Characterization of polyprenylated xanthones in Garcinia xipshuanbannaensis using liquid chromatography coupled with electrospray ionization quadrupole time-of-flight tandem mass spectrometry

A reliable and sensitive on-line high-performance liquid chromatography (HPLC) coupled with electrospray quadrupole time-of-flight tandem mass spectrometry (ESI-QTOF-MS/MS/MS) method has been optimized and established for the analysis of polyprenylated xanthones in the plant Garcinia xipshuanbannaensis. Collision induced MS/MS techniques were used to fragment the precursor molecular ions and MS/MS/MS techniques based on cone voltage fragmentation were used to further break down the resulting product ions sequentially. It was found that Retro-Diels-Alder rearrangement occurred from the xanthone skeleton in the MS/MS/MS process and produced characteristic fragment ions, which are useful for differentiating some positional isomers containing the prenyl unit on the A ring or B ring. Complementary fragmentation information, for instance the successive loss of prenyl residues, is also valuable for the identification of this class of xanthones. Under optimized HPLC-MS/MS/MS method, a total of 15 prenylated xanthones could be separated within 10min. This method also provided information about the molecular formula of a precursor molecule and its fragments, which could be used for dereplication of known or likely new prenylated xanthones in Garcinia plants before the purification and structural elucidation process.     

山竹果皮中两种杂氧蒽酮化学成分的分析研究

建立了山竹果皮中杂氧蒽酮类化合物的快速提取、分离、鉴定方法。以无水乙醇为夹带剂,应用超临界萃取技术对山竹果皮中的杂氧蒽酮类活性化合物进行提取,快速制备色谱装置Isolera One对粗提物进行分离,得到2种杂氧蒽酮化合物,经质谱鉴定其为α-倒捻子素(α-Mangostin)和Gartanin,两者经高效液相色谱检测纯度均不低于90%,并辅以电喷雾多级串联质谱对两种化合物的碎裂规律进行了研究。     

Electrospray tandem mass spectrometry of lexitropsins

Several compounds, representative of the class of lexitropsins, were analyzed by electrospray tandem mass spectrometry. The study of the fragmentations of the protonated molecular species ([M + H](+)) and of selected fragment ions allowed proposals for the main fragmentation pathways of compounds of this type. The interpretation of the fragmentation pathways of these compounds was complicated because of intramolecular hydrogen migration. In order to better understand the fragmentation pathways, the MS/MS/MS spectra of several compounds, and the MS/MS and MS/MS/MS spectra of the deuterated compounds, were obtained. Accurate mass measurements helped elucidate the structures of smaller fragment ions. Low-energy collision-induced decomposition (CID) tandem mass spectrometry of lexitropsins with electrospray ionization has proven to be a good method for the structural characterization and identification of this class of compounds. Main fragmentation pathways occur by cleavage of the peptide bond followed by the elimination of the substituted pyrrole ring, and their elucidation will facilitate structural characterization of new lexitropsins.     

Characterization of novel nucleoside analogs by electrospray ionization mass spectra

In this paper, we synthesized a novel nucleoside analog by coupling thymine with dimethyl dicarboxylate biphenyl (DDB). The structure of the target compound was determined using 1H nuclear magnetic resonance (NMR) and electrospray ionization tandem mass spectrometry (ESI-MS/MS). The fragmentation pathways were studied in details through ESI-MS/MS. By comparing with unsubstituted nucleosides, such as AZT, MCI, d4T and DDI, it was found that the nucleoside analog coupled with DDB would not yield the daughter ions corresponding to the fragments of the nucleoside base and arabinofuranose analogs, but would lose a neutral molecule HF and DDB easily. However, the unsubstituted nucleosides could lightly yield the fragment ions of the nucleoside base and sugar ring. Hence, electrospray ionization mass spectrometry combined with tandem mass spectrometry (MS/MS) provides a convenient method to recognize the substituted and unsubstituted nucleosides.     

