Structure-Guided Conformational Restriction Leading to High-Affinity, Selective, and Cell-Active Tetrahydroisoquinoline-Based Noncovalent Keap1-Nrf2 Inhibitors

Inhibition of the protein–protein interaction between Kelch-like ECH-associated protein 1 (Keap1) and nuclear factor erythroid 2-related factor 2 (Nrf2) has been recognized as an attractive approach for treating oxidative stress-related diseases. Here, we present a new series of noncovalent Keap1-Nrf2 inhibitors developed by a conformational restriction strategy of our fluorenone-based compounds previously identified by fragment-based drug discovery. The design was guided by X-ray cocrystal structures, and the subsequent optimization process aimed at improving affinity, cellular activity, and metabolic stability. From the noncyclic compound 7 (K_i = 2.9 μM), a new series of tetrahydroisoquinoline-based Keap1 inhibitors with up to 223-fold improvement in binding affinity (57, K_i = 13 nM), better metabolic stability, and enhanced cellular activity was obtained. In addition, the compounds showed selectivity for the Keap1 Kelch domain across a panel of 15 homologous proteins. We thereby demonstrate the utility of cyclic rigidification in the design of potent and more drug-like Keap1-Nrf2 inhibitors.