Xiangjun Meng

Determination of rabeprazole enantiomers in dog plasma by supercritical fluid chromatography tandem mass spectrometry and its application to a pharmacokinetic study

Rabeprazole is a novel benzimidazole proton pump inhibitor used for the treatment of gastrointestinal disorders. It is a chiral molecule that gives rise to the possibility of stereoselective pharmacokinetics. To investigate this phenomenon, a rapid and sensitive chiral assay based on supercritical fluid chromatography tandem mass spectrometry was developed and applied to the determination of (R)-rabeprazole and (S)-rabeprazole in dog plasma. Sample preparation involved protein precipitation with acetonitrile after the addition of (R)-lansoprazole as internal standard. Baseline separation of enantiomers in 4.5 min was achieved on an Acquity UPC2 system using an ACQUITY UPC2 Trefoil CEL2 column maintained at 60°C and a mobile phase consisting of methanol/CO2 (30:70, v/v) delivered at 2.5 mL/min. Detection was achieved by multiple reaction monitoring of the transitions at m/z 360.0→242.2 (rabeprazole) and 370.3→252.0 (internal standard) in the positive ion mode. The assay was linear in the range of 1-1000 ng/mL and free of matrix effects. Intra- and interday precisions were less than 10.0% with accuracy in the range of -2.6 to 3.1%. The method was successfully applied to a pharmacokinetic study of rabeprazole enantiomers after administration of a single oral dose of 10 mg racemate to beagle dogs.

Determination of lansoprazole enantiomers in dog plasma by column-switching liquid chromatography with tandem mass spectrometry and its application to a preclinical pharmacokinetic study

Lansoprazole, a selective proton pump inhibitor, has a chiral benzimidazole sulfoxide structure and is used for the treatment of gastric acid hypersecretory related diseases. To investigate its stereoselective pharmacokinetics, a column-switching liquid chromatography with tandem mass spectrometry method was developed for the determination of lansoprazole enantiomers in dog plasma using (+)-pantoprazole as an internal standard. After a simple protein precipitation procedure with acetonitrile, matrix components left behind after sample preparation were further eliminated from the sample by reversed-phase chromatography on a C18 column. The fluent was fed to a chiral column for the separation of lansoprazole enantiomers. Baseline separation of lansoprazole enantiomers was achieved on a Chiralcel OZ-RH column using acetonitrile/0.1% formic acid in water (35:65, v/v) as the mobile phase at 40°C. The linearity of the calibration curves ranged from 3 to 800 ng/mL for each enantiomer. Intra- and inter-day precisions ranged from 2.1 to 7.3% with an accuracy of ±1.7% for (+)-lansoprazole, and from 1.6 to 6.9% with an accuracy of ±3.5% for (-)-lansoprazole, respectively. The validated method was successfully applied for the stereoselective pharmacokinetic study of lansoprazole in beagle dog after intravenous infusion.

Simultaneous quantitation of two diastereoisomers of lobaplatin in rat plasma by supercritical fluid chromatography with tandem mass spectrometry and its application to a pharmacokinetic study

Lobaplatin, consisting of two diastereoisomers, is a third-generation platinum antineoplastic agent that has shown encouraging anticancer activity in a variety of tumor types. To investigate any stereospecificity in the pharmacokinetics of lobaplatin, a novel, simple, rapid and sensitive supercritical fluid chromatography with tandem mass spectrometry method was developed for the simultaneous quantitation of lobaplatin diastereoisomers in rat plasma. After a simple protein precipitation with methanol, the analytes and dexpantoprazole (internal standard) were chromatographed on an Acquity UPC(2) system with a Chiralcel OZ-RH column using a mobile phase consisting of carbon dioxide and methanol (65:35, v/v) at 40°C over 6 min. The assay was linear over a concentration range of 25-15,000 ng/mL for both diastereoisomers using 100 μL of rat plasma for sample preparation. The lower limit of quantification was 25 ng/mL for both compounds, which was sufficient to detect the diastereoisomers in the incurred samples within this study. Intra- and inter-day precisions were below 11.8% and the accuracies were below 4.5%. The validated method was successfully applied to a pharmacokinetic study after an intravenous administration of 7.6 mg/kg lobaplatin to rats. There was no apparent stereospecificity in the pharmacokinetics between the two diastereoisomers of lobaplatin.

