Coupling of HPLC with 19F- and 1H-NMR spectroscopy to investigate the human urinary excretion of flurbiprofen metabolites

Effect of deglucuronidation on the results of the Basel phenotyping cocktail

We investigated the effect of deglucuronidation on the plasma concentration of the constituents of the Basel phenotyping cocktail and on the interpretation of the phenotyping results under basal conditions and after cytochrome P450 (CYP) induction with metamizole. The cocktail containing caffeine (CYP1A2), efavirenz (CYP2B6), flurbiprofen (CYP2C9), omeprazole (CYP2C19), metoprolol (CYP2D6) and midazolam (CYP3A4) was administered to 12 healthy subjects before (basal) and after treatment with metamizole for 1 week. In the basal state, deglucuronidation caused an increase in the plasma concentrations and area under the curve (AUC) of metoprolol, 8'-hydroxyefavirenz, 4'-hydroxyflurbiprofen and 1'-hydroxymidazolam. This effect could be visualized in Bland-Altman plots, where the values for 8'-hydroxyefavirenz, 4'-hydroxyflurbiprofen and 1'-hydroxymidazolam were mostly above the +20% threshold. As a result, the metabolic ratio (MR), calculated as AUC_{parent drug} /AUC_metabolite , decreased with deglucuronidation for CYP2B6, CYP2C9 and CYP3A4 and increased for CYP2D6. Treatment with metamizole, a constitutive androstane receptor-dependent inducer of CYP2B6, CYP2C9, CYP2C19 and CYP3A4, accentuated the effect of deglucuronidation on AUC and MR. The correlation of MRs calculated as the plasma concentration ratio parent drug/metabolite with the MR calculated as the AUC ratio showed that 1 sample obtained between 2 and 6 hours after cocktail ingestion and analysed with and without deglucuronidation is sufficient to obtain reliable phenotyping results. Importantly, CYP2C9 and 3A4 induction would have been missed without deglucuronidation of the plasma samples. In conclusion, deglucuronidation of the plasma samples improves the stability of the phenotyping results of the Basel phenotyping cocktail and is necessary to reliably detect CYP induction.

Metamizole is a Moderate Cytochrome P450 Inducer Via the Constitutive Androstane Receptor and a Weak Inhibitor of CYP1A2

Metamizole is an analgesic and antipyretic drug used intensively in certain countries. Previous studies have shown that metamizole induces cytochrome (CYP) 2B6 and possibly CYP3A4. So far, it is unknown whether metamizole induces additional CYPs and by which mechanism. Therefore, we assessed the activity of 6 different CYPs in 12 healthy male subjects before and after treatment with 3 g of metamizole per day for 1 week using a phenotyping cocktail approach. In addition, we investigated whether metamizole induces CYPs by an interaction with the constitutive androstane receptor (CAR) or the pregnane X receptor (PXR) in HepaRG cells. In the clinical study, we confirmed a moderate induction of CYP2B6 (decrease in the efavirenz area under the plasma concentration time curve (AUC) by 79%) and 3A4 (decrease in the midazolam AUC by 68%) by metamizole. In addition, metamizole weakly induced CYP2C9 (decrease in the flurbiprofen AUC by 22%) and moderately CYP2C19 (decrease in the omeprazole AUC by 66%) but did not alter CYP2D6 activity. In addition, metamizole weakly inhibited CYP1A2 activity (1.79‐fold increase in the caffeine AUC). We confirmed these results in HepaRG cells, where 4‐MAA, the principal metabolite of metamizole, induced the mRNA expression of CYP2B6, 2C9, 2C19, and 3A4. In HepaRG cells with a stable knockout of PXR or CAR, we could demonstrate that CYP induction by 4‐MAA depends on CAR and not on PXR. In conclusion, metamizole is a broad CYP inducer by an interaction with CAR and an inhibitor of CYP1A2. Regarding the widespread use of metamizole, these findings are of substantial clinical relevance.

