Quantitative studies on the urinary metabolic fate of 2-chloro-4-trifluoromethylaniline in the rat using 19F-NMR spectroscopy and directly coupled HPLC-NMR-MS

Nuclear Magnetic Resonance Spectroscopy in Clinical Metabolomics and Personalized Medicine: Current Challenges and Perspectives

Personalized medicine is probably the most promising area being developed in modern medicine. This approach attempts to optimize the therapies and the patient care based on the individual patient characteristics. Its success highly depends on the way the characterization of the disease and its evolution, the patient’s classification, its follow-up and the treatment could be optimized. Thus, personalized medicine must combine innovative tools to measure, integrate and model data. Towards this goal, clinical metabolomics appears as ideally suited to obtain relevant information. Indeed, the metabolomics signature brings crucial insight to stratify patients according to their responses to a pathology and/or a treatment, to provide prognostic and diagnostic biomarkers, and to improve therapeutic outcomes. However, the translation of metabolomics from laboratory studies to clinical practice remains a subsequent challenge. Nuclear magnetic resonance spectroscopy (NMR) and mass spectrometry (MS) are the two key platforms for the measurement of the metabolome. NMR has several advantages and features that are essential in clinical metabolomics. Indeed, NMR spectroscopy is inherently very robust, reproducible, unbiased, quantitative, informative at the structural molecular level, requires little sample preparation and reduced data processing. NMR is also well adapted to the measurement of large cohorts, to multi-sites and to longitudinal studies. This review focus on the potential of NMR in the context of clinical metabolomics and personalized medicine. Starting with the current status of NMR-based metabolomics at the clinical level and highlighting its strengths, weaknesses and challenges, this article also explores how, far from the initial “opposition” or “competition”, NMR and MS have been integrated and have demonstrated a great complementarity, in terms of sample classification and biomarker identification. Finally, a perspective discussion provides insight into the current methodological developments that could significantly raise NMR as a more resolutive, sensitive and accessible tool for clinical applications and point-of-care diagnosis. Thanks to these advances, NMR has a strong potential to join the other analytical tools currently used in clinical settings.

The integration of LC-MS and NMR for the analysis of low molecular weight trace analytes in complex matrices

This review discusses the integration of liquid chromatography (LC), mass spectrometry (MS), and nuclear magnetic resonance (NMR) in the comprehensive analysis of small molecules from complex matrices. We first discuss the steps taken toward making the three technologies compatible, so as to create an efficient analytical platform. The development of online LC-MS-NMR, highlighted by successful applications in the profiling of highly concentrated analytes (LODs 10 μg) is discussed next. This is followed by a detailed overview of the alternative approaches that have been developed to overcome the challenges associated with online LC-MS-NMR that primarily stem from the inherently low sensitivity of NMR. These alternative approaches include the use of stop-flow LC-MS-NMR, loop collection of LC peaks, LC-MS-SPE-NMR, and offline NMR. The potential and limitations of all these approaches is discussed in the context of applications in various fields, including metabolomics and natural product discovery.

Hemoglobin Adducts and Urinary Metabolites of Arylamines and Nitroarenes

Arylamines and nitroarenes are intermediates in the production of pharmaceuticals, dyes, pesticides, and plastics and are important environmental and occupational pollutants. N-Hydroxyarylamines are the toxic common intermediates of arylamines and nitroarenes. N-Hydroxyarylamines and their derivatives can form adducts with hemoglobin (Hb-adducts), albumin, DNA, and tissue proteins in a dose-dependent manner. Most of the arylamine Hb-adducts are labile and undergo hydrolysis in vitro, by mild acid or base, to form the arylamines. According to current knowledge of arylamine adduct-formation, the hydrolyzable fraction is derived from the reaction products of the arylnitroso derivatives that yield arylsulfinamide adducts with cysteine. Hb-adducts are markers for the bioavailability of N-hydroxyarylamines. Hb-adducts of arylamines and nitroarenes have been used for many biomonitoring studies for over 30 years. Hb-adducts reflect the exposure history of the last four months. Biomonitoring of urinary metabolites is a less invasive process than biomonitoring blood protein adducts, and urinary metabolites have served as short-lived biomarkers of exposure to these hazardous chemicals. However, in case of intermittent exposure, urinary metabolites may not be detected, and subjects may be misclassified as nonexposed. Arylamines and nitroarenes and/or their metabolites have been measured in urine, especially to monitor the exposure of workers. This review summarizes the results of human biomonitoring studies involving urinary metabolites and Hb-adducts of arylamines and nitroarenes. In addition, studies about the relationship between Hb-adducts and diseases are summarized.

