1
|
Schmidt J, Kuck D, Franke K, Sultani H, Laub A, Wessjohann LA. The unusual fragmentation of long-chain feruloyl esters under negative ion electrospray conditions. JOURNAL OF MASS SPECTROMETRY : JMS 2019; 54:549-556. [PMID: 30912235 DOI: 10.1002/jms.4357] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/14/2019] [Revised: 03/18/2019] [Accepted: 03/20/2019] [Indexed: 06/09/2023]
Abstract
Long-chain ferulic acid esters, such as eicosyl ferulate (1), show a complex and analytically valuable fragmentation behavior under negative ion electrospay collision-induced dissociation ((-)-ESI-CID) mass spectrometry, as studied by use of a high-resolution (Orbitrap) mass spectrometer. In a strong contrast to the very simple fragmentation of the [M + H]+ ion, which is discussed briefly, the deprotonated molecule, [M - H]- , exhibits a rich secondary fragmentation chemistry. It first loses a methyl radical (MS2 ) and the ortho-quinoid [M - H - Me]-• radical anion thus formed then dissociates by loss of an extended series of neutral radicals, Cn H2n + 1 • (n = 0-16) from the long alkyl chain, in competition with the expulsion of CO and CO2 (MS3 ). The further fragmentation (MS4 ) of the [M - H - Me - C3 H7 ]- ion, discussed as an example, and the highly specific losses of alkyl radicals from the [M - H - Me - CO]-• and [M - H - Me - CO2 ]-• ions provide some mechanistic and structural insights.
Collapse
Affiliation(s)
- Jürgen Schmidt
- Department of Bioorganic Chemistry, Leibniz Institute of Plant Biochemistry, Weinberg 3, D-06120, Halle/Saale, Germany
| | - Dietmar Kuck
- Department of Chemistry, Bielefeld University, Universitätsstraße 25, D-33615, Bielefeld, Germany
| | - Katrin Franke
- Department of Bioorganic Chemistry, Leibniz Institute of Plant Biochemistry, Weinberg 3, D-06120, Halle/Saale, Germany
| | - Haider Sultani
- Department of Bioorganic Chemistry, Leibniz Institute of Plant Biochemistry, Weinberg 3, D-06120, Halle/Saale, Germany
| | - Annegret Laub
- Department of Bioorganic Chemistry, Leibniz Institute of Plant Biochemistry, Weinberg 3, D-06120, Halle/Saale, Germany
| | - Ludger A Wessjohann
- Department of Bioorganic Chemistry, Leibniz Institute of Plant Biochemistry, Weinberg 3, D-06120, Halle/Saale, Germany
| |
Collapse
|
2
|
Polguj M, Frański R, Zalas M, Gierczyk B, Jankowski W, Hoffmann M. Intramolecular hydrogen exchange prior to methanol loss from protonated methyl benzoates bearing different ring substituents under CID conditions. JOURNAL OF MASS SPECTROMETRY : JMS 2018; 53:1022-1025. [PMID: 30035836 DOI: 10.1002/jms.4273] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/28/2018] [Revised: 07/11/2018] [Accepted: 07/12/2018] [Indexed: 06/08/2023]
Affiliation(s)
- Monika Polguj
- Faculty of Chemistry, Adam Mickiewicz University, Umultowska 89B, 61-614, Poznań, Poland
| | - Rafał Frański
- Faculty of Chemistry, Adam Mickiewicz University, Umultowska 89B, 61-614, Poznań, Poland
| | - Maciej Zalas
- Faculty of Chemistry, Adam Mickiewicz University, Umultowska 89B, 61-614, Poznań, Poland
| | - Błażej Gierczyk
- Faculty of Chemistry, Adam Mickiewicz University, Umultowska 89B, 61-614, Poznań, Poland
| | - Wojciech Jankowski
- BioInfoBank Institute, Św. Marcin 80/82 lok. 355, 61-809, Poznań, Poland
| | - Marcin Hoffmann
- Faculty of Chemistry, Adam Mickiewicz University, Umultowska 89B, 61-614, Poznań, Poland
| |
Collapse
|
3
|
Xia H, Zhang Y, Attygalle AB. Experimental and Theoretical Studies on Gas-Phase Fragmentation Reactions of Protonated Methyl Benzoate: Concomitant Neutral Eliminations of Benzene, Carbon Dioxide, and Methanol. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2018; 29:1601-1610. [PMID: 29881998 DOI: 10.1007/s13361-018-1997-8] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/17/2018] [Revised: 05/07/2018] [Accepted: 05/13/2018] [Indexed: 06/08/2023]
Abstract
Protonated methyl benzoate, upon activation, fragments by three distinct pathways. The m/z 137 ion for the protonated species generated by helium-plasma ionization (HePI) was mass-selected and subjected to collisional activation. In one fragmentation pathway, the protonated molecule generated a product ion of m/z 59 by eliminating a molecule of benzene (Pathway I). The m/z 59 ion (generally recognized as the methoxycarbonyl cation) produced in this way, then formed a methyl carbenium ion in situ by decarboxylation, which in turn evoked an electrophilic aromatic addition reaction on the benzene ring by a termolecular process to generate the toluenium cation (Pathway II). Moreover, protonated methyl benzoate undergoes also a methanol loss (Pathway III). However, it is not a simple removal of a methanol molecule after a protonation on the methoxy group. The incipient proton migrates to the ring and randomizes to a certain degree before a subsequent transfer of one of the ring protons to the alkoxy group for the concomitant methanol elimination. The spectrum recorded from deuteronated methyl benzoate showed two peaks at m/z 105 and 106 for the benzoyl cation at a ratio of 2:1, confirming the charge-imparting proton is mobile. However, the proton transfer from the benzenium intermediate to the methoxy group for the methanol loss occurs before achieving a complete state of scrambling. Graphical Abstract ᅟ.
