Electron and chemical ionization mass spectrometry in stereochemical differentiation of some 1,3-amino alcohols

Mass spectral fragmentations of two cyclopentane, eight cyclohexane and four norbornane/one 1,3-amino alcohols were studied under electron ionization (EI) by low-resolution, high-resolution, metastable ion analysis and collision-induced dissociation (CID) techniques. All stereoisomeric compounds gave rise to identical 70 eV EI mass spectra. However, the spectra of positional isomers clearly differed. The main fragmentation pathway for the saturated compounds began as an α-cleavage reaction with respect to the nitrogen atom. For the norbornene compounds a retro-Diels—Alder reaction was favoured. Relative to the aminomethyl-substituted compounds the fragmentation patterns for the compounds having the amino group connected directly to the ring were more complicated. The chemical ionization (CI) mass spectra were recorded using ammonia, isobutane, methane, dichloromethane and acetone as reagent gas. From the norbornane/One compounds the di-exo isomers decomposed more easily than the di-endo isomers with most of the reagent gases used. Differences between stereoisomers were observed directly only under methane CI. The decomposition products of the [M + H]⁺ ions generated under ammonia and isobutane CI were studies by recording their CID mass spectra. These spectra allowed the differentiation of the stereoisomers, at least to some extent.     

Mass spectrometric behaviour of cyclopentane-and cyclohexane-condensed pyrimidinediones under electron impact

Mass spectral fragmentations of four cyclopentane-condensed cis-pyrimidinediones and of six cyclohexane-condensed cis- or trans-pyrimidinediones were examined using metastable ion analyses and exact mass measurements. The fragmentation patterns of all of these compounds were clearly different and also cis- and trans-fused isomers were easy to distinguish from each other by their mass spectra. In spite of the differences in their mass spectral fragmentations, all compounds formed phenylisocyanates (m/z 119 and 153) and anilines (m/z 93 and m/z 127), the structures of which were verified by collision-induced dissociation experiments.     

Laccase-catalyzed mediated oxidation of benzyl alcohol: the role of TEMPO and formation of products including benzonitrile studied by nanoelectrospray ionization Fourier transform ion cyclotron resonance mass spectrometry

Substituted benzyl alcohol was oxidized enzymatically with a laccase-mediator system and the products were investigated as a function of time by nanoelectrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (nanoESI-FTICRMS). With Trametes versicolor laccase (TVL), the mediator, 2,2',6,6'-tetramethylpiperidine-N-oxyl radical (TEMPO), undergoes oxidation and forms oxoammonium ion. Oxidized TEMPO oxidizes the alcohol and is simultaneously reduced to the N-OH form. The laccase then restores TEMPO back to the normal radical form and the oxidation cycle starts again. The role of TEMPO and the structures of its oxidized and reduced forms in the enzymatic oxidation process were clarified in collision-induced dissociation experiments and gas-phase hydrogen/deuterium (H/D) exchange reactions. The amounts of enzyme and mediator were significant for product formation: with greater amounts overoxidation products, the corresponding benzoic acid and benzonitrile were formed. Smaller amounts of laccase and mediator generated benzaldehyde in high yield. The reaction pathway for benzonitrile formation is discussed and it is suggested to start from benzaldehyde and the ammonia in the ammonium acetate buffer.     

Studies on the biomimetic preparation of the sarpagan ring system. Attempts to apply the spontaneous “biogenetic-type cyclization” of van Tamelen to bond formation between C-5 and C-16 in the corynantheine series

Attempts were made to apply the spontaneous “biogenetic-type cyclization” of van Tamelen to the preparation of the sarpagan ring system by utilizing indolo [2,3-a]quinolizidines 10, 11, 12, and 14. The fact that the spontaneous “biogenetic-type cyclization” did not take place casts some doubt on the correctness of the earlier results.     

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.     

