The LC-MS analysis of the incubated samples was performed using the same system as described in the General Methods and Chemistry section. The chosen analytical conditions are based on the method that has already been published for identifying tacrine derivative metabolites . Briefly, a reverse-phase Kinetex 1.7 µm PFP column (100 × 2.1 mm; Phenomenex, Torrance, CA, USA) was used as a stationary phase, and purified water with 0.1% formic acid (mobile phase A) and LC-MS grade acetonitrile with 0.1% formic acid (mobile phase B) were used as the mobile phases. The method started with 2% B for 1 min, then the gradient gradually switched to 30% B in the eighth min, after that switched to 100% B in the ninth min, remained at 100% B for 1 min, and then went back to 2% B with equilibration for 3.5 min. The total run time of the method was 13.5 min. The column temperature was kept constant at 40 °C, the flow of the mobile phase was 0.5 mL/min, and the injection volume was 5