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  • Analytical Chemistry and Spectroscopy  (4)
  • Prostaglandins  (2)
  • 2020-2022
  • 1990-1994  (6)
  • 1
    Electronic Resource
    Electronic Resource
    Alkane loss from collisionally activated alkylmethyleneimmonium ionsParts of this work were presented at the 12th International Mass Spectrometry Conference, Amsterdam, August 1991. (1991)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 26 (1991), S. 1061-1064 
    Details
    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The collision-induced dissociation (CID) spectra of five alkylmethyleneimmonium ions (H2C-N+R1R2, (a) R1 = R2 = C2H5, (b) R1 = n-C3H7, R2 = H, (c) R1 = n-C3H7, R2 = CH3, (d) R1 = n-C3H7, R2 = C2H5, (e) R1 = R2 = n-C3H7) are reported and discussed in terms of the mechanism of alkane loss. The most abundant alkane losses result from 2-azaallylic bond cleavages within R1 and R2 leading to daughter ions of m/z 84. Ion d (R1 = n-C3H7, R2 = C2H5) was chosen for a deuterium-labelling study because it exhibited methane loss nearly free from interferences with other fragmentations. The methane lost consists to a great extent (95%) of the methyl moiety of R2. Whereas the methyl moiety obviously stays intact during the fragmentation process, the hydrogen additionally needed originates from all positions of R1 and the double-bonded methylene in an approximately random distribution, suggesting extensive hydrogen migrations preceding the transfer step.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/oms.1210261206
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  • 2
    Electronic Resource
    Electronic Resource
    Alkene loss from metastable methyleneimmonium ions: Unusual inverse secondary isotope effect in ion-neutral complex intermediate fragmentations (1991)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 26 (1991), S. 1097-1108 
    Details
    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The mechanism of propene elimination from metastable methyleneimmonium ions is discussed. The first field-free region fragmentations of complete sets of isotopically labelled methyleneimmonium ions (H2C = \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm N}\limits^{\rm +} $\end{document}+R1R2: R1 = R2 = n-C3H7; R1 = R2 = i-C3H7; R1 = n -C3H7; R2 = C2H5; R1 = n-C3H7; R2 = CH3; R1 = n-C3H7; R2 = H) were used to support the mechanism presented. The relative amounts of H/D transferred are quantitatively correlated to two distinct mathematical concepts which allow information to be deduced about influences on reaction pathways that cannot be measured directly. Propene loss from the ions examined proceeds via ion-neutral complex intermediates. For the di-n-propyl species rate-determining and H/D distribution-determining steps are clearly distinct Whereas the former corresponds to a 1,2-hydride shift in a 1-propyl cation coordinated to an imine moiety, the latter is equivalent to a proton transfer to the imine occurring from the 2-propyl cation generated by the previous step. For the diisopropyl-substituted ions which directly form the 2-propyl cation-containing complex, the rate-determining hydride shift vanishes. The 2-propyl cation-containing complex can decompose directly or via an intermediate proton-bridged complex. Competition of these routes is not excluded by the experimental results. Assuming a 2:1:3 distribution, a preference for the α- and β-methylene of the initial n-propyl chain as the source of the hydrogen transferred is detected for n-propylimmonium ions containing a second alkyl chain R2. This preference shows a clear dependence on the steric influence of R2. During the transfer step isotopic substitution is found to affect the H/D distribution strongly. For the alternative route of McLafferty rearrangement leading to C2H4 loss, specific γ-H transfer is observed.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/oms.1210261214
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  • 3
    Electronic Resource
    Electronic Resource
    Propene loss of phenylpropylmethyleneiminium ions (1994)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 29 (1994), S. 153-154 
    Details
    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/oms.1210290307
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  • 4
    Electronic Resource
    Electronic Resource
    14N and 15N NMR spectroscopic characterization and analysis of cyclic sulfur imides (1992)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 30 (1992), S. 177-182 
    Details
    ISSN: 0749-1581
    Keywords: 14N and 15N NMR ; Cyclic sulfur imides ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The 14N and 15N NMR spectra of natural abuadance and 15N-enriched samples of S7NH and S4(NH)4 were obtained by direct detection and by a variety of polarization transfer techniques. Sensitivity enhancements of ca 10 (compared with direct detection) for the INEPT pulse sequence and ca 100 for the HMQC (heteronuclear multiple quantum coherence) + BIRD (bilinear rotation decoupling) sequence were observed for the imides. 15N spin-lattice relaxation constants (T1) of 10.2 ± 0.1 and 12.6 ± 0.1 s were determined for S7NH and S4(NH)4, respectively. The HMQC procedure was used to obtain the 15N and 1H NMR chemical shifts and 11J(15N, 1H) values for 1,3-,1,4- and 1,5-S6(NH)2, 1,3,5- and 1,3,6-S5(NH)3. The trends in NMR chemical shifts and coupling constants are discussed in the context of the known molecular structurts of cyclic sulfur imides. The use of NMR techniques for the analysis of mixtures of cyclic sulfur imides is compared with the well established methods of infrared spectroscopy and thin-layer chromatography.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrc.1260300216
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  • 5
    Electronic Resource
    Electronic Resource
    Electroorganic synthesis, 56. Synthesis of advanced prostaglandin precursors by Kolbe electrolysis, I. - Preparation of (1′R,4′S,3RS)-3-(cis-4-acetoxycyclopent-2-enyloxy)-3-ethoxypropionic acid (1994)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1994 (1994), S. 225-233 
    Details
    ISSN: 0170-2041
    Keywords: Kolbe electrolysis ; Radical cyclization ; Electrochemical dehalogenation ; Prostaglandins ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The key intermediate of a novel synthesis of prostaglandin precursors, (1′R,4′S,3R/S)-3-(cis-4-acetoxycyclopent-2-enyl oxy)-3-ethoxypropionic acid (3), is prepared by two different synthetic sequences: In a first strategy transacetalization of ethyl 3,3-diethoxypropionate (6) with (1R, 4S)-4-acetoxy-1-hydroxy-2-cyclopentene (7) leads to the formation of the mixed acetal 8. By subsequent hydrolysis and acylation 8 could be converted into acid 3 in six steps in 6% overall yield. However, the generation of acid 3 by bromoalkoxidation of 3-ethoxyacrylates 13d, e and subsequent electrochemical reduction proved to be more efficient. In this reduction it is possible to debrominate the α-bromo esters 14d, e and to remove the 2-haloethyl ester group in one step. Using this reaction sequence, we could synthesize acid 3 in five steps in 38% overall yield.
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199419940302
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  • 6
    Electronic Resource
    Electronic Resource
    Electroorganic synthesis, 57. Synthesis of advanced prostaglandin precursors by Kolbe electrolysis, II. - Preparation of coacids and anodic initiated tandem radical-addition / radical-coupling reaction with (1′R,4′S,3R/S)-3-(cis-4-acetoxycyclopent -2-enyloxy)-3-ethoxypropionic acid (1994)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1994 (1994), S. 235-242 
    Details
    ISSN: 0170-2041
    Keywords: Kolbe electrolysis ; Radical cyclization ; Si-C bond oxidation ; Prostaglandins ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The α-silyl-substituted carboxylic acids 4 and 10 were prepared and with other coacids subjected to a mixed Kolbe electrolysis with β-cyclopentenyloxypropanoate 1. The stereochemical course of this cyclization reaction was determined on the basis of the 4-methyl-substituted product 23 by 1H-NMR-NOE spectroscopy. Conversion of the bicyclic reaction products 21b-d to advanced prostaglandin precursors such as lactone 30 was achieved in few steps.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199419940303
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