Rational Design and Optimization of a Novel Class of Macrocyclic Apoptosis Signal-Regulating Kinase 1 Inhibitors

Abstract

Structural analysis of a known apoptosis signal-regulating kinase 1 (ASK1) inhibitor bound to its kinase domain led to the design and synthesis of the novel macrocyclic inhibitor <b>8</b> (cell IC₅₀ = 1.2 μM). The profile of this compound was optimized for CNS penetration following two independent strategies: a rational design approach leading to <b>19</b> and a parallel synthesis approach leading to <b>26</b>. Both analogs are potent ASK1 inhibitors in biochemical and cellular assays (<b>19</b>, cell IC₅₀ = 95 nM; <b>26</b>, cell IC₅₀ = 123 nM) and have moderate to low efflux ratio (ER) in an MDR1-MDCK assay (<b>19</b>, ER = 5.2; <b>26</b>, ER = 1.5). In vivo PK studies revealed that inhibitor <b>19</b> had moderate CNS penetration (<i>K</i>_puu = 0.17) and analog <b>26</b> had high CNS penetration (<i>K</i>_puu = 1.0).