Significant Improvement of Metabolic Characteristics and Bioactivities of Clopidogrel and Analogs by Selective Deuteration

In the search for prodrug analogs of clopidogrel with improved metabolic characteristics and antiplatelet bioactivity, a group of clopidogrel and vicagrel analogs selectively deuterated at the benzylic methyl ester group were synthesized, characterized, and evaluated. The compounds included clopidogrel-d3 (8), 2-oxoclopidogrel-d3 (9), vicagrel-d3 (10a), and 12 vicagrel-d3 analogs (10b–10m) with different alkyl groups in the thiophene ester moiety. The D3C-O bond length in 10a was shown by X-ray single crystal diffraction to be shorter than the H3C-O bond length in clopidogrel, consistent with the slower rate of hydrolysis of 8 than of clopidogrel in rat whole blood in vitro. A study of the ability of the compounds to inhibit ADP-induced platelet aggregation in fresh rat whole blood collected 2 h after oral dosing of rats with the compounds (7.8 μmol/kg) showed that deuteration increased the activity of clopidogrel and that increasing the size of the alkyl group in the thiophene ester moiety reduced activity. A preliminary pharmacokinetic study comparing 10a with vicagrel administered simultaneously as single oral doses (72 μmol/kg of each drug) to male Wistar rats showed 10a generated more of its active metabolite than vicagrel. These results suggest that 10a is a potentially superior antiplatelet agent with improved metabolic characteristics and bioactivity, and less dose-related toxicity.

Simultaneous determination of carboprost methylate and its active metabolite carboprost in dog plasma by liquid chromatography-tandem mass spectrometry with positive/negative ion-switching electrospray ionization and its application to a pharmacokinetic study.

A liquid chromatography-tandem mass spectrometric (LC-MS/MS) method using positive/negative electrospray ionization (ESI) switching for the simultaneous quantitation of carboprost methylate and carboprost in dog plasma has been developed and validated. After screening, the esterase inhibitor, dichlorvos was added to the whole blood at a ratio of 1:99 (v/v) to stabilize carboprost methylate during blood collection, sample storage and LLE. Indomethacin was added to plasma to inhibit prostaglandins synthesis after sampling. After liquid-liquid extraction of 500μL plasma with ethyl ether-dichloromethane (75:25, v/v), analytes and internal standard (IS), alprostadil-d4, were chromatographed on a CAPCELL PAK Phenyl column (150×2.0mm, 5μm) using acetonitrile-5mM ammonium acetate as mobile phase. Carboprost methylate was detected by positive ion electrospray ionization followed by multiple reaction monitoring (MRM) of the transition at m/z 400.5→329.3; the carboprost and IS were detected by negative ion electrospray ionization followed by MRM of the transitions at m/z 367.2→323.2, and 357.1→321.2, respectively. The method was linear for both analytes in the concentration range 0.05-30ng/mL with intra- and inter-day precisions (as relative standard deviation) of ≤6.75% and accuracy (as relative error) of ≤7.21% and limit of detection (LOD) values were 10 and 20pg/mL, respectively. The method was successfully applied to a pharmacokinetic study of the analytes in beagle dogs after intravaginal administration of a suppository containing 0.5mg carboprost methylate.

Establishment of a Charge Reversal Derivatization Strategy to Improve the Ionization Efficiency of Limaprost and Investigation of the Fragmentation Patterns of Limaprost Derivatives Via Exclusive Neutral Loss and Survival Yield Method

AbstractSensitivity is generally an issue in bioassays of prostaglandins and their synthetic analogs due to their extremely low concentration in vivo. To improve the ionization efficiency of limaprost, an oral prostaglandin E1 (PGE1) synthetic analog, we investigated a charge reversal derivatization strategy in electrospray ionization mass spectrometry (ESI-MS). We established that the cholamine derivative exhibits much greater signal intensity in the positive-ion mode compared with limaprost in the negative ion mode. Collision-induced dissociation (CID) involved exclusive neutral mass loss and positive charge migration to form stable cationic product ions with the positive charge on the limaprost residue rather than on the modifying group. This has the effect of maintaining the efficiency and specificity of multiple reaction monitoring (MRM) and avoiding cross talk. CID fragmentation patterns of other limaprost derivatives allowed us to relate the dissociation tendency of different neutral leaving groups to an internal energy distribution scale based on the survival yield method. Knowledge of the energy involved in the production of stabilized positive ions will potentially assist the selection of suitable derivatization reagents for the analysis of a wide variety of lipid acids. Graphical Abstractᅟ

Development and Application of an MSALL-Based Approach for the Quantitative Analysis of Linear Polyethylene Glycols in Rat Plasma by Liquid Chromatography Triple-Quadrupole/Time-of-Flight Mass Spectrometry

