Repurposing of the RIPK1-Selective Benzo[1,4]oxazepin-4-one Scaffold for the Development of a Type III LIMK1/2 Inhibitor

Benzoxazepinones have been extensively studied as exclusively selective RIP kinase 1 inhibitors. This scaffold binds to an allosteric pocket created by an αC-out/DFG-out conformation. This inactive conformation results in a large expansion of the kinase back pocket, a conformation that has also been reported for LIM kinases. Scaffold hopping is common in the design of orthosteric kinase inhibitors but has not been explored in the design of allosteric inhibitors, mainly due to the typically exclusive selectivity of type III inhibitors. Here, we hypothesized that the shared structural properties of LIMKs and RIPKs could lead to novel type III LIMK inhibitors using the benzoxazepinone scaffold. We report the discovery of a novel LIMK1/2 inhibitor that relies on this scaffold-based approach. The discovered compound 10 showed low nanomolar potency on LIMK1/2 and exceptional selectivity, as confirmed by a comprehensive selectivity panel with residual RIPK activity as the only off-target. The study provides one of the few examples for scaffold hopping for allosteric inhibitors, which are usually associated with exclusive target selectivity.