Tandem Mass Spectrometric Study Research Articles

Electrospray Ionization Tandem Mass Spectrometric Study of Selected Phosphine-Based Ligands for Catalytically Active Organometallics.

Selected organometallic compounds are nowadays extensively used as highly efficient catalysts in organic synthesis. A great variety of different ligand systems exists, of which phosphine-based ligands are a significant subgroup. While mass spectrometry, predominantly electrospray ionization mass spectrometry (ESI-MS), is a standard analytical technique for the identification of new ligands and their metal complexes, there is little information on the behavior of phosphine-based ligands/molecules by electrospray ionization collision-induced dissociation tandem mass spectrometry (ESI-CID-MS/MS) at low collision energies (<100 eV) in the literature. Here, we report a study on the identification of typical product ions occurring in tandem mass spectra of selected phosphine-based ligand systems by ESI-CID-MS/MS. The influence on the fragmentation behavior of different backbones (pyridine, benzene, triazine) as well as different spacer groups (amine, methylamine, methylene), which are directly linked to the phosphine moiety, is investigated by tandem mass spectrometry. In addition, possible fragmentation pathways are elaborated based on the assigned masses in the tandem mass spectra with high-resolution accurate mass determination. This knowledge may be particularly useful in the future for the elucidation of fragmentation pathways for coordination compounds by MS/MS, where the studied compounds serve as building blocks.

Separation, identification and characterization of stress degradation products of bortezomib using HPLC and LC-MS.

Bortezomib (BT) is a reversible inhibitor of proteasome which is used in the treatment of hematological cancers. To study the degradation behavior, BT was subjected to acidic, basic, neutral, photolytic, oxidative and thermal degradation conditions as per ICH guideline Q1A (R2). A gradient HPLC method has been developed for separating all the degradation products formed under various degradation conditions on Waters XBridge C18 column (150 mm × 4.6 mm × 3.5 µm) using the mobile phase composed of ammonium formate and acetonitrile. A total of six degradation products were formed in various stress conditions and these were separated identified, and characterized using high performance liquid chromatography in combination with electrospray ionization tandem mass spectrometric studies.

Study on complexation of palladium with thiourea-based ligands and its determination in simulated high-level liquid waste using solid phase extraction-electrospray mass spectrometry

ESI–MS was used to investigate the complexation of Pd(II) with thiourea based ligands such as thiourea (TU), N-benzoylthiourea (BTU), N,N-diethyl N′-benzoylthiourea (DEBT) in gas phase. Experimental parameters like quadrupole ion energy and collision energy were optimized for acquiring the spectra of Pd complexes with TU, BTU, and DEBT. Tandem mass spectrometric (ms/ms) studies were carried out to investigate the relative stability of various Pd species in the gas phase. Studies showed that DEBT forms a predominately ML2 type complex and hence is a better chelating agent for ESI–MS determination of Pd compared to TU and BTU. Based on these studies, an automated solid phase extraction method was developed for separation of Pd using DEBT, followed by its determination using ESI–MS. Developed method was used for determination of Pd in simulated high level liquid waste.

Characterization of acetylated histidine b1-ion structure: A competition between oxazolone and side chain imidazole moiety

The detection of post-translational modifications of proteins is an important comprehensive research area. Over the years, proteomic studies involving protein acetylation have attracted a great deal of attention. In the present study, we have focussed on the acetylation of histidine and the intrinsic stability of b1-ion of oxazolone ring and/or with side chain imidazole bicyclic product. The formation of oxazolone structure may occur when an amino moiety undergoes acetylation reaction and when it is present in the vicinity of the side chain imidazole moiety. Tryptic peptides generated from the proteins of Acenitobacter radioresistens MMC5-containing N-terminal histidine were explored in a standard proteomic workflow. Formation of [Formula: see text] ion with an oxazolone ring in these peptides has been supported by a tandem mass spectrometric study of a synthetic peptide and density functional theory calculations. The results obtained from this study have implications in understanding the fragmentation of the peptides generated in the proteomic workflows.

