Discovery of 6‑Fluoro-5-{4-[(5-fluoro-2-methyl-3-oxo-3,4-dihydroquinoxalin-6-yl)methyl]piperazin-1-yl}‑N‑methylpyridine-2-carboxamide (AZD9574): A CNS-Penetrant, PARP1-Selective Inhibitor

PARP inhibitors have attracted considerable interest in drug discovery due to the clinical success of first-generation agents such as olaparib, niraparib, rucaparib, and talazoparib. Their success lies in their ability to trap PARP to DNA; however, first-generation PARP inhibitors were not strictly optimized for trapping nor for selectivity among the PARP enzyme family. Previously we described the discovery of the second-generation PARP inhibitor AZD5305, a selective PARP1-DNA trapper. AZD5305 maintained the antitumor efficacy of first-generation PARP inhibitors while exhibiting lower hematological toxicity. Recently, there has been interest in central nervous system (CNS)-penetrant PARP inhibitors for CNS malignancies and other neurological conditions; however, AZD5305 is not CNS penetrant. Herein we describe the discovery and optimization of a series of CNS-penetrant, PARP1-selective inhibitors and PARP1-DNA trappers, culminating in the discovery of AZD9574, a compound that maintains the PARP1 selectivity of AZD5305 with improved permeability, reduced efflux, and increased CNS penetration.