Alternate strategies to obtain mass balance without the use of radiolabeled compounds: application of quantitative fluorine (19F) nuclear magnetic resonance (NMR) spectroscopy in metabolism studies

Nuclear magnetic resonance (NMR) spectroscopy is playing an increasingly important role in the quantitation of small and large molecules. Recently, we demonstrated that (1)H NMR could be used to quantitate drug metabolites isolated in submilligram quantities from biological sources. It was shown that these metabolites, once quantitated by NMR, were suitable to be used as reference standards in quantitative LC/MS-based assays, hence circumventing the need for radiolabeled material or synthetic standards to obtain plasma exposure estimates in humans and preclinical species. The quantitative capabilities of high-field NMR is further demonstrated in the current study by obtaining the mass balance of fluorinated compounds using (19)F-NMR. Two fluorinated compounds which were radio-labeled with carbon-14 on metabolically stable positions were dosed in rats and urine and feces collected. The mass balance of the compounds was obtained initially by counting the radioactivity present in each sample. Subsequently, the same sets of samples were analyzed by (19)F-NMR, and the concentrations determined by this method were compared with data obtained using radioactivity counting. It was shown that the two methods produced comparable values. To demonstrate the value of this analytical technique in drug discovery, a fluorinated compound was dosed intravenously in dogs and feces and urine collected. Initial profiling of samples showed that this compound was excreted mainly unchanged in feces, and hence, an estimate of mass balance was obtained using (19)F-NMR. The data obtained by this method was confirmed by additional quantitative studies using mass spectrometry. Hence cross-validations of the quantitative (19)F-NMR method by radioactivity counting and mass spectrometric analysis were demonstrated in this study. A strategy outlining the use of fluorinated compounds in conjunction with (19)F-NMR to understand their routes of excretion or mass balance in animals is proposed. These studies demonstrate that quantitative (19)F-NMR could be used as an alternate technique to obtain an estimate of the mass balance of fluorinated compounds, especially in early drug development where attrition of the compounds is high, and cost savings could be realized through the use of such a technique rather than employing radioactive compounds. The potential application of qNMR in conducting early human ADME studies with fluorinated compounds is also discussed.

High-performance liquid chromatography-mass spectrometry (HPLC-MS)-based drug metabolite profiling

The identification of drug metabolites in biofluids such as urine, plasma, and bile, as well as in in vitro systems, is an important step in drug discovery and development. Mass spectrometry, particularly when combined with high-performance liquid chromatography (HPLC-MS), can enable detailed structural information to be obtained on the metabolites of a drug or xenobiotic as a result of metabolism. The successful identification of drug metabolites by HPLC-MS-based techniques requires careful optimisation of a number of factors. First, the chromatographic separation should provide good resolution of the individual xenobiotic metabolites present in the sample. There is also the need to minimise the interference caused by the presence of endogenous metabolites, which may interfere with MS detection. Ideally, untreated samples should be profiled to reduce the likelihood of missing important metabolites due to losses during sample processing, but, depending upon the matrix, some degree of sample cleanup/extraction and concentration of the metabolites may be required using liquid-liquid or liquid-solid extraction. Second, the MS conditions must be carefully selected in order to maximise the potential of detecting the separated metabolites, which may have a very different character to the parent compound. The use of radiolabelled drugs in metabolism experiments greatly aids in the detection (and quantification) of metabolites, directing the investigator towards peaks that need to be characterised by MS. The presence of characteristic isotope patterns from either the incorporation of stable isotopes (e.g. (13)C, (15)N) or naturally occurring isotope patterns from substituents on the molecule (e.g. (35/37)Cl, (79/81)Br) can also provide a useful handle on the drug and its metabolites for the purposes of detection and spectrometric interpretation. This chapter provides guidelines for, and examples of, HPLC-MS-based drug metabolite profiling.

