Synthesis of highly substituted tetrahydropyrans: preparation of the C20-C28 moiety of phorboxazoles

A propionate-derived polyketide building block A whose 2-methyl-1,3-diol moiety was built by a Ti(III)-mediated ring opening reaction of a trisubstituted 2,3-epoxy alcohol precursor was employed as a common starting material for the syntheses of highly substituted tetrahydropyrans 1-5, the first one being the C20-C28 fragment of cytotoxic natural products, phorboxazoles

Generation of alkoxide anions from a series of aliphatic diols and alcohols and their ion-molecule reactions with carbon dioxide in the gas phase

Alkoxide anions, [M – H– from a series of aliphatic diols and alcohols are generated in the source under negative ion electrospray ionisation conditions by cone- voltage fragmentation of the corresponding [M + F]– ions. The collision-induced dissociation (CID) spectra of [M – H]– ions consist of [M – H2H]– ions, in addition to the other characteristic fragment ions, and the relative abundance of [M – H2H– ions among the series of diols varies as a function of chain length that could be explained based on their stabilities through intramolecular hydrogen bonding. The reactivity of alkoxide anions is studied through ion–molecule reactions with CO2 in the collision cell of a triple quadrupole mass spectrometer. All the alkoxide anions reacted with CO2 and formed corresponding carbonate anions, [M – H + CO2]– ions. The reactivity of alkoxide anions within the series of diols also reflected the stability of their [M – H]– ion

Ion-pair solid-phase extraction and gas chromatography-mass spectrometric determination of acidic hydrolysis products of chemical warfare agents from aqueous samples

The chemical warfare agents (CWA) degrade rapidly in aqueous samples and convert to acidic degradation products. Extraction and identification of the degradation products from complex matrices using simple sample preparation and sensitive detection and identification is the most important step in the off-site analysis of samples. In this present study, we report a simple sample preparation step based on ion-pair (IP) solid-phase extraction (SPE) for the extraction of acidic degradation products of CWA namely methyl, ethyl, propyl phosphonic acids, thiodiglycolic acid and benzilic acid. The analysis was performed on GC-MS in electron impact ionization mode. Three IP reagents triethylamine (TEA), tetrabutylammonium bromide (TBAB) and cetyltrimethyl ammonium bromide (CTAB) were used. The recoveries were estimated using the internal and external standard methods. The recovery of the compounds was almost negligible when TEA was used as IP reagent. The recoveries obtained when TBAB and CTAB were used as IP reagents were high and reproducible. The recovery of test chemicals is above 90%, except for methyl phosphonic acid and ethylphosphonic acid (20.6 ± 3.2% and 35.8 ± 2.5%, respectively). The minimum detection limits of the method were calculated for all chemicals in both full scan and selected ion monitoring modes. The test chemicals could be detected in microgram per litre quantities by the IP-SPE method

Dissociation of gas-phase dimeric complexes of lactic acid and transition-metal ions formed under electrospray ionization conditions; the role of reduction of the metal ion

Dimeric complex ions of the type [M(A-H)A]<SUP>+</SUP>, where M = metal ion (Co, Ni, Cu, and Zn) and A = ligand (lactic acid, methyl lactate or ethyl lactate), were generated in the gas phase under electrospray ionization conditions. The collision-induced dissociation spectra of [M(A-H)A]<SUP>+</SUP> ions were recorded to study the behaviour of ligand and metal ions in decomposition of these dimeric complex ions. Based on the fragmentation pathways observed for complex ions of lactic acid, it is found that both the carboxylic and hydroxyl groups of lactic acid are involved in the complex formation following displacement of a proton by the metal ion. The dimeric complex ions of Co, Ni, and Zn dissociated to yield similar types of ions, whereas that of Cu behaved differently. The dissociations of Co-, Ni-, and Zn-bound dimeric complexes involved losses of neutral molecules while keeping the oxidation state of the metal ion unchanged. However, elimination of radicals is found in the dissociation of dimeric complex ions of Cu, and the oxidation state of copper is reduced from Cu(II) to Cu(I) in the resulting fragment ions. The deprotonated ligand is involved in the fragmentation pathway of Cu complexes, whereas it is intact in other complexes. The oxidation state of the metal ion, nature of the ligand, and site of attachment to the metal ion are found to control the dissociation of these dimeric complex ions

