Hypotaurine australia br Results and discussion br Conclusio
Results and discussion
Conclusion Novel and selective aziridine-based inhibitors for the Leishmania mexicana protease LmCBP2.8 were discovered. Compounds 7d (Ki = 0.8 μM), 9d (Ki = 1.36 μM), 12d (Ki = 0.77 μM), 14d (Ki = 0.9 μM) and 18 (Ki = 0.441 μM) showed the highest potency and selectivity over related parasite and human homologues within the investigated series. For an analysis of the predicted binding modes and binding pockets a homology model for the leishmanial protease was built and compared to the structure of cruzain. This indicated that the S2 pocket of LmCBP2.8 is a deep, lipophilic pocket, favorably being occupied by sterically demanding and lipophilic aromatic moieties of the ligands, while a tyrosine to glutamate substitution was observed in cruzain. This significant difference between the two Hypotaurine australia may also be the selectivity-determining feature. Attachment of a carboxylate group at the aziridine ring leads to a time-dependent inhibition and to an improved affinity to LmCPB2.8 (18 (Ki = 0.441 μM) k2nd = 190,569 M−1 min−1) likely to be caused by an ionic interaction with His163 as indicated by the docking studies performed. This strong interaction could be the reason for higher affinity and the fast irreversible inhibition. Furthermore, LE and LLE values were improved, compared to the corresponding diesters.
Conflicts of interest
Acknowledgements Financial support by the DFG (Deutsche Forschungsgemeinschaft, SFB630 PTA4) is gratefully acknowledged. JCM is supported by the Medical Research Council (MR/K019384). We thank Sabine Maehrlein, Ulrike Nowe and Nicole Denk for technical support with the enzyme assays.
Introduction Malaria, sleeping sickness and Chagas disease are among the most important tropical diseases, and the last two are considered neglected.1, 2 Human African trypanosomiasis (HAT) or sleeping sickness, caused by the protozoan Trypanosoma brucei, is fatal when untreated, and current treatments are ineffective and have side effects. The cysteine protease rhodesain, being essential for the development of T. brucei, has been identified as an interesting target for the search of new drugs against this disease. Chagas disease is caused by the protozoan Trypanosoma cruzi. Approximately 7–8 million people are infected by T. cruzi in Central and South America, with over 100 million people at risk of infection. It has recently emerged in North America and Europe as well. Benznidazole and nifurtimox are drugs currently available but both have variable efficacy and side effects. The cysteine protease cruzain has been identified as a target for the search of new drugs against this disease. Malaria is the most widespread and severe tropical infectious disease; in humans, it is caused by several species of the Plasmodium genus, with Plasmodium falciparum being the most dangerous and most prevalent. The cysteine protease falcipain-2 has been recognized as a potential drug target. All three above mentioned parasitic cysteine proteases rhodesain, cruzain and falcipain-2 belong to the papain superfamily. The alignment of these three proteases with their homologous cathepsin B and L shows striking similarities at three main functional regions (see Supplementary Material) despite of some other structural differences allowing the potential design of inhibitors selectivity as antiparasitic compounds. Michael acceptors are among the most interesting inhibitors of cysteine proteases. For example, K1777 a dipeptidyl vinyl sulfone is a potent irreversible inhibitor. We previously reported dipeptidyl enoates as efficient inhibitors against rhodesain, and we now report a structure–activity study of dipeptidyl enoates as irreversible inhibitors against the parasitic cysteine proteases falcipain-2, cruzain and rhodesain as compared to their activity against human cathepsins B and L. As it is reported herein in vitro and antiprotozoal activity of these inhibitors which contain an enoate moiety at the carboxyl terminus depended very much on the residues within the peptidic framework and the protecting group of the amino terminus.