Design and synthesis of cysteine protease inhibitors

This work describes the synthesis and evaluation of small inhibitors of cysteine proteases of parasitic origin. New epoxysuccinyl inhibitors carrying the unnatural amino acids D-homophenylalanine and D-homotyrosine were synthesized and determined to be potent irreversible inhibitors of cruzain-1, the major cysteine protease from T. cruzi, the ethiological agent of Chagas' disease. A new convergent synthesis of E-64 analogs is reported. X-ray crystal structures of 5 inhibitors bound to cruzain were elucidated and proved the alternative binding of D-hPhe and L-hPhe containing epoxysuccinates. The synthesis and evaluation of vinyl sulfonyl inhibitors that target cruzain-1 and falcipain-2 is also reported. Falcipain-2 is the best characterized and most important of the 3 major cysteine proteases from P. falciparum the most virulent malarial parasite. From small libraries of vinyl sulfonyl inhibitors new vinyl, N-benzyloxy sulfonamides, vinyl phenyl sulfonates and vinyl phenyl sulfones were found to be very potent and irreversible inhibitors of cruzain-1 and falcipain-2 in vitro . Some of these compounds show in vivo activity in parasite-infected cell culture experiments and represent the leads for future improvement of inhibitors of parasitic cysteine proteases.