Electron ionization mass spectral fragmentation study of sulfation derivatives of polychlorinated biphenyls

Background  

Polychlorinated biphenyls are persistent organic pollutants that can be metabolized via hydroxylated PCBs to PCB sulfate metabolites. The sensitive and selective analysis of PCB sulfate monoesters by gas chromatography-mass spectrometry (GC-MS) requires their derivatization, for example, as PCB 2,2,2-trichloroethyl (TCE) sulfate monoesters. To aid in the identification of unknown PCB sulfate metabolites isolated from biological samples, the electron impact MS fragmentation pathways of selected PCB TCE sulfate diesters were analyzed and compared to the fragmentation pathways of the corresponding methoxylated PCBs.     

Amidine mass spectral fragmentation patterns

Electron impact mass spectrometry of a range of amidines (R′NC(R)NHR′) including formamidines, acetamidines, benzamidines and tert-butylamidine, has been undertaken, and comparisons made of the fragmentation pathways followed by the different families of compounds. Fragmentation of all the molecular ions is characterized by skeletal carbon-nitrogen bond cleavage to form [R′NCR]⁺ and [R′NH]⁺ fragments, both of which are observed. For formamidines (R?H), the positive charge remains with the [R′NH]⁺ fragment which leads to the base peak at m/z93 corresponding to [R′NH₂]⁺˙. In contrast, for acetamidines and benzamidines the charge prefers to remain with the [R′NCR]⁺ fragment which gives the base peak for these compounds. The spectra of unsubstituted amidines (HNC(R)NH₂) are characterized by cleavage of the carbon substituent from the NCN skeleton, [CN₂H₃]⁺ (m/z 43) being produced in all cases.     

The mass spectral fragmentation of isoxazolyldihydropyridines

The mass spectral fragmentation of 4-isoxazolyl-1,4-dihydropyridines has been examined with the aid of linked metastable scanning. Three prominent pathways involve (i) O-N bond cleavage of the isoxazole followed by the loss of R²CN, (ii) loss of carboalkoxy from the 3- and/or 5- position of the dihydropyridine and, (iii) loss of the 4-isoxazolyl-substituent.     

Acetylenic fragmentation of acyl derivatives of the Fischer base

Indolenium salts, which readily undergo cleavage in aqueous alkali to give a monosubstituted acetylene and 1,3,3-trimethyl-2-oxindole, are formed when acyl derivatives of the Fischer base are heated with phosphorus oxychloride. Various aryl- and hetarylacetylenes can be conveniently obtained by this method.Translated from Khimiya Geterotsiklicheskikh Soedenii, No. 7, pp. 915–918, July, 1987.     

The mass spectral fragmentation of 1,4-butanediol

The behaviour of 1,4-butanediol under electron impact at 70 and 12.5 eV has been studied with the aid of high resolution mass spectra. Based on metastable ion decompositions and deuterium labelling, mechanisms are proposed for the formation of the abundant ions of this compound.     

Mass spectral fragmentation and rearrangement of isatin derivatives

Mass spectral fragmentation pathways were formulated for 1-alkylisatins, 1-alkyl-3-arylimino-2-indolinones and 3-arylimino-2-indolinons bearing no substituent at the 1-position. Deuterium-labelled and ¹³C-labelled compounds were utilized in this study. An interesting rearrangement of the 1-alkyl compounds, in which the 1-alkyl substituent is incorporated into a fulvene ion, was established.     

Field desorption mass spectral fragmentation of monosaccharide isomers

Field desorption ionization of selected monosaccharide isomers by potassium ion attachment in high fields is described. The ionization is obtained with a tungsten wire activated with carbon needles and covered with KH₂PO₄ salt. In addition to the potassium cationized molecular ions, reproducible fragmentation was obtained at 10 mA and 20 mA typical of the various monosaccharides. For instance, D-glucose tends to lose a water molecule, whereas D-fructose loses primarily methanol under similar conditions. Methanol elimination is suggested to be characteristic of furanoidal ketoses and water elimination for pyranoidal aldoses, whereas glycol elimination occurs for furanoidal aldoses.     

