Niraparib R-enantiomer (MK-4827 R-enantiomer) is an excellent PARP1 inhibitor with IC 50 of 2.4 nM. In Vitro Niraparib R-enantiomer (MK-4827 R-enantiomer) resolution of Niraparib R-enantiomer give compounds Niraparib R-enantiomer and Niraparib S-enantiomer, both showing excellent inhibition of PARP-1. Niraparib R-enantiomer has somewhat lower in vitro metabolic clearance than the Niraparib S-enantiomer in rat liver microsomes, but Niraparib S-enantiomer is more potent in cell based assays (PARylation EC 50 , Niraparib R-enantiomer=30 nM, Niraparib S-enantiomer=4.0 nM; BRCA1-HeLa CC 50 , Niraparib R-enantiomer=470, Niraparib S-enantiomer=34 nM). Given this improved potency and similar in vitro turnover in human liver microsomes (HLM Cl int , Niraparib R-enantiomer=4, Niraparib S-enantiomer=3 μL/min/mgP), Niraparib S-enantiomer (Niraparib) is focused on. MCE has not independently confirmed the accuracy of these methods. They are for reference only. Form:Solid IC50& Target:PARP-1 2.4 nM (IC 50 )