To assess the microsomal stability, the test compounds (10 µM) were incubated in 100 mM potassium phosphate-based buffer at pH 7.4 (total volume of 100 µL) containing 0.5 mg/mL male rat liver microsomes (Sprague-Dawley, #M9066, Sigma Aldrich) and 1 mM NADPH for 0, 15, 30, or 60 min. At the end of the incubation time, microsomal activity was terminated by addition of 500 µL MeCN, subsequent centrifugation at 1700g for 5 minutes. A reaction mixture containing heatinactivated microsomes (95 °C, 10 min) served as a matrix control. 5 µL supernatant of each sample were analyzed and the remaining concentrations of the respective test compounds at each time point was determined by LC-MS/MS on an API-3200-QTrap (Sciex) with an Agilent Technologies 1100 series setup including a binary pump (G1311A), a degasser (G1322A), and a Shimadzu SIL 20A HT autosampler under the control of Analyst 1.6 (Sciex). A XBridge BEH C18 (3.5 µm, 150 mm x 3 mm, Waters, protected with a 0.5 µm frit) stationary phase was used in combination with a gradient method starting with 0.1% formic acid in water (A) and MeCN (B) as mobile phase (A:B = 80:20) for 6 min going to A:B = 50:50 after 8 min. 5 µL of supernatant diluted in mobile phase starting conditions was loaded onto the column, separated at a flow rate of 400 µL/min, and detected and quantified per Area of MRM (multiple reaction monitoring) with the following transitions: 293.932/103.100 Da (6); 291.919/165.100 Da (36); 320.909/103.100 Da (53); 354.812/309.800 Da (55); 318.887/273.900 Da (57); 306.902/102.900 Da (58). Data are expressed as means±SD of single determinations obtained in three independent experiments. For determination of half-lives the remaining compound [%] values after the indicated incubation time [min] were used in the equation "one phase dacay" in GraphPad Prism (version 10, GraphPad Software).