Mass spectrometry of natural products: VIII—Mass spectrometric studies of ring a saturated gibberellins

The fragmentation behaviour of gibberellin A₁ methyl ester and gibberellin C methyl ester has been studied by means of positive and negative ion mass spectrometry, high resolution techniques and metastable ion transitions. The results obtained allow a mass spectrometric distinction to be made between both structural types.     

Mass spectrometric studies on azidomorphine derivatives

The mass spectrometric behaviour of nine azidomorphine derivatives have been studied. These compounds proved to have surprisingly specific and selective fragmentation under electron-impact. For 6-deoxy-6-azido-dihydro-isomorphine derivatives (I to V) the main decomposition pathway involves the loss of an N₂ molecule followed by a very rapid and selective fragmentation process. On the other hand, the molecular ions of 6-deoxy-8-azido-pseudomorphine derivatives (VI to VIII) and 6-deoxy-6-azido-14-hydroxy-isocodein (IX) primarily decompose by loss of the N₃ radical. This is due to the allylic effect of the double bond in ring C, corresponding to the chemical behaviour of these compounds.     

Mass spectrometric studies of 2-nitrosophenols

The mass spectra of 2-nitrosophenols are independent of the insertion temperature, suggesting that the compounds either do not exhibit tautomerism in the vapour phase or that the enthalpy of isomerization is low. However, their fragmentation patterns suggest tautomerism in the molecular ion.     

Mass spectrometric studies of benzoxazine resorcarenes

Eleven differently substituted 3,4-dihydro-2H-1,3-benzoxazine resorcarenes were studied by electrospray ionisation (ESI) and matrix-assisted laser desorption/ionisation (MALDI) mass spectrometry, using Fourier transform ion cyclotron resonance (FT-ICR) and time-of-flight (TOF) mass spectrometers, respectively. Under ESI conditions it was possible to transfer the intact resorcarenes from solution to the gas phase, yielding [M + H](+) and [M + 2H](+) ions as the main ions observed. Energy increase of the ions induced ready decomposition through successive eliminations of four CH(2)NR groups. Ion-molecule reactions showed that the ionising proton was situated somewhere inside the molecule and could not be reached with neutral reagent gases. In the host-guest complexation experiments, the benzoxazine resorcarenes studied turned out to be poor hosts for alkali metal and ammonium ions. In MALDI experiments, 2,5-dihydroxybenzoic acid proved to be the best matrix for these compounds. However, the intensity of the [M + H](+) ions was low for all compounds, and extensive fragmentation with consecutive elimination of CH(2)NR groups was observed.     

Mass spectrometric studies of phenoxarsine derivatives

Nine phenoxarsine derivatives with arsenic in the trivalent state and the pentavalent state are synthesized and studied by mass spectrometry. Their characteristic fragmentation modes and the fragment ions with common structures are discussed. Phenoxarsinic acids are found to be unstable in the gaseous phase at the temperatures studied and tend to form their corresponding anhydrides.     

Mass spectrometric studies of anomeric glycopyranosyl azides

We studied the mass spectrometric behaviour of peracetylated and underivatized anomeric hexopyranosyl azides and 5-thioglucopyranosyl azides by means of different mass spectrometric techniques. The unstable molecular ions fragment predominantly by losing either N3 radical or N2 molecule. Loss of N2 molecule and the protonation of the derived nitrene were characteristic of the studied compounds. The presence of BF3.Et2O in the ion source is favorable for producing the protonated nitrene form. The protonated nitrene shows a new type of ring expansion rearrangement. The abundances of the [M + H - N2]+ ion makes it possible to identify the anomeric configuration of the azido group.     

Mass spectrometric studies on platinum (II) complexes

Several platinum(I1) complexes were subjected to mass spectrometric investigation. The major fragmentation pathways for dichloro-bis(phosphine) platinum(II) were elucidated to be: (i) successive loss of hydrogen chloride or chlorine depending on the structure of the phosphine, (ii) cleavage of P–R bond with the loss of R group, (iii) the presence of [R¹R²R³P—Cl]+ in the mass spectra and (iv) fragmentation of the free phosphine.     

Mass spectrometric studies of the pterocarpan skeleton

The mass spectrometric characteristics of the pterocarpan skeleton have been studied with the aid of metastable decomposition (CAD-MIKES), high resolution mass measurements and specific deuterium labeling. New structural rotations have been postulated for the [M - H](+) ions which can explain the fragmentation routes for the pterocarpan skeleton.     

Mass spectrometric studies of some novel sulfonamides

A recent paper described the overall 5-endo cyclisation of homoallylic sulfonamides to give pyrrolidines. This reaction was also used to prepare polycyclic systems. Mass spectrometric analysis using classical electron ionisation spectra and accurate mass measurement played a vital role in confirming the proposed structures for the products. These materials were not amenable to newer mass spectrometric methods and this study shows the continuing importance of older techniques.     