ESI-QqTOF-MS/MS and APCI-IT-MS/MS analysis of steroid saponins from the rhizomes of Dioscorea panthaica

Using high-resolution quadrupole time-of-flight mass spectrometry along with an electrospray ionization source (ESI-QqTOF-MS), accurate molecular weights of 13 steroid saponins extracted from the rhizomes of Dioscorea panthaica were acquired and the corresponding molecular formulae obtained. In order to elucidate the fragmentation pathways of steroid saponins in D. panthaica, 10 authentic samples were investigated using ESI-QqTOF-MS/MS. In addition, atmospheric pressure chemical ionization mass spectrometry combined with ion trap tandem mass spectrometry (APCI-IT-MS/MS) was used to analyze the structures of 13 steroid saponins in D. panthaica. Through the analysis of their tandem mass data, diagnostic fragment ions of the spirostanol and furostanol steroid saponins in D. panthaica were detected as m/z 271.2056 and 253.1951. In addition, four pairs of isomers were detected and the possible structures of four unknown steroid saponins in D. panthaica speculated. ESI-TOF and APCI-MS(n) have proved to be effective tools for research on fragmentation mechanism of steroid saponins and the rapid determination of native steroid saponins in extract mixture, thereby avoiding tedious derivation and separation steps.     

Synthesis and electrospray ionization mass spectra of AZT/d4T boranophosphates

New anti-HIV prodrugs, conjugates of AZT and d4T with boranophosphates, were prepared by the H-phosphonate method. Their structures were determined by negative ion electrospray ionization mass spectrometry (ESI-MS) in conjunction with tandem mass spectrometry (MS/MS). The fragmentation pathways were investigated, and most of the fragment ions contained the boranophosphate or phosphinate group.     

Electrospray ionization mass spectrometry of AZT H-phosphonates conjugated with steroids

AZT H-phosphonates conjugated with steroids were synthesized and determined by positive and negative ion electrospray ionization mass spectrometry (ESI-MS) in conjunction with tandem mass spectrometry (MS/MS). The fragmentation pathways were investigated in detail. There are very different characteristic fragment ions in the positive and negative ion MS/MS spectra. The azide group of compounds 6a and 6b underwent either elimination of HN(3) or rearrangement to an amine in both positive and negative ion mass spectrometry.     

Characteristic fragmentation behavior of phosphoamino acid conjugates with 3'-azido-3'-deoxythymidine by electrospray ionization tandem mass spectrometry

The conjugates of phosphoamino acids with 3'-azido-3'-deoxythymidine were synthesized and their structures were determined by various spectral methods. In positive and negative ion electrospray mass spectrometry (ESI-MS), the fragmentation pathways were investigated in conjunction with tandem mass spectrometry (MS/MS). The results showed that there were very different characteristic fragment ions in the positive ion MS/MS spectra and the negative ion MS/MS spectra.     

Electrospray ionization mass spectra of amino acid phosphoramidates of adenosine

Amino acid phosphoramidates of adenosine were synthesized and determined by positive and negative ion electrospray ionization mass spectrometry (ESI-MS) in conjunction with tandem mass spectrometry (MS/MS). The fragmentation pathways were investigated. In the positive ion mass spectra abundant characteristic fragment ions appeared, and many complementary ions were found. In the negative ion mass spectra only a few fragment ions were observed, and most of them contained phosphoryl groups. The results show that ESI-MS is a useful tool for structural determination of amino acid phosphoramidates of nucleosides.     

Structural analysis of oligosaccharides by a combination of electrospray mass spectrometry and bromine isotope tagging of reducing-end sugars with 2-amino-5-bromopyridine

Model reducing-end oligosaccharides were successfully labeled by a brominated aromatic amine reagent, 2-amino-5-bromopyridine (ABP), through reductive amination. Using either a combination of liquid chromatography/electrospray ionization mass spectrometry (LC/ESI-MS) with in-source fragmentation or liquid chromatography/electrospray ionization tandem mass spectrometry (LC/ESI-MS/MS), sequence information corresponding to the model oligosaccharides was revealed with little ambiguity via the diagnostic unique twin peaks arising from the bromine isotopes, for both the molecular ions of the derivatized oligosaccharides and their fragments. No fragment ions arising from loss of the bromine atom were observed.     