Combining Hydrophilic Interaction Chromatography (HILIC) and Isotope Tagging for Off-Line LC-NMR Applications in Metabolite Analysis

The complementary use of liquid chromatography (LC) and nuclear magnetic resonance (NMR) has shown high utility in a variety of fields. While the significant benefit of spectral simplification can be achieved for the analysis of complex samples, other limitations remain. For example, (1)H LC-NMR suffers from pH dependent chemical shift variations, especially during urine analysis, owing to the high physiological variation of urine pH. Additionally, large solvent signals from the mobile phase in LC can obscure lower intensity signals and severely limit the number of metabolites detected. These limitations, along with sample dilution, hinder the ability to make reliable chemical shift assignments. Recently, stable isotopic labeling has been used to detect quantitatively specific classes of metabolites of interest in biofluids. Here we present a strategy that explores the combined use of two-dimensional hydrophilic interaction chromatography (HILIC) and isotope tagged NMR for the unambiguous identification of carboxyl containing metabolites present in human urine. The ability to separate structurally related compounds chromatographically, in off-line mode, followed by detection using (1)H-(15)N 2D HSQC (two-dimensional heteronuclear single quantum coherence) spectroscopy, resulted in the assignment of low concentration carboxyl-containing metabolites from a library of isotope labeled compounds. The quantitative nature of this strategy is also demonstrated.

Stable isotope-resolved metabolomics and applications for drug development

Advances in analytical methodologies, principally nuclear magnetic resonance spectroscopy (NMR) and mass spectrometry (MS), during the last decade have made large-scale analysis of the human metabolome a reality. This is leading to the reawakening of the importance of metabolism in human diseases, particularly cancer. The metabolome is the functional readout of the genome, functional genome, and proteome; it is also an integral partner in molecular regulations for homeostasis. The interrogation of the metabolome, or metabolomics, is now being applied to numerous diseases, largely by metabolite profiling for biomarker discovery, but also in pharmacology and therapeutics. Recent advances in stable isotope tracer-based metabolomic approaches enable unambiguous tracking of individual atoms through compartmentalized metabolic networks directly in human subjects, which promises to decipher the complexity of the human metabolome at an unprecedented pace. This knowledge will revolutionize our understanding of complex human diseases, clinical diagnostics, as well as individualized therapeutics and drug response. In this review, we focus on the use of stable isotope tracers with metabolomics technologies for understanding metabolic network dynamics in both model systems and in clinical applications. Atom-resolved isotope tracing via the two major analytical platforms, NMR and MS, has the power to determine novel metabolic reprogramming in diseases, discover new drug targets, and facilitates ADME studies. We also illustrate new metabolic tracer-based imaging technologies, which enable direct visualization of metabolic processes in vivo. We further outline current practices and future requirements for biochemoinformatics development, which is an integral part of translating stable isotope-resolved metabolomics into clinical reality.

Approaches for the rapid identification of drug metabolites in early clinical studies

Understanding the metabolism of a novel drug candidate in drug discovery and drug development is as important today as it was 30 years ago. What has changed in this period is the technology available for proficient metabolite characterization from complex biological sources. High-efficiency chromatography, sensitive MS and information-rich NMR spectroscopy are approaches that are now commonplace in the modern laboratory. These advancements in analytical technology have led to unequivocal metabolite identification often being performed at the earliest opportunity, following the first dose to man. For this reason an alternative approach is to shift from predicting and extrapolating possible human metabolism from in silico and nonclinical sources, to actual characterization at steady state within early clinical trials. This review provides an overview of modern approaches for characterizing drug metabolites in these early clinical studies. Since much of this progress has come from technology development over the years, the review is concluded with a forward-looking perspective on how this progression may continue into the next decade.

