A selective, rapid and sensitive ultra performance liquid chromatography mass spectrometry (UPLC/MS) method was developed and validated to quantitate a highly selective mixed-affinity sigma receptor ligand, CM156 (3-(4-(4-cyclohexylpiperazin-1-yl)butyl)benzo[d] thiazole-2(3H)-thione), in rat plasma. CM156 and the internal standard (aripiprazole) were extracted from plasma samples by a single step liquid–liquid extraction using chloroform. The analysis was carried out on an ACQUITY UPLC™ BEH HILIC column (1.7 μm, 2.1 mm × 50 mm) with isocratic elution at flow rate of 0.2 mL/min using 10 mM ammonium formate in 0.1% formic acid and acetonitrile (10:90) as the mobile phase. The detection of the analyte was performed on a mass spectrometer operated in selected ion recording (SIR) mode with positive electrospray ionization (ESI). The validated analytical method resulted in a run time of 4 min and the retention times observed were 2.6 ± 0.1 and 2.1 ± 0.1 min for CM156 and the IS, respectively. The calibration curve exhibited excellent linearity over a concentration range of 5–4000 ng/mL with the lower limit of quantification of 5 ng/mL. The intra- and inter-day precision values were below 15% and accuracy ranged from −6.5% to 5.0%. The mean recovery of CM156 from plasma was 96.8%. The validated method was applied to a pilot intravenous pharmacokinetic study in rats.Highlights► A selective, rapid and sensitive UPLC/MS method was developed and validated to quantitate a highly selective mixed-affinity sigma receptor ligand. ► The validated analytical method resulted in a run time of 4 min. The calibration curve exhibited excellent linearity over a concentration range of 5–4000 ng/mL (LLOQ, 5 ng/mL). The intra- and inter-day precision values were below 15% and accuracy ranged from −6.5% to 5.0%. ► The validated method was successfully applied to an intravenous pharmacokinetic study of CM156 in rats.

A simple, sensitive and rapid ultra-performance liquid chromatography-mass spectrometry (UPLC-MS) method was developed and validated for the quantification of mitragynine in rat plasma using amitriptyline hydrochloride as an internal standard. Sample preparation involved a one-step liquid–liquid extraction using methyl t-butyl ether. Mitragynine was separated on an Acquity UPLC™ BEH HILIC column using isocratic elution with a mobile phase of 10 mM ammonium formate buffer containing 0.1% formic acid:acetonitrile (15:85, v/v). At a flow rate of 0.2 mL min−1, the retention time of mitragynine was found to be 1.3 min. Ionization was performed in the positive ion electrospray mode. The selected mass-to-charge (m/z) ratio transition of mitragynine ion [M + H]+ used in the selected ion recording (SIR) was 399.1. The calibration curve was found to be linear over a concentration range of 1–5,000 ng mL−1 (r = 0.999) with a lower limit of quantification (LLOQ) of 1 ng mL−1. Intra- and inter-day assay variations were found to be less than 15%. The extraction recoveries ranged from 85–93% at the three concentrations (2, 400 and 4,000 ng mL−1) in rat plasma. This method was successfully used to quantify mitragynine in rat plasma following intravenous administration of the compound.

The purpose of the present investigation was to characterize the partitioning of artemisinin and its derivatives into both non-parasitized as well as Plasmodium falciparum parasitized red blood cells (RBCs). Artemisinin and selected derivatives at concentrations of 3.55 μM were incubated in RBCs with a hematocrit of 33% for 2 h at 37 °C, extracted from RBCs by solid phase extraction, and analyzed using liquid chromatography–mass spectrometry in positive electro-spray ionization mode with methanol as mobile phase. The uptake percent of artemisinin and selected derivatives into the non-parasitized RBCs ranged between 35% and 45%, while that into parasitized RBCs was between 51% and 72%. The results suggested that artemisinin and selected derivatives were preferentially distributed in parasitized RBCs. A Multiple Linear Regression model was built to gain insight about the essential structural properties required for the uptake of this class of compounds in parasitized RBCs and will provide instruction for designing of new derivatives of this class of compounds with improved uptake.Uptake studies of artemisinin and selected derivatives into normal and parasitized red blood cells (RBCs) and Multiple Regression Model for percent uptake of artemisinin and its derivates into the parasitized RBCs.

A rapid and sensitive ultra-performance liquid chromatography–tandem mass spectrometry (UPLC-MS/MS) method was developed and validated to quantify artemisinin in rat serum. The lower limit of quantification (LLOQ) was 4 ng/mL. The calibration curve was linear from 4 ng/mL to 10,000 ng/mL (R = 0.998). The assay was based on the selected reaction monitoring (SRM) transitions at m/z 305.4–151.10 for artemisinin and m/z 335.2–163.10 for arteether (internal standard). The artemisinin and internal standard can be separated from endogenous interferences in rat serum. Inter- and intra-day assay variation was less than 15%. The extraction recoveries ranged from 80.0 to 107.3% at the three concentrations (5000, 2000, and 200 ng/mL). This method was successfully applied to pharmacokinetic studies of artemisinin after intravenous and oral administration to rats.