Charge-induced geometrical reorganization of DNA oligonucleotides studied by tandem mass spectrometry and ion mobility.

Mass spectrometry is applied as a tool for the elucidation of molecular structures. This premises that gas-phase structures reflect the original geometry of the analytes, while it requires a thorough understanding and investigation of the forces controlling and affecting the gas-phase structures. However, only little is known about conformational changes of oligonucleotides in the gas phase. In this study, a series of multiply charged DNA oligonucleotides (n = 15-40) has been subjected to a comprehensive tandem mass spectrometric study to unravel transitions between different ionic gas-phase structures. The nucleobase sequence and the chain length were varied to gain insights into their influence on the geometrical oligonucleotide organization. Altogether, 23 oligonucleotides were analyzed using collision-induced fragmentation. All sequences showed comparable correlation regarding the characteristic collision energy. This value that is also a measure for stability, strongly correlates with the net charge density of the precursor ions. With decreasing charge of the oligonucleotides, an increase in the fragmentation energy was observed. At a distinct charge density, a deviation from linearity was observed for all studied species, indicating a structural reorganization. To corroborate the proposed geometrical change, collisional cross-sections of the oligonucleotides at different charge states were determined using ion mobility-mass spectrometry. The results clearly indicate that an increase in charge density and thus Coulomb repulsion results in the transition from a folded, compact form to elongated structures of the precursor ions. Our data show this structural transition to depend mainly on the charge density, whereas sequence and size do not have an influence.

A systematic tandem mass spectrometric study of anion attachment for improved detection and acidity evaluation of nitrogen-rich energetic compounds.

The development of rapid, efficient, and reliable detection methods for the characterization of energetic compounds is of high importance to security forces concerned with terrorist threats. With a mass spectrometric approach, characteristic ions can be produced by attaching anions to analyte molecules in the negative ion mode of electrospray ionization mass spectrometry (ESI-MS). Under optimized conditions, formed anionic adducts can be detected with higher sensitivities as compared with the deprotonated molecules. Fundamental aspects pertaining to the formation of anionic adducts of 1,3,5,7-tetranitro-1,3,5,7-tetrazocane (HMX), 1,3,5-trinitro-1,3,5-triazinane (RDX), pentaerythritol tetranitrate (PETN), nitroglycerin (NG), and 1,3,5-trinitroso-1,3,5-triazinane energetic (R-salt) compounds using various anions have been systematically studied by ESI-MS and ESI tandem mass spectrometry (collision-induced dissociation) experiments. Bracketing method results show that the gas-phase acidities of PETN, RDX, and HMX fall between those of HF and acetic acid. Moreover, PETN and RDX are each less acidic than HMX in the gas phase. Nitroglycerin was found to be the most acidic among the nitrogen-rich explosives studied. The ensemble of bracketing results allows the construction of the following ranking of gas-phase acidities: PETN (1530-1458kJ/mol)>RDX (approximately 1458kJ/mol)>HMX (approximately 1433kJ/mol)>nitroglycerin (1427-1327.8kJ/mol).

Electrospray ionization tandem mass spectrometric study of protonated and alkali- cationized α/ε-hybrid peptides: differentiation of a pair of dipeptide positional isomers.

