Identification and structural characterization of in vivo metabolites of ketorolac using liquid chromatography electrospray ionization tandem mass spectrometry (LC/ESI-MS/MS)

In vivo metabolites of ketorolac (KTC) have been identified and characterized by using liquid chromatography positive ion electrospray ionization high resolution tandem mass spectrometry (LC/ESI-HR-MS/MS) in combination with online hydrogen/deuterium exchange (HDX) experiments. To identify in vivo metabolites, blood urine and feces samples were collected after oral administration of KTC to Sprague-Dawley rats. The samples were prepared using an optimized sample preparation approach involving protein precipitation and freeze liquid separation followed by solid-phase extraction and then subjected to LC/HR-MS/MS analysis. A total of 12 metabolites have been identified in urine samples including hydroxy and glucuronide metabolites, which are also observed in plasma samples. In feces, only O-sulfate metabolite and unchanged KTC are observed. The structures of metabolites were elucidated using LC-MS/MS and MS(n) experiments combined with accurate mass measurements. Online HDX experiments have been used to support the structural characterization of drug metabolites. The main phase I metabolites of KTC are hydroxylated and decarbonylated metabolites, which undergo subsequent phase II glucuronidation pathways.     

Porphyrinogen fragmentation profiles by ultra-high-performance liquid chromatography/electrospray ionisation tandem mass spectrometry

An ultra-high-performance liquid chromatography/electrospray ionisation tandem mass spectrometry system is described for the separation and characterisation of uroporphyrinogen, heptacarboxylic acid porphyrinogen, hexacarboxylic acid porphyrinogen, pentacarboxylic acid porphyrinogen and coproporphyrinogen. The separation was carried out on a 100 mm × 2.1 mm Thermo-Hypersil BDS column (2.4 μm average particle size) by gradient elution with a mixture of acetonitrile, methanol and 1 mol/L aqueous ammonium acetate buffer, pH 5.16, as eluent. The fragmentation pattern of each compound was established by collision-induced dissociation tandem mass spectrometry. The most characteristic fragmentation was ring opening at one of the four methylene bridges of the protonated porphyrinogen molecule followed by further cleavages of methylene bridges linking the four pyrrole rings at various points to give product ions with methylenepyrrolenine, methylene-dipyrrolenine and methylene-tripyrrolenine structures.     

Characterization of amino acid-derived betaines by electrospray ionization tandem mass spectrometry

Betaines belong to the naturally occurring osmoprotectants or compatible solutes present in a variety of plants, animals and microorganisms. In recent years, metabolomic techniques have been emerging as a fundamental tool for biologists because the constellation of these molecules and their relative proportions provide with information about the actual biochemical condition of a biological system. Therefore, identification and characterization of biologically important betaines are crucial, especially for metabolomic studies. Most of the natural betaines are derived from amino acids and related homologues. Although, theoretically, all the amino acids can be converted to corresponding betaines by simple methylation of the amine group, only a few of the amino acid-derived betaines were fully characterized in the literature. Here, we report a combined electrospray ionization tandem and high-resolution mass spectrometry study of all the betaines derived from amino acids, including the isomeric betaines. The decomposition pathway of protonated, sodiated and potassiated molecule ions that enable unambiguous characterization of the betaines including the isomeric betaines and overlapping ionic species of different betaines is distinctive.     

Analysis of furanocoumarins from Yemenite Dorstenia species by liquid chromatography/electrospray tandem mass spectrometry

A series of prevailing prenylated furanocoumarins from leaves of Dorstenia gigas and Dorstenia foetida (Moraceae) were investigated by liquid chromatography/electrospray tandem mass spectrometry. The mass spectral behavior of the furanocoumarins under positive ion electrospray conditions is discussed using both an ion trap and a triple quadrupole system. It is demonstrated that both methods represent valuable tools not only for the rapid classification of this type of compounds, but also with respect to their substitution pattern.     