A holistic strategy for characterizing the safety of metabolites through drug discovery and development

The subject of metabolites in safety testing has had much debate in the recent past and has shown itself to be a complex issue with no simple solutions to providing absolute assurance of drug safety. Much of the attention has focused on the ability to identify metabolites and then demonstrate that their risk has been adequately characterized, either through their exposure in toxicology species or, failing this, by direct safety testing. In this review, we summarize our forward operational strategy that combines the principles summarized in the FDA Guidance, together with discussions at scientific meetings and literature opinions. It is a balance between the primary goal of assuring patient safety with one of reasonable investment. A key principle in striking this balance is to build stepwise information on metabolites through the drug discovery and development continuum. This allows assessments to be made from early nonclinical studies onward as to whether or not metabolite safety is underwritten by exposure in toxicology species. This strategy does not require absolute quantitation of the metabolites in early clinical trials but relies upon comparison of relative exposures between animals and humans using the capabilities of modern analytical techniques. Through this strategy, human disproportionate metabolites can be identified to allow a decision regarding the need for absolute quantitation and direct safety testing of the metabolite. Definitive radiolabeled studies would be initiated following proof of pharmacology or efficacy in humans, and nonclinical safety coverage would be adequately assessed prior to large-scale clinical trials. In cases where metabolite safety is not supported through the parent compound toxicology program, approaches for the direct safety testing of metabolites with regard to general and reproductive toxicology, safety pharmacology, and genetic safety have been defined.

Metabolism of [14C]-5-chloro-1,3-benzodioxol-4-amine in male Wistar-derived rats following intraperitoneal administration

[14C]-5-chloro-1,3-benzodioxol-4-amine was administered intraperitoneally (i.p.) to bile duct-cannulated rats (Alpk:ApfSD, Wistar derived) at 25 mg kg-1 to determine the rates and routes of excretion of the compound and to investigate its metabolic fate. A total of 89.1% of the dose was excreted in the 48 h following administration, the majority being recovered in the urine during the first 12 h. The main metabolite in both urine and bile, detected by high-performance liquid chromatography (HPLC) with radioprofiling and mass spectrometry, was identified as a demethylenated monosulfate conjugate. Unchanged parent compound formed a major component of the radiolabel excreted in urine and, in addition to unchanged parent and demethylenated sulphate conjugate, a large number of minor metabolites were detected in urine and bile. The overall metabolic fate of 5-chloro-1,3-benzodioxol-4-amine in the rat was complex, with some similarities to previously studied methylenedioxyphenyl compounds.

Metabolism of 3-chloro-4-fluoroaniline in rat using [14C]-radiolabelling,19F-NMR spectroscopy, HPLC-MS/MS, HPLC-ICPMS and HPLC-NMR

The metabolic fate of 3-chloro-4-fluoroaniline was investigated in rat following intraperitoneal (i.p.) administration at 5 and 50 mg kg(-1) using a combination of HPLC-MS, HPLC-MS/MS, (19)F-NMR spectroscopy, HPLC-NMR spectroscopy and high-pressure liquid chromatography-inductively coupled plasma mass spectrometry (HPLC-ICPMS) with (35)Cl and (34)S detection. The metabolism of 3-chloro-4-fluoroaniline at both doses was rapid and extensive, to a large number of metabolites, with little unchanged compound excreted via the urine. Dosing at 5 mg kg(-1) with [(14)C]-labelled compound enabled the comparison of standard radioassay analysis methods with (19)F-NMR spectroscopy. (19)F-NMR resonances were only readily detectable in the 0-12 h post-dose samples. Dosing at 50 mg kg(-1) allowed the facile and specific detection and quantification of metabolites by (19)F-NMR spectroscopy. Metabolite profiling was also possible at this dose level using HPLC-ICPMS with (35)Cl-specific detection. The principal metabolites of 3-chloro-4-fluoroaniline were identified as 2-amino-4-chloro-5-fluorophenyl sulfate and 2-acetamido-4-chloro-5-fluorophenyl glucuronide. N-acetylation and hydroxylation followed by O-sulfation were the major metabolic transformations observed.