Collapse
Affiliation(s)
- Hanxue Xia
- Center for Mass Spectrometry, Department of Chemistry and Chemical Biology, Stevens Institute of Technology, Hoboken, NJ, 07030, USA
| | - Yong Zhang
- Center for Mass Spectrometry, Department of Chemistry and Chemical Biology, Stevens Institute of Technology, Hoboken, NJ, 07030, USA
| | - Athula B Attygalle
- Center for Mass Spectrometry, Department of Chemistry and Chemical Biology, Stevens Institute of Technology, Hoboken, NJ, 07030, USA.
| |
Collapse
|
4
|
Nikolić D, Macias C, Lankin DC, van Breemen RB. Collision-induced dissociation of phenethylamides: role of ion-neutral complexes. RAPID COMMUNICATIONS IN MASS SPECTROMETRY : RCM 2017; 31:1385-1395. [PMID: 28558170 PMCID: PMC5555735 DOI: 10.1002/rcm.7915] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/15/2017] [Revised: 04/21/2017] [Accepted: 05/25/2017] [Indexed: 06/07/2023]
Abstract
RATIONALE Phenethylamides are a large group of naturally occurring molecules found both in the plant and animal kingdoms. In addition, they are used as intermediates for the synthesis of pharmaceutically important dihydro- and tetrahydroisoquinolines. To enable efficient characterization of this class of molecules, a detailed mass spectrometric fragmentation study of a broad series of analogs was carried out. METHODS The test compounds were synthesized using standard methods for amide bond formation. Low-energy high-resolution tandem mass spectra were acquired on a hybrid quadrupole/time-of-flight mass spectrometer using positive ion electrospray ionization. RESULTS A total of 26 analogs were investigated in the study. Fragmentation of phenethylamides was found to proceed via intermediate ion-neutral complexes. The complexes can break down via multiple pathways including dissociation, proton transfer, Friedel-Crafts acylation, and single electron transfer. The relative contribution of each of these pathways strongly depends on the structure of the coupling amine and acid. CONCLUSIONS A general scheme for the fragmentation of phenethylamides was developed. This study further extends the knowledge base of the ion-neutral complex by discovering Friedel-Crafts acylation as a novel reaction. The strong influence of minor structural modifications on the fragmentation patterns highlights the importance of testing many analogs in order to fully predict a fragmentation pattern of a particular class of molecules.
Collapse
Affiliation(s)
- Dejan Nikolić
- Corresponding Author: Dejan Nikolić, Department of Medicinal Chemistry and Pharmacognosy, University of Illinois at Chicago, 833 S. Wood St., Chicago, IL 60612-7231, Telephone (312) 413-5867, FAX (312) 996-7107,
| | | | | | | |
Collapse
|
5
|
Shen S, Chai Y, Dai L, Li C, Pan Y. Gas-phase C α C β double bond cleavage in the dissociation of protonated 2-benzylidenecyclopentanones: Dissociative proton transfer and intramolecular proton-transport catalysis. Tetrahedron 2017. [DOI: 10.1016/j.tet.2017.04.010] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
|
6
|
Xu S, Pavlov J, Attygalle AB. Collision-induced dissociation processes of protonated benzoic acid and related compounds: competitive generation of protonated carbon dioxide or protonated benzene. JOURNAL OF MASS SPECTROMETRY : JMS 2017; 52:230-238. [PMID: 28171689 DOI: 10.1002/jms.3920] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/12/2016] [Revised: 02/01/2017] [Accepted: 02/02/2017] [Indexed: 06/06/2023]
Abstract
Upon activation in the gas phase, protonated benzoic acid (m/z 123) undergoes fragmentation by several mechanisms. In addition to the predictable water loss followed by a CO loss, the m/z 123 ion more intriguingly eliminates a molecule of benzene to generate protonated carbon dioxide (H - O+ ═ C ≡ O, m/z 45), or a molecule of carbon dioxide to yield protonated benzene (m/z 79). Experimental evidence shows that the incipient proton ambulates during the fragmentation processes. For the CO2 or benzene loss, protonated benzoic acid transfers the charge-imparting proton initially to the ortho position and then to the ipso position to generate a transient species which dissociates to form an ion-neutral complex between benzene and protonated CO2 . The formation of the m/z 45 ion is not a phenomenon unique to benzoic acid: spectra from protonated isophthalic acid, terephthalic acid, trans-cinnamic acid and some aliphatic acids also displayed a peak for m/z 45. However, the m/z 45 peak is structurally diagnostic only for certain benzene polycarboxylic acids because the spectra of compounds with two carboxyl groups on adjacent ring carbons do not produce a peak at m/z 45. For the m/z 79 ion to be formed, an intramolecular reaction should take place in which protonated CO2 within the ion-neutral complex acts as the attacking electrophile to transfer a proton to benzene. Copyright © 2017 John Wiley & Sons, Ltd.