Improved high-performance liquid chromatographic method for simultaneous determination of 12 cytotoxic caged xanthones in gamboges, a potential anticancer resin from Garcinia hanburyi

The potential anti-tumor activity of gamboges, a herbal medicine derived from Garcinia hanburyi, has increasingly gained the interest of scientist worldwide. The major components of gamboges are cytotoxic caged xanthones. In the present study, an improved HPLC method was developed to simultaneously quantify 12 caged xanthones, including three pairs of epimers and four pairs of trans-cis isomers, i.e. forbesione, isomorellic acid, morellic acid, R-30-hydroxygambogic acid, S-30-hydroxygambogic acid, isogambogenic acid, gambogenic acid, gambogellic acid, R-isogambogic acid, S-isogambogic acid, R-gambogic acid and S-gambogic acid. This method was validated to be sensitive, precise and accurate with limits of detection of 0.03-0.08 microg/mL, overall intra-day and inter-day variations less than 7.9% and overall recovery over 93.2%. The correlation coefficients (r(2)) of the calibration curves were higher than 0.995 for all analytes. The newly established method was successfully applied to reveal the difference in the chemical profiles and contents of these analytes in gamboges from different origins. It can be concluded that this method was not only an effective quality control method to ensure the safety and efficacy consistency of gamboges, but also a useful tool for screening and determining more potent cytotoxic xanthones with potential anticancer activity.     

Synthesis and Electrospray Ionization Mass Spectra of N-（1,3, 2-Dioxaphosphorinan-2-ylmethyl）thiophosphoramidates

N-（1,3,2-Dioxaphosphorinan-2-ylmethyl）thiophosphoramidates were synthesized and determined by NMR spectra and positive ion electrospray ionization mass spectrometry （ESI-MS） in conjunction with tandem mass spectrometry （MS/MS）. The fragmentation pathways were investigated. The results show that these characteristic ions in ESI mass spectra are useful in the structural determination of N-（1,3,2-dioxaphosphorinan-2-ylmethyl）- thiophosphoramidates.     

The characterisation of selected antidepressant drugs using electrospray ionisation with ion trap mass spectrometry and with quadrupole time-of-flight mass spectrometry and their determination by high-performance liquid chromatography/electrospray ionisation tandem mass spectrometry

The electrospray ionisation ion trap tandem mass spectrometry (ESI-MS(n)) of selected antidepressant drugs, i.e., citalopram, fluoxetine, mirtazapine, paroxetine, sertraline, and venlafaxine, has been investigated. Sequential product ion fragmentation experiments (MS(n)) have been performed in order to elucidate the degradation pathways for the [M+H](+) ions and their predominant product ions. These MS(n) experiments show certain characteristic fragmentations in that functional groups are generally cleaved from the ring systems as molecules such as H(2)O, amines and phenols. When an aromatic entity is present in a drug molecule together with a nitrogen-containing saturated ring structure as with mirtazapine, fragmentation initially occurs at the latter ring with the former being predictably resistant to fragmentation. Also, when an amine-containing drug molecule such as fluoxetine also contains a functional group, which liberates a phenol with a significantly lower DeltaH(f) (0) value than that of the corresponding amine, the phenol is preferentially liberated. The structures of product ions proposed for ESI-MS(n) can be supported by electrospray ionisation quadrupole-time-of-flight tandem mass spectrometry (ESI-QToF-MS/MS). These molecules can be identified and determined in mixtures at low ng/mL concentrations by the application of high-performance liquid chromatography/electrospray ionisation tandem mass spectrometry (HPLC/ESI-MS(2)), which can also be used for their analysis in hair samples.     

