Synthesis of N-(3,5-dichlorophenyl)-2-hydroxysuccinimide-O-sulfate: A potential metabolite of the nephrotoxicant N-(3,5-dichlorophenyl)succinimide

The sulfate conjugate 2 of N-(3,5-dichlorophenyl)-2-hydroxysuccinimide, a potential metabolite of the nephrotoxicant N-(3,5-dichlorophenyl)succinimide, is prepared from the 2-hydroxysuccinimide ( 1 ) by the reaction with chlorosulfonic acid in chloroform and ether mixture at ?78°.     

Identification of an N-(hydroxysulfonyl)oxy metabolite using in vitro microorganism screening, high-resolution and tandem electrospray ionization mass spectrometry

Preliminary metabolic profiling of a drug under pre-clinical development revealed the presence of a minor unknown metabolite with a positive ion electrospray ionization (ESI) mass spectrum identical to that of the unchanged compound. Since the low concentration of the compound did not allow any additional experiments, preparative bioconversion using fungi was used to obtain a substantial amount of the molecule. Negative ion ESI-MS and tandem mass spectrometry (MS/MS) in combination with accurate mass measurements obtained on a quadrupole/time-of-flight instrument (Q-TOF) led to the positive identification of a hydroxylamide sulfoconjugated metabolite.     

Characterization of oxysterols by electrospray ionization tandem mass spectrometry after one-step derivatization with dimethylglycine

We report a novel approach to derivatize the primary, secondary, and tertiary hydroxy group(s) of oxysterols with N,N-dimethylglycine (DMG) in the presence of both 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide and 4-(N,N-dimethylamino)pyridine to yield their corresponding mono- or di-DMG esters. Eight oxysterols including 7-oxocholesterol, 5alpha,6alpha- and 5beta,6beta-epoxycholesterols, as well as 7alpha-, 7beta-, 24(S)-, 25-, and 27-hydroxycholesterols, were studied. Electrospray ionization tandem mass spectrometric characterization of these singly or doubly protonated derivatives demonstrates the presence of an informative fragmentation pattern for each oxysterol derivative. Potential dissociation pathways for the production of these unique fragmentation patterns are proposed and discussed. Collectively, these informative and unique fragmentation patterns allow rapid and direct discrimination of the identities of 7alpha-, 7beta-, 24(S)-, 25-, and 27-hydroxycholesterol isomers, as well as 5alpha,6alpha- and 5beta,6beta-epoxycholesterol isomers, thereby potentially providing a foundation for quantitative analysis of oxysterols in biological samples in combination with a chromatographic separation.     

Analysis of alcohols, as dimethylglycine esters, by electrospray ionization tandem mass spectrometry

Dimethylglycine (DMG) esters are new derivatives for the rapid, sensitive and selective analysis of primary and secondary alcohols, in complex mixtures, by electrospray ionization tandem mass spectrometry (ESI-MS/MS). Their development was inspired by the use of the complementary dimethylaminoethyl esters for the trace, rapid analysis of fatty acids. DMG esters are simply prepared by heating a dichloromethane solution of the imidazolide of dimethylglycine, containing triethylamine, and an alcohol. DMG esters of long-chain fatty alcohols, isoprenoidal alcohols and hydroxy-acids are analysed by electrospray ionization tandem mass spectrometry with a precursor ion of m/z 104 scan. Diols, glyceryl esters, glyceryl ethers and some sterols are analysed by a neutral loss of 103 Da scan. Trimethylglycine (TMG) ester iodides, prepared by alkylation of DMG esters with methyl iodide, are more sensitive derivatives for molecules containing secondary alcohol groups, such as cholesterol and gibberellic acid. They are analysed by a precursor ion of m/z 118 scan. DMG or TMG derivatives were shown to be at least comparable and sometimes an order of magnitude more sensitive than N-methylpyridyl ether derivatives for ESI-MS/MS analysis of the different classes of alcohols. Applications of these derivatives for the diagnosis of inherited disorders and the analysis of natural products are presented.     