A new class of Boc-N-protected hybrid peptides derived from L- Ala and ε6-Caa (L-Ala=L-Alanine, Caa=C-linked carboamino acid derived from D-xylose) have been studied by positive ion electrospray ionization (ESI) ion-trap tandem mass spectrometry (MS/MS). MSn spectra of protonated and alkali-cationized hybrid peptides produce characteristic fragmentation involving the peptide backbone, the tert-butyloxycarbonyl (Boc) group, and the side chain. The dipeptide positional isomers are differentiated by the collision-induced dissociation (CID) of the protonated and alkali-cationized peptides. The CID of [M+H]+ ion of Boc-NH-L-Ala-ε-Caa- OCH3 (1) shows a prominent [M+H-C4H8]+ ion, which is totally absent for its positional isomer Boc-NH-ε-Caa-L-Ala-OCH3 (6), which instead shows significant loss of t-butanol. The formation of the [M+Cat-C4H8]+ ion is totally absent and [M+Cat-Boc+H]+ is prominent in the CID of the [M+Cat]+ ion of Boc-NH-L-Ala-ε-Caa- OCH3 (1), whereas the former is highly abundant and the latter is of low abundance for its positional isomer Boc-NH-ε-Caa-L-Ala-OCH3 (6). It is observed that 'b' ions are abundant when oxazolone structures are formed through a five-membered cyclic transition state in tetra-, penta-, and hexapeptides and the cyclization process for larger 'b' ions led to an insignificant abundance. However, the significant 'b' ion is formed in ε,α-dipeptide, which may have a seven-membered substituted 2-oxoazepanium ion structure. The MSn spectra of [M+Cat-Boc+H]+ ions of these peptides are found to be significantly different to those of [M+H-Boc+H]+ ions. The CID spectra of [M+Cat-Boc+H]+ ions of peptide acids containing L-Ala at the C-terminus show an abundant N-terminal rearrangement ion, [bn+17+Cat]+, which is absent for the peptide acids containing ε-Caa at the C-terminus. Thus, the results of these hybrid peptides provide sequencing information, the structure of the cyclic intermediate involved in the formation of the rearrangement ion, and distinguish a pair of dipeptide positional isomers.

Tandem Mass Spectrometry for Structural Identification of Sesquiterpene Alkaloids from the Stems of Dendrobium nobile Using LC-QToF.

Dendrobium nobile is one of the fundamental herbs in traditional Chinese medicine. Sesquiterpene alkaloids are the main active components in this plant. Due to weak ultraviolet absorption and low content in D. nobile, these sesquiterpene alkaloids have not been extensively studied using chromatographic methods. Herein, tandem mass spectrometry combined with liquid chromatography separation provides a tool for the identification and characterization of the alkaloids from D. nobile. A total of nine sesquiterpene alkaloids were characterized by ultrahigh-performance liquid chromatography tandem mass spectrometry. These alkaloids can be classified into two subgroups that are represented by dendrobine and nobilonine. Tandem mass spectrometric studies revealed the fragmentation pathways of these two subgroup alkaloids that were used for the identification and characterization of other alkaloids in D. nobile. Characterization of these alkaloids using accurate mass and diagnostic fragments provided a reliable methodology for the analysis of D. nobile by ultrahigh-performance liquid chromatography tandem mass spectrometry. The limit of detection was defined as the signal-to-noise ratio equal to 3 : 1. Limits of detection of dendrobine and nobilonine were less than 30 ng/mL. The developed method was applied for the analysis of various Dendrobium species and related dietary supplements. Alkaloids were identified from D. nobile, but not detected from commercial samples including 13 other Dendrobium species and the 7 dietary supplements.

Liquid Chromatography Electrospray Ionization Tandem Mass Spectrometric (LC/ESI-MS/MS) Study for the Identification and Characterization of In Vivo Metabolites of Cisplatin in Rat Kidney Cancer Tissues: Online Hydrogen/Deuterium (H/D) Exchange Study.

