Structure-Guided\nConformational Restriction Leading\nto High-Affinity, Selective, and Cell-Active Tetrahydroisoquinoline-Based\nNoncovalent Keap1-Nrf2 Inhibitors

Inhibition of the protein–protein interaction\nbetween Kelch-like\nECH-associated protein 1 (Keap1) and nuclear factor erythroid 2-related\nfactor 2 (Nrf2) has been recognized as an attractive approach for\ntreating oxidative stress-related diseases. Here, we present a new\nseries of noncovalent Keap1-Nrf2 inhibitors developed by a conformational\nrestriction strategy of our fluorenone-based compounds previously\nidentified by fragment-based drug discovery. The design was guided\nby X-ray cocrystal structures, and the subsequent optimization process\naimed at improving affinity, cellular activity, and metabolic stability.\nFrom the noncyclic compound <b>7</b> (<i>K</i><sub>i</sub> = 2.9 μM), a new series of tetrahydroisoquinoline-based\nKeap1 inhibitors with up to 223-fold improvement in binding affinity\n(<b>57</b>, <i>K</i><sub>i</sub> = 13 nM), better\nmetabolic stability, and enhanced cellular activity was obtained.\nIn addition, the compounds showed selectivity for the Keap1 Kelch\ndomain across a panel of 15 homologous proteins. We thereby demonstrate\nthe utility of cyclic rigidification in the design of potent and more\ndrug-like Keap1-Nrf2 inhibitors.