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C1s-IN-1 trihydrochloride (Compound A1) is the selective inhibitor for C1s protease with the Ki of 5.8 μM. C1s-IN-1 trihydrochloride inhibits cleavage of C2 by C1s with an IC50 of 85 μM, inhibits the activation of classic pathway with an IC50 of 22 μM. C1s-IN-1 trihydrochloride is the competitive inhibitor for thrombin with the Ki of 51.2 μM[1].

[1] Xu X, et al., Inhibition of the C1s Protease and the Classical Complement Pathway by 6-(4-Phenylpiperazin-1-yl)Pyridine-3-Carboximidamide and Chemical Analogs. J Immunol. 2024 Feb 15;212(4):689-701. DOI:10.4049/jimmunol.2300630