Collapse
Affiliation(s)
- Sihang Xu
- Center for Mass Spectrometry, Department of Biomedical Engineering, Chemistry and Biological Sciences, Stevens Institute of Technology, 1 Castle Point on the Hudson, Hoboken, NJ, USA, 07030
| | - Julius Pavlov
- Center for Mass Spectrometry, Department of Biomedical Engineering, Chemistry and Biological Sciences, Stevens Institute of Technology, 1 Castle Point on the Hudson, Hoboken, NJ, USA, 07030
| | - Athula B Attygalle
- Center for Mass Spectrometry, Department of Biomedical Engineering, Chemistry and Biological Sciences, Stevens Institute of Technology, 1 Castle Point on the Hudson, Hoboken, NJ, USA, 07030
| |
Collapse
|
7
|
Hassan I, Pavlov J, Errabelli R, Attygalle AB. Oxidative Ionization Under Certain Negative-Ion Mass Spectrometric Conditions. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2017; 28:270-277. [PMID: 27822704 DOI: 10.1007/s13361-016-1527-5] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/22/2016] [Revised: 10/09/2016] [Accepted: 10/10/2016] [Indexed: 06/06/2023]
Abstract
1,4-Hydroquinone and several other phenolic compounds generate (M - 2) -• radical-anions, rather than deprotonated molecules, under certain negative-ion mass spectrometric conditions. In fact, spectra generated under helium-plasma ionization (HePI) conditions from 1,4-hydroquinone and 1,4-benzoquinone (by electron capture) were practically indistinguishable. Because this process involves a net loss of H• and H+, it can be termed oxidative ionization. The superoxide radical-anion (O2-•), known to be present in many atmospheric-pressure plasma ion sources operated in the negative mode, plays a critical role in the oxidative ionization process. The presence of a small peak at m/z 142 in the spectrum of 1,4-hydroquinone, but not in that of 1,4-benzoquinone, indicated that the initial step in the oxidative ionization process is the formation of an O2-• adduct. On the other hand, under bona fide electrospray ionization (ESI) conditions, 1,4-hydroquinone generates predominantly an (M - 1) - ion. It is known that at sufficiently high capillary voltages, corona discharges begin to occur even in an ESI source. At lower ESI capillary voltages, deprotonation predominates; as the capillary voltage is raised, the abundance of O2-• present in the plasma increases, and the source in turn increasingly behaves as a composite ESI/APCI source. While maintaining post-ionization ion activation to a minimum (to prevent fragmentation), and monitoring the relative intensities of the m/z 109 (due to deprotonation) and 108 (oxidative ionization) peaks recorded from 1,4-hydroquinone, a semiquantitative estimation of the APCI contribution to the overall ion-generation process can be obtained. Graphical Abstract ᅟ.
Collapse
Affiliation(s)
- Isra Hassan
- Center for Mass Spectrometry, Department of Chemistry, Chemical Biology, and Biomedical Engineering, Stevens Institute of Technology, Hoboken, NJ, 07030, USA
| | - Julius Pavlov
- Center for Mass Spectrometry, Department of Chemistry, Chemical Biology, and Biomedical Engineering, Stevens Institute of Technology, Hoboken, NJ, 07030, USA
| | - Ramu Errabelli
- Center for Mass Spectrometry, Department of Chemistry, Chemical Biology, and Biomedical Engineering, Stevens Institute of Technology, Hoboken, NJ, 07030, USA
| | - Athula B Attygalle
- Center for Mass Spectrometry, Department of Chemistry, Chemical Biology, and Biomedical Engineering, Stevens Institute of Technology, Hoboken, NJ, 07030, USA.
| |
Collapse
|