No 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...

We report the discovery of a new potent allosteric effector of sickle cell hemoglobin, GBT440 (), that increases the affinity of hemoglobin for oxygen and consequently inhibits its polymerization when subjected to hypoxic conditions. Unlike earlier allosteric activators that bind covalently to hemoglobin in a 2:1 stoichiometry, binds with a 1:1 stoichiometry. Compound is orally bioavailable and partitions highly and favorably into the red blood cell with a RBC/plasma ratio of ∼150. This partitioning onto the target protein is anticipated to allow therapeutic concentrations to be achieved in the red blood cell at low plasma concentrations. GBT440 () is in Phase 3 clinical trials for the treatment of sickle cell disease (NCT03036813).