Mass spectrometry of the trimethylsilyl derivatives of medicinal barbiturates

The electron ionization mass spectra of the trimethylsilyl derivatives of a number of medicinal barbiturates have been examined. The trimethylsilyl derivatives are useful in the identification of barbiturates by gas liquid chromatography/mass spectrometry (g.l.c.-m.s.). Mass spectra of these derivatives are characterized by abundant high mass ions which permit the ready distinction of one barbiturate from another. The prominent and characteristic [M - 15] ion is an effective monitor of molecular weight, while other unique fragmentations and/or varying patterns of relative abundance serve to differentiate isomers.     

Sites of protonation in phenothiazines: Methane and ammonia chemical ionization mass spectra

Positive ion methane and ammonia chemical ionization mass spectra for ten phenothiazine derivatives are reported. The fragmentations observed in the chemical ionization mass spectra are rationalized in terms of the location of the added proton. High-resolution measurements are used to confirm empirical formulae of the ions in the mass spectra. Changes in the mass spectra with a change in the chemical ionization reagent gas from methane to ammonia are described. A comparison with positive ion secondary ion mass spectra of the same compounds show that the amount of fragmentation is higher in the secondary ion mass spectra, but the same types of ions are observed in spectra produced by both ionization methods.     

Electron ionization mass spectra and their reproducibility for trialkylsilylated derivatives of organic acids, sugars and alcohols

Mass spectra of trialkylsilyl derivatives of fatty acids, dicarboxylic acids, hydroxyacids, oxoacids, sugars, amino acids and alcohols were obtained. Amino acids were analyzed as tert-butyldimethylsilyl derivatives; all other model compounds were analyzed as trimethylsilyl derivatives. Reproducibility of the electron ionization (EI) mass spectra for the derivatives obtained was discussed. It was shown that, for many investigated derivatives, composition of the respective mass spectra depended greatly on ion source contamination. The trimethylsilylated alpha-tocopherol mass spectrum composition was most significantly influenced by ion source contamination. This compound can be used to test ion source contamination.     

Electron ionization and atmospheric pressure photochemical ionization in gas chromatography-mass spectrometry analysis of amino acids

The mass spectra of tert-butyldimethylsilyl (TBDMS) derivatives of 17 amino acids were obtained using electron ionization (EI) and atmospheric pressure photochemical ionization (APPhCI) mass spectrometry. The APPhCI mass spectra for all of the derivatives except arginine were shown to consist of only molecular [M](+.) and quasimolecular [MH](+) ions whereas, in the case of EI, the compounds in question underwent a drastic fragmentation. The application of APPhCI to gas chromatography-mass spectrometry enables a reliable identification of the TBDMS derivatives of amino acids in a mixture, even if its components are only partially resolved, due to the unique molecular masses for each compound. Comparison of the respective positive-ion chemical ionization (PICI) mass spectra available in the literature with APPhCI spectra has shown that, in the case of PICI, unlike APPhCI, noticeable fragmentation occurs.     

Amino-acid sequence study in peptides by mass spectometry-II. Investigation of pentadeuterobenzoyl-peptide methyl esters

The utility of benzoyl and pentadeuterobenzoyl derivatives of peptide methyl esters for mass spectrometric analysis was investigated. The mass spectra of the glu-his and the val-tyr-pro derivatives are discussed. Treatment of the peptide methyl esters with the mixed benzoic-ethyl-carbonic anhydride did in some cases lead to benzoyl derivatives as well as to ethoxycarbonyl derivatives.     

