Mixed-Lineage Kinase 1 and Mixed-Lineage Kinase 3 Subtype-Selective Dihydronaphthyl[3,4-a]pyrrolo[3,4-c]carbazole-5-ones: Optimization, Mixed-Lineage Kinase 1 Crystallography, and Oral in Vivo Activity in 1-Methyl-4-phenyltetrahydropyridine Models

The optimization of the dihydronaphthyl[3,4-a]pyrrolo[3,4-c]carbazole-5-one R2 and R12 positions led to the identification of the first MLK1 and MLK3 subtype-selective inhibitors within the MLK family. Compounds 14 (CEP-5104) and 16 (CEP-6331) displayed good potency for MLK1 and MLK3 inhibition with a greater than 30- to 100-fold selectivity for related family members MLK2 and DLK. Compounds 14 and 16 were orally active in vivo in a mouse MPTP biochemical efficacy model that was comparable to the first-generation pan-MLK inhibitor 1 (CEP-1347). The MLK1 structure−activity relationships were supported by the first-reported X-ray crystal structure of MLK1 bound with 16.