A fragmentation study on four C₁₉-diterpenoid alkaloids by electrospray ionization ion-trap time-of-flight tandem mass spectrometry

Abstract

High-resolution electrospray ionization ion-trap time-of-flight tandem mass spectrometry (HR-ESI-IT-TOF-MS(n)) in positive-ion mode was used to determine the accurate masses and fragmentation pathways of four C(19)-diterpenoid alkaloids, aconitine (1), yunnaconitine (2), crassicauline A (3), and benzoylmesaconine (4). The [M+H](+) ions of compounds 1-4 were readily observed in conventional single-stage mass spectrometry. Based on the MS(1-6) analyses, detailed fragmentation rules of the four compounds were proposed. The neutral losses of AcOH, MeOH, H(2)O, CO, C(2)H(4), PhCOOH and p-OMePhCOOH segments were the characteristic eliminations from the precursor ions due to the presence of acetyl, methoxyl, hydroxyl, N-ethyl, benzoyl and p-methoxyl-benzoyl units in the structures. Benefited from the high resolution of the mass analyzer, the loss of 28 Da corresponding to CO or CH(4) segment in product ions was unambiguously distinguished. The losing sequence of the main substituent groups was summarized as: C(8)-acetyl>C(16)-methotyl>C(15)-hydroxyl>C(6)-methoxyl>C(1)-methoxyl/C(3)-hydroxyl>C(18)-methoxyl>>C(13)-hydroxyl. The sequential loss of (16)-methoxyl moiety and CO (generating from enol-ketone tautomerism) groups could be recognized as the characteristic eliminations for the compounds with C(16)-methoxyl and C(15)-hydroxyl groups simultaneously. The application of HR-ESI-IT-TOF-MS(n) technique to investigate the fragmentation of C(19)-diterpenoid alkaloids provided useful information to understand their fragmentation behaviors.

Intramolecular hydrogen exchange prior to methanol loss from protonated methyl benzoates bearing different ring substituents under CID conditions

“…However, this process may be useful for identification of compounds (eg, isomer differentiation) and can be very interesting from