In vivo rat kidney tissue metabolites of an anticancer drug, cisplatin (cis-diamminedichloroplatinum [II]) (CP) which is used for the treatment of testicular, ovarian, bladder, cervical, esophageal, small cell lung, head and neck cancers, have been identified and characterized by using liquid chromatography positive ion electrospray ionization tandem mass spectrometry (LC/ESI-MS/MS) in combination with on line hydrogen/deuterium exchange (HDX) experiments. To identify in vivo metabolites, kidney tissues were collected after intravenous administration of CP to adult male Sprague-Dawley rats (n = 3 per group). The tissue samples were homogenized and extracted using newly optimized metabolite extraction procedure which involves liquid extraction with phosphate buffer containing ethyl acetate and protein precipitation with mixed solvents of methanol-water-chloroform followed by solid-phase clean-up procedure on Oasis HLB 3cc cartridges and then subjected to LC/ESI-HRMS analysis. A total of thirty one unknown in vivo metabolites have been identified and the structures of metabolites were elucidated using LC-MS/MS experiments combined with accurate mass measurements. Online HDX experiments have been used to further support the structural characterization of metabolites. The results showed that CP undergoes a series of ligand exchange biotransformation reactions with water and other nucleophiles like thio groups of methionine, cysteine, acetylcysteine, glutathione and thioether. This is the first research approach focused on the structure elucidation of biotransformation products of CP in rats, and the identification of metabolites provides essential information for further pharmacological and clinical studies of CP, and may also be useful to develop various effective new anticancer agents.

A liquid chromatography electrospray ionization tandem mass spectrometric study (LC/ESI-MS/MS) of in vivo metabolites of cisplatin in rat liver and brain tissues: deuterated experiments

In vivo rat liver and brain tissue metabolites of an anticancer drug, cisplatin, have been identified and characterized by using LC/ESI-MS/MS in combination with on-line H/D exchange experiments.

Tandem mass spectrometric study of annelation isomers of the novel thieno[3′,2′:4,5]pyrido[2,3-d]pyridazine ring system

In the present communication, we describe tandem combinations of Suzuki – condensation ring closure reactions to obtain a novel thieno[3 �,2 �:4,5]pyrido[2,3-d]pyridazine ring system. These compounds were studied by tandem mass spectrometry in detail and characteristic fragmentations were observed, which can be useful to confirm the presence of N-substituted pyridazine ring in synthesized compounds.

Liquid Chromatography/Electrospray Ionisation Tandem Mass Spectrometric Study of Sitagliptin and its Stressed Degradation Products

A sensitive UPLC positive ion electrospray tandem mass spectrometry method was developed and validated for identification of degradation products of sitagliptin formed during stress study. Six of the major degradants were identi-fied with the proposed method. The separation of sitagliptin and its degradation products was achieved on a Acquity BEH C-18 column (50×2.1 mm, 1.7 µm) using a gradient programme. The mobile phase consists of solvent A (10 mM ammonium formate, pH 6.4 adjusted with formic acid) and solvent B (acetonitrile) and quantitative evaluation was performed at 267 nm with a flow rate of 0.15 mL min(-1). Suitability of this method for the quantitative determination of the drugs was proved by validation in accordance with International Conference on Harmonization (ICH) guidelines and can be used for routine analysis of sitagliptin formulations in quality control.

Aldehyde Stress-Mediated Novel Modification of Proteins: Epimerization of the N-Terminal Amino Acid

Various kinds of aldehyde-mediated chemical modifications of proteins have been identified as being exclusively covalent. We report a unique noncovalent modification: the aldehyde-mediated epimerization of the N-terminal amino acid. Epimerization of amino acids is thought to cause conformational changes that alter their biological activity. However, few mechanistic studies have been performed, because epimerization of an amino acid is a miniscule change in a whole protein. Furthermore, it does not produce a mass shift, making mass spectrometric analysis difficult. Here, we have demonstrated epimerization mediated by endogenous aldehydes. A model peptide, with an N-terminal l- or d-FMRFamide, was incubated with an endogenous or synthetic aldehyde [acetaldehyde, methylglyoxal, pyridoxal 5'-phosphate (PLP), 4-oxo-2(E)-nonenal, 4-hydroxy-2(E)-nonenal, d-glucose (Glc), 4- or 2-pyridinecarboxaldehyde] under physiological conditions. Each reaction mixture was analyzed by liquid chromatography with ultraviolet detection and/or electrospray ionization mass spectrometry. Considerable epimerization occurred after incubation with some endogenous aldehydes (PLP, 40.6% after 1 day; Glc with copper ions, 6.5% after 7 days). Moreover, the epimerization also occurred in whole proteins (human serum albumin and PLP, 26.3% after 1 day). Tandem mass spectrometric studies, including deuterium labeling and sodium borohydride reduction, suggested that the epimerization results from initial Schiff base formation followed by tautomerization to ketimine that causes the chirality to be lost. This suggests that the epimerization of the N-terminal amino acid can also occur in vivo as a post-translational modification under a high level of aldehyde stress.

