Structure-Based Discovery of ( <i>E</i> )- and ( <i>Z</i> )-4-Oxobut-2-enoate Derivatives as Novel Covalent Pin1 Inhibitors with Antitumor Activity

Peptidyl-prolyl cis – trans isomerase Pin1 is a promising anticancer target that is overexpressed in numerous cancers and associated with poor prognosis. Herein, two series of covalent Pin1 inhibitors featuring an ( E )- or a ( Z )-4-oxobut-2-enoate moiety as the electrophilic warhead were discovered, and their binding features were revealed by six cocrystal structures. The binding kinetic investigations revealed that both ( E )- and ( Z )-4-oxobut-2-enoate warheads exhibited an appropriate electrophilic activity ( k inact = 0.006–3.60 min –1 ), conferring them as favorable covalent warheads for developing potent Pin1 inhibitors. The SAR investigations resulted in four ( Z )-isomers ( T29, T39–T41: enzymatic IC 50 = 0.02–0.08 μM) with excellent enzymatic activity, while the ( E )-isomer T7 (enzymatic IC 50 = 1.54 μM) was found to potently suppress the proliferation of MDA-MB-468 cancer cells by downregulating the Pin1 substrates c-Myc and Cyclin D1. Altogether, 4-oxobut-2-enoate derivatives were disclosed as new templates for further developing potent covalent Pin1 inhibitors.