Integrated HPLC-MS and (1)H-NMR spectroscopic studies on acyl migration reaction kinetics of model drug ester glucuronides

Acyl glucuronides (AGs) are common, chemically reactive metabolites of acidic xenobiotics. Concerns about the potential of this class of conjugate to cause toxicity in man require efficient methods for the determination of reactivity, and this is commonly done by measuring transacylation kinetics. High-performance liquid chromatography-mass spectrometry (HPLC-MS) and nuclear magnetic resonance (NMR) spectroscopy were applied to the kinetic analysis of AG isomerization and hydrolysis for the 1-beta-O-AGs of ibufenac, (R)- and (S)-ibuprofen, and an alpha,alpha-dimethylated ibuprofen analogue. Each AG was incubated in either aqueous buffer at pH 7.4 or human plasma at 37 degrees C. Aliquots of these samples, taken throughout the reaction time course, were analysed by HPLC-MS and (1)H-NMR spectroscopy and the results compared. For identification of the AGs incubated in pH 7.4 buffer and for analysis of kinetic rates, (1)H-NMR spectroscopy generally gave the most complete set of data, but for human plasma the use of (1)H-NMR spectroscopy was impractical and HPLC-MS was more suitable. HPLC-MS was more sensitive than (1)H-NMR spectroscopy, but the lack of suitable stable-isotope labelled internal standards, together with differences in response between glucuronides and aglycones, made quantification problematic. Using HPLC-MS a specific 1-beta-O-AG-related ion at m/z 193 (the glucuronate fragment) was noted enabling selective determination of these isomers. In buffer, transacylation reactions predominated, with relatively little hydrolysis to the free aglycone observed. In human plasma incubations the observed rates of reaction were much faster than for buffer, and hydrolysis to the free aglycone was the major route. These results illustrate the strengths and weaknesses of each analytical approach for this class of analyte.

Heteronuclear 19F-1H statistical total correlation spectroscopy as a tool in drug metabolism: study of flucloxacillin biotransformation

We present a novel application of the heteronuclear statistical total correlation spectroscopy (HET-STOCSY) approach utilizing statistical correlation between one-dimensional 19F/1H NMR spectroscopic data sets collected in parallel to study drug metabolism. Parallel one-dimensional (1D) 800 MHz 1H and 753 MHz 19F{1H} spectra (n = 21) were obtained on urine samples collected from volunteers (n = 6) at various intervals up to 24 h after oral dosing with 500 mg of flucloxacillin. A variety of statistical relationships between and within the spectroscopic datasets were explored without significant loss of the typically high 1D spectral resolution, generating 1H-1H STOCSY plots, and novel 19F-1H HET-STOCSY, 19F-19F STOCSY, and 19F-edited 1H-1H STOCSY (X-STOCSY) spectroscopic maps, with a resolution of approximately 0.8 Hz/pt for both nuclei. The efficient statistical editing provided by these methods readily allowed the collection of drug metabolic data and assisted structure elucidation. This approach is of general applicability for studying the metabolism of other fluorine-containing drugs, including important anticancer agents such as 5-fluorouracil and flutamide, and is extendable to any drug metabolism study where there is a spin-active X-nucleus (e.g., 13C, 15N, 31P) label present.

Virtual Chromatographic Resolution Enhancement in Cryoflow LC−NMR Experiments via Statistical Total Correlation Spectroscopy

A new approach to enhancing information recovery from cryogenic probe "on-flow" LC-NMR spectroscopic analyses of complex biological mixtures is demonstrated using a variation on the statistical total correlation spectroscopy (STOCSY) method. Cryoflow probe technology enables sensitive and efficient NMR detection of metabolites on-flow, and the rapid spectral scanning allows multiple spectra to be collected over chromatographic peaks containing several species with similar, but nonidentical, retention times. This enables 1H NMR signal connectivities between close-eluting metabolites to be identified resulting in a "virtual" chromatographic resolution enhancement visualized directly in the NMR spectral projection. We demonstrate the applicability of the approach for structure assignment of drug and endogenous metabolites in urine. This approach is of wide general applicability to any complex mixture analysis problem involving chromatographic peak overlap and with particular application in metabolomics and metabonomics.

