitute a new class of hydrolytically stable phosphorylating agents.

Ionic inhibitors of human leukocyte elastase: pyridinium and phenyl carboxylate derivatives of 3-alkyl-N-hydroxysuccinimide.

A series of pyridinium and phenyl carboxylate derivatives of 3-alkyl-N-hydroxysuccinimide has been synthesized; the compounds have been shown to be highly effective, time-dependent inactivators of human leukocyte elastase. The cationic inhibitor having an isobutyl side chain as the P1 residue (3) was found to be the most effective. Human leukocyte cathepsin G and chymotrypsin are also inactivated by these compounds.

Inhibition of human leukocyte elastase by derivatives of N-hydroxysuccinimide. A structure-activity-relationship study.

A series of compounds derived from 3-alkyl-N-hydroxysuccinimide have been synthesized and their inhibitory activity toward human leukocyte elastase has been investigated. Compounds having an isobutyl or isopropyl group at the C-3 position have been found to be particularly effective inactivators of the enzyme. The introduction of a trans-styryl group (as in compounds 16 and 18) results in a drastic enhancement in inhibitory activity indicative of a favorable interaction between the phenyl ring and the S2' subsite of the enzyme. The compounds were found to be highly stable in buffer solution with no apparent change in structural integrity after 17 h (the period of observation). Studies with model compounds and high-field NMR indicate that these compounds function as mechanism-based inhibitors of the enzyme. Porcine pancreatic elastase is not inhibited by these compounds, while chymotrypsin and human leukocyte cathepsin G are also efficiently inactivated.

The Lossen rearrangement in biological systems. Inactivation of leukocyte elastase and alpha-chymotrypsin by (dl)-3-benzyl-N-(methanesulfonyloxy) succinimide.

(dl)-3-Benzyl-N-(methanesulfonyloxy) succinimide 5 has been found to inactivate human leukocyte elastase and alpha-chymotrypsin efficiently and irreversibly. The kobsd/[I] values were 1170 and 9000 M-1 s-1 respectively. Porcine pancreatic elastase was not inhibited by 5. Compound 5 may constitute the first example of a mechanism-based inhibitor of a serine proteinase that appears to exert its effect via an unprecedented enzyme-induced Lossen rearrangement.

Inactivation of leukocyte elastase by aryl azolides and sulfonate salts. Structure-activity relationship studies.

The inhibitory activity of a series of aryl azolides and sulfonate salts toward human leukocyte elastase is reported. Several of the compounds were found to be potent inhibitors of the enzyme. Active compounds were obtained only when the specificity group and the reactive moiety were separated by a two-carbon chain. The introduction of hydrophobic groups enhanced the inhibitory activity of these compounds, with the exception of the sulfonate salts. The nature of the leaving group had a profound effect on inhibitory activity, with compounds 23 and 26 being the most active (kobsd/[I] = 11,722 and 13,500 M-1 s-1, respectively).

Substituted 2-pyrones, 2-pyridones, and other congeners of elasnin as potential agents for the treatment of chronic obstructive lung diseases.

Several congeners of elasnin (I) have been synthesized and shown to inhibit human leukocyte elastase (HLE). The C-3 alkyl substituted 2-pyrones 11 and 12 were found to be the most effective inhibitors of the enzyme. These compounds are highly specific in their inhibitory activity.

Sulfonate salts of amino acids: novel inhibitors of the serine proteinases.

A series of amino acid-derived sulfonate salts have been synthesized. They were found to inactivate efficiently and selectively human leukocyte elastase. The sulfonate salts of the methyl esters of L-norleucine, L-norvaline and L-valine were the most potent. The enzyme is inactivated irreversibly with concomitant release of bisulfite ion. The results demonstrate for the first time that ionic compounds can indeed function as novel inhibitors for the serine proteinases.

Amino acid derived latent isocyanates: irreversible inactivation of porcine pancreatic elastase and human leukocyte elastase.

Several amino acid derived azolides (I) have been synthesized and investigated for their inhibitory activity toward human leukocyte elastase and porcine pancreatic elastase. The inhibitory activity was found to be dependent on the nature of the precursor amino acid ester. Thus, compounds derived from L-valine methyl ester 3, L-norvaline methyl ester 5, DL-norleucine methyl ester 9, and L-methionine methyl ester 10 were found to inhibit irreversibly both enzymes. Compound 10 was found to be a specific and selective inhibitor of human leukocyte elastase. In contrast to these, inhibitors derived from glycine methyl ester 1, D-valine methyl ester 4, and D-norvaline methyl ester 6 were found to be inactive. The results of the present study show that latent isocyanates derived from appropriate amino acids can serve as selective inhibitors of serine proteases and are of potential pharmacological value.