Structural determination of lysophosphatidylcholines extracted from marine sponges by fast atom bombardment tandem mass spectrometry

A series of lysophosphatidylcholines were isolated from the marine sponge Spirastrella abata by reversed-phase high performance liquid chromatography (HPLC) and analyzed by fast atom bombardment mass spectrometry (FAB-MS). Their structural elucidation was carried out with fast atom bombardment tandem mass spectrometry (FAB-MS/MS). The collision-induced dissociation (CID) of protonated and sodiated molecular ions produced diverse product ions via a series of dissociative processes. Because of the positive charge of the amine group at the end of the molecules, charge-remote fragmentation patterns of specific ions, [M + H](+) or [M + Na](+), were very helpful for the identification of product ions which are characteristic for choline and long hydrocarbon chains substituted at the glycerol back bone. Moreover, the CID-MS/MS spectra of sodium adducted molecular ions for lysophosphatidylcholines yielded common characteristic fragment ions for the choline moiety and characteristic ions [M + Na-103](+), [M + Na-85](+) and [M + Na-59](+) in the higher mass region.     

Structural determination of monoacylglycerols extracted from marine sponge by fast atom bombardment tandem mass spectrometry

Five new monoacylglycerols (MAGs) were isolated from the marine sponge Stelletta sp. by reversed-phase high-performance liquid chromatography and analyzed by positive ion fast atom bombardment mass spectrometry (FAB-MS). FAB mass spectra of these compounds produced abundant sodium-adducted molecules [M+Na]+ from a mixture of 3-nitrobenzyl alcohol and sodium iodide. The structural elucidation of these sponge MAGs was carried out by FAB tandem mass spectrometry (MS/MS). To find diagnostic ions for the characterization of the MAGs, authentic MAGs were initially analyzed by collision-induced dissociation (CID) MS/MS. The CID MS/MS of [M+Na]+ precursor ions resulted in the formation of numerous characteristic product ions via a series of dissociative processes. The product ions formed by charge-remote fragmentation (CRF) provided important information for the characterization of acyl chains substituted at the glycerol backbone, and product ions at m/z 84, 97, 113 and 139 were diagnostic for the sodiated glycerol backbone. On the basis of these fragmentation patterns, the structures of five MAGs extracted from marine sponge were elucidated. In addition, high-resolution mass measurement was performed to obtain the elemental compositions of the MAGs.     

Structural characterization of isoxazolidinyl nucleosides by fast atom bombardment tandem mass spectrometry.

4'-Aza-2',3'-dideoxyerythrofuranosyl derivatives of thymine (AdT, 1) and uracil (AdU, 2) are analogues of 2',3'-dideoxyribofuranosyl thymine (ddT, 3) and uracyl (ddU, 4). Compounds 1 and 2 are representative of a new class of antiviral agents where the sugar moiety is replaced by an isoxazolidine ring. The increasing importance of isoxazolidinyl nucleosides has encouraged the exploitation of simple mass spectrometric rules for unambiguously assigning their structure. The species 1, 2, 5 and 6 were therefore synthesized in order to evaluate the role of the basic centre of the modified sugar moiety in their gas-phase chemistry. The tandem mass spectra of these compounds are similar to those of the wild-type nucleosides and display fragment ions corresponding to [B + 2H](+),[M - BH](+) and [B + 27](+) species, where B is the nucleobase. The last species derives from a retrocycloaddition process which is less evident in 2'-deoxyribosides. This behaviour is consistent with protonation of the analytes at the pyrimidine rings. Model isoxazolidines, in which the nucleobase was replaced by a phenyl or a naphthyl moiety, displayed the expected behaviour of species with a localized charge on the N-O moiety of the isoxazolidine ring.     

