Synthesis and characterization of bicyclo[1.1.0]butane amides and 5-methylene-3-azabicyclo[5.1.0]octan-4-ones as covalent modifiers

Covalent inhibitors have re-emerged as powerful therapeutic agents, offering the ability to modulate "undruggable" proteins including oncogenic drivers that have eluded traditional drug discovery efforts. Expanding the repertoire of electrophilic moieties remains a critical frontier in covalent drug discovery. Here, we report a Rh(I)-catalyzed cycloisomerization of N-allyl bicyclo[1.1.0]butane amides (BCB amides) to access the 5-methylene-3-azabicyclo[5.1.0]octan-4-one (MABO) scaffold via strain-release reactivity. Both N-allyl BCB amides and MABOs can react with nucleophiles, highlighting their potential as electrophilic moieties for covalent drug design. Kinetic assays against glutathione revealed that selected N-allyl BCB amides and MABOs exhibit half-lives comparable to that of (±)-sotorasib, whose enantiomerically pure form received FDA approval as an anticancer drug. Biological evaluation in human-derived head and neck squamous cell carcinoma (HNSCC) models identified specific BCB amides and MABO compounds capable of modulating cancer cell growth. The toxicity of the compounds was evaluated by flow cytometry in human peripheral blood mononuclear cells (PBMCs) and by monitoring LDH release in the monocytic cell line THP-1, both under basal and activated conditions. Together, these findings suggest that BCB amides and MABOs represent promising classes of electrophilic scaffolds for covalent drug discovery.