Determination of lodenosine and its major metabolite in human plasma by liquid chromatography/electrospray ionization tandem mass spectrometry

A sensitive and selective method for the determination of 2'-beta-fluoro-2',3'-dideoxyadenosine (lodenosine, F-ddA), an experimental anti-AIDS drug, and its major metabolite, 2'-beta-fluoro-2',3'-dideoxyinosine (F-ddI), in human plasma was developed and validated. The procedure employs two internal standards and a simple ultrafiltration step followed by chromatography on a Betasil C(18) minibore column. An in-line valve is used to remove salts before reaching the ion source. Detection is by electrospray ionization tandem mass spectrometry with selected reaction monitoring. The method has a limit of quantitation of 4 ng ml(-1) (16 nM) for F-ddA and 8 ng ml(-1) (32 nM) for F-ddI with a linear range up to 2000 ng ml(-1) (7.9 microM) for each. Predicted concentrations from a three-day validation study were within 5% of the nominal values for F-ddA and 16% for F-ddI. Intra- and inter-assay precision, as measured by relative standard deviation, was 13% or better for both compounds. To achieve good reproducibility, many variables related to the electrospray ionization were optimized for both precision and sensitivity. The method was successfully employed to analyze samples and evaluate plasma pharmacokinetics from a Phase I clinical trial.     

Determination of micelle mass by electrospray ionization mass spectrometry

By electrospray ionization (ESI) mass spectrometry, micelle solutions of sodium cholate were investigated in detail in the presence and absence of ethanol. The average aggregation number could be evaluated from the spectra acquired under conditions where soft collisions adequate to measure the micelle solution were induced, and the value agreed well with that obtained previously by other methods. From the dependence on ethanol content, it was also found that the average aggregation number in aqueous solution without organic solvent could be reliably estimated. The ESI method proved to be a useful tool for determining the micelle mass in the original aqueous phase.     

Characterization of ageing products of ester-based synthetic lubricants by liquid chromatography with electrospray ionization mass spectrometry and by electrospray ionization (tandem) mass spectrometry

Ageing products of a commercial jet engine oil based on pentaerythritol tetraesters which were formed upon operation in an aviation turbine were detected by electrospray ionization mass spectrometry (ESI-MS) and characterized by LC-ESI-MS. The fatty acid composition of these ageing products was investigated by ESI-MS-MS analysis. The ammonium adducts of the newly formed pentaerythritol tetraester degradation products were found to be suitable parent ions for further structure elucidation work. ESI-MS, LC-ESI-MS and ESI-MS-MS proved to be versatile tools to study the chemical composition (distribution of homologues) as well as the mechanism of ageing of ester based lubricants on a molecular level. Due to its high sensitivity, ESI-MS can also be used to characterize and identify trace levels of ester-based lubricants.     

Analysis of amino acids as formamidene butyl esters by electrospray ionization tandem mass spectrometry.

Amino acid formamidene butyl esters are optimally prepared by heating amino acids with dimethylformamide dimethylacetal (DMF-DMA) for 2 minutes at 65 degrees C and then with n-butanol/hydrogen chloride for 15 minutes at 65 degrees C. The formamidene butyl esters of simple alpha-amino acids and beta-amino acids afford between 1.1 and 20 times the signal intensity of the corresponding butyl esters during electrospray ionization tandem mass spectral analysis. Complex alpha-amino acids, such as ornithine, arginine and citrulline, and gamma-amino acids are better analyzed as butyl esters. Secondary alpha-amino acids, such as proline and sarcosine, give a mixture of two iminium salts with the DMF-DMA derivatization method. A derivative incorporating two molecules of the amino acid predominates at higher derivatization temperatures. Contrary to a previous report, N-formylamino acids were not detected. The presence of secondary amino acids in amino acid mixtures, derivatized as formamidene butyl esters, affords derivatives that incorporate two different amino acids. The new formamidene butylation method is unlikely to replace the butylation procedure used by neonatal blood spot screening programs for amino acid disorders, since a much poorer response was obtained with formamidene butyl esters of arginine and citrulline, important in the diagnosis of arginase deficiency and citrullinaemia.     

