Characterisation of oxazepam degradation products by high‐performance liquid chromatography/electrospray ionisation mass spectrometry and electrospray ionisation quadrupole time‐of‐flight tandem mass spectrometry

Oxazepam has been subjected to controlled degradation at 100°C for 3 h in 0.5 M HCl and 0.5 M NaOH. Following neutralisation of the degradation mixture and removal of salts by solid‐phase extraction (SPE), isocratic high‐performance liquid chromatography/mass spectrometry (HPLC/MS) using water/methanol (25:75 v/v) as the mobile phase was carried out using a flow diverter to collect fractions prior to their characterisation by electrospray ionisation multi‐stage mass spectrometry (ESI‐MSⁿ) and proposal of the corresponding fragmentation patterns. The elemental compositions of the degradation products and their MS fragments were evaluated using electrospray ionisation quadrupole time‐of‐flight tandem mass spectrometry (ESI‐QTOF‐MS/MS) which was then used to support the proposed fragmentation patterns. Copyright © 2010 John Wiley & Sons, Ltd.     

Metabolite identification of tanshinol borneol ester in rats by high‐performance liquid chromatography combined with electrospray ionization quadrupole time‐of‐flight mass spectrometry

Tanshinol borneol ester (DBZ) is a potential drug candidate composed of danshensu and borneol. It shows anti‐ischemic and anti‐atherosclerosis activity. However, little is known about its metabolism in vivo. This research aimed to elucidate the metabolic profile of DBZ through analyzing its metabolites using high‐performance liquid chromatography combined with electrospray ionization quadrupole time‐of‐flight mass spectrometry. Chromatographic separation was performed on an Agilent TC‐C₁₈ column (150 × 4.6 mm, 5.0 μm) with gradient elution using methanol and water containing 0.2% (v/v) formic acid as the mobile phase. Metabolite identification involved analyzing the retention behaviors, changes in molecular weights and MS/MS fragment patterns of DBZ and its metabolites. As a result, 20 potential metabolites were detected and tentatively identified in rat plasma, urine and feces after administration of DBZ. DBZ could be metabolized to O‐methylated DBZ, DBZ‐O‐glucuronide, O‐methylated DBZ‐O‐glucuronide, hydroxylated DBZ and danshensu. Danshensu, a hydrolysis product of DBZ, could further be transformed into 12 metabolites. The proposed method was confirmed to be a reliable and sensitive alternative for characterizing metabolic pathways of DBZ and providing valuable information on its druggability.     

Characterization of isochlorogenic acid A metabolites in rats using high‐performance liquid chromatography/quadrupole time‐of‐flight mass spectrometry

Isochlorogenic acid A is widely present in fruits, vegetables and herbal medicines, and is characterized by anti‐inflammatory, hepatoprotective and antiviral properties. However, little is known about its metabolic fate and pharmacokinetic properties. This study is thus designed to investigate the metabolic fate of isochlorogenic acid A. An analytical method based on high‐performance liquid chromatography/quadrupole time‐of‐flight mass spectrometry (HPLC/Q‐TOF MS) was established to characterize the metabolites of isochlorogenic acid A in the plasma, urine and feces of rats. A total of 32 metabolites were identified. The metabolic pathways mainly include hydrolyzation, dehydroxylation, hydrogenation and conjugation with methyl, glucuronic acid, glycine, sulfate, glutathione and cysteine. Moreover, the pharmacokinetic profiles of all the circulating metabolites were investigated. M11 resulting from hydrolyzation, dehydroxylation and hydrogenation was the dominant circulating metabolite after the intragastric administration of isochlorogenic acid A. The results obtained will be useful for further study of elucidating potential bioactive metabolites which can provide better explanation of the pharmacological and/or toxicological effects of this compound.     

Identification of monovinyl tripropionic acid porphyrins and metabolites from faeces of patients with hereditary coproporphyria by high‐performance liquid chromatography/electrospray ionization quadrupole time‐of‐flight tandem mass spectrometry

The original article to which this Erratum refers was published in Rapid Commun. Mass Spectrom. 2004; 18 : 2309–2316     

Identification of metabolites of rupestonic acid in rat urine by liquid chromatography combined with electrospray ionization quadrupole time‐of‐flight tandem mass spectrometry

Rupestonic acid, a potential anti‐influenza agent, is an important and characteristic compound in Artemisia rupestris L., a well‐known traditional Uighur medicine for the treatment of colds. In the present study, high‐performance liquid chromatography combined with electrospray ionization quadrupole time‐of‐flight tandem mass spectrometry was used to detect and identify the metabolites in rat urine after oral administration of rupestonic acid. A total of 10 metabolites were identified or partially characterized. The structure elucidations of the metabolites were performed by comparing the changes in accurate molecular masses and fragment ions with those of the parent compound. The results showed that the main metabolites of rupestonic acid in rat urine were formed by oxidation, hydrogenation and glucuronidation. A metabolism pathway was proposed for the first time based on the characterized structures. This metabolism study can provide essential information for drug discovery, design and clinical application of rupestonic acid. Copyright © 2014 John Wiley & Sons, Ltd.     