Structural characterization of mono- and bisphosphonium salts by fast atom bombardment mass spectrometry and tandem mass spectrometry

Positive-ion fast atom bombardment (FAB) mass spectra are reported for a representative series of mono- and bisphosphonium halides derived from triphenylphosphine. The mass spectra of the monoalkyltriphenylphosphonium salts typically contain abundant intact cations that can be used to establish the cationic relative molecular mass and diagnostic fragment ions that allow the characterization of structural subgroups. Depending on the functional group substitution on the alkyl group, additional fragment ions are observed which are formed by loss of small neutral molecules from the intact cation and that can be used for the differentiation of isomeric phosphonium salts. Molecular dication are typically observed in the FAB mass spectra of the bisphosphonium salts when they are analysed in 3-nitrobenzyl alcohol. In addition, production of singly charged ions by clustering with a counter ion, decomposition involving removal of one of the charge centres and one-electron reduction are generally observed. Structurally diagnostic fragments are also obtained. The fragmentation pathways of the ions derived from the phosphonium salts were elucidated by precursor ion and product ion tandem mass spectrometric experiments. For the phosphonium salts containing a long-chain hydrocarbon alkyl group, high-energy collision-induced decomposition of the intact cation is needed to obtain unambiguous structural information.     

Continuous-flow fast atom bombardment mass spectrometry

The continuous-flow fast atom bombardment probe performs equally well with or without a high-performance liquid chromatography column producing clean spectra containing little or no background noise. Its function as a liquid chromatography-mass spectrometry interface for labile and involatile samples has been illustrated with reference to dansylated amino acids. The versatility of the new probe has been exemplified by on-line enzymatic peptide sequencing.     

Structural determination of saponins extracted from starfish by fast atom bombardment collision-induced dissociation mass spectrometry.

Three saponins were extracted and isolated from starfish by reversed-phase high performance liquid chromatography (HPLC), and analyzed by fast atom bombardment mass spectrometry (FAB-MS). Their molecular weight information could be obtained by the presence of abundant [M+Na]+ ions and weak [M+H]+ ions in FAB-MS spectra. Moreover, high resolution mass measurements of their [M+Na]+ ions were performed at the resolution of 10000 to elucidate the element composition of extracted saponins. The collision-induced dissociation (CID) of sodium-adducted molecules [M+Na]+ yielded diverse product ions via dissociated processes. In the collision-induced dissociation (CID)-MS/MS analysis of [M+Na]+ ion, the sulfate-containing saponins produced characteristic ions such as SO4Na+, [NaHSO4+Na]+, [M+Na-sugar]+ and [M+Na-2sugar]+ ions, whereas the sulfate-free compound showed characteristic ions produced by cleavage of sugar moiety and side chain of aglycone. The fragmentation patterns could provide information on the linkage position of sugar groups in aglycone and sulfate groups.     

Structural determination of cyclitol derivatives by fast-atom bombardment tandem mass spectrometry

Three cyclitol derivatives were isolated from the marine sponge Sarcotragus sp. by reversed-phase high-performance liquid chromatography and analyzed by fast-atom bombardment mass spectrometry (FAB-MS). Their structural elucidation was carried out with FAB tandem mass spectrometry (FAB-MS/MS). FAB-MS spectra produced a significant abundance of the sodium adducts [M+Na]+ and [M+2Na-H]+ from a mixture of m-NBA and NaI. In addition, trifluoroacetylation of the cyclitol derivatives was used for confirmation of the presence of the cyclitol ring. High abundance [M-5H+5CF3CO+Na]+ ions were observed in the FAB-MS spectra of the trifluoroacetyl-cyclitol derivatives. Collision-induced dissociation (CID) of the [M+Na]+ ions produced diverse product ions via a series of dissociative processes. Charge-remote fragmentation (CRF) patterns of [M+Na]+ ions were very useful for the identification of product ions which are characteristic for the cyclitol ring and long hydrocarbon chains substituted at the glycerol backbone. Moreover, the CID-MS/MS spectra of the [M+Na]+ ions yielded characteristic product ions at m/z 53, 83, 113, 155 and 171 for the cyclitol moiety, and at m/z 213, 229 and 245 for the glycerol backbone attached to the cyclitol ring.     