Mass spectrometric studies of dithiophosphinato metal complexes

Electron impact induced fragmentation reactions of planar, tetrahedral, octahedral and oligomeric metal dithiophosphinates Me(II)L₂ (L=Et₂PS₂^?; Me(II)=Zn, Cd, Hg, Pb, Co, Mn, Ni, Pd, Pt), Me(III)L₃ (Me(III) = Sb, Bi, In, Rh, Ir) and (Me(I)I)_n (Me(I)/n=Tl/1, Au/2, Cu/4) have been studied. Fragmentation patterns, which are in accordance with metastable peak determinations by linked scans, are reported. In the case of the transition metals the spectra of the complexes show abundant [M]^+· predominantly metal containing ions and, the former being weak and the intensities of the latter being considerably reduced in the case of metal complexes with filled d shells. With planar or tetrahedral transition metal complexes no dependence of fragmentation on the coordination geometry can be observed. The dependence of fragmentation on d configuration, ionization energy of the metal and metal ligand π bonding is discussed. In the case of the oligomeric complexes strong metal-metal interaction is observed even under electron impact.     

Mass spectrometric and pyrolytic studies of diphenylarsine derivatives

The trivalent diphenylarsine derivatives studied gave molecular ions and diagnostic common fragment ions at m/e 229, 227, 154, 153, 152, 151, 77 and 51. The diphenylarsine odd electron ion, m/e 229, undergoes the “ortho coupling” reaction before splitting off the arsenic atom. The correlation between the ion fragmentation and the pyrolytic decompositions is discussed.     

Mass spectrometric studies of 4-oxo-4,5,6,7-tetrahydrobenzofurans

The mass spectra of alkyl and aryl 4-oxo-4,5,6,7-tetrahydrobenzofurans have been determined and the fragmentation patterns are established unambiguously by deuterium labelling in the 5,5,7,7-d₄ position.     

Mass spectrometric studies of cisplatin-induced changes of hemoglobin

This study reports on structural changes of hemoglobin (Hb) that were induced by cisplatin binding. Two techniques, nanoelectrospray quadrupole time-of-flight mass spectrometry (nanoES-MS) and high-performance liquid chromatography with inductively coupled plasma mass spectrometry (HPLC/ICPMS), were developed to facilitate this study. Nanospray MS analyses of cisplatin and Hb reaction mixtures demonstrated that the ion at m/z 616.5, the heme group, increased with an increase of cisplatin concentration, indicating the loss of heme groups from the intact protein. This conclusion was also supported by the increase of cisplatin-alpha or -beta complex formation. The change of the Hb-bound Fe was further investigated by monitoring Fe signals using size-exclusion HPLC/ICPMS. After incubation with cisplatin at clinically relevant concentrations, under physiological conditions, the amount of Fe bound to Hb was reduced while formation of cisplatin-Hb complexes increased. Flow-injection ICPMS analysis of the Fe contents in the low molecular weight fraction (<3000 Da) of the reaction mixtures after size fractionation further demonstrated a corresponding increase of Fe with the increase of cisplatin concentrations. HPLC/ICPMS detected three Hb-cisplatin complexes, one of which eluted at the same retention time as Hb while the other two complexes eluted later than Hb. With clinically relevant concentrations of cisplatin (0.05-1.0 microM) and 10 microM of Hb, the concentrations of the Hb-cisplatin complexes were determined in the range 0.1-64 nM. These results, obtained from nanoES-MS, HPLC/ICPMS, and FIA-ICPMS, demonstrate that cisplatin binding to Hb resulted in the dissociation of the heme group from the intact protein.     

Mass spectrometric studies on the formation of chiral N-sulphonylated oxazaborolidinones

The formation of N-tosyl-2-phenyl-1,3,2-oxazaborolidin-5-one 1 as a result of a condensation reaction between N-tosyl valine 2 and phenyl boronic acid was studied as a model of the formation of chiral oxazaborolidines used as Lewis acidic catalysts for various enantioselective syntheses. Intermediates of the formation of 1 along with those arising from further reactions (of 1) were investigated by electrospray ionization mass spectrometry (ESI-MS). Results of the study indicate that one phenyl boronic acid may react with one or two molecules of 2 and/or with one or two molecules of phenyl boronic acid. In addition, side-products implying dephenylation of 1 and self-condensation of phenyl boronic acid (formation of triphenylboroxine) were found.     

Mass spectrometric studies on the decomposition of trialkylgallium on gaas surfaces

The thermal decomposition of trimethylgallium [(CH₃)₃Ga] and triethylgallium [(C₂H₅)₃Ga] on gallium arsenide (GaAs) surfaces was studied under an ultra-high vacuum using mass spectrometry. It was observed that the decomposition process of (CH₃)₃Ga and (C₂H₅)₃Ga depends on the arsenic coverage of the substrate surface. On a (100)-oriented surface, increasing the arsenic coverage basically enhances the decomposition of (CH₃)₃Ga and (C₂H₅)₃Ga to gallium atoms above 350 and 300°C, respectively. The decomposition of (CH₃)₃Ga proceeds by emitting CH₃ radicals. On a surface with low arsenic coverage, the decomposition of (CH₃)₃Ga is imperfect and fewer than three methyl groups of alkylgallium are desorbed. On a (111)B-oriented surface, however, an increase in the surface arsenic coverage suppresses the decomposition of alkylgallium, which is different from the case for a (100) surface.     

Mass spectrometric studies on a β-ketosulfone

The fragmentation of the β-ketosulfone-γ-methylsulfonyl-γ-benzoylbutyronitrile under electron bombardment follows a number of different pathways: formation of the benzoyl ion (Major path); remova of acrylonitrile; liberation of the methylsulfonyl radical or of methylsulfonic acid; and finally elimination of a methylenecyano radical. The fragments observed can be explained by these five degradation paths. The reactions are compared with the photochemical cleavage of this β-ketosulfone in benzene solution.