Analysis of curcuminoids by positive and negative electrospray ionization and tandem mass spectrometry

The curcuminoids are a group of diarylheptanoid molecules that possess important pharmacological activities, particularly acting as anti-inflammatory agents. The main purpose of this study was to investigate the fragmentation behavior of the three major curcuminoids in ion trap liquid chromatography/tandem mass spectrometry (LC/MS/MS). Both positive and negative mode electrospray ionization in tandem and multidimensional MS(n) experiments in quadrupole ion trap instruments and high-resolution and accurate mass MS and sustained off-resonance irradiation (SORI) MS/MS experiments in a Fourier transform ion cyclotron resonance (FTICR) mass spectrometer were used to elucidate the main fragmentation channels of these compounds. These experiments yielded essentially the same fragmentation results in both ion trap and ICR instruments for all three curcuminoids and for their phenolic monoacetates. Major and diagnostic fragment ions were identified and their origins are proposed.     

Differentiation of three pairs of aconite alkaloid isomers from Aconitum nagarum var. lasiandrum by electrospray ionization tandem mass spectrometry

Three pairs of isomers of aconite alkaloids from Aconitum nagarum var. lasiandrum have been investigated by electrospray ionization mass spectrometry (ESI-MS) and tandem mass spectrometry (MS/MS) employing ion-trap and quadrupole time-of-flight mass spectrometers in positive mode. Based on the differences of their fragmentation pathways and special fragment ions, three pairs of isomers of aconite alkaloids were differentiated. In addition, fragmentation laws of some veatchines and the discrepancy of fragmentation mechanisms between veatchine-type and aconitine-type alkaloid were also concluded. In the case of veatchines, a radical would be formed by homolysis of C18--C4 or C18--H bonds, followed by elimination of a series of C(2)H(2) and C(2)H(4). Moreover, the retro-Diels-Alder (RDA) reaction occurred in the E-ring and double-electron transfer triggered by the positive charge on C1 led to the formation of diagnostic ions at m/z 216. With regard to aconitine-type alkaloids, the N-substituent is not eliminated easily. Although there is no carbonyl group on some aconitine-type alkaloids, with hydroxyl and methoxyl on C15 and C16 respectively, CO was readily eliminated through tautomerization.     

Energy-dependent collision-induced dissociation study of buprenorphine and its synthetic precursors

The collision-induced dissociation (CID) of protonated buprenorphine ([M+H](+) ) and four related compounds was studied by electrospray quadrupole/time-of-flight mass spectrometry (ESI-QTOF MS). The fragmentation pathways were investigated by using energy-dependent CID and pseudo-MS(3) (in-source CID combined with tandem mass spectrometry (MS/MS)) methods. The first steps of the fragmentation are the parallel losses of the substituents from the non-aromatic ring moieties. Depending on the applied collision energies, a large number of further fragment ions arising from the cross-ring cleavages of the core-ring structure were observed. Based on the experimental results, a generalized fragmentation scheme was developed for the five buprenorphine derivatives highlighting the differences for the alternatively substituted compounds. The collision-energy-dependent fragmentation profile of buprenorphine is visualized in a two-dimensional plot to aid its fingerprint identification.     

Investigation of uremic analytes in hemodialysate and their structural elucidation from accurate mass maps generated by a multi‐dimensional liquid chromatography/mass spectrometry approach