Polyethylene glycols (PEGs) are synthetic polymers composed of repeating ethylene oxide subunits. They display excellent biocompatibility and are widely used as pharmaceutical excipients. To fully understand the biological fate of PEGs requires accurate and sensitive analytical methods for their quantitation. Application of conventional liquid chromatography-tandem mass spectrometry (LC-MS/MS) is difficult because PEGs have polydisperse molecular weights (MWs) and tend to produce multicharged ions in-source resulting in innumerable precursor ions. As a result, multiple reaction monitoring (MRM) fails to scan all ion pairs so that information on the fate of unselected ions is missed. This Article addresses this problem by application of liquid chromatography-triple-quadrupole/time-of-flight mass spectrometry (LC-Q-TOF MS) based on the MSALL technique. This technique performs information-independent acquisition by allowing all PEG precursor ions to enter the collision cell (Q2). In-quadrupole collision-induced dissociation (CID) in Q2 then effectively generates several fragments from all PEGs due to the high collision energy (CE). A particular PEG product ion (m/z 133.08592) was found to be common to all linear PEGs and allowed their total quantitation in rat plasma with high sensitivity, excellent linearity and reproducibility. Assay validation showed the method was linear for all linear PEGs over the concentration range 0.05-5.0 μg/mL. The assay was successfully applied to the pharmacokinetic study in rat involving intravenous administration of linear PEG 600, PEG 4000, and PEG 20000. It is anticipated the method will have wide ranging applications and stimulate the development of assays for other pharmaceutical polymers in the future.

A Unique Collision-Induced Dissociation Reaction of Cholamine Derivatives of Certain Prostaglandins

AbstractProstaglandins (PGs) are biologically active metabolites of arachidonic acid containing 20 carbon atoms, a cyclic moiety, and two side chains (A and B) in common. The bioassay of PGs requires high sensitivity because of their low concentration in tissues and blood and has usually been carried out by electrospray ionization tandem mass spectrometry (ESI-MS/MS) in the negative ion mode. Chemical derivatization of PG carboxylic acid groups to introduce positive charge-carrying groups is an established strategy to improve the sensitivity and selectivity of such assays. In this study, we exploited this approach for structural identification of a series of PGs using cholamine derivatization through an amidation reaction. However, we observed that collision-induced dissociation of these derivatives gave rise to unexpected product ions that we postulated were formed by unique long-range intramolecular reactions resulting in dehydration of the B chain accompanied by fragmentation of the A chain through an unusual Hofmann rearrangement. Evidence for the proposed mechanism is presented based on ESI-MS/MS and high resolution mass spectrometry studies of cholamine derivatives of PGE1, PGE2, PGD2, PGI2, and C-17 methyl deuterium-labeled limaprost. Graphical Abstract

Differential mobility spectrometry followed by tandem mass spectrometry with multiple ion monitoring for bioanalysis of eptifibatide in rat plasma

HighlightsCombining differential mobility spectrometry with MIM for quantitation of eptifibatide in rat plasma.Using differential mobility spectrometry to reduce the background noise to achieve a higher S/N ratio.The method was successfully applied to pharmacokinetic study of eptifibatide in Wistar rats. ABSTRACT Eptifibatide is a therapeutic cyclic peptide with poor collision‐induced dissociation (CID) efficiency for multiple reaction monitoring (MRM), which limits the development of a traditional liquid chromatography‐tandem mass spectrometry (LC–MS/MS) bioassay with MRM. In this study, a method combining differential mobility spectrometry (DMS) with liquid chromatography‐multiple ion monitoring (LC‐DMS‐MIM) was developed for the quantitation of eptifibatide in rat plasma. After solid phase extraction (SPE) of 100 &mgr;L plasma on an Oasis® HLB cartridge, the analyte and I.S. (octreotide) were analyzed using a SCIEX QTRAP 6500 operated in the positive ion mode and preceded by a DMS device. The lower limit of quantitation (LLOQ) for eptifibatide was 0.5 ng/mL using only 100 &mgr;L plasma. The method was linear in the concentration range 0.5–300 ng/mL with good precision and accuracy. Compared to regulated quantitative LC–MS/MS bioanalysis of eptifibatide, the LC‐DMS‐MIM method effectively overcomes the sensitivity challenge in the LC‐MRM method and reduces the high background noise and matrix interference in LC‐MIM method without DMS. The method was successfully applied to a pharmacokinetic study involving intravenous injection of eptifibatide to Wistar rats.

Quantitation of lovastatin and its hydroxy acid in human plasma by high-performance liquid chromatography-tandem mass spectrometry

Abstract An HPLC-MS/MS method was described for the quantitation of lovastatin and its main hydroxy acid metabolite lovastatin acid in human plasma. Lovastatin was detected in the positive ion mode, while Lovastatin acid was detected in the negative mode in a single injection, with simvastatin and simvastatin acid as internal standard, respectively. Plasma sample was treated by one-step liquid-liquid extraction with dichloromethane-diethyl ether (2:3 v/v). LC separation was performed within 4 min on a Zorbax Eclipse XDB-C8 column (5 μm, 4.6 × 150 mm I.D.) using 90% methanol-10% – 10 mmol/l ammonium acetate solution which contains 0.02% formic acid as mobile phase. Linear calibration curves were obtained in the concentration range 0.05–30.0 ng/ml. The intra- and inter-day precision values were below 15% and the accuracy was within ±15% at three quality control levels for both lovastatin and lovastatin acid. It was successfully applied to a pharmacokinetic study in 12 healthy volunteers after a single oral dose of 40 mg per subject. Graphical Abstract