Electron ionization mass spectra of some 4β-phenyl-substituted cycloalkane-cis-fused 1,3-oxazin-2(3H)-ones, -2(3H)-thiones and 1,4-oxazepin-3(4H)-ones

The 70 eV mass spectra of 4β-phenyl-substituted cyclopentane- and cyclohexane cis-fused 1,3-oxazin-2(3H)-ones, the two related 2-thiones, 6,7-cis-trimethylene-5β-phenyl-1,4-oxazepin-3(4H)-one and its 2β-methyl derivative were recorded and their fragmentations examined by means of metastable ion analysis, collision induced dissociation technique and exact mass measurement. The fragmentation patterns of the 1,3-oxazin-2(3H)-ones were relatively simple: the favored formation of cycloalkene ions implied that a considerable proportion of the molecular ions might possess an enol structure. Changes in the size of the fused cycloalkane ring had little or no effect on the fragmentations. Instead, small changes in the heterocyclic part of the molecule caused remarkable effects on the fragmentation behavior. Compared to 1,3-oxazin-2(3H)-ones studied, both 1,3-oxazine-2(3H)-thiones and 1,4-oxazepin-3(4H)-ones showed much more complicated fragmentation patterns.     

Reduction of 6/7-substituted 3-phenyltrop-3-en-2-ones: stereoselectivity and conformational analysis of the products

Reduction of 6/7-carboethoxy-3-phenyltrop-3-en-2-ones with H₂/Pd/C and NaBH₄ was studied in order to find a stereoselective route to the corresponding 3-phenyltropan-2-ones and 2α/2β-hydroxy-3-phenyltropanes. The 6/7-exo-carboethoxy-3-phenyltrop-3-en-2-ones were selectively reduced by Pd/C to 3β-phenyltropan-2-ones and 2α-hydroxy-3β-phenyltropanes. The corresponding 2β-hydroxy-3β-phenyl analogues were synthesized using NaBH₄, with a yield of 40%. Reduction of 6-endo-carboethoxy-3-phenyltrop-3-en-2-one yielded several products. The corresponding 7-endo-substituted analogue was selectively reduced with both Pd/C and NaBH₄ to 7-endo-carboethoxy-3β-phenyltropin-2-one. Analysis of stereochemically important ¹H NMR spectroscopy parameters was performed for all the products and used for conformational analysis in solution. X-ray analysis was performed for selected compounds.     

Characterization of the pH-dependent dissociation of a multimeric metalloprotein Streptomyces rubiginosus xylose isomerase by ESI FT-ICR mass spectrometry

We report an analysis of the pH-dependent dissociation of a multimeric metalloprotein, xylose isomerase from Streptomyces rubiginosus (XI), by electrospray ionization (ESI) Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry. Xylose isomerases are industrially significant enzymes that catalyze interconversion of aldose and ketose sugars. XI is biologically active as a approximately 173-kDa tetrameric complex, comprised of four identical approximately 43-kDa subunits and eight metal cations, unequivocally identified as the Mg(2+) cations in this work. ESI FT-ICR mass spectra of XI measured in the pH range of 3.0-6.9 indicated that the dissociation of the intact holo-tetramer is initiated by the loss of all eight Mg(2+) cations at pH 相似文献   

Synthesis and characterization of some derivatives of lupinine and aminolupinine. Collision induced dissociation mass spectrometry studies of protonated molecules

Some ester, amide and thioether derivatives of lupinine, aminolupinine and bromolupinine were synthesized and characterized in order to search biologically active compounds. The protonated molecules were studied by tandem mass spectrometry using collision induced dissociation (CID) technique in order to find out how different structural features and functional groups in different quinolizidine derivatives influence fragmentation behavior. Some theoretical calculations were also made to clarify the conformations of neutral and protonated molecules, to reveal the fragmentation routes and the product ions obtained. The functional groups clearly directed the fragmentations although the typical fragments for lupinine were still observed in all the cases. Theoretical calculations were in agreement with observed fragmentations and greatly helped interpretation of the CID spectra.     

Diastereochemical differentiation of β-amino acids using host-guest complexes studied by fourier transform ion cyclotron resonance mass spectrometry

Host-guest complexes where tetraethyl resorcarene was the host molecule were used to study the stereoselectivity of diasteromeric pairs of di-endo- and di-exo-2,3-disubstituted norbornane and norbornene amino acids by ion-molecule reactions and collision-induced dissociation with electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI FT-ICR MS). Both methods showed stereoselectivity for the diastereomeric pairs. Particularly high selectivity was achieved for di-endo- and di-exo-2,3-disubstituted norbornane amino acids with ion-molecule reactions. Also, ab initio and hybrid density functional theory calculations were performed to study the different structures of the host-guest complexes. Hydrogen bonding was crucial for the calculated lowest energy structures, and sterical considerations satisfactorily explained the ion-molecule reaction results.