Schizandrin a

High-Performance Liquid Chromatography-ElectroSpray Ionization-Mass Spectrometry (HPLC-ESI-MS) analyses of the lignans were performed using an Agilent-1100 HPLC system equipped with a UV detector coupled to a LC-MSD Trap VL ion-trap mass spectrometer with an ESI source (Agilent Technologies, Palo Alto, CA, USA). The HPLC separation conditions were identical to those used for HPLC-DAD analysis. Negative-ion (PI) mode was used for the MS analysis of lignans.
ESI was performed using the following conditions: capillary voltage, 5.0 kV; nebulization pressure, 241.3 kPa; gas (N²) temperature, 350°C; and flow rate, 8.0 L min^-1. The capillary offset and exit voltage were 68.4 V and 100.6 V, respectively. The skim 1 voltage was 29.5 V, the skim 2 voltage was 6.0 V, and the MS and MS² spectra were recorded over an m/z range of 150 to 2000 NI. The MS² scan of the target ions used normalized collision energy of 20%–45%. The experimental standards of Schizandrol A, Schizandrol B, Schizandrin B, Schizandrin A, and isoschizandrin were purchased from Sigma-Aldrich (Steinheim, Germany); data obtained for experimental standards and information regarding the identified compounds were combined to identify the lignans.

Schizandrin A (>99%) and DTX (>99%) were purchased from Sigma-Aldrich Co., Ltd. (Poole, UK). Labrafil M CS1944 and Cremophor RH40 were offered by BASF Co., Ltd. (Ludwigshafen, Germany). PEG400 was purchased from Aladdin Chemical Co., Ltd. (Shanghai, China). MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] assay was sourced from Amresco (Solon, OH). Water in this study was obtained using a Milli Q-water purification system (Merck-Millipore, Billerica, MA). All other chemicals and solvents were of analytical grade. RPMI 1640 medium, fetal bovine serum (FBS), penicillin–streptomycin solution, and phosphate buffer salt (PBS) were obtained from Hyclone (Thermo Scientific, UT).