In vitrometabolite identification of ML3403, a 4-pyridinylimidazole-type p38 MAP kinase inhibitor by LC-Qq-TOF-MS and LC-SPE-cryo-NMR/MS

Prediction of the metabolic profile of a potential new drug is recommended at an early stage in industrial drug discovery process to determine whether or not any potentially reactive or toxic metabolites are formed. In the present study, we investigated the in vitro metabolism of ML3403 ({4- [5-(4-Fluorophenyl)-2-methylsulfanyl-3H-imidazol-4-yl]-pyridin-2-yl -(1-phenylethyl)-amine), a potent and selective p38 MAP kinase inhibitor using mouse liver microsomes. The combination of LC-ESI-Qq-TOF (tandem quadrupole time-of-flight)-MS (mass spectrometer) and LC-SPE (solid phase extraction)-cryo-NMR (nuclear magnetic resonance)/MS at 600 MHz has been applied for comprehensive and straightforward structural elucidation of ML3403 metabolites. It was possible to determine the metabolic profile of ML3403, revealing eight different metabolites formed by N-desalkylation, S-mono- and di-oxidation, aliphatic hydroxylation and pyridine-N-oxidation. The ESI-Qq-TOF-MS data yielded elemental compositions of all metabolites and their fragments by evaluation of the accurate mass and isotopic pattern information using the sigma-fit algorithm. Evaluation of 2D NMR spectra obtained from pure ML3403 an its major metabolite ML3603 allowed the unequivocal assignment of the resonances in 1D NMR spectra obtained directly from the microsomal incubation by LC-SPE-cryo-NMR/MS. The presented method significantly decreases the time required for a complete structural assignment of metabolites from microsomal in vitro assays.

Analytical strategies for identifying drug metabolites

With the dramatic increase in the number of new chemical entities (NCEs) arising from combinatorial chemistry and modern high-throughput bioassays, novel bioanalytical techniques are required for the rapid determination of the metabolic stability and metabolites of these NCEs. Knowledge of the metabolic site(s) of the NCEs in early drug discovery is essential for selecting compounds with favorable pharmacokinetic credentials and aiding medicinal chemists in modifying metabolic "soft spots". In development, elucidation of biotransformation pathways of a drug candidate by identifying its circulatory and excretory metabolites is vitally important to understand its physiological effects. Mass spectrometry (MS) and nuclear magnetic resonance (NMR) have played an invaluable role in the structural characterization and quantification of drug metabolites. Indeed, liquid chromatography (LC) coupled with atmospheric pressure ionization (API) MS has now become the most powerful tool for the rapid detection, structure elucidation, and quantification of drug-derived material within various biological fluids. Often, however, MS alone is insufficient to identify the exact position of oxidation, to differentiate isomers, or to provide the precise structure of unusual and/or unstable metabolites. In addition, an excess of endogenous material in biological samples often suppress the ionization of drug-related material complicating metabolite identification by MS. In these cases, multiple analytical and wet chemistry techniques, such as LC-NMR, enzymatic hydrolysis, chemical derivatization, and hydrogen/deuterium-exchange (H/D-exchange) combined with MS are used to characterize the novel and isomeric metabolites of drug candidates. This review describes sample preparation and introduction strategies to minimize ion suppression by biological matrices for metabolite identification studies, the application of various LC-tandem MS (LC-MS/MS) techniques for the rapid quantification and identification of drug metabolites, and future trends in this field.