The mass spectral fragmentation of 1,1,4a-trimethyl-1,2,3,4,4a,9,10,10a-octahydrophenanthrene,its 2-oxo and 2-oxy derivatives,and their deuteriomethyl analogues

The mass spectra of the title compounds have been compared with those of their 4a-trideuteriomethyl and 1,1-bis(trideuteriomethyl) analogues. Some fragmentation pathways proposed for ring C aromatic diterpenes by earlier workers have been corrected in the light of the shifts in peak positions and metastable refocusing experiments.     

Hydrogen and trimethylsilyl transfers during EI mass spectral fragmentation of hydroxycarboxylic and oxocarboxylic acid trimethylsilyl derivatives

This paper, describing electron ionization mass spectral fragmentation of some hydroxycarboxylic and oxocarboxylic acid trimethylsilyl derivatives, focuses on the formation of fragment ions resulting from the interactions between the two functionalities of these compounds. These interactions result in the formation of fragment ions at [CH2=C(OTMS)2]+., [CH2=CHC(OTMS)=OTMS]+, [M-31]+, [M-105]+, and [M-RCHO]+. in the case of hydroxycarboxylic acid trimethylsilyl derivatives of formula RCHOTMS(CH2)nCOOTMS and at [RC(OTMS)=CH2]+., [RC(=OTMS)CH=CH2]+, and [M-RC(=O)CH2]+ in the case of oxocarboxylic acid trimethylsilyl esters of formula RC(=O)(CH2)nCOOTMS. Some of these fragmentations appeared to be sufficiently specific to be used to characterize these compounds. Several fragmentation pathways involving trimethylsilyl and hydrogen transfers were proposed to explain the formation of these different fragment ions and were substantiated by deuterium labeling.     

Characterizing the electrospray ionization mass spectral fragmentation pattern of indole derivatives synthesized from 2-keto glycosides

Four indole derivatives synthesized from 2-keto glycosides were analyzed by electrospray ionization tandem mass spectrometry (ESI-MSn) with low-energy collision-induced dissociation to establish a general structural elucidation of indole derivatives. Their fragmentation pathways are proposed on the basis of the MSn studies and deuterium-labeled experiments. Indole derivatives undergo complicated gas-phase rearrangements in addition to simple bond cleavages. A rearrangement, which involves a contraction of the six-membered ring, was observed and a mechanism was proposed. The observations may have some potential applications in the interpretation of the mass spectra of indole derivatives.     

Synthesis and antagonistic activities of enantiomers of cyclic platelet-activating factor analogues

Enantiomers of platelet-activating factor (PAF) antagonists, 3-(6-[O-(trans-3-heptadecylcarbamoyloxytetrahydropyran-2-yl)methyl ] phosphonoxy)hexylthiazolium (inner salt) (3), 3-[5-(trans-3-heptadecylcarbamoyloxytetrahydropyran-2-yl) methoxycarbonylamino]pentylthiazolium bromide (4) and 3-(5-[O-(cis-3-heptadecylcarbamoylthiotetrahydropyran-2-yl) methyl]phosphonoxy)pentylthiazolium (inner salt) (5), were synthesized, starting from (2R,2R)- and (2S,2S)-tartaric acid. Antagonistic activities of these compounds against C16-PAF were measured in vitro (rabbit platelet aggregation, IC50) and in vivo (hypotension in rats, ID50). In these three enantiomeric pairs, the (3S)-(tetrahydropyran numbering) enantiomers were one order more potent than the (3R)-isomers: (2R,3S)-3a (R-74,654), IC50 0.59 microM and ID50 0.054 mg/kg, i.v.; (2S,3R)-3b, IC50 4.7 microM and ID50 0.30 mg/kg, i.v.; (2R,3S)-4a, IC50 0.20 microM and ID50 0.032 mg/kg, i.v.; (2S,3R)-4b, IC50 2.2 microM and IC40 0.21 mg/kg, i.v.; (2R,3R)-5a, IC50 1.1 microM and ID50 0.92 mg/kg, i.v.; (2S,3S)-5b (R-74,717), IC50 0.27 microM and ID50 0.064 mg/kg, i.v.     