含2-苯基-1,2,3-连三唑环的1,3,4-噁二唑衍生物的质谱研究

对两类非共轭的１，３，４－噁二唑衍生物Ⅰａ～ｅ和Ⅱａ～ｅ的电子轰击质谱进行了研 究，并通过Ｂ／Ｅ联动扫描对它们可能的裂解途径进行了探讨。     

GC-MS analysis of ring and side chain regioisomers of ethoxyphenethylamines

Mass spectral differentiation of 3,4-methylenedioxymethamphetamine (3,4-MDMA), a controlled drug, and its 2,3-regioisomer from the ring substituted ethoxyphenethylamines is possible after formation of the perfluoroacyl derivatives, pentafluoropropionamides (PFPA), and heptafluorobutyrylamides (HFBA). The ring substituted ethoxyphenethylamines constitute a unique set of compounds having an isobaric relationship with 3,4-MDMA. These isomeric forms of the 2-, 3-, and 4-ethoxy phenethylamines have mass spectra essentially equivalent to 3,4-MDMA; all have molecular weight of 193 and major fragment ions in their electron ionization mass spectra at m/z 58 and 135/136. All the side chain regioisomers of 2-ethoxy phenethylamine having equivalent mass spectra to 3,4-MDMA are synthesized and compared via gas chromatography-mass spectrometry to 2,3- and 3,4-methylenedioxymethamphetamine. The mass spectra for the perfluoroacyl derivatives of the primary and secondary amine regioisomers are significantly individualized, and the side chain regioisomers yield unique hydrocarbon fragment ions at m/z 148, 162, and 176. Additionally, the substituted ethoxymethamphetamines are distinguished from the methylenedioxymethamphet-amines via the presence of the m/z 107 ion. Gas chromatographic separation on relatively non-polar stationary phases successfully resolves these derivatives.     

A study of the tautomerism of 5-as-triazinones by mass spectrometry

The tautomeric equilibria of variously substituted 5-triazinones have been studied by comparing their mass spectra with those of their methylated derivatives. The results for 6-methyl-5-triazinone have been confirmed by comparison with the mass analysed ion kinetic energy spectra of ions generated from N-ethyl derivatives. The equilibria are dependent upon the nature of the substituents in the 3- and 6-positions.     

Identification of the products of nonregioselective organic reactions by chromatography-mass spectrometry: Chloro derivatives of dialkyl ethers

The possibilities of GC-MS identification of the products of free-radical chlorination of dialkyl ethers are considered. The principal feature of this problem was the absence of appropriate reference information (both mass spectra and GC retention indices) for chloro derivatives of ethers. It was shown that all monochloro and selected dichloro derivatives can be identified on the basis of joint interpretation of their mass spectra combined with evaluating the retention indices using different additive schemes.     

Mass spectrometry of carbohydrate derivatives

Mass spectra of carbohydrate methyl ethers of different types and other monosaccharide derivatives have been measured. Fragmentation patterns of these compounds, characteristic features of their mass spectra and potential analytical importance of mass spectrometry for structural study in the carbohydrate field are discussed.     

GC-MS analysis of acylated derivatives of the side-chain regioisomers of 4-methoxy-3-methyl-phenethylamines related to methylenedioxymethamphetamine

The five side-chain regioisomers of 4-methoxy-3-methylphenethylamine constitute a unique set of compounds having an isobaric relationship with the controlled drug substance 3,4-methylenedioxymethamphetamine (3,4-MDMA or Ecstasy). These isomeric forms of the 4-methoxy-3-methylphenethylamines have mass spectra essentially equivalent to 3,4-MDMA, and all have a molecular weight of 193 and major fragment ions in their electron ionization mass spectra at m/z 58 and 135/136. Mass spectral differentiation of 2,3- and 3,4-MDMA from primary and secondary amine regioisomeric side chains of 4-methoxy-3-methylphenethylamines was possible after formation of the perfluoroacyl derivatives, pentafluoropropionamides and heptafluorobutyrylamides. The mass spectra for these derivatives are significantly individualized, and the resulting unique fragment ions allow for specific side-chain identification. The individualization is the result of fragmentation of the alkyl carbon-nitrogen bond, which yielded unique hydrocarbon fragments. The heptafluorobutyrylamide derivatives offer more fragment ions for molecular individualization among these regioisomeric substances. Gas chromatographic separation on relatively non-polar stationary phases successfully resolves these derivatives.     

Electron-impact promoted fragmentation of alkyl-N-(1-phenylethyl)-carbamates of primary,secondary and tertiary alcohols

The mass spectra of twenty N-alkyl-(1-phenylethyl)-carbamates derived from primary, secondary and tertiary alcohols have been investigated using deuterium labeling and high resolution mass spectrometry. These derivatives are suitable for the determination of the isotopic purity of primary and secondary, but not of tertiary alcohols. Several of the primary and secondary alcohol derivatives yield an ion formally equivalent to the product ion of a McLafferty rearrangement. Deuterium labeling established, however, that the usual site specificity associated with the McLafferty rearrangement process was lacking in these carbamate derivatives. In addition a double hydrogen rearrangement process was observed in the mass spectra of several of the carbamates derived from tertiary alcohols.     