Online hyphenated liquid chromatography-nuclear magnetic resonance spectroscopy-mass spectrometry for drug metabolite and nature product analysis

Screening analysis that aims at rapidly distinguishing new molecules in the presence of a large number of known compounds becomes increasingly important in the fields of drug metabolite profiling and nature product investigation. In the past decade, online-coupled liquid chromatography-nuclear magnetic resonance spectroscopy-mass spectrometry (LC-NMR-MS) has emerged as a powerful tool for the detection and identification of known and, more important, emerging compounds in complex clinical, pharmaceutical samples and nature product extracts, due to the complementary information provided by the two detectors for unambiguous structure elucidation. This review discusses the practical conditions under which LC-NMR-MS is suitable as a routine tool for unknown analysis, as well as the fundamental concepts and their advantage aspects. Particular attention is paid to its major operating parameters that include the instrumental configurations, working modes, NMR probe improvement and LC mobile phase selection. Finally, the recent applications of LC-NMR-MS to clinical metabolite and nature product analysis are summarized which have shown the benefit of this promising hyphenated technique.

Metabolism of a novel nucleoside analogue, OGT 719, in the isolated perfused rat liver model, in rats, in tumour models and in patients

1. The metabolic pathway(s) of OGT 719, a novel nucleoside analogue in which galactose is covalently attached to the N1 of 5-fluorouracil (FU), have been investigated with (19)F-NMR spectroscopy in (1) the isolated perfused rat liver (IPRL) model, (2) normal rats, (3) rats bearing the HSN LV10 sarcoma, (4) nude mice xenografted with the human hepatoma HepG2 and (5) urine from patients. 2. The administration of OGT 719 results in the formation of small amounts of FU. IPRL experiments with OGT 719 in combination with asialofetuin, a natural asialoglycoprotein receptor (ASGP-r), suggest competitive binding of OGT 719 to the ASGP-r. 3. The data obtained in non-tumour rats also demonstrated an extremely low metabolization of OGT 719 into FU and alpha-fluoro-beta-alanine, the well-known major metabolite of FU. 4. A comparison of tumour extracts from rats bearing the HSN LV10 sarcoma treated with FU or OGT 719 showed the incorporation of FU into RNA in rats treated with FU but not in rats treated with OGT 719; nevertheless, the incorporation of FU into RNA was observed in the liver from rats treated with OGT 719. 5. In a human hepatoma xenografted to nude mice, both the OGT 719 and FU contents of the tumour were markedly higher than in the corresponding liver, suggesting a tumour-specific trapping of OGT 719 in hepatoma. 6. The metabolism of OGT 719 was also extremely low in patients. 7. In conclusion, the present study shows the value of (19)F-NMR for demonstrating for the first time that OGT 719 is a prodrug of FU although very poorly metabolized.

The metabolism of 2-trifluormethylaniline and its acetanilide in the rat by 19F NMR monitored enzyme hydrolysis and 1H/19F HPLC-NMR spectroscopy

The urinary excretion profile and identity of the metabolites of 2-trifluoromethyl aniline (2-TFMA) and 2-trifluoromethyl acetanilide (2-TFMAc), following i.p. administration to the rat at 50 mg kg(-1), were determined using a combination of 19F NMR monitored enzyme hydrolysis, SPEC-MS and 19F/1H HPLC-NMR. A total recovery of approximately 96.4% of the dose was excreted into the urine as seven metabolites. The major routes of metabolism were N-conjugation (glucuronidation), and ring-hydroxylation followed by sulphation (and to a lesser extent glucuronidation). The major metabolites excreted into the urine for both compounds were a labile N-conjugated metabolite (a postulated N-glucuronide) and a sulphated ring-hydroxylated metabolite (a postulated 4-amino-5-trifluoromethylphenyl sulphate) following dosing of 2-TFMA. These accounted for approximately 53.0 and 31.5% of the dose, respectively. This study identifies problems on sample component instability in the preparation and analysis procedures.

Structure-metabolism relationships of substituted anilines: prediction of N-acetylation and N-oxanilic acid formation using computational chemistry