Electrospray ionization mass spectrometric fragmentation of hydroquinone derivatives

The fragmentation patterns of nine di-, tri- and tetracyclic hydroquinones with potential antitumor activity were rationalized by invoking competing mechanisms that included sterically accelerated homolytic cleavage, Meerwein-type rearrangements and dehydrations through elimination or intramolecular nucleophilic substitution.     

Electron impact mass spectral fragmentation of chiral bisbenzoxazole,bisbenzothiazole and biscarbamide derivatives of 2,2-dimethyl-1,3-dioxolane

The mass spectrometric fragmentation behaviour of five pairs of (R,R)- and (S,S)-4,5-bis(benzoxazol-2-yl)-2,2-dimethyl-1,3-dioxolane derivatives, one pair of (R,R)- and (S,S)-4,5-bis(benzothiazol-2-yl)-2,2-dimethyl-1,3-dioxolanes, and three pairs of (R,R)- and (S,S)-N,N'-bis(2-hydroxyaryl)-2,2-dimethyl-1,3-dioxolane-4,5-dicarbamides, all important compounds for asymmetric catalysis (P. Jiao et al., Tetrahedron Asymmetry 2001; 12: 3081), has been studied with the aid of mass-analyzed ion kinetic energy spectrometry and accurate mass measurements under electron impact ionization conditions. The spectral observations have been rationalized in terms of fragment ion structures and fragmentation mechanisms that will provide an aid to spectral interpretation for new compounds of this type.     

Semi-empirical Scf-Mo study of the mass spectral fragmentation of tetramethyldiphosphine

Structures and enthalpies of formation have been calculated, in the MNDO approximation using UHF wave-functions for open shell species, for tetramethyldiphosphine, Me₄P₂, and the major ions in its mass spectrum: Me₄P₂⁺, Me₃P₂H⁺, Me₃P₂⁺, Me₂P₂H₂⁺ (3 forms), Me₂P₂H⁺ (3 forms), Me₂P₂⁺ (3 forms), MePPCH₂⁺ (3 forms), MeP₂⁺ and MePCH₂⁺, together with all the corresponding neutral fragments. Appearance potentials are calculated for all the ions, and possible fragmentation pathways deduced.     

Substituent effects in the mass spectral fragmentation of aryl esters

The mass spectra of m- and p-substituted phenyl acetates, phenyl propionates, phenyl chloroacetates and phenyl fluoroacetates have been determined. The fragmentation of aryl esters is affected by acyl substituents as well as by aryl substituents. Esters having acyl groups of low ionization potential show greater changes in fragmentation because of aryl substituents than those having acyl groups of high ionization potential. Each series has a fairly definite crossover point where fragmentation changes from predominant rearrangement to predominant cleavage.     

Electron ionization mass spectral fragmentation of deoxynivalenol and related tricothecenes

Careful analysis of the electron impact (EI) mass spectral data obtained for the trimethylsilyl (TMS) ethers of known trichothecene mycotoxins of the deoxynivalenol group permitted the construction of a database useful for the identification of these mycotoxins directly from a gas chromatography/mass spectrometry (GC/MS) run. Structures of the ions at m/z 103, 117, 147 and 191 were elucidated by high-resolution mass spectrometry (HRMS) and a fragmentation scheme was suggested. The relative abundances of these ions in the mass spectra of the trichothecenes allowed a fast structural diagnosis during analysis of biological matrices. A new mycotoxin of this group, 3-acetylnivalenol, was tentatively identified by using MS data interpretation only.