Promise and Challenge of β-Lactone Electrophiles to Target Aspartate 12 of Mutant KRAS.

The clinical success of covalent KRAS inhibition prompts further expansion of the concept to target non-cysteine oncogenic mutation sites as in KRAS. This endeavor was hampered by the lack of suitable electrophiles for the selective, covalent engagement of aspartate. Thanks to the recent discovery of β-lactone-bearing covalent inhibitors, new opportunities are emerging. Based on X-ray crystallographic insights and quantum chemical calculations, we herein describe the elucidation of structure-activity and -stability correlations to advance such electrophiles for drug discovery. Guided by predictions of transition state barrier heights for the attack of aspartate 12 at the β-lactone electrophile and structure-based design, we generated substituted β-lactones aiming to balance specific reactivity and chemical and metabolic stability. Our optimization strategy is driven by MS-based and cellular covalent target occupancy assays and PD marker analysis, proteome-wide profiling, and synthetic chemistry. With this work, we aim to expand the use of β-lactones as chemoselective electrophiles in medicinal chemistry.