Characterization of cytokinins from plant pathogenic Pseudomonades by fast atom bombardment tandem mass spectrometry

Naturally occurring cytokinins produced from two phytopathogenic Pseudomonas bacteria, and some of their derivatives and analogues, were characterized by fast atom bombardment tandem mass spectrometry. The proto-nated molecular ions of the examined cytokinins can be fingerprinted from breakdown pattern of their gaseous unimolecular dissociations, thus providing means for their identification by desorption ionization methods.     

Field desorption mass spectrometry,fast atom bombardment mass spectrometry and fast atom bombardment tandem mass spectrometry of echinacoside,the main caffeoyl-glycoside from Echinacea angustifolia roots (Asteraceae)

The mass spectral fragmentation of echinacoside, a pharmacologically active caffeoyl-glycoside isolated from Echinacea angustifolia roots, has been investigated using different soft-ionization techniques, field desorption and fast atom bombardment (positive and negative ions) mass Spectrometry. Both ionization modes are successful in molecular mass determination and furnish approximately equivalent structural information. A fast atom bombardment tandem mass spectrometry approach (negative ions) was developed for the study of the fragmentation pathways and for the detection of echinacoside in crude plant extracts. The results demonstrate the usefulness of this technique for the rapid search of this important caffeoyl-glucoside directly in natural complex matrices.     

Analysis of xanthates by negative-ion fast atom bombardment mass spectrometry

A new technique using negative-ion fast atom bombardment mass spectrometry for the analysis of xanthates and related compounds is described. Electron impact and positive-ion fast atom bombardment mass spectrometry produced no structurally related fragment ions or observable molecular ions at the expected m/z values. It was demonstrated that negative-ion fast atom bombardment ionization was the most suitable method of ionization for structure elucidation studies for the compounds described.     

Continuous-flow fast atom bombardment mass spectrometry of oligonucleotides

Although frit-fast atom bombardment (frit-FAB) and continuous-flow FAB mass spectrometry have become standard methods for the analysis of peptides and peptide mixtures, these techniques have not been applied previously to the analysis of oligonucleotides. Mobilephase composition, flow rate, and sample size were optimized for the analysis of oligonucleotides by negative ion frit-FAB mass spectrometry (a type of continuous-flow FAB mass spectrometry). With a mobile phase consisting of methanol/water/triethanolamine (80:20:0.5, v/v/w), flow injection frit-FAB analysis of oligonucleotides showed lower limits of detection compared to standard probe FAB mass spectrometry. For example, in order to obtain a signal-to-noise ratio of 3:1, 38 prnol of d(GTIAAC) were required for frit-FAB mass spectrometry and 62 pmol were required for standard probe FAB mass spectrometry. The largest difference between frit-FAB and standard probe FAB was observed for d(pC)₅, for which the limit of detection by frit-FAB was approximately 11-fold lower than by standard FAB mass spectrometry. Adjustment of the mobile phase to pH 7 with trifluoroacetic acid increased the limit of detection (reduced sensitivity) a minimum of sixfold. Equimolar mixtures of two or three oligonucleotides produced deprotonated molecules in identical relative abundances whether analyzed by frit-FAB or standard probe FAB mass spectrometry. Finally, frit-FAB liquid chromatography mass spectrometry was demonstrated by separating mixtures of oligonucleotides on a β -cyclodextrin high-performance liquid chromatography column with a mobile phase containing methanol, water, and triethanolamine.     

Chemical reactions in fast atom bombardment mass spectrometry

Examples of various chemical reactions occurring in the matrix or in the selvedge region in fast atom bombardment (FAB) mass spectrometry are discussed. These are categorized as oxidations and reductions; substitutions; clusterings and additions; and sample decomposition or transformation. Some reactions observed showed significant time behaviour and in one case it was possible to determine rate constants. These data suggest that chemical reactions can be accelerated significantly by fast atom bombardment.     

Direct microanalysis by negative ion fast atom bombardment mass spectrometry

In negative ion fast atom bombardment (FAB) mass spectrometry, the use of a liquid matrix comprised of 15-crown-5—glycerol (1:10, v/v) enabled the molecular weight determination of small amounts of non-volatile acidic molecules. This ionization process could result in detection limits of less than one-fifth of those obtained using only glycerol as matrix. The function of the matrix as a proton acceptor is emphasized.     