The Mechanism of 2-Furaldehyde Formation from d-Xylose Dehydration in the Gas Phase. A Tandem Mass Spectrometric Study

The mechanism of reactions occurring in solution can be investigated also in the gas phase by suited mass spectrometric techniques, which allow to highlight fundamental mechanistic features independent of the influence of the medium and to clarifying controversial hypotheses proposed in solution studies. In this work, we report a gas-phase study performed by electrospray triple stage quadrupole mass spectrometry (ESI-TSQ/MS) on the dehydration of D-xylose, leading mainly to the formation of 2-furaldehyde (2-FA). It is generally known in carbohydrate chemistry that the thermal acid catalyzed dehydration of pentoses leads to the formation of 2-FA, but several aspects on the solution-phase mechanism are controversial. Here, gaseous reactant ions corresponding to protonated xylose molecules obtained from ESI of a solution containing D-xylose and ammonium acetate as protonating reagent were allowed to undergo collisionally activated decomposition (CAD) into the triple stage quadrupole analyzer. The product ion mass spectra of protonated xylose are characterized by the presence of ionic intermediates arising from xylose dehydration, which were structurally characterized by their fragmentation patterns. As expected, the xylose triple dehydration leads to the formation of the ion at m/z 97, corresponding to protonated 2-FA. On the basis of mass spectrometric evidences, we demonstrated that in the gas phase, the formation of 2-FA involves protonation at the OH group bound to the C1 atom of the sugar, the first ionic intermediate being characterized by a cyclic structure. Finally, energy resolved product ion mass spectra allowed to obtain information on the energetic features of the D-xylose→2-FA conversion. ᅟ

ESI-MS study of self-assembly-formed tetraglycine macrocyclic ligand complex of Cu(II)

Copper–tetraglycine system is considered as a suitable candidate for the investigation of metal–peptide complexes as those related to the origin of life on Earth. Besides, the interaction of Cu(II) with prion protein as well as the transport of copper by albumin assumes copper reaction with glycine residues. Here, we investigated copper–tetraglycine (Cu–G4) complexes by electrospray ionization mass spectrometry (ESI-MS) under various pH and concentration conditions. Tandem mass spectrometric (MS/MS and MS/MS/MS) study of Cu(II)–G4 structure revealed copper- and pH-induced oligomerization of G4. ESI-MS has provided direct information on pH- and copper-induced oligomerization of G4 and brought about evidence that G4 mobilizes a large amount of copper ions from insoluble salts at high pH values. Copper ion showed a high affinity toward tetraglycine and this interaction is clearly demonstrated by the presence of copper adducts of b2 and b3 fragments of G4. Gas-phase MS measurements proved to afford information on the metal–peptide complexes, which may be complementary to that given by X-ray diffraction studies in solid state.

Non-Ketotic Hyperglycinaemia: A Case Report

A 18-day-old male infant was referred to our neonatal intensive care unit with complaints of hypotonia, poor feeding, seizure and serious apnea. Medical history revealed that these complaints had begun at the third postnatal day after an asymptomatic period. Hyperammonemia, hypoglycemia, acidosis and ketosis were not revealed by laboratory examinations. High plasma glycine level was measured in Tandem mass spectrometric study. Cerebrospinal fluid / plasma glycine ratio was 0.115. The neonate was diagnosed as non-ketotic hyperglycinaemia. This case was reported in order to emphasize the diagnostic and treatment approaches for non-ketotic hiperglycinaemia, a rare disorder of which diagnosis is difficult to make with routine screening tests.

