The plasma stability assay, the metabolic stability assay, and the plasma protein binding assay were conducted as described previously. For the HPLC-MS measurements, samples were analyzed using an Agilent 1290 Infinity II HPLC system coupled to an AB Sciex QTrap 6500plus or an AB Sciex Qtrap7500 mass spectrometer. LC conditions were as follows: column: Agilent Zorbax Eclipse Plus C18, 50×2.1 mm, 1.8 µm; temperature: 30 °C; injection volume: 5 µL per sample; flow rate: 700 µL min -1 .