Discovery\nof a Potent Triazole-Based Reversible Targeted\nCovalent Inhibitor of Cruzipain

Cruzipain (CZP) is an essential cysteine protease of <i>Trypanosoma\ncruzi</i>, the etiological agent of Chagas disease, and a promising\ndruggable target. To date, no CZP inhibitors have reached clinical\nuse, with research efforts mostly hampered by insufficient potency,\nlimited target selectivity or lack of bioactivity translation from\nthe isolated enzyme to the parasite in cellular environments. In this\nstudy, we report the design of <b>SH-1</b>, a 1,2,3-triazole-based\ntargeted covalent inhibitor with nanomolar potency (IC<sub>50</sub> = 28 nM) and null inhibition of human cathepsin L. <b>SH-1</b> demonstrates bioactivity translation comparable to that of K777\n(1–10 μM), a CZP inhibitor previously advanced to clinical\ntrials. Experimental findings indicate that <b>SH-1</b> forms\na reversible covalent bond with Cys25 in CZP, while <i>in silico</i> and structure–activity relationship studies suggest that\nthis interaction is guided by acid–base equilibrium dynamics.\nThe potential of <b>SH-1</b> for preclinical development is\ndiscussed alongside detailed structure–activity relationships\nfor the further optimization of CZP inhibitors.