High-throughput screening for stability and inhibitory activity of compounds toward cytochrome P450-mediated metabolism

With the advent of combinatorial chemistry and high-throughput screening technology, thousands of molecules can now be rapidly synthesized and screened for biological activity against large numbers of protein targets, greatly increasing the speed with which lead compounds are identified during the early stages of drug discovery. However, rapid optimization of parameters that determine whether a high-affinity ligand or a potent inhibitor will become a successful drug remains a challenge in improving the efficiency of the drug discovery process. Parameters that define absorption, distribution, metabolism, and excretion properties of drug candidates are important determinants of therapeutic efficacy, and thus should be optimized during early stages of drug discovery. Although the speed with which drugs are screened for properties such as absorption, cytochrome P450 (CYP) inhibition, and metabolic stability has increased over the past several years, the screening rate/capacity is still several orders of magnitude lower than those for high-throughput methods used in lead identification, resulting in a bottleneck in the drug discovery process. This review discusses current methods used in the in vitro screening of drugs for their stability toward CYP-mediated oxidative metabolism. This is a critical screen in the drug discovery process because metabolism by CYP represents an important clearance mechanism for the vast majority of compounds, thus affecting their oral bioavailability and/or duration of action.

Hyphenation and hypernation the practice and prospects of multiple hyphenation

In the past two decades, combining a chromatographic separation system on-line with a spectroscopic detector in order to obtain structural information on the analytes present in a sample has become the most important approach for the identification and/or confirmation of the identity of target and unknown chemical compounds. In most instances, such hyphenation can be accomplished by using commercially available equipment For most (trace-level) analytical problems encountered today, the combination of column liquid chromatography or capillary gas chromatography with a mass spectrometer (LC-MS and GC-MS, respectively) is the preferred approach. However, it is also true that additional and/or complementary information is, in quite a number of cases, urgently required. This can be provided by, for example, atomic emission, Fourier-transform infrared, diode-array UV-vis absorbance or fluorescence emission, or nuclear magnetic resonance spectrometry. In the present review, the various options are briefly discussed and a few relevant applications are quoted for each combination. Special attention is devoted to systems in which multiple hyphenation, or hypernation, is an integral part of the setup. As regards this topic, the relative merits of various combinations--which turn out to include a mass spectrometer as one of the detectors in essentially all cases--are discussed and the fundamental differences between GC- and LC-based systems are outlined. Finally, the practicability of more extensive hypernation in LC, viz. with up to four spectrometers, is discussed. It is demonstrated that, technically, such multiple hyphenation is possible and that, from a practical point of view, rewarding results can be obtained. In other words, further research in this area is certainly indicated. However, in the foreseeable future, using several separate conventional hyphenated systems will be the commonly implemented solution in most instances.

Verapamil: identification of novel metabolites in cultures of primary human hepatocytes and human urine by LC-MS(n) and LC-NMR

1. Verapamil is a well-known and world-wide prescribed calcium antagonist, but it suffers from extensive first-pass metabolism. Although it has been marketed for many years, a complete understanding of its biotransformation in humans is still lacking. 2. The metabolism of verapamil was therefore investigated in cultures of primary human hepatocytes and in extracts of human urine after oral dosing. Identification of metabolites was done with LC-MS(n) and LC-NMR (600 MHz) to obtain in-depth information on its biotransformation products and definitive proof of the proposed chemical structures of metabolites. 3. Hyphenation of LC-MS(n) and LC-NMR was shown to be a powerful and effective platform for the identification of metabolites. Indeed, 21 Phase I and 16 Phase II metabolites were identified. Basically, all the Phase II metabolites (glucuronides) and 11 of the Phase I (oxidative) metabolites were not reported previously. 4. New insight into verapamil's biotransformation pathway is provided as well as evidence about its true complexity of metabolic disposal.

