Vinyl Sulfonate Esters and Vinyl Sulfonamides:  Potent, Irreversible Inhibitors of Cysteine Proteases

Abstract

Cysteine proteases are an important class of enzymes involved in the degradative processing of peptides and proteins. 1,2 They are ubiquitous in nature and play vital roles in numerous physiological processes including arthritis, osteoporosis, Alzheimer's disease, cancer cell invasion, and apoptosis. 1-3 Cysteine proteases are also essential to the life cycles of many pathogenic protozoa. 4,5 One such parasite is Trypanosoma cruzi, the etiologic agent of Chagas' disease. Cruzain, 6,7 the major cysteine protease of T. cruzi, has been identified as a potential therapeutic target for treatment of Chagas' disease. [7][8][9] Several strategies have been pursued in the design of cysteine protease inhibitors. 2,10,11 Peptidyl aldehydes, 12 diamino ketones, 13 and nitriles 14 are reversible inhibitors that form hemithioacetals, peptide ketals, and thioimidates, respectively, with the thiol of the active site cysteine residue, mimicking the initial covalent enzyme adduct in normal proteolytic turnover. Epoxysuccinyl derivatives, 15 peptidyl Michael acceptors, 16-18 (acyloxy)methyl ketones, 19 and halomethyl ketones are examples of inhibitors which irreversibly inactivate cysteine proteases via alkylation of the active site cysteine residue. Several classes of nonpeptidic reversible inhibitors of cysteine proteases also have been described. [20][21][22] In connection with efforts to develop potent and selective inhibitors of cruzain, we became interested in the vinyl sulfone inhibitor series first introduced by Hanzlik 17 and further developed by Palmer et al. 18,23 Compound 1a is a potent and selective inhibitor of cruzain, with a second-order rate constant (k inact /K i ) of 203 000 s -1 M -1 . 18 Inhibitors 1a and especially 1b have also proven highly effective against T. cruzi, both in tissue culture and in vivo experiments (mouse model). 24 Although considerable effort has been devoted to the optimization of interactions of inhibitors with the cruzain S 1 and S 2 binding sites, 18,23,25 virtually nothing is known about the interactions of substrates or inhibitors with the S 1 ′ and S 2 ′ sites. The prime site region in cruzain contains a large open surface defined by Trp 177, and available X-ray structures suggest that there is considerable room for prime site inhibitor binding. 7,13,22,25 A recent X-ray structure of cathepsin K, the active site of which is homologous to that of cruzain, with covalently bound APC3328, a dipeptidyl phenyl vinyl sulfone inhibitor related to 1b, reveals that the phenyl residue of the phenyl sulfonyl unit does not make optimal interactions with prime site residues. 26 Accordingly, we decided to probe the possibility that additional selectivity and potency in the vinyl sulfonyl series could be achieved by extending the inhibitor structure into the prime site region, via modification of the sulfonyl substituent as suggested by structure 2. However, we anticipated that it might be easier to synthesize a family of vinyl sulfonamides 3 or vinyl sulfonate esters 4, using the vinyl sulfonyl chl...

Structure-Activity Relationships for Inhibition of Cysteine Protease Activity and Development of Plasmodium falciparum by Peptidyl Vinyl Sulfones

“…Peptidyl vinyl sulfones were originally developed as inhibitors of papain (14,19) and were later optimized as specific inhibitors of human cysteine proteases (3,23). Related phenyl vinyl sulfones also inhibit cruzain, a cysteine protease of Trypanosoma cruzi (31,32,35), and one of these compounds is currently undergoing preclinical studies for the treatment of Chagas' disease (34). While the clinical use of peptidyl protease inhibitors is potentially problematic due to limited bioavailability or poor pharmacokinetics, there are numerous recent reports of peptidyl inhibitors of renin (17), thrombin (11), leukocyte elastase (42), neutrophil elastase (8), and human immunodeficiency virus type 1 protease (2,16,40) that are biologically active after oral administration.…”

“…1). These inhibitors were synthesized by using appropriate modifications of previously described methods (31,32). The series of phenyl vinyl sulfones was prepared by a Horner-Wadsworth-Emmons reaction of N-tert-butoxycarbonyl (N-BOC)-homophenylalanal (Fig.…”

Identification of a New Class of Nonpeptidic Inhibitors of Cruzain

“…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).…”

The Hendrickson ‘POP’ reagent and analogues thereof: synthesis, structure, and application in organic synthesis

“…The group acts as a transition state mimetic of peptide hydrolysis and has been shown to be the critical pharmacophore for potent inhibitors of cysteine proteases. 13 These enzymes have been implicated in the degradative processing of peptides and proteins, and play key roles in a number of physiological processes including arthritis, Alzheimer's disease, and apoptosis. Traditional methods for the generation of sulfonamides have used sulfonyl chlorides and nucleophiles such as amines.…”