Potent Fluoromethyl Ketone Inhibitors of Recombinant Human Calpain I+

We report on a series of potent and selective dipeptide fluoromethyl ketone inhibitors of recombinant human calpain I. Compound 4f, having a tetrahydroisoquinoline containing urea motif as N-terminus capping group, is the most potent member (kobsI = 276,000 M−1 s−1) of this class. This compound was shown to prefer calpain I by >36-fold and approximately 4-fold over the related cysteine proteases, cathepsin B and cathepsin L, respectively.