Mass spectrometric and NMR characterization of metabolites of roxifiban, a potent and selective antagonist of the platelet glycoprotein IIb/IIIa receptor

1. The methyl ester prodrug roxifiban is an orally active, potent and selective antagonist of the platelet glycoprotein GPIIb/IIIa receptor and is being developed for the prevention and treatment of arterial thrombosis. 2. Roxifiban was rapidly hydrolyzed to the zwitterion XV459 in vivo and by liver slices from the rat, mouse and human and by intestinal cores from dog. XV459 was metabolized to only a small extent in vitro and in vivo. 3. Studies with rat and dog given radiolabelled roxifiban showed limited oral absorption with the majority of the radiolabel being excreted in faeces. After i.v. doses of 14C-roxifiban, most of the radioactivity was recovered in the urine of rat whereas the dog excreted significant amounts of radioactivity in bile and urine. 4. XV459 could be metabolized extrahepatically by dog gut flora to produce an isoxazoline ring-opened metabolite. In vitro hepatic metabolism of XV459 was mainly by hydroxylation at the prochiral and chiral centres of the isoxazoline ring. These hydroxylated metabolites were not detected in the urine and plasma of human volunteers administered roxifiban. 5. Initial LC/MS identification of metabolites was achieved by dosing the rat with an equimolar mixture of d0:d4 roxifiban and detecting isotopic clusters of pseudomolecular ions. Unequivocal characterization of these metabolites was achieved by LC/MS, LC/NMR and high-field NMR techniques using synthetic standards of the metabolites. 6. The synthesis of one hydroxylated metabolite enabled the assignment of the correct stereochemistry of the substituted hydroxyl group on the isoxazoline ring.

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.

Hyphenated HPLC-NMR and its applications in drug discovery

Hyphenated HPLC-NMR is a fast growing technology, allowing rapid and detailed structural characterization of unknown mixtures. The technical aspects of the technology are reviewed on the basis of system configuration, operation, solvent suppression, HPLC and NMR optimization, and detection. The combined use of HPLC-NMR and HPLC-MS is also described and discussed. Various applications of HPLC-NMR and integrated HPLC-NMR-MS in drug discovery, especially in the separation and structure elucidation of drug impurities, reaction mixtures, degradation products, in vitro and in vivo metabolites, and combinatorial library samples, are illustrated.

Mass spectrometrically detected directly coupled high performance liquid chromatography/nuclear magnetic resonance spectroscopy/mass spectrometry for the identification of xenobiotic metabolites in maize plants

Reconstructed ion chromatograms have been used to identify relevant high performance liquid chromatography (HPLC) peaks in a directly coupled high performance liquid chromatography/nuclear magnetic resonance spectroscopy/mass spectrometry (HPLC/NMR/MS) experiment. This has been applied to a study of the metabolism of a model compound, 5-nitropyridone (2-hydroxy-5-nitropyridine), in maize plants grown hydroponically. By monitoring the on-flow reconstructed ion chromatogram corresponding to the 5-nitropyridone fragment at m/z 143, and additional molecular ions corresponding to metabolites identified as products from similar compounds, relevant peaks were identified rapidly for subsequent stopped-flow 1H NMR spectroscopic analysis. The combination of coupled HPLC/NMR/MS enabled the direct identification of three metabolites, namely the N-glucoside, N-malonylglucoside, and O-malonylglucoside. This work demonstrates the power of HPLC/NMR/MS for the structural elucidation of xenobiotic metabolites in complex biological matrices (such as plant material) with minimal sample preparation. In particular, using mass spectrometry for the initial identification of relevant HPLC peaks allows the analysis of complex samples without the necessity for other spectroscopic markers, such as 19F NMR signal for fluorinated compounds or UV spectroscopy for molecules with strong UV chromophores.

