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

19F-NMR and directly coupled 19F/1H-HPLC-NMR spectroscopic investigations of the metabolism of the model ecotoxin 3-trifluoromethylaniline in the earthworm species Eisenia veneta

1. The metabolic fate of the model ecotoxin 3-trifluoromethylaniline (3-TFMA) in earthworm was studied by (19)F- and directly coupled (19)F/(1)H-HPLC-NMR spectroscopy. Earthworms of Eisenia veneta spp. were subjected to the ecotoxin during a filter papercontact toxicity test at exposure levels of 1000, 100, 10, 1 and 0.1 micro g cm(-2). A metabolic profile was obtained previously by (19)F-NMR spectroscopy and metabolites were observed at all the exposure levels. 2. Identification of metabolites in individual worm extracts at the (lethal) exposure levels of 1000 and 100 micro g cm(-2) could be achieved on-line without sample preparation by (19)F/(1)H-HPLC-NMR spectroscopy. (19)F-HPLC-NMR spectroscopy was used in the continuous-flow mode, which enabled the HPLC chromatographic retention times (t(R)) of the metabolites to be established in a single analytical step. 3. In total, three (19)F-NMR signals could be detected, of which one was identified as the parent compound. Two earlier eluting metabolites were identified to be alpha- and beta-glucoside conjugates of 3-TFMA. 4. Metabolites at the lower (sublethal) exposure levels of 10, 1 and 0.1 micro g cm(-2) escaped identification by (19)F/(1)H-HPLC-NMR spectroscopy as outlined here and will require concentration prior to analysis.

Metabolism of 4-fluoroaniline and 4-fluorobiphenyl in the earthworm Eisenia veneta characterized by high-resolution NMR spectroscopy with directly coupled HPLC-NMR and HPLC-MS

1. Little is known about metabolism of xenobiotics by earthworms, despite their importance in soil ecotoxicity testing. Normal earthworms and earthworms treated with antibiotics to ensure inhibition of gut microflora were exposed to two model xenobiotic compounds, 4-fluoroaniline and 4-fluorobiphenyl, to determine which metabolites were produced, and whether the pattern of metabolism was affected by the presence of microbial transformation ability. 2. (19)F-NMR spectroscopy detected the number and relative proportions of metabolites and directly coupled HPLC-(1)H-NMR spectroscopy and HPLC-MS then identified the metabolites. 3. Despite uptake, no metabolism of 4-fluorobiphenyl was observed at any stage, which appears to be a consequence of the lack of oxidative Phase I metabolic activity of the earthworms towards this substrate. In contrast, 4-fluoroaniline exhibited dose-dependent metabolism. At high doses (leading to mortality within 24 h) one predominant metabolite was observed, which was identified as the N-beta-glucoside conjugate. At lower dose levels, the predominant metabolite was the gamma-glutamyl conjugate, although the glucoside and another as yet unidentified metabolite were also detected. 4. The inhibition of gut microflora did not have any influence on metabolism. The study represents the first evidence for glucoside and glutamyl conjugation as a pathway for xenobiotic metabolism in earthworms.

Recent applications of stereoselective chromatography

Some recent applications of stereoselective chromatography in the fields of clinical pharmacy, drug analysis, food, and natural products are reviewed. The review is documented with up-to-date literature, which will assist further expansion of research in these areas.

Glucuronidation of statins in animals and humans: a novel mechanism of statin lactonization

The active forms of all marketed hydroxymethylglutaryl (HMG)-CoA reductase inhibitors share a common dihydroxy heptanoic or heptenoic acid side chain. In this study, we present evidence for the formation of acyl glucuronide conjugates of the hydroxy acid forms of simvastatin (SVA), atorvastatin (AVA), and cerivastatin (CVA) in rat, dog, and human liver preparations in vitro and for the excretion of the acyl glucuronide of SVA in dog bile and urine. Upon incubation of each statin (SVA, CVA or AVA) with liver microsomal preparations supplemented with UDP-glucuronic acid, two major products were detected. Based on analysis by high-pressure liquid chromatography, UV spectroscopy, and/or liquid chromatography (LC)-mass spectrometry analysis, these metabolites were identified as a glucuronide conjugate of the hydroxy acid form of the statin and the corresponding delta-lactone. By means of an LC-NMR technique, the glucuronide structure was established to be a 1-O-acyl-beta-D-glucuronide conjugate of the statin acid. The formation of statin glucuronide and statin lactone in human liver microsomes exhibited modest intersubject variability (3- to 6-fold; n = 10). Studies with expressed UDP glucuronosyltransferases (UGTs) revealed that both UGT1A1 and UGT1A3 were capable of forming the glucuronide conjugates and the corresponding lactones for all three statins. Kinetic studies of statin glucuronidation and lactonization in liver microsomes revealed marked species differences in intrinsic clearance (CL(int)) values for SVA (but not for AVA or CVA), with the highest CL(int) observed in dogs, followed by rats and humans. Of the statins studied, SVA underwent glucuronidation and lactonization in human liver microsomes, with the lowest CL(int) (0.4 microl/min/mg of protein for SVA versus approximately 3 microl/min/mg of protein for AVA and CVA). Consistent with the present in vitro findings, substantial levels of the glucuronide conjugate (approximately 20% of dose) and the lactone form of SVA [simvastatin (SV); approximately 10% of dose] were detected in bile following i.v. administration of [(14)C]SVA to dogs. The acyl glucuronide conjugate of SVA, upon isolation from an in vitro incubation, underwent spontaneous cyclization to SV. Since the rate of this lactonization was high under conditions of physiological pH, the present results suggest that the statin lactones detected previously in bile and/or plasma following administration of SVA to animals or of AVA or CVA to animals and humans, might originate, at least in part, from the corresponding acyl glucuronide conjugates. Thus, acyl glucuronide formation, which seems to be a common metabolic pathway for the hydroxy acid forms of statins, may play an important, albeit previously unrecognized, role in the conversion of active HMG-CoA reductase inhibitors to their latent delta-lactone forms.

