Vinyl Sulfones as Mechanism-Based Cysteine Protease Inhibitors

Abstract

Proteases regulate a broad spectrum of physiological functions by the specific processing of proteins and peptides. Elevated levels of active proteases can result in an array of physiological processes ultimately leading to disease states. Therefore, compounds designed to restore the natural equilibrium of proteases present excellent opportunities for drug candidates. Cysteine proteases, for example cathepsins B, L, and S, have been implicated in a number of diseases, including progressive cartilage and bone degradation associated with arthritis.1 Inhibitors of these cathepsins have reduced inflammation and prevented joint destruction in animal models of arthritis.2 Recently, human cathepsin 02 has been found to be highly expressed in osteoclastoma tissue.3 Cathepsins B and L have been linked to metastasis and invasion by cancer cells.4 The calcium-associated cysteine proteases calpains I and II have been associated with ischemia and hypoxia,5 Alzheimer's disease,6 and cataracts.7 Inhibition of the trypanosomal cysteine protease cruzain has proven effective in models of Chagas's disease.8Reversible inhibitors of cysteine proteases include peptide aldehydes,9 nitriles,10 and a-ketocarbonyl compounds.11 Irreversible inhibitors include peptide halomethyl ketones,12 diazomethyl ketones,13 (acyloxy)methyl ketones,14 and ketomethylsulfonium salts,15 believed to alkylate the active site thiol by formal Sn2 displacement, either directly or through a proposed hemithioketal-episulfonium ion pathway. Other irreversible inhibitors include various epoxysuccinyl compounds,16 whose oxiranes are opened through nucleophilic attack by the thiol. Previous work by Hanzlik and co-workers17 demonstrated peptide Michael acceptors as inactivators of the plant protease papain, which displayed second-order rate constants of inactivation from 0.05 to 70 M'1 s'1. However, to serve as disease modifying agents, inhibitors must inactivate target enzymes sufficiently in vivo as well as in vitro. Therefore, we designed potent inhibitors against disease-associated cysteine proteases such as the cathepsins B, L, S, and 02, calpains, and cruzain, concentrating on structures or scaffolds suitable for pharmaceutical development.

Identification of a New Class of Nonpeptidic Inhibitors of Cruzain

“…Substrate 18 incorporating a morpholine moiety was prepared because this substituent has led to potent vinyl sulfone inhibitors of cruzain. 16 However, this substituent resulted in a decrease in substrate cleavage efficiency.…”

“…4,5,16,17 Vinyl sulfone inhibitor 38 was prepared via a Horner-Wadsworth-Emmons olefination (Scheme 3). Kinetic analysis of the vinyl sulfone inhibitor, surprisingly, indicated no time dependence and was consistent with competitive reversible inhibition (Figure 4a).…”

Peptidyl vinyl sulphones: a new class of potent and selective cysteine protease inhibitors: S2P2 specificity of human cathepsin O2 in comparison with cathepsins S and L

“…However, the secondorder rate constants of inactivation of papain with these compounds were only in the range of 1-30 M −" :s −" and did not promise a potent inactivation of mammalian cysteine proteases. We have developed peptidyl vinyl sulphones as extremely potent and specific cysteine protease inactivators of human cathepsins [13]. The structure of peptidyl vinyl sulphones (R n -NH-CH(R " )-Ψ(CH CH-SO # -R x ) permits variation in the P as well as Ph region of the inhibitors, thus allowing selective control of their affinity and reactivity towards the enzyme.…”

Proteasome inhibitors mechanism; source for design of newer therapeutic agents

“…This class of electrophilic peptide proved to be valuable in affinity labeling and mechanistic studies of the proteasome. 29,30 Bi-functional synthetic inhibitors-rational design based on structure. The complex biochemical mechanism of the proteasome was understood by the determination of its three-dimensional structure.…”

“…Peptide vinyl sulfones have also been developed as affinity labeling probes of the proteasome. 25,29 Kinetic studies of the proteasome using inhibitors This section will discuss some of the uses of proteasome inhibitors in kinetic studies of peptide hydrolysis. This makes conventional strategies of the kinetic anal study become ineffective because of the complexity resulting from the proteasome's multiple active sites.…”