NMR spectroscopy in pharmacy

Since drugs in clinical use are mostly synthetic or natural products, NMR spectroscopy has been mainly used for the elucidation and confirmation of structures. For the last decade, NMR methods have been introduced to quantitative analysis in order to determine the impurity profile of a drug, to characteristic the composition of drug products, and to investigate metabolites of drugs in body fluids. For pharmaceutical technologists, solid state measurements can provide information about polymorphism of drug powders, conformation of drugs in tablets etc. Micro-imaging can be used to study the dissolution of tablets, and whole-body imaging is a powerful tool in clinical diagnostics. Taken together, this review covers applications of NMR spectroscopy in drugs analysis, in particular, methods of international pharmacopoeiae, pharmaceutics and pharmacokinetics. The authors have repeated many of the methods describe in their own laboratories.

Comparison of LC detection methods in the investigation of non-UV detectable organic impurities in a drug substance

HPLC Analysis with different detection methods was shown to be essential in the separation and identification of unknown organic impurities in a drug substance. The impurities were found to exhibit very weak or no response to standard ultraviolet (UV) absorption detection. LC-MS, LC-NMR, indirect, refractive index and evaporative light-scattering detection were used to quantify and identify the impurities in this specific case. The drug substance studied was found to be an ideal analyte for demonstrating the advantages and limitations of several chromatographic detection systems for impurity profile analysis.

Investigation of the feasibility of directly-coupled HPLC-NMR with 2H detection with application to the metabolism of N-dimethylformamide-d7

The use of 2H NMR spectroscopy as a detector for HPLC has been investigated using the continuous flow method in which rat urine containing metabolites of N-dimethylformamide-d7 was employed as a test case. Three xenobiotic-related species, including DMF-d7 itself, were detected. It is shown that for small molecules which give relatively sharp 2H NMR resonances, 2H HPLC-NMR spectroscopy is a feasible technique. For larger molecules, the resulting broad lines are likely to preclude the determination of detailed structural information. However, extension of the approach is possible by the use of selectively 2H-labelled xenobiotics to determine HPLC retention times of metabolites with continuous-flow 2H NMR spectroscopy detection, followed by stop-flow 1H HPLC-NMR spectroscopy for structural characterisation.

High-performance thin-layer chromatographic determination of flurbiprofen in plasma

A high-performance thin-layer chromatographic (HPTLC) method for the assay of flurbiprofen in plasma is reported. The drug was extracted from acidified plasma with hexane-diethyl ether (80:20). The mobile phase composition was n-hexane-ethyl acetate-glacial acetic acid (60:30:10). Densitometric analysis of flurbiprofen was carried out at 247 nm. The calibration curves of flurbiprofen in methanol and in plasma were linear in the range 40-400 ng. The mean values of correlation coefficient, slope and intercept were 0.995 +/- 0.003, 0.075 +/- 0.002 and 4.39 +/- 0.05 for standard curves in methanol and 0.992 +/- 0.002, 0.066 +/- 0.007 and 3.40 +/- 0.72 for standard curves in plasma, respectively. The limit of quantitation for flurbiprofen in human plasma was 40 ng, and no interference was found from endogenous compounds. The recovery of flurbiprofen from human plasma using the described extraction procedure was about 87%. The coefficient of variation for within-day and between-day analyses was 2.53% and 3.96% for 200 ng and 1.76% and 2.30% for 400 ng flurbiprofen concentration, respectively. The method was utilized to monitor plasma concentration of flurbiprofen post administration of sustained release capsules in human patient volunteers.