1. The relationship between the in vivo metabolism of substituted anilines, in particular N-acetylation and subsequent formation of oxanilic acids, and their molecular physico-chemical properties has been investigated using computational chemistry and pattern-recognition methods. The methods revealed that the physico-chemical properties most important for N-acetylation and subsequent oxanilic acid formation were electronic descriptors based on partial atomic charges and the susceptibility of the molecules to nucleophilic attack at certain ring positions. 2. The calculated partial atom charge on the amine nitrogen was the parameter most important for predicting that an aniline would be N-acetylated. The calculated nucleophilic susceptibility of the aromatic carbon para to the amino group (NS4) was the most significant parameter for determining oxanilic acid formation following N-acetylation. Thus, highly electron-withdrawing groups substituted at this position gave higher nucleophilic susceptibilities that were related to the presence of an oxanilic acid metabolite. 3. If the parameters relating to N-acetylation were modified by other electron-withdrawing groups in the ring (particularly at the position ortho to the amino group), then acetylation and subsequent oxanilic acid formation did not occur. The introduction of groups that allow the possibility of competing oxidative metabolic pathways elsewhere in the molecule (e.g. CH(3)) also affected the production of oxanilic acids. 4. Using chemometric analysis of the computed physico-chemical properties, the result has been the generation of a model that classifies the metabolism of a number of anilines. This could be used to predict the acetylation and oxanilic formation propensity of a number of substituted anilines whose metabolism was unknown to the system, demonstrating that such techniques may be of use for predicting metabolism and hence could provide support for rational drug design.

Determination of tacrine metabolites in microsomal incubate by high performance liquid chromatography-nuclear magnetic resonance/mass spectrometry with a column trapping system

A column trapping system has been incorporated into high performance liquid chromatography-nuclear magnetic resonance-mass spectrometry (HPLC-NMR-MS) to reduce data acquisition time of NMR experiments. The system uses a trapping column to capture analytes after the HPLC column and back flush trapped analyte to the flow cell of the NMR probe for detection. A dilution solvent is mixed with eluent from HPLC column to reduce the influence of the organic content in the mobile phase before column trapping. The trapping column is also coupled with a mass spectrometer (MS) to get complementary MS data on the same peak. Studies on 1-hydroxylated 9-amino-1,2,3,4-tetrahydro-acridine (1-OH tacrine), indomethacin and testosterone with the column trapping system showed good recovery of analytes and over 3-fold mean increase in UV-VIS signal intensity. The time saving on NMR experiments with the column trapping system was demonstrated by the analysis of dog microsomal incubate with tacrine.

HPLC analysis of ecdysteroids in plant extracts using superheated deuterium oxide with multiple on-line spectroscopic analysis (UV, IR, 1H NMR, and MS)

HPLC, using superheated D20 as the mobile phase, combined with on-line characterization via a combination of diode array UV, 1H NMR, FT-IR spectroscopy, and mass spectrometry has been used for the analysis of a standard of 20-hydroxyecdysone- and ecdysteroid-containing plant extracts. This combination of spectrometers enabled the on-flow collection of UV, 1H NMR, IR, and mass spectra not only for pure 20-hydroxyecdysone (100-400 microg on column) but also the major ecdysteroids present in crude extracts of Silene otites, Silene nutans, and Silene frivaldiskyana. The ecdysteroids unequivocally identified in these extracts included 20-hydroxyecdysone, polypodine B, and integristerone A.

Flow injection analysis with multiple on-line spectroscopic analysis (UV, IR, 1H-NMR and MS)

Studies on the capabilities of flow injection analysis (FIA) combined with on-line characterisation of model compounds via a combination of diode array UV, 1H-NMR, FT-IR spectroscopy and mass spectrometry are described. Using this combination of spectrometers enabled the on-flow collection of UV, 1H-NMR, IR and MS for a range of model compounds. Samples were introduced into the system as solutions in deuterium oxide in concentrations ranging from 1.4 to 8.4 mg ml(-1). A sample volume of 100 microl was used for FIA at a flow rate of 1 ml min(-1). From these studies a practical working quantity of ca. 140 microg/sample of analyte was determined which provided characteristic spectra.

Metabolism of fluorine-containing drugs

This article reviews current knowledge of the metabolism of drugs that contain fluorine. The strategic value of fluorine substitution in drug design is discussed in terms of chemical structure and basic concepts in drug metabolism and drug toxicity.