Analysis of impurities in streptomycin and dihydrostreptomycin by hydrophilic interaction chromatography/electrospray ionization quadrupole ion trap/time‐of‐flight mass spectrometry

Impurities in streptomycin (STR) and dihydrostreptomycin (DHS) were investigated by hydrophilic interaction chromatography/electrospray ionization quadrupole ion trap/time‐of‐flight mass spectrometry (HILIC/ESI‐QIT/TOFMS). Samples were separated on a fused‐core silica column (100 mm × 2.1 mm i.d., particle size: 2.7 µm) with isocratic elution using 200 mM ammonium formate buffer (pH 4.5) and acetonitrile as mobile phase. Constant neutral loss survey in accurate mass measurement was carried out by QIT/TOFMS. Formulae, chemical structures of impurities in an STR sample were suggested with supporting results on the probable pathways of STR biosynthesis by Streptomyces griseus. Copyright © 2009 John Wiley & Sons, Ltd.     

Systematic screening and characterization of novel bufadienolides from toad skin using ultra‐performance liquid chromatography/electrospray ionization quadrupole time‐of‐flight mass spectrometry

During the discovery process of novel compounds, it is of significant importance to differentiate novel from known compounds in crude extracts before starting the time‐consuming process of purification. Bufadienolides are the main active components of the skin of the toad Bufo bufo gargarizans Cantor (toad skin), an important traditional Chinese medicine. The fragmentation behavior and mass spectra profiles of bufadienolides standards were investigated using ultra‐performance liquid chromatography/electrospray ionization quadrupole time‐of‐flight mass spectrometry (UPLC/ESI‐Q‐TOFMS). Several fragmentation rules were summarized and applied to characterize novel and known bufadienolides in toad skin. Characteristic substituent groups could be identified by both diagnostic ions and their relative abundance. Bufadienolide stereoisomers could be differentiated from positional isomers by comparing fragment abundance profiles. This was used to characterize new stereoisomers for known bufadienolides. A total of 39 bufadienolides were screened out using a systematic method developed in our laboratory. In addition to 19 known bufadienolides, 20 putative novel compounds, including 8 stereoisomers, were characterized. UPLC/Q‐TOFMS was demonstrated to be a powerful tool for the characterization of low‐abundance bufadienolides in complex samples. This study provides guidelines for the targeted isolation of novel bufadienolides from natural products. Copyright © 2010 John Wiley & Sons, Ltd.     

Identification of the major metabolites of quinocetone in swine urine using ultra‐performance liquid chromatography/electrospray ionization quadrupole time‐of‐flight tandem mass spectrometry

Quinocetone (QCT), 3‐methyl‐2‐cinnamoylquinoxaline‐1,4‐dioxide, is a quinoxaline‐N,N‐dioxide used in veterinary medicine as a feed additive. QCT is broadly used in China to promote animal growth, but few studies have been performed to reveal the metabolism of QCT in animals until now. In the present study, the metabolites of QCT in swine urine were investigated using ultra‐performance liquid chromatography/electrospray ionization quadrupole time‐of‐flight mass spectrometry (UPLC/ESI‐QTOF‐MS). Multiple scans of metabolites in MS and MS/MS modes and accurate mass measurements were performed simultaneously through data‐dependent acquisition. Most measured mass errors were less than ±5 mDa for both protonated molecules and product ions using external mass calibration. The structures of metabolites and their product ions were easily and reliably characterized based on the accurate MS² spectra and known structure of QCT. As expected, extensive metabolism was observed in swine urine. Thirty‐one metabolites were identified in swine urine, most of which were reported for the first time. The results reveal that the N‐O group reduction at position 1 and the hydroxylation reaction occurring at the methyl group, the side chain or on the benzene ring are the main metabolic pathways of quinocetone in swine urine. There was abundant production of 1‐desoxyquinocetone and hydroxylation metabolites of 1‐desoxyquinocetone. The proposed metabolic pathway of quinocetone in vivo can be expected to play a key role in food safety evaluations. Copyright © 2010 John Wiley & Sons, Ltd.     

Identification of the metabolites of gigantol in rat urine by ultra‐performance liquid chromatography combined with electrospray ionization quadrupole time‐of‐flight tandem mass spectrometry

Gigantol is a typical bibenzyl compound isolated from Dendrobii Caulis that has been widely used as a medicinal herb in China for the treatment of diabetic cataract, cancer and arteriosclerosis obliterans and as a tonic for stomach nourishment, saliva secretion promotion and fever reduction. However, few studies have been carried out on its in vivo metabolism. In the present study, a rapid and sensitive method based on ultra‐performance liquid chromatography/electrospray ionization quadrupole time‐of‐flight tandem mass spectrometry (UPLC‐Q/TOF‐MS) in positive ion mode was developed and applied to identify the metabolites of gigantol in rat urine after a single oral dose (100 mg/kg). Chromatographic separation was performed on an Acquity UPLC HSS T3 column (100 × 2.1 mm i. d., 1.8 µm) using acetonitrile and 0.1% aqueous formic acid as mobile phases. A total of 11 metabolites were detected and identified as all phase II metabolites. The structures of the metabolites were identified based on the characteristics of their MS, MS² data and chromatographic retention times. The results showed that glucuronidation is the principal metabolic pathway of gigantol in rats. The newly identified metabolites are useful to understand the mechanism of elimination of gigantol and, in turn, its effectiveness and toxicity. As far as we know, this is the first attempt to investigate the metabolic fate of gigantol in vivo. Copyright © 2014 John Wiley & Sons, Ltd.