Liquid chromatography/electrospray ionization tandem mass spectrometric study of milnacipran and its stressed degradation products

Rapid Communications in Mass SpectrometryVolume 27, Issue 2 p. 369-374 Letter to the Editor Liquid chromatography/electrospray ionization tandem mass spectrometric study of milnacipran and its stressed degradation products Roshan M. Borkar, Roshan M. Borkar National Centre for Mass Spectrometry, Indian Institute of Chemical Technology, Hyderabad, 500 607 IndiaSearch for more papers by this authorB. Raju, B. Raju National Centre for Mass Spectrometry, Indian Institute of Chemical Technology, Hyderabad, 500 607 IndiaSearch for more papers by this authorPrashant S. Devrukhakar, Prashant S. Devrukhakar United States Pharmacopeia – India Private Limited, Research and Development Laboratory, ICICI Knowledge Park, Turkapally, Shameerpet, Hyderabad, 500078 Andhra Pradesh, IndiaSearch for more papers by this authorNaresh Tondepu, Naresh Tondepu United States Pharmacopeia – India Private Limited, Research and Development Laboratory, ICICI Knowledge Park, Turkapally, Shameerpet, Hyderabad, 500078 Andhra Pradesh, IndiaSearch for more papers by this authorABN. Nageswara Rao, ABN. Nageswara Rao Division of Organic Chemistry II, Indian Institute of Chemical Technology, Hyderabad, 500 607 IndiaSearch for more papers by this authorR. Srinivas, Corresponding Author R. Srinivas National Centre for Mass Spectrometry, Indian Institute of Chemical Technology, Hyderabad, 500 607 India R. Srinivas, National Centre for Mass Spectrometry, Indian Institute of Chemical Technology, Hyderabad 500 607, India. E-mail: [email protected]; [email protected]Search for more papers by this author Roshan M. Borkar, Roshan M. Borkar National Centre for Mass Spectrometry, Indian Institute of Chemical Technology, Hyderabad, 500 607 IndiaSearch for more papers by this authorB. Raju, B. Raju National Centre for Mass Spectrometry, Indian Institute of Chemical Technology, Hyderabad, 500 607 IndiaSearch for more papers by this authorPrashant S. Devrukhakar, Prashant S. Devrukhakar United States Pharmacopeia – India Private Limited, Research and Development Laboratory, ICICI Knowledge Park, Turkapally, Shameerpet, Hyderabad, 500078 Andhra Pradesh, IndiaSearch for more papers by this authorNaresh Tondepu, Naresh Tondepu United States Pharmacopeia – India Private Limited, Research and Development Laboratory, ICICI Knowledge Park, Turkapally, Shameerpet, Hyderabad, 500078 Andhra Pradesh, IndiaSearch for more papers by this authorABN. Nageswara Rao, ABN. Nageswara Rao Division of Organic Chemistry II, Indian Institute of Chemical Technology, Hyderabad, 500 607 IndiaSearch for more papers by this authorR. Srinivas, Corresponding Author R. Srinivas National Centre for Mass Spectrometry, Indian Institute of Chemical Technology, Hyderabad, 500 607 India R. Srinivas, National Centre for Mass Spectrometry, Indian Institute of Chemical Technology, Hyderabad 500 607, India. E-mail: [email protected]; [email protected]Search for more papers by this author First published: 13 December 2012 https://doi.org/10.1002/rcm.6460Citations: 22Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Citing Literature Volume27, Issue230 January 2013Pages 369-374 RelatedInformation

Structure-fragmentation relationship and rapid dereplication ofBuxussteroidal alkaloids by electrospray ionization-quadrupole time-of-flight mass spectrometry

