Utilisation of water soluble iridium catalysts for signal amplification by reversible exchange.

The catalytic hyperpolarisation of pyridine, 3-hydroxypyridine and oxazole by the Signal Amplification By Reversible Exchange (SABRE) process is achieved by a series of water soluble iridium phosphine and N-heterocyclic carbene dihydride complexes. While the efficiency of the SABRE process in methanol-d4 solution or ethanol-d6 solution is high, with over 400-fold (1)H polarisation of pyridine being produced by [Ir(H)2(NCMe)(py)(IMes)(monosulfonated-triphenylphosphine)]BF4, changing to a D2O or a D2O-ethanol solvent mixture leads to dramatically reduced activity which is rationalised in terms of low H2 solubility.

Evaluation of preparative high performance liquid chromatography and cryoprobe-nuclear magnetic resonance spectroscopy for the early quantitative estimation of drug metabolites in human plasma.

Definitive information on the metabolism of a drug candidate in humans is achieved through dosing radiolabelled drug as part of a clinical study, and is typically conducted post-proof of concept in Phase III of the clinical development plan. Here we describe a novel approach, using preparative high performance liquid chromatography and cryoprobe-nuclear magnetic resonance spectroscopy, to determine the human systemic exposure to a drug and its metabolites using samples derived from Phase I clinical studies. Using the described methodology, novel human plasma metabolites, as low as 10 ng/ml can be detected and quantified. This provides an opportunity, early in the development process to understand the potential role of metabolites in the safety and efficacy of drugs in humans.

Utilizing a -100 degrees C microplate CCD Imager, yttrium silicate coated 384-microplates and ultra-performance liquid chromatography for improved profiling of radiolabeled drug metabolites in complex biological samples.

The recent commercial availability of small particle packed columns (<2 microm) and associated instrumentation capable of withstanding the high pressures of such columns, has lead to an increase in the application of so called ultra-performance liquid chromatography. The improved efficiency, resolution and peak capacity of these columns, when coupled to mass spectrometry, provides particular benefit for the identification of drug metabolites in complex biological samples. In this work, the ability of ViewLux, a microplate imager, to act as a suitable radiodetection system for ultra-performance liquid chromatography methods is assessed. The system demonstrates robustness and sensitivity comparable to a microplate scintillation counter (TopCount) more typically used for off-line metabolite radiodetection. The ViewLux is also used here to undertake successful metabolite profiling of actual samples, for two investigational drug candidates, using both 96- and 384-well yttrium silicate microplates.

TopCount coupled to ultra-performance liquid chromatography for the profiling of radiolabeled drug metabolites in complex biological samples.

The recent commercial availability of small particle packed columns (<2microm) and associated instrumentation capable of withstanding the high pressures of such columns, has lead to an increase in the application of so called ultra-performance liquid chromatography (UPLC). It has recently been shown that the improved efficiency, resolution and peak capacity of these columns, when coupled to mass spectrometry, provides particular benefit for the identification of drug metabolites in complex biological samples. In this work, the ability of TopCount, a microplate scintillation counter, to act as a suitable radiodetection system for ultra-performance liquid chromatography methods is tested. TopCount, has innumerable benefits over more traditional on-line radioactivity flow detection methods, when dealing with the narrow peak widths and small peak volumes associated with the enhanced efficiency of sub-2microm columns. The system is tested for robustness and sensitivity, and then used to undertake successful metabolite profiling of actual samples, and the data compared to traditional HPLC with on-line radioactivity flow detector.

Ultra-performance liquid chromatography coupled to linear ion trap mass spectrometry for the identification of drug metabolites in biological samples.

The coupling of ultra-performance liquid chromatography, operating at elevated pressures, to a linear ion trap mass spectrometer provides a high-performance system suitable for drug metabolite characterisation. This system demonstrates improved chromatographic efficiency and sensitivity and at the same time provides diagnostic MSn data often critical for metabolite structural assignment. The linear ion trap was capable of dealing with the high chromatographic efficiencies and hence narrow peak widths associated with 1.7 microm particle-packed column separations. Polarity switching and data-dependent MSn data were generated with ease, and applied to the identification of metabolites found in human plasma.

The determination of nicotinic acid in plasma by mixed-mode liquid chromatography-tandem mass spectrometry following ion exchange solid phase extraction.