Synthesis, isolation and identification of glucuronides and mercapturic acids of a novel antiparasitic agent, licochalcone A

1. Four glucuronic acid conjugates of licochalcone A (Lica), and their metabolites, have been synthesized using rabbit and pig liver microsomes and purified by preparative hplc. 2. The glucuronides were identified as E-Lica 4'-O-beta-glucuronide, E and Z-Lica 4-O-beta-glucuronide and a mono-glucuronide conjugate of a beta-hydroxylated Lica metabolite. The metabolites were identified by hplc-nmr (one and two-dimensional nmr) as well as hplc-ms. 3. At pH 8.5 Lica reacted with N-acetyl-L-cysteine giving the two epimeric conjugates, which were then isolated by preparative hplc and identified by one and two-dimensional nmr spectroscopic methods. 4. Only two glucuronic acid conjugates (E- and Z-Lica 4-O-beta-glucuronide) were found in the urine of rat after i.p. administration of a single dose of Lica.

Novel metabolites of warfarin produced by Beauveria bassiana and Streptomyces rimosus: a novel application of hplc-nmr

1. Biotransformation of warfarin by the fungus Beauveria bassiana (ATCC 7159) yielded the first reported phase II warfarin metabolite, 3'4'-dihydroxywarfarin-3'-[4-methoxyglucoside], another previously unreported metabolite, 3',4'-dihydroxywarfarin and also 4'-hydroxywarfarin. 2. Biotransformation of warfarin by Streptomyces rimosus (NRRL 2234) yielded the previously unreported metabolites, 12-hydroxywarfarin, 4'-hydroxy-11-methoxywarfarin, and also 7-hydroxywarfarin and 4'-hydroxywarfarin, which have not been previously reported as biotransformation products from this organism. 3. Hplc-nmr has been used to identify biotransformation products of warfarin by S. rimosus directly from the microbial broth without prior isolation and purification.

Direct characterization of drug glucuronide isomers in human urine by HPLC-NMR spectroscopy: application to the positional isomers of 6,11-dihydro-11-oxodibenz[b,e]oxepin-2-acetic acid glucuronide

In this work, 400 and 600 MHz 1H HPLC-NMR spectroscopic methods were developed and applied to separate and identify the positional glucuronide isomers and anomers of the model nonsteroidal antiinflammatory drug, 6,11-dihydro-11-oxodibenz[b,e]oxepin-2-acetic acid, in whole human urine. The HPLC methods utilized either an isocratic system, comprising 30% acetonitrile in water at pH 2.5, or a gradient elution system increasing from 30% to 60% acetonitrile, in order to achieve improved separation of the 2-, 3-, and 4-O-acylglucuronide isomers from the faster eluting endogenous urinary metabolites. Directly coupled stop-flow 1H HPLC-NMR spectroscopic measurements were made at the retention times indicated by the UV-monitored chromatographic peaks. The glucuronide isomers were identified from the 1H NMR spectra on the basis of their chemical shifts and spin-spin coupling patterns. The elution order was 4-O-acyl-, 3-O-acyl-, and finally 2-O-acylglucuronide, with tR values of 10.04, 11.68, and 12.64 min, respectively. Although the alpha- and beta-anomers of each of the positional isomers could not be separated in these solvent systems, they could be identified in the individual 1H NMR spectra. This work shows for the first time that directly coupled HPLC-NMR spectroscopy can be used directly to isolate and characterize acyl-migrated isomers of drug glucuronides in whole urine. This approach will be of value in the study of glucuronide acyl migration reactions of nonsteroidal antiinflammatory drugs and other xenobiotic ester glucuronides in whole biofluids.