Tandem mass spectrometric studies of natural products revealed the identification of key fragments which can be helpful for their rapid dereplication in plant extracts utilizing a liquid chromatography/tandem mass spectrometry (LC/MS/MS) approach, particularly for the thermally labile compounds. The knowledge of the collision-induced dissociation (CID) fragmentation pattern of the molecule is essentially required prior to the analysis by LC/MS/MS. The fragmentation patterns of eleven Buxus steroidal alkaloids were studied by using a positive ion electrospray ionization quadrupole time-of-flight mass spectrometry (ESI-QqTOF-MS/MS) hybrid instrument. Chromatographic separation of a Buxus papillosa extract was achieved using a capillary HPLC system coupled with the mass instrument. ESI-QqTOF-MS (positive ion mode) showed the presence of several characteristic fragments which can be used to rapidly identify various classes of Buxus steroidal alkaloids. The presence of a cyclopropane ring in the cycloartenol skeleton and the hydroxyl group at C-10 was found to effect on the fragmentation pattern and afford characteristic peaks. This study distinguishes between different types of Buxus steroidal alkaloids based on logical fragmentation pathways. This strategy was successfully applied in LC/ESI-QqTOF-MS/MS analysis of Buxus papillosa extract to investigate and characterize Buxus steroidal alkaloids and 14 compounds were identified as steroidal alkaloids. The knowledge of the fragmentation pattern was used for the rapid identification of this bioactive group of biosynthetically unique steroidal alkaloids in complex plant extracts of Buxus species, especially in the absence of any reference material, by combining key fragments, exact mass measurements and relative abundances of diagnostic fragment ions.

Liquid chromatography tandem mass spectrometric studies of indinavir sulphate and its forced degradation products

Indinavir sulphate was subjected to forced degradation under hydrolysis (acidic, basic and neutral), oxidation, photolysis and thermal stress as prescribed by ICH guidelines. It was degraded under acidic, basic, neutral and oxidative stress conditions, while it was stable under other conditions. After degradation total eight degradation products were formed. The degradation products were identified and their separation was accomplished on Waters XTerra® C18 column (250mm×4.6mm i.d., 5μm) using 20mM ammonium actate:acetonitrile as (50:50, v/v) mobile phase in an isocratic elution mode by LC. The method was extended to LC–MS/MS for characterization of the degradation products and the fragmentation pathways were proposed. The proposed structures of degradation products were also confirmed by HRMS studies. No previous reports were found in the literature regarding the characterization of degradation products of indinavir sulphate.

Electrospray tandem mass spectrometric analysis of a dimeric conjugate, salvialeriafone and related compounds

BackgroundElectrospray tandem mass spectrometry approach is widely used for the rapid characterization of natural products. This paper describes the gas-phased ESI-MS/MS fragmentation of abietane-type diterpenoids and their novel dimeric conjugate, salvialeriafone (1) using both positive and negative ion electrospray ionization quadropole time-of-flight mass spectrometry (ESI-QqTOF-MS/MS) hybrid instrument. Diterpenoids are widely distributed throughout the plant kingdom and posses interesting biological activities.ResultsESI-QqTOF-MS (positive ion mode) of diterpenoids 1–6 under collision-induced dissociation tandem mass spectrometric analysis (CID-MS/MS) showed the characteristic losses of water, carbonmonoxide and propene molecules, while analysis in negative ion mode showed the characteristic losses of water, carbon monoxide, methane molecules and methyl radical. Results demonstrated the differences in the product ions and base peaks due to the differences in the skeleton. A novel dimeric conjugate, salvialeriafone (1) showed characteristic fragmentation pattern and was found to be more prone to form radical ions, as compared to monomeric diterpenoids. The fragmentation pathways of characteristic fragments were proposed with the aid of HRESIMS.ConclusionsExtensive tandem mass spectrometric studies of salvialeriafone (1) and related diterpenoids 2–6 were conducted and their characteristic fragments were identified. The knowledge of the fragmentation pattern of these diterpenoids will be useful for the characterization of new dimers of this class of compounds.