An assay for nicotinic acid in plasma samples has been developed using ion exchange solid phase extraction in 96-well format followed by mixed-mode ion exchange/reversed-phase liquid chromatography with positive ion tandem mass spectrometry detection. The assay avoids the need for time-consuming derivatisation procedures or involatile ion-pair chromatography reagents. The assay is linear over the wide range 0.05-20 microg/mL, based on a 100 microL sample (correlation coefficient>0.99). The assay is accurate and precise (bias and coefficient of variation<18%) over this calibration range.

Characterization of the metabolites of alosetron in experimental animals and human.

The metabolism of radiolabelled alosetron was studied in rat, dog, rabbit, mouse and human. The metabolism in rat and dog was studied at a low and an elevated dose designed to generate sufficient quantities of metabolite for definitive identification. A strategy for the characterization of metabolites in cases of extensive metabolism was developed and demonstrated for alosetron. Semi-preparative high-performance liquid chromatography (HPLC), liquid chromatography-mass spectrometry (LC-MS), nuclear magnetic resonance (NMR) and liquid chromatography-nuclear magnetic resonance (HPLC-NMR) enabled the isolation and characterization of 28 metabolites of alosetron. The characterization of the metabolites in animal excreta facilitated the identification of human systemic metabolites.

N-O glucuronidation: a major human metabolic pathway in the elimination of two novel anti-convulsant drug candidates.

1. The urinary metabolites of the anti-convulsant compound 4-amino-1-(2,6-difluorobenzyl)-1H-1,2,3-triazolo[4,5-c]-pyridine hydrochloride (GI265080) obtained following a single oral dose to man have been detected and quantified relative to each other using 19F-NMR spectroscopy. 2. The human urinary metabolites of GI265080 were isolated using semipreparative HPLC and unequivocally characterized using 1H-NMR spectroscopy, two-dimensional heteronuclear NMR spectroscopy and mass spectrometry. The assignments of the N-(5)-oxide and the N-(5)-O-glucuronide metabolites of GI265080 were further confirmed by independent synthesis. The urinary metabolites obtained following single oral doses to dog and rat have also been isolated and characterized. 3. The human urinary metabolites of GI265080 comprise the N-(5)-oxide, the quaternary N+-(5)-glucuronide, the 7-hydroxy glucuronide and a glucuronide conjugate of the N-(5)-oxide. The N-(5)-O-glucuronide conjugate is a novel species in human metabolism and is a significant route of elimination of GI265080 in man. 4. The urinary metabolites of the potential anti-convulsant GW273293 (6-amino-3-(2,3,5-trichlorophenyl)pyrazin-2-ylamine) obtained following a single oral dose to man have also been isolated and characterized. The formation of a novel N-O-glucuronide was also observed and was shown to constitute a significant route of elimination of GW273293 in man.

Quantitative analysis of pharmaceuticals in biological fluids using high-performance liquid chromatography coupled to mass spectrometry: a review.

1. The development of bio-analysis of drug molecules over the last 10 years is reviewed, focusing on advances in sample preparation, liquid chromatography and detection. 2. Developments have led to improvements in detection sensitivity, enhancements in specificity and increased capacity. 3. Emerging technologies such as monolithic column chromatography and miniaturized chip-based systems are discussed.

Formation of a defluorinated metabolite of a quinoxaline antiviral drug catalysed by human cytochrome P450 1A2.

The in-vitro metabolism of GW420867X ((S)-2-ethyl-7-fluoro-3-oxo-3, 4-dihydro-2H-quinoxaline-1-carboxylic acid isopropyl ester), a quinoxaline drug for the potential treatment of HIV, has been studied with singly expressed human cytochromes P450 (CYP 450). No biotransformation of [14C]GW420867X was evident in the presence of any of the CYP 450 isoforms, with the exception of CYP 450 1A2, where a single metabolite was observed in the HPLC radiochromatograms of enzyme incubations with the test compound. The structure of this metabolite was determined by nuclear magnetic resonance spectroscopy and mass spectrometry, and was shown to correspond to the replacement of the aromatic fluorine of GW420867X with a hydroxyl group. Thus, it appeared that CYP 450 1A2 catalysed the specific defluorination of GW420867X, presumably during formation of an arene oxide intermediate during aromatic hydroxylation.

Determination of 4-hydroxytamoxifen in mouse plasma in the pg/mL range by gradient capillary liquid chromatography/tandem mass spectrometry.

Capillary high-performance liquid chromatography (HPLC; 300 microm i.d.) coupled to tandem mass spectrometry has been used to determine the concentration of 4-hydroxytamoxifen in mouse plasma in the pg/mL range following the administration of Tamoxifen. A limit of quantification (LOQ) of 100 pg/mL was achieved using only 25 microL of plasma. The on-column sensitivity was determined to be 100 fg. The column performance was determined isocratically before and after the assay and showed only a 15% reduction in performance after 70 injections of plasma extract. No significant peak band broadening was observed due to the mass spectrometer interface using a standard TurboIonspray source.