Determination of aranidipine and its active metabolite in human plasma by liquid chromatography/negative electrospray ionization tandem mass spectrometry

A simple, sensitive and rapid high-performance liquid chromatography/negative electrospray ionization tandem mass spectrometry method was developed and validated for the assay of aranidipine (AR) and its active metabolite (AR-M) in human plasma. Following a liquid-liquid extraction, the analytes were separated using an isocratic mobile phase on a reversed-phase column and analyzed by mass spectrometry in the multiple reaction monitoring mode using the respective [M-H]- ions, m/z 387.0 --> 164.0 for AR, m/z 389.1 --> 208.1 for AR-M and m/z 359.0 --> 121.8 for the internal standard. The assay exhibited a linear dynamic range of 0.02-10 ng x mL(-1) for AR and 0.2-100 ng x mL(-1) for AR-M in human plasma. The limits of quantitation were 0.02 ng x mL(-1) for AR and 0.2 ng x mL(-1) for AR-M. Acceptable precision and accuracy were obtained for concentrations over the standard curve range. A run time of 2.8 min for each sample exhibited its high-throughout analysis ability. The validated method can be applied to analyze human plasma samples for pharmacokinetic studies.     

A novel hydrogen migration of dialkylphosphonic acid esters using electrospray ionization tandem mass spectrometry

In this paper, attention is focused on analysis of the fragmentation of α-hydroxy-β-amino phosphonate esters designed as inhibitors of protein kinase A. An interesting proton migration mechanism in the cleavage of the P-C bond is investigated by electrospray ionization tandem mass spectrometry. A possible rearrangement mechanism is proposed and verified by high-resolution mass spectra using isotope deuterium/hydrogen-exchange technology and additionally checked by detailed DFT calculation based on Gaussian software. The result clearly indicates that this mechanism proceeds by a five-membered ring concerted transition state with activation energy 11.3 kcal mol(-1) for the compound 3f. The overall reaction is endothermic with an energy 13.2 kcal mol(-1). The effect of different substituents and different metal ions for rearrangement of these esters is studied by experiment and theory. It is concluded that this rearrangement process is energetically unfavorable and hence only occurs in the mass spectrometer.     

高效液相色谱-串联质谱法测定纺织品中的致癌芳香胺

建立了高效液相色谱-串联质谱法(LC/MS/MS)测定纺织品中致癌芳香胺的检测方法.纺织品中的偶氮染料在柠檬酸缓冲液中用连二亚硫酸钠还原为芳香胺,用硅藻土提取还原液中的芳香胺,用乙醚洗脱,浓缩至近干后用甲醇定容.使用液相色谱-串联质谱进行测定,色谱柱为XTerra MS C18柱,流动相为甲醇和0.025 mol/L乙...     

Determination of binding sites in carboplatin-bound cytochrome c using electrospray ionization mass spectrometry and tandem mass spectrometry

Interaction of carboplatin with cytochrome c (Cyt. c) has been investigated by electrospray ionization mass spectrometry (ESI-MS) and tandem mass spectrometry (MS/MS). ESI-MS studies revealed that the ring-opened adducts of carboplatin with Cyt. c were formed in the stoichiometric ratio of 1:1 and 2:1 at pH 5.0 and 37 degrees C and in the stoichiometric ratio of 1:1 only at pH 7.0 and 37 degrees C. It was also found that Cyt. c could be cleaved by carboplatin at pH 2.5 and 50 degrees C. The cleaved fragments of Cyt. c were determined by ESI-MS and MS/MS analysis to be Glu66 approximately Met80, Ac-Gly01 approximately Met65, Glu66 approximately Glu104, Ac-Gly01 approximately Met80 and Ile81 approximately Glu104. The carboplatin prefers to anchor to Met65 first, then to Met80. To further confirm the binding site of Met, AcMet-Gly was used as the model molecule to investigate its interaction with carboplatin and its hydrolysis reaction. On the basis of species detected during the reaction monitored by ESI-MS, a possible pathway of the cleavage reaction was proposed.     