Study of structural characteristic features of phenanthriondolizidine alkaloids by fast atom bombardment with tandem mass spectrometry

The mass spectrometric behavior of phenanthroindolizidine alkaloids has been investigated in detail by positive ion fast atom bombardment tandem mass spectrometry (FAB-MS/MS) combined with collision-induced dissociation (CID). The fragmentation has been correlated with the skeleton structure and positions of substituents. The product ions arising from retro-Diels-Alder cleavages differ clearly for compounds with different skeletons. The substituents at C-14 were observed to markedly influence the fragmentation pathway of [M + H](+) ions. A diversity of dissociation behavior initiated by the variation of substituents on the aromatic ring was also observed in the CID spectra. Product ions resulting from loss of CH(4) were obtained for compounds in which both C-6 and C-7 are occupied by methoxy groups. FAB-MS/MS spectra can reflect the connection between the fragmentation behavior and structural features of these phenanthroindolizidine alkaloids rapidly and effectively, and should prove to be a powerful method to determine the structures of related compounds.     

Characterization of sphingosine long-chain bases by fast atom bombardment and high-energy collision-induced decomposition tandem mass spectrometry

The fragmentation of protonated and cationized sphingosine and sphinganine under metastable and high-energy collision-induced decomposition is reported. The protonated compounds undergo abundant charge-remote fragmen tation of the long alkyl chain, while the cationized molecules yield much less abundant fragmentation and little or no electrocyclic fission of the hydrocarbon portion.     

Characterization of pyoverdins and their hydrolytic degradation products by fast atom bombardment and tandem mass spectrometry

All types of pyoverdins (siderophores produced by Pseudomonas strains) have the following ‘chromophore’ substructure in common: (1S)-5-amino-2,3-dihydro-8,9-dihydroxy-lH-pyrimido[l,2-α]quinoline-1-carboxyhic acid. Its hydrolysis product, (1S)-2,3-dihydro-5,8,9-trihydroxy-lH-pyrimido[l,2-α]quinoline-1-carboxylic acid, has been isolated and analysed for the first time by means of fast atom bombardment (FAB) and tandem mass spectrometry. This allows the pyoverdin chromophore to be identified. It was established that the fragmentation of pyoverdin [M + H]⁺ ions under FAB conditions is initiated by a retro-Diels-Alder decomposition of the tetrahydropyrimidine ring of the chromophore moiety, contributing to the structure elucidation of pyoverdins.     

Structural study of Mn(III)-tetraarylporphyrin complexes by fast atom bombardment mass spectrometry

A series of 27 Mn(III)-tetraarylporphyrins bearing heterogeneous substituents on the phenyl rings at the meso positions were subjected to positive ion fast atom bombardment mass spectrometry The source spectra yielded the molecular ion and a few peaks confirmative of the chemical structure. Major processes were hydrogenolytic loss of the aryl rings or of their substituents. Molecules carrying a side-chain underwent loss of the chain either as a solution process (amide linkage) or as a gas-phase process (phenolic ether linkage). Collisionally activated dissociation mass-analysed ion kinetic energy spectroscopy allowed discrimination between the two types of fragmentation processes and some other previously unreported gas-phase reaction channels to be recognized.     

Structural analysis of bufadienolide and cardenolide type cardiac glycosides by fast atom bombardment mass spectrometry

Summary Structural Analysis of Bufadienolide and Cardenolide Type Cardiac Glycosides by Fast Atom Bombardment Mass Spectrometry The direct analysis of underivatized cardiac glycosides of bufadienolide and cardenolide type and of their aglycones has been demonstrated by positive ion fast atom bombardment mass spectrometry. The technique allows unambiguous molecular weight determination. Furthermore it is extremely useful for determining the carbohydrate sequence and structural information of the aglycone. Positive ion spectra obtained with triethanolamine and 1,1,3,3-tetramethylurea as the supporting matrix is compared with data obtained from glycerol.This paper is dedicated to Univ.-Prof. Dr. A. Neckel on the occasion of his 60th birthday.