Mass directed peak selection, an efficient method of drug metabolite identification using directly coupled liquid chromatography-mass spectrometry-nuclear magnetic resonance spectroscopy.

Mass spectrometry (both MS and MS-MS) has been used to determine which eluting chromatography peaks in an LC-MS-nuclear magnetic resonance (NMR) experiment should be selected for extended NMR spectroscopic measurement. This mass directed selection of chromatographic peaks has been applied to test mixtures and urine samples for identification of drug metabolites. It was used to simultaneously determine when drug-related material was eluting and provided molecular mass information on these components. Stop-flow LC-NMR was used to acquire data for structural characterisation of drug-related components. This work further serves to demonstrate the potential of coupling tandem mass spectrometry using an ion trap spectrometer with LC-NMR spectroscopy, to provide an extremely powerful tool in structural elucidation.

Use of directly coupled ion-exchange liquid chromatography-mass spectrometry and liquid chromatography-nuclear magnetic resonance spectroscopy as a strategy for polar metabolite identification.

Ion-exchange LC-MS and LC-NMR have been successfully used to identify a novel N-acetyl metabolite of a highly polar drug candidate [2-(ethanimidoylamino)ethyl]sulfonyl alanine (GW273629) under development as a therapeutic agent. This has been achieved using a simple HPLC method without the need for complicated and time consuming pre- or post-column derivatisation. Ion-exchange chromatography using simple ionic strength buffer and organic solvent mobile phases, as applied here, should be suitable for the analysis of other charged polar species. Optimisation of the system described could result in the development of a rational generic HPLC approach specifically designed for the characterisation of polar drug molecules and their metabolites.

Urinary metabolites of a novel quinoxaline non-nucleoside reverse transcriptase inhibitor in rabbit, mouse and human: identification of fluorine NIH shift metabolites using NMR and tandem MS.

1. The urinary metabolites of (S)-2-ethyl-7-fluoro-3-oxo-3,4-dihydro-2H-quinoxaline-carboxylic acid isopropylester (GW420867X) have been investigated in samples obtained following oral administration to rabbit, mouse and human. GW420867X underwent extensive biotransformation to form hydroxylated metabolites and glucuronide conjugates on the aromatic ring, and on the ethyl and isopropyl side-chains in all species. In rabbit urine, a minor metabolite was detected and characterized as a cysteine adduct that was not observed in mouse or man. 2. The hydroxylated metabolites and corresponding glucuronide conjugates were isolated by semi-preparative HPLC and characterized using NMR, LC-NMR and LC-MS/MS. The relative proportions of fluorine-containing metabolites were determined in animal species by 19F-NMR signal integration. 3. The fluorine atom of the aromatic ring underwent NIH shift rearrangement in the metabolites isolated and characterized in rabbit, mouse and human urine. 4. The characterization of the NIH shift metabolites in urine enabled the detection and confirmation of the presence of these metabolites in human plasma.

The use of capillary high performance liquid chromatography with electrospray mass spectrometry for the analysis of small volume blood samples from serially bled mice to determine the pharmacokinetics of early discovery compounds.

The methodology described demonstrates, for the first time, the feasibility of performing pharmacokinetic studies in the serially bled mouse model to support the early development of discovery compounds. Sample analysis, using capillary high performance liquid chromatography combined with tandem mass spectrometry, has facilitated the achievement of this milestone and has successfully been applied to determine pharmacokinetic information following both intravenous and oral administration of a single discovery compound. The methodologies described demonstrate potential for a reduction in the amount of new chemical entity required to undertake pharmacokinetic studies. Typically, such studies are performed in larger rodents with a significantly increased body mass (ten times in the case of the rat) and therefore it follows that to undertake the same experiment in the mouse would require ten times less compound to effect an equivalent dose. Conventionally, pharmacokinetic studies to obtain both intravenous and oral information, e.g. clearance and half-life, and the resultant bioavailability have been performed using two parallel groups of rodents, collecting blood by exsanguination, separating off the plasma and analysing this using conventional liquid chromatography/tandem mass spectrometry. The use of capillary high performance liquid chromatography (HPLC) has facilitated the analysis of small volume blood samples by increasing the effective sensitivity of the analytical method. Consequently, we have established a protocol for serially bleeding mice thus reducing the number of animals and so further reducing the amount of compound required for such experiments. This paper reports data obtained from collected and processed blood volumes of <20 microL with the subsequent injection of only 1 microL of precipitated extract onto a capillary column.