Heterocyclic analogues of steroids: VIII—Mass spectrometry of the stereoisomeric derivatives of 8-aza-16-oxaestrane

Using high resolution mass spectra, metastable ions and selective deuteration the decomposition pathways of 8-aza-16-oxasteroid derivatives have been investigated. There is a dependence of the mass spectra on the stereochemistry of the C/D ring fusion in 8-aza-16-oxaestrane derivatives.     

Analysis of amino acids as N-dithiocarbamic derivatives. A comparison of electron impact and field ionization mass spectra

Amino acids were converted to their N-dithio-alkylcarbamate derivatives by reaction with carbon bisulfide in basic solution followed by reaction with ethyl bromide to form an ethyl thioester. The derivatives are sufficiently volatile for mass spectrometric analysis via the direct inlet probe, without the need for further esterification of the carboxylic acid group. The electron impact spectra exhibit relatively intense molecular in peaks and structurally diagnostic fragment ions. The general features of the electron impact and field ionization mass spectra are compared.     

Observations on the mass spectrometry of monensin and related compounds

Monensin and nigericin are structurally related compounds belonging to a family of biologically active, polycylic, monocarboxylic acids produced by Streptomyces. Partial interpretation of their mass spectra has been achieved with the aid of high resolution data and by correlation with spectra of derivatives. These results have been applied to structure elucidation of several minor factors produced along with monensin. An interesting aspect of the mass spectrometry of these compounds is that their alkali-metal salts are sufficiently volatile to yield mass spectra. Fragmentation of the salts is markedly different from that of the free acids and their derivatives. A scheme is proposed to account for the formation of a number of fragment ions which contain the metal atom.     

有机磷化合物的质谱研究(Ⅺ)——1,3,2—二氮磷杂环戊烷衍生物的化学电离质谱

本文报道了11种1,3,2-二氮磷杂环戊烷衍生物的化学电离质谱(CIMS),对热不稳定的化合物采用了解吸化学电离技术(DCI),着重探讨了三价磷和五价磷化合物质谱的差异及均三氮苯取代基的引入对质谱行为的影响;对该类化合物的CIMS和EIMS进行了比较。     

Structure analysis of the propionic–pentafluoropropionic anhydride derivatives of norepinephrine and serotonin

Gas chromatographic/mass spectrometric analysis was used for the examination of norepinephrine and serotonin derivatives formed from their sequential reaction with propionic anhydride and pentafluoropropionic anhydride. The structures of the resulting derivatives were determined by the analysis of the mass spectra of the proteo and deutero homologs and by nuclear magnetic resonance spectroscopy. Mechanisms for the synthesis and electron impact fragmentation of these derivatives are proposed.     

Mass spectroscopy of natural products. XXIII,Comparative positive and negative ion mass spectral studies of scapanin-type diterpenoidst

The mass spectral behaviour of 15 scapanin-type diterpenoids (8α,12-epoxylabdanes) was elucidated using accurate mass measurements and deuterium-labelled derivatives. The results obtained allow a localization of the functional groups in the diterpenoid system. Furthermore, the negative ion mass spectra of the scapanin-type diterpenoids are discussed and compared with the positive ion spectra.     

Metastable transitions in the mass spectra of methyl and phenylthiohydantoin derivatives of amino acids

The mass spectra of a number of methyl- and phenylthiohydantoin amino acid derivatives have been obtained. The major metastable transitions occurring in the mass spectra of these derivatives have been identified and measured. The major fragmentation pathways associated with the metastable transitions have been outlined and are discussed for each group of compounds. Inspection of the metastable data has shown that there is at least one unique metastable transition occurring for each thiohydantoin derivative which may be used to uniquely identify that derivative in the presence of a mixture of thiohydantoin derivatives obtained from the Edman degradation of a peptide or protein. The use of metastable ions to uniquely identify thiohydantoin derivatives in mixtures has proven useful in the identification of the MTH and PTH derivatives of glycine whose molecular ions are not unique and for resolving such ambiguities as occur for example in the mixture of leucine and isoleucine.     

Electron impact mass spectra of some substituted aromatic boronate derivatives of bifunctional compounds

The electron impact mass spectra of the 3,5-bis(trifluoromethyl)benzeneboronate, 2,4-dichlorobenzene-boronate and 4-bromobenzeneboronate derivatives of some bifunctional diols and aminoalcohols are characterized by prominent molecular ions with diagnostically useful modes of fragmentation. Many of the principal ions in the mass spectra retain boron in their structure.