Negative ion electrospray ionization mass spectral study of dicarboxylic acids in the presence of halide ions

The negative ion electrospray ionization (ESI) mass spectra of a series of dicarboxylic acids, a pair of isomeric (cis/trans) dicarboxylic acids and two pairs of isomeric (positional) substituted benzoic acids, including a pair of hydroxybenzoic acids, were recorded in the presence of halide ions (F-, Cl-, Br- and I-). The ESI mass spectra contained [M--H]- and [M+X]- ions, and formation of these ions is found to be characteristic of both the analyte and the halide ion used. The analytes showed a greater tendency to form adduct ions with Cl- under ESI conditions compared with the other halide ions used. The isomeric compounds yielded distinct spectra by which the isomers could be easily distinguished. The collision-induced dissociation mass spectra of [M+X]- ions reflected the gas-phase basicities of both the halide ion and [M--H]- ion of the analyte. However, the relative ordering of gas-phase basicities of all analyte [M--H]- and halide ions could not account for the dominance of chloride ion adducts in ESI mass spectra of the analytes mixed with equimolar quantities of the four halides

Trace level detection and identification of chemicals related to the chemical weapons convention from complex organic samples

A solid-phase extraction (SPE) method involving selective usage of solvents has been developed for trace level identification of chemical warfare agents (CWAs) present in a complex organic background. The total ion chromatograms obtained from direct gas chromatography-electron ionization mass spectrometric analysis of samples spiked with CWAs in the presence of diesel are very complex and dominated by hydrocarbon peaks and the same after treatment with SPE show distinct peaks corresponding to spiked chemicals. The recovery of samples from SPE is found to be 70-85% at the 10 ppm level

Evaluation of methyl 3-(4-methoxy-1-naphthyl)-(E)-2-propenoate and methyl 5-(4-methoxy-1-naphthyl)-(2E,4E)-2,4-pentadienoate as new charge-transfer matrices for matrix-assisted laser desorption/ionization mass spectrometry

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In situ nucleophilic substitution reaction of N,N-dialkylaminoethyl-2-chlorides monitored by gas chromatography/mass spectrometry

The detection and identification of degradation products of scheduled chemicals, which are characteristic markers of Chemical Warfare agents (CWAs), plays a key role in verification analysis. Identification of such non-scheduled but specific markers of CWAs helps in deciphering the kind of agent that was present in the sample submitted for off-site analysis. This paper describes the stability of N,N-dialkylaminoethyl-2-chlorides, which are precursors for highly toxic chemicals like VX, in different solvents. These compounds are stable in chloroform, acetonitrile, hexane and dichloromethane but tend to undergo in situ nucleophilic substitution reaction in the presence of alcohols giving the corresponding alkyl ether. The study shows that N,N-dialkylaminoethyl alkyl ethers can be used as markers of N,N-dialkylaminoethyl-2-chlorides. A detailed degradation study of these compounds in the presence of alcohols was carried out and it was found that the reaction follows pseudo-first order kinetics. Electron ionization mass spectral data for the methyl ethers of all the compounds are briefly discussed

Mass spectral studies of N,N-dialkylaminoethanols

Some dialkylaminoethanols, precursors of chemical warfare agents such as V-agents and nitrogen mustards, were analyzed by electron impact (EI) and electrospray ionization (ESI) mass spectrometry. The fragmentation pathways in EI and ESI-MS/MS methods are rationalized. The collision-induced dissociation (CID) spectra of [M+H]+ ions of aminoethanols in ESI mode are clearly distinguishable from one another, including those of isomeric normal and branched chain dialkylaminoethanols. Structures can be proposed based on the general fragmentation pathways of these molecules