Historically, structural elucidation of unknown analytes by mass spectrometry alone has involved tandem mass spectrometry experiments using electron ionization. Most target molecules for bioanalysis in the metabolome are unsuitable for detection by this previous methodology. Recent publications have used high‐resolution accurate mass analysis using an LTQ‐Orbitrap with the more modern approach of electrospray ionization to identify new metabolites of known metabolic pathways. We have investigated the use of this methodology to build accurate mass fragmentation maps for the structural elucidation of unknown compounds. This has included the development and validation of a novel multi‐dimensional LC/MS/MS methodology to identify known uremic analytes in a clinical hemodialysate sample. Good inter‐ and intra‐day reproducibility of both chromatographic stages with a high degree of mass accuracy and precision was achieved with the multi‐dimensional liquid chromatography/tandem mass spectrometry (LC/MS/MS) system. Fragmentation maps were generated most successfully using collision‐induced dissociation (CID) as, unlike high‐energy CID (HCD), ions formed by this technique could be fragmented further. Structural elucidation is more challenging for large analytes >270 Da and distinguishing between isomers where their initial fragmentation pattern is insufficiently different. For small molecules (<200 Da), where fragmentation data may be obtained without loss of signal intensity, complete structures can be proposed from just the accurate mass fragmentation data. This methodology has led to the discovery of a selection of known uremic analytes and two completely novel moieties with chemical structural assignments made. Copyright © 2009 John Wiley & Sons, Ltd.     

Rapid structural characterization of isomeric benzo[c]phenanthridine alkaloids from the roots of Zanthoxylum nitidium by liquid chromatography combined with electrospray ionization tandem mass spectrometry

The fragmentation mechanism of six alkaloids, namely: dihydronitidine, dihydrochelerythrine, 8-acetonyldihydronitidine, 8-acetonyldrochelerythrine, nitidine and 1,3-bis(8-dihydronitidinyl)acetone, was investigated by electrospray ionization multi-stage tandem mass spectrometry (ESI-MSn). Tandem mass spectrometry experiments indicated that different substitution sites of the methoxyl groups at C-9 and C-10 or at C-10 and C-11 determined the different abundances of the MS2 fragmentation ions using the same collision energy. According to the different abundances of MS2 product ions, positional isomeric benzo[c]phenanthridine alkaloids can be differentiated. Moreover, ten constituents in the crude alkaloidol extract from the roots of Zanthoxylum nitidium were rapidly identified by high-performance liquid chromatography coupled with tandem mass spectrometry (HPLC/MSn), through comparing the retention times and ESI-MSn spectra with the authentic standards. This work demonstrates that not only the characteristic fragments but also the characteristic abundances of the fragment ions can be used for detailed structural characterization.     

Stereochemical differentiation of C‐7 hydroxyltaxane isomers by electrospray ionization mass spectrometry

In this study, different electrospray ionization mass spectrometric (ESI‐MS) methods were utilized to analyze several pairs of taxane stereoisomers including paclitaxel and 7‐epi‐paclitaxel. Both ESI‐MS and tandem mass spectrometry (MS/MS) techniques provided stereochemically dependent mass spectra in negative‐ion mode, and all studied stereoisomers could be easily distinguished based on their characteristic ions or distinct fragmentation patterns. MS/MS experiments for several taxane analogues at various collision energies were performed to elucidate potential dissociation pathways. The gas‐phase deprotonation potentials were also calculated to estimate the most thermodynamically favorable deprotonation site using DFT B3LYP/6‐31G(d). The results of the theoretical studies agreed well with the fragmentation patterns of paclitaxel and 7‐epi‐paclitaxel observed from MS/MS experiments. In addition, it was found that liquid chromatography (LC)/ESI‐MS was a useful and sensitive technique for assignment of C‐7 taxane stereoisomers from realistic samples. Copyright © 2009 John Wiley & Sons, Ltd.     

合成多肽的电喷雾质谱研究

利用电喷雾多极串联质谱对3种合成多肽进行了系统的鉴定和分析研究。首先通过全扫描模式测定了其分子量，然后选择[M H]^ 或[M 2H]^2 离子通过串联质谱(MS／MS)得到碎片离子，采用y离子和b离子互补的方法测定了多肽序列。利用文献数据对这种方法进行了验证，实验结果表明，该方法简便、快速、实用。