Determination of flomoxef in human plasma by liquid chromatography/electrospray ionization tandem mass spectrometry

A specific, sensitive, rapid and reproducible method for the determination of flomoxef in human plasma using high‐performance liquid chromatography–tandem mass spectrometry was developed and validated. Flomoxef was detected using an electrospay ionization method operated in negative‐ion mode. Chromatographic separation was performed in gradient elution mode on a Luna® C₁₈(2) column (3 μm , 20 × 4.0 mm) at a flow rate of 1 mL/min and runtime 3.5 min. The mobile phase consisted of acetonitrile and water containing 0.1% formic acid as additive. Extraction of flomoxef from plasma and precipitation of plasma proteins was performed with acetonitrile with an absolute recovery of 86.4 ± 1.6%. The calibration curve was linear with a correlation coefficient of 0.999 over the concentration range 10–5000 ng/mL and the lower limit of quantification was 10 ng/mL. The intra‐ and inter‐day precisions were <11.8%, while the accuracy ranged from 99.6 to 109.0%. A stability study of flomoxef revealed that it could be successfully analyzed at 4ºС over 24 h, but it was unstable in solutions at room temperature during short‐term storage (4 h) and several freeze–thaw cycles. Copyright © 2013 John Wiley & Sons, Ltd.     

Determination of azide in gastric fluid and urine by flow-injection electrospray ionization tandem mass spectrometry

A rapid method was developed to identify and quantify the azide ion (N(3)(-)) in gastric fluid and urine. N(3)(-) in diluted biological fluids was reacted with NaAuCl(4) to produce Au(N(3))(2)(-), which was extracted with octanol. Five microliters of the extract were flow-injected into an electrospray ionization tandem mass spectrometric instrument. Quantification of N(3)(-) was performed by selected reaction monitoring of the product ion Au(N)(N(3))(-) at m/z 253, which was derived from the precursor ion Au(N(3))(2)(-) at m/z 281, using 50 μL of aqueous solution within 10 min. This method was found to be linear up to 10(-5) M, to have a limit of quantification of 10(-7) M, a limit of detection of 3.0?×?10(-8) M, and a coefficient of variation of ≦10% at 10(-7) M. In the case of urine, 50 μL of urine were spiked with N(3)(-), this was diluted 10-fold and passed through 1 mL of a resin, and finally diluted to 100-fold of the original. This method was linear up to 10(-3) M, had a limit of quantification of 10(-5) M, a limit of detection of 3.0?×?10(-6) M, and coefficient of variation of ≦8.8% for an original urine concentration of 10(-5) M. The practical applicability of this method was checked by diluting 1 μL of a suspected suicide victim's gastric fluid 20,000-fold and 1 μL of the victim's urine 5,000-fold and then measuring the N(3)(-) levels. These levels were found to be (7.5?±?1.0)?×?10(-2) M and (3.2?±?0.4)?×?10(-3) M, respectively.     

Structural determination of sphingomyelin by tandem mass spectrometry with electrospray ionization

Alkaline metal adduct ions of sphingomyelin were formed by electrospray ionization in positive ion mode. Under low energy collisionally activated dissociation (CAD), the product ion spectra yield abundant fragment ions representative of both long chain base and fatty acid which permit unequivocal determination of the structure. Tandem spectra obtained by constant neutral loss scanning permit identification of sphingomyelin class and specific long chain base subclass in the mixture. The fragmentation pathways under CAD were proposed, and were further confirmed by source CAD tandem mass spectrometry. The total analysis of sphingomyelin mixtures from bovine brain, bovine erythrocytes, and chicken egg yolk is also presented.