Tandem mass spectrometry of poly(ethylene imine)s by electrospray ionization (ESI) and matrix-assisted laser desorption/ionization (MALDI)

In this contribution, linear poly(ethylene imine) (PEI) polymers, which are of importance in gene delivery, are investigated in detail by using electrospray ionization-quadrupole-time of flight (ESI-Q-TOF) and matrix-assisted laser desorption/ionization-time of flight (MALDI-TOF) mass spectrometry (MS). The analyzed PEIs with different end groups were synthesized using the polymerization of substituted 2-oxazoline via a living cationic ring-opening polymerization (CROP) and a subsequent hydrolysis under acidic conditions. The main goal of this study was to identify linear PEI polymers in a detailed way to gain information about their fragmentation pathways. For this purpose, a detailed characterization of three different linear PEIs was performed by using ESI-Q-TOF and MALDI-TOF MS in combination with collision-induced dissociation (CID) experiments. In ESI-MS as well as MALDI-MS analysis, the obtained spectra of PEIs resulted in fitting mass distributions for the investigated PEIs. In the tandem MS analysis, a 1,2-hydride shift with a charge-remote rearrangement via a four-membered cyclic transition state, as well as charge-induced fragmentation reactions, was proposed as the main fragmentation mechanisms according to the obtained fragmentation products from the protonated parent peaks. In addition, heterolytic and homolytic cleavages were proposed as alternative fragmentation pathways. Moreover, a 1,4-hydrogen elimination was proposed to explain different fragmentation products obtained from the sodiated parent peaks.     

Quantification of glycopeptides by multiple reaction monitoring liquid chromatography/tandem mass spectrometry

Protein glycosylation has a major influence on functions of proteins. Studies have shown that aberrations in glycosylation are indicative of disease conditions. This has prompted major research activities for comparative studies of glycoproteins in biological samples. Multiple reaction monitoring (MRM) is a highly sensitive technique which has been recently explored for quantitative proteomics. In this work, MRM was adopted for quantification of glycopeptides derived from both model glycoproteins and depleted human blood serum using glycan oxonium ions as transitions. The utilization of oxonium ions aids in identifying the different types of glycans bound to peptide backbones. MRM experiments were optimized by evaluating different parameters that have a major influence on quantification of glycopeptides, which include MRM time segments, number of transitions, and normalized collision energies. The results indicate that oxonium ions could be adopted for the characterization and quantification of glycopeptides in general, eliminating the need to select specific transitions for individual precursor ions. Also, the specificity increased with the number of transitions and a more sensitive analysis can be obtained by providing specific time segments. This approach can be applied to comparative and quantitative studies of glycopeptides in biological samples as illustrated for the case of depleted blood serum sample. Copyright ? 2012 John Wiley & Sons, Ltd.     

六聚吡咯/丝组缀合物结构的NMR和 ESI-MS/MS表征

利用片断合成法合成了具有DNA切割能力的六聚吡咯/丝组缀合物, 检测了该化合物的¹H、¹³C NMR 和ESI-MS/ MS 图谱, 确证了该化合物的结构, 通过¹H-¹H COSY, HSQC,HMBC等2D NMR 技术对其¹H 和¹³C NMR 数据进行了归属和解析, 并探讨了其ESI-MS/ MS 质谱裂解规律.     

Determination of the relative ligand-binding strengths in heteroleptic Ir(III) complexes by ESI-Q-TOF tandem mass spectrometry

An electrospray ionization quadrupole time-of-flight mass spectrometer has been utilized to investigate the relative ligand-binding strengths in a series of heteroleptic-charged iridium(III) complexes of the general formula [(C^N)(2) Ir(III) (S-tpy)](PF(6) ) by using variable collision energies. Collision-induced dissociation experiments were performed in order to study the stability of the Ir(III) complexes that are, for instance, suitable phosphors in light-emitting electrochemical cells. The ratio of signal intensities belonging to the fragment and the undissociated complex depends on the collision energy applied for the tandem mass spectra (MS/MS) analysis. By defining the threshold collision energy and the point of complete complex dissociation, it is possible to estimate the relative complex stabilities depending on the nature of the coordinated ligands [i.e. type of cyclometalating ligand (C^N), substituents on the S-shaped terpyridine (S-tpy)]. The collision energy values differed as a function of the coordination sphere of the Ir(III) centers.