Spectroscopic characterisation and identification of ecdysteroids using high-performance liquid chromatography combined with on-line UV--diode array, FT-infrared and 1H-nuclear magnetic resonance spectroscopy and time of flight mass spectrometry

A prototype multiply hyphenated reversed-phase HPLC system has been applied to the analysis of a mixture of pure ecdysteroids and an ecdysteroid-containing plant extract. Characterisation was achieved via a combination of diode array UV, 1H NMR, FT-IR spectroscopy and time of flight (TOF) mass spectrometry. This combination of spectrometers allowed the collection of UV, 1H NMR, IR and mass spectra for a mixture of pure standards enabling almost complete structural characterisation to be performed. The technique was then applied to a partially purified plant extract in which 20-hydroxyecdysone and polypodine B were identified despite incomplete chromatographic resolution and the presence of co-chromatographing interferents. The experimental difficulties in the use of such a systems for these analytes are described.

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.

Directly coupled HPLC-NMR and HPLC-NMR-MS in pharmaceutical research and development

The methodology for the direct coupling of HPLC with NMR spectroscopy and the simultaneous double coupling of HPLC with NMR and mass spectrometry (MS) is described. Indications of the necessary technical developments to achieve this are given, and the applications of these new techniques to studies of pharmaceutical relevance are reviewed. These include studies of combinatorial chemistry libraries, synthetic chemical impurities, characterisation of drug mixtures, identification of natural products of possible pharmaceutical interest and identification of xenobiotic metabolites in human, animal and in vitro systems. In addition, HPLC-NMR has been used to investigate xenobiotic metabolite reactivity. Finally, the potential future directions of the techniques are discussed.

Identification and quantification of metabolites of 2,3,5,6-tetrafluoro-4-trifluoromethylaniline in rat urine using 19F nuclear magnetic resonance spectroscopy, high-performance liquid chromatography-nuclear magnetic resonance spectroscopy and high-performance liquid chromatography-mass spectrometry

The urinary excretion profile and identity of the metabolites of 2,3,5,6-tetrafluoro-4-triflouromethylaniline, following i.p. administration to the rat at 50 mg kg(-1), were determined using a combination of 19F-NMR, HPLC-NMR and HPLC-MS. A total of 38% of the dose was eliminated in the urine as five metabolites. The major routes of metabolism were N-glucuronidation, sulfation and oxidation with a significant amount of metabolic defluorination to give a number of ortho-ring hydroxylated metabolites. The oxidised metabolites were excreted as glucuronide and/or sulfate conjugates.

Multiple hyphenation of liquid chromatography with nuclear magnetic resonance spectroscopy, mass spectrometry and beyond

The advent of sensitive and reliable HPLC-NMR and HPLC-MS systems has revolutionised the identification of compounds eluting from chromatographic systems. More recently systems have been described wherein both NMR and MS are used together to provide an immensely powerful means of characterising compounds in chromatographic eluents. Here the construction and application of combined HPLC-NMR-MS systems to the analysis of mixtures of pharmaceuticals, drug metabolites in biological fluids and natural products in plant extracts is reviewed. In addition preliminary work with alternative systems such as HPLC-UV-NMR-FTIR-MS is highlighted and the prospects for such complex systems considered.

Investigation of the metabolism of 14C/13C-practolol in rat using directly coupled radio-HPLC-NMR-MS

1. The metabolic fate of 14C/13C-practolol was investigated using on-line HPLC-NMR-MS following oral administration to rat. The major route of elimination for the radiolabel was via the urine with the principal biotransformation products confirmed as the 2-hydroxy- and 2-hydroxyglucronide metabolites. 2. In addition, futile deacetylation, determined by the replacement of 13C-labelled acetyl groups with endogenous 12C-acetyls accounted for approximately 7-10% of the urinary metabolites, corresponding to approximately 5% of the dose undergoing N-deacetylation. 3. Evidence for chiral metabolism was sought via NMR of isolated metabolites using beta-cyclodextrin as a chiral shift agent. Practolol was excreted as a racemate. However, some enantioselective metabolism/excretion had occurred as the hydroxy- and hydroxyglucuronide were not excreted as racemic mixtures. 4. Directly coupled radio-HPLC-NMR-MS is extremely effective for the identification of the metabolites of radiolabelled xenobiotics in urine samples.