5-Phenyl-1,3,4-oxadiazol-2(3<i>H</i>)-ones Are Potent Inhibitors of Notum Carboxylesterase Activity Identified by the Optimization of a Crystallographic Fragment Screening Hit

Abstract

Carboxylesterase Notum is a negative regulator of the Wnt signaling pathway. There is an emerging understanding of the role Notum plays in disease, supporting the need to discover new small-molecule inhibitors. A crystallographic X-ray fragment screen was performed, which identified fragment hit 1,2,3-triazole <b>7</b> as an attractive starting point for a structure-based drug design hit-to-lead program. Optimization of <b>7</b> identified oxadiazol-2-one <b>23dd</b> as a preferred example with properties consistent with drug-like chemical space. Screening <b>23dd</b> in a cell-based TCF/LEF reporter gene assay restored the activation of Wnt signaling in the presence of Notum. Mouse pharmacokinetic studies with oral administration of <b>23dd</b> demonstrated good plasma exposure and partial blood-brain barrier penetration. Significant progress was made in developing fragment hit <b>7</b> into lead <b>23dd</b> (>600-fold increase in activity), making it suitable as a new chemical tool for exploring the role of Notum-mediated regulation of Wnt signaling.