1H NMR characterization of the product from single solid-phase resin beads using capillary NMR flow probes

A capillary NMR flow probe was designed to generate high-resolution (1)H NMR spectra at 600 MHz from the cleaved product of individual 160-microm Tentagel combinatorial chemistry beads. By injecting a dissolved sample sandwiched between an immiscible, perfluorinated organic liquid directly into the probe, NMR spectra of the product cleaved from single beads were acquired in just 1 h of spectrometer time without diffusional dilution. Sample handling efficiency on the single bead scale was comparable to that obtained with a bulk sample. Using the relative intensity of the DMSO-d(5)H versus the analyte signals in a fully relaxed CPMG spectrum, the amount of product cleaved from a single bead was determined to be 540+/-170 pmol in one of the samples. Following the NMR data collection, the samples were examined with electrospray ionization mass spectrometry to provide additional structural information. By coupling with microliter-volume fluidic capabilities, the capillary flow probe described here will enable multidimensional characterization of single solid-phase resin products in an online manner.

Union of capillary high-performance liquid chromatography and microcoil nuclear magnetic resonance spectroscopy applied to the separation and identification of terpenoids

This paper describes the first coupling of a commercial capillary HPLC system with a diode array spectrophotometric detector and a custom-built nuclear magnetic resonance (NMR) flow microprobe. The eluent from a 3-microm diameter C18 HPLC column is linked to a 500 MHz 1H-NMR microcoil probe with an observe volume of 1.1 microl. The separation and structurally-rich detection of a mixture of terpenoids under both isocratic and gradient solvent elution conditions is presented. The lowest limits of detection yet reported for capillary HPLC on-line measurement (i.e., 37 ng for alpha-pinene) are achieved with this system. The complementary nature of diode array and NMR detection allows stopped-flow data collection from analytes which would otherwise go unnoticed in continuous-flow NMR. Moreover, stopped-flow NMR data is presented for the detection of a trace (sub-nmol) impurity in the sample mixture. Since NMR signals degrade and shift during solvent gradients, flow injection analysis studies are conducted with injected solvent plugs differing in mobile phase composition. The NMR signal degradation accompanying these injections is largely due to the variance in chemical shift with the solvent composition rather than to changes in magnetic susceptibility of the solvent. Characterization of such effects enables the development of improved NMR probes for the coupling of capillary HPLC and NMR.

Combination of matrix solid-phase dispersion extraction and direct on-line liquid chromatography-nuclear magnetic resonance spectroscopy-tandem mass spectrometry as a new efficient approach for the rapid screening of natural products: application to the total asterosaponin fraction of the starfish Asterias rubens

A combination of matrix solid-phase dispersion extraction (MSPD) and LC-NMR-MS hyphenation is proposed as a rapid screening method of natural products for unknown compounds. In this report, this new analytical approach is applied for the first time. MSPD represents a significant simplification compared to classical extraction procedures and is thus an excellent complement to the fast and powerful LC-NMR-MS: MSPD yields extracts suitable for LC-NMR-MS in one simple preparation step, while LC-NMR-MS yields a wealth of information in one single chromatographic run. The suitability of this technique to characterise glycosidic compounds in the molecular mass range of 1200 to 1400 a.m.u. is demonstrated. The information on the number of exchangeable protons provided by an additional back-exchange experiment proved to be particularly valuable for structural elucidation. The possibility of semi-quantitative LC-NMR measurements through methyl signals H(3)-18 and 19 of the steroidal skeleton is demonstrated and is ensuingly used to provide relative quantitative data of the steroid oligosaccharide fraction.