Nuclear magnetic resonance and high-performance liquid chromatography-nuclear magnetic resonance studies on the toxicity and metabolism of ifosfamide

A combination of high-resolution nuclear magnetic resonance (NMR) and high-performance liquid chromatography (HPLC)-NMR spectroscopic methods has been used to analyse urine from humans and rats treated with the anticancer drug ifosfamide. It was possible to detect a range of abnormal endogenous metabolites in urine after ifosfamide administration to human subjects undergoing cancer therapy and to relate the metabolic perturbations to the nephrotoxic effects of the drug. Changes observed by 1H NMR included increases in levels of urinary glucose, glycine, alanine, histidine, lactate, acetate, succinate, and trimethylamine-N-oxide and decreases in the levels of hippurate and citrate. Additional evidence was gained that ifosfamide-induced nephrotoxicity might be related to the level of oxidation of the coadministered drug mesna. By using both directly coupled continuous-flow 31P HPLC-NMR spectroscopy to determine the retention times of the phosphorus-containing metabolites and, subsequently, stop-flow 1H HPLC-NMR of the urine, it was possible to isolate and identify on-line the metabolites ifosfamide mustard, 4-hydroxy-ifosfamide, 2-dechloroethylifosfamide, and the parent compound itself. These studies illustrate the potential of combining 1H NMR spectroscopy of biofluids and HPLC-NMR spectroscopy for the investigation of drug metabolism and toxicity in humans and animals.

Hplc-nmr identification of the human urinary metabolites of (-)-cis-5-fluoro-1-[2-(hydroxymethyl)-1,3-oxathiolan-5-yl] cytosine, a nucleoside analogue active against human immunodeficiency virus (HIV)

1. Human urine samples from a clinical trial of the anti-HIV compound (-)-cis-5-fluoro-1-[2-(hydroxymethyl)-1,3-oxathiolan-5-yl]-cyto sin e (BW524W91) have been analysed using 19F-nmr and 1H-hplc-nmr spectroscopy. 2. The identities and relative levels of the xenobiotic species in the urine have been determined by 470-MHz 19F-nmr spectroscopy and by directly coupled 600-MHz 1H-hplc-nmr in the stop-flow mode with confirmation of the metabolite identities being made by comparison with nmr spectra of synthetic standard compounds. 3. The principal urinary xenobiotic was the unchanged drug, but the glucuronide ether conjugate at the 5' position of BW524W91, one of the two diastereomeric sulphoxides and the deaminated metabolite were also characterized. 4. The detection limit of directly coupled hplc-600-MHz 1H-nmr spectroscopy was evaluated by measuring two-dimensional nmr spectra of the glucuronide conjugate of BW524W91 and shown to be approximately 1 microgram material for 1H-1H-TOCSY and 20 micrograms metabolite for 1H-13C-HMQC spectra for overnight (16 h) acquisition.

Characterization of in vitro metabolites from human liver microsomes using directly coupled hplc-nmr: application to a phenoxathiin monoamine oxidase-A inhibitor

1. The metabolism of 1-ethylphenoxathiin-10,10-dioxide (BW1370U87), an experimental compound designed as an inhibitor of monoamine oxidase-A for use as a possible anti-depression agent, has been studied in a human liver microsome preparation. 2. The identities of the metabolites have been determined using directly coupled hplc-1H nmr at 600 MHz in the stop-flow mode in this first study of in vitro xenobiotic metabolism using hplc-nmr. 3. The xenobiotic substances that were identified comprised the parent compound BW1370U87 (with -CH2CH3 at C1) together with sidechain-oxidized metabolites with C1 substituents of -CHOH.CH3, -CH2.CH2OH, -CHOH.CH2OH and -CH2.COOH, plus the unsubstituted phenoxathiin-10,10-dioxide.

Application of the one-dimensional TOCSY pulse sequence in 750 MHz 1H-NMR spectroscopy for assignment of endogenous metabolite resonances in biofluids

The complex 1H-NMR spectrum arising from an intact biofluid has been simplified using a one-dimensional homonuclear polarization transfer experiment (known as TOCSY or HOHAHA). This approach establishes connectivity between sequentially coupled multiplets, and the method is illustrated by the confirmation of the chemical shifts and hence resonance assignment of a number of endogenous metabolites in the 750 MHz 1H-NMR spectrum of seminal fluid. This has allowed the detection and assignment of pyroglutamate and uracil in this fluid for the first time.