Synthesis of a Sugar-Based Thiosemicarbazone Series and Structure-Activity Relationship versus the Parasite Cysteine Proteases Rhodesain, Cruzain, and Schistosoma mansoni Cathepsin B1

Abstract

gThe pressing need for better drugs against Chagas disease, African sleeping sickness, and schistosomiasis motivates the search for inhibitors of cruzain, rhodesain, and Schistosoma mansoni CB1 (SmCB1), the major cysteine proteases from Trypanosoma cruzi, Trypanosoma brucei, and S. mansoni, respectively. Thiosemicarbazones and heterocyclic analogues have been shown to be both antitrypanocidal and inhibitory against parasite cysteine proteases. A series of compounds was synthesized and evaluated against cruzain, rhodesain, and SmCB1 through biochemical assays to determine their potency and structure-activity relationships (SAR). This approach led to the discovery of 6 rhodesain, 4 cruzain, and 5 SmCB1 inhibitors with 50% inhibitory concentrations (IC 50 s) of <10 M. Among the compounds tested, the thiosemicarbazone derivative of peracetylated galactoside (compound 4i) was discovered to be a potent rhodesain inhibitor (IC 50 ‫؍‬ 1.2 ؎ 1.0 M). The impact of a range of modifications was determined; removal of thiosemicarbazone or its replacement by semicarbazone resulted in virtually inactive compounds, and modifications in the sugar also diminished potency. Compounds were also evaluated in vitro against the parasites T. cruzi, T. brucei, and S. mansoni, revealing active compounds among this series. N ew drugs for parasitic diseases are urgently needed, but these globally important infections are often "neglected" because they most commonly afflict poor and marginalized communities. Current therapies are limited by poor efficacy, toxicity, high costs, and parasite resistance. Chagas disease, African sleeping sickness, and schistosomiasis are examples of diseases for which new therapies are needed (1, 2). Among the most studied and exploited molecular targets for these diseases are cysteine proteases. These enzymes have essential roles in parasite nutrition, immune evasion, host cell invasion, and metacyclogenesis (3-6). Indeed, the cysteine proteases cruzain, rhodesain, and Schistosoma mansoni CB1 (SmCB1) from Trypanosoma cruzi, Trypanosoma brucei, and S. mansoni, respectively, are validated molecular targets and have been the subject of numerous medicinal chemistry projects (7-17) that have yielded trypanocidal inhibitors, both in parasite culture and in animal models of infection (13,15,(18)(19)(20)(21).The diverse inhibitors of these enzymes comprise compound classes which bind noncovalently (11, 12) and scaffolds containing a "warhead" that binds covalently to the catalytic cysteine. Within the latter category, vinylsulfones (8,(22)(23)(24)(25), oxy-methyl ketones (7, 26), nitriles (16), epoxides, and thiosemicarbazones (13-15, 27-29) have been described previously. Thiosemicarbazones present as advantages their low molecular weight, low cost of synthesis, and nonpeptidic nature (27). Greenbaum and coworkers synthesized and evaluated the cysteine protease inhibitory and antiparasitic activities of a library of thiosemicarbazones, with promising results (13). According to those authors, the thiosemicarbazones are...

Structure-Bioactivity Relationship for Benzimidazole Thiophene Inhibitors of Polo-Like Kinase 1 (PLK1), a Potential Drug Target in Schistosoma mansoni

“…Phenotypic screens involving S . mansoni somules and adults were carried out as described [ 20 , 21 , 55 , 62 ]. For somules, approximately 300 newly transformed parasites were dispensed into flat-bottomed 96-well plates in 100 μL complete Basch medium (Corning Inc., cat.…”

“…Efforts continue to identify and develop small synthetic compounds or natural products as anti-schistosomal drugs, e . g ., [ 18 – 21 ]. In the hope of decreasing both the time and cost associated with developing drugs, researchers have also looked to either reposition registered drugs ‘as is,’ or use drugs or drug candidates as starting points for further chemical exploration and development [ 20 , 22 – 25 ].…”

Cruzain structures: apocruzain and cruzain bound to S-methyl thiomethanesulfonate and implications for drug design

“…The reaction was interrupted by placement of the sample tubes on ice. These samples were analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis under denaturing conditions and by a fluorescence-based activity assay using the peptide substrate Z-Phe-Arg-AMC (Fonseca et al, 2015). After activation, DTT was removed using the activation buffer without reducing agents on NAP-5 desalting columns (GE Healthcare).…”

New Approaches for Chagas’ Disease Chemotherapy

“…Molecules containing thiosemicarbazones have been extensively explored [58][59][60]. Among these, 3, 4-dichlorophenyl thiosemicarbazone (26) is one of the most potent cruzipain inhibitor [61].…”