Natural Products Inspired Scaffold Diversification Leads to Unnatural Molecular Warhead and Covalent Strategy to Modulating Protein Function through Electrophilic Bromine Transfer

We discovered a thiolate-reactive α,α-gem-dibromo lactam warhead that activates transcription factor Nrf2 and demonstrates anti-inflammatory activities, which have implications in cancer, neurodegeneration, and cardiovascular diseases. Our findings originated from new compounds accessed through aza-oxyallyl cation-mediated [3+2]-cycloadditions of ajmalicine and inspired indoles. RNA-seq and Ingenuity Pathway Analysis illuminated detailed transcriptional profiles of α,α-gem-dibromo lactams to show activation of the antioxidant Keap1/Nrf2 pathway and suppressed NF-κB-mediated inflammatory signaling. We demonstrated the importance of the α,α-gem-dibromo lactam, as the corresponding α,α-gem-dichloro lactam is unable to activate the Nrf2 pathway. Chemical reactions with cysteine-containing compounds suggested α,α-gem-dibromo lactams react with cysteine residues to transfer electrophilic bromine to target molecules, linking unique chemistry to our biological findings. In contrast to electrophiles that activate the canonical Nrf2 pathway by covalently targeting C151 of Keap1, the α,α-gem-dibromo lactams function in a C151-independent manner, indicating a distinct selectivity and consequently mode of action. Pharmacological profiling of several α,α-gem-dibromo lactams compared with ajmalicine against adrenergic receptors revealed substantial differences, indicating tunability and novel pharmacology. Future investigations aim to explore the fundamental activities of the dibromo lactam warhead related to human disease. Installation of this warhead into various molecular scaffolds may be a generalizable method to create cystein-reactive electrophiles.