Urinary metabolites of a novel quinoxaline non-nucleoside reverse transcriptase inhibitor in dog, cynomolgus monkey and mini-pig.

1. The metabolism of (S)-2-ethyl-7-fluoro-3-oxo-3,4-dihydro-2H-quinoxalinecarboxylic acid isopropylester (GW420867X) has been investigated following oral administration to dog, cynomolgus monkey and mini-pig. 2. The urinary metabolites were isolated and characterized using semi-preparative HPLC, NMR and LC-MS/MS. The relative proportions of fluorine-containing metabolites were determined for each species by 19F-NMR signal integration. 3. The metabolite profiles for each species were similar, although the proportion of individual components varied, suggesting that similar metabolic pathways are involved in the biotransformation of GW420867X in the species studied. 4. The urinary metabolites indicated that the major routes of biotransformation included hydroxylation and subsequent glucuronic acid conjugation on the aromatic ring, and on the ethyl and isopropyl side chains. A component was observed in mini-pig urine that corresponded to hydroxylation and glucuronidation accompanied by loss of the fluorine atom.

Ultra-high flow rate capillary liquid chromatography with mass spectrometric detection for the direct analysis of pharmaceuticals in plasma at sub-nanogram per millilitre concentrations.

Ultra-high flow rate liquid chromatography on large particle size stationary phases coupled with mass spectrometric detection (particularly tandem mass spectrometry, MS/MS) is gaining increasing usage for the direct determination of pharmaceuticals in biological fluids. The lack of sample preparation required prior to chromatographic and MS/MS analysis, together with the extremely high throughput of the chromatography, make the technique extremely attractive to the modern pharmaceutical bioanalyst. However, this lack of sample preparation also means that there is no potential for concentration of the sample and, as a consequence, the sensitivity of the technique has been limited. Liquid chromatography on the capillary scale offers sensitivity benefits compared with conventional liquid chromatography as the volume in which the analyte peaks are eluted is greatly reduced. In this paper, we present the use of ultra-high flow rate liquid chromatography on the capillary scale. This enables the quantification of drugs in plasma at sub-nanogram per millilitre concentrations from a very small (2.5 micromgL) aliquot of plasma without sample preparation. We also compare the resolution obtained by ultra-high flow rate liquid chromatography with that achieved on short columns packed with conventional size packing materials operated in an isocratic manner.

The use of preparative high performance liquid chromatography with tandem mass spectrometric directed fraction collection for the isolation and characterisation of drug metabolites in urine by nuclear magnetic resonance spectroscopy and liquid chromatography/sequential mass spectrometry.

Preparative high performance liquid chromatography (HPLC) coupled to tandem mass spectrometry has been used successfully for the isolation of several drug metabolites from urine. Nuclear magnetic resonance (NMR) spectroscopy has been employed to determine the exact chemical structure of these metabolites. The use of preparative HPLC has allowed the isolation of relatively large quantities of drug metabolites (> 0.5 mg) allowing insensitive, information-rich NMR experiments such as NOE, HMBC and HMQC to be performed. The coupling of the ion-trap mass spectrometer, operating in automatic MS/MS mode, to preparative HPLC allows the simultaneous collection and mass spectrometric analysis of eluting analytes to be performed, thus allowing the position of fractions containing drug-related material to be identified very rapidly.

The application of fast gradient capillary liquid chromatography/mass spectrometry to the analysis of pharmaceuticals in biofluids.

Fast gradient capillary high performance liquid chromatography (HPLC) coupled to a mass spectrometer has been successfully used for the analysis of pharmaceutical compounds from biological matrices, in the femtogram on column range. In the work reported in this paper, the use of capillary HPLC, on the 180-micron internal diameter scale, has shown a 30-fold improvement in detection limits when compared to conventional 2-mm scale chromatography. The use of fast gradient elution resulted in a generic methodology which gave excellent chromatographic reproducibility and column longevity. This technique has been used in conjunction with simple protein precipitation, with no deleterious effect on either the column life or the chromatographic performance. The use of capillary HPLC in bioanalysis has the potential to give a significant increase in assay sensitivity with the equipment currently in use. In this paper the authors also present a modification to the current PE-Sciex ion-spray source which allows excellent spray adjustment in three dimensional accessibility, which is important when working with low flow rates, as well as reducing the inherent system dead volume.