PIN1 and cancer: To demonstrate the generality of this approach, we have chosenan additional challenging target—peptidyl-prolyl isomeraseNIMA-interacting-1 (Pin1), an important cancer target.44,45 Recently, we have developed sulfopin as a selective covalent inhibitorof Pin1, which blocks Myc-driven tumors in vivo.38 Sulfopin has a chloroacetamide electrophile, and previousattempts to switch it to an acrylamide or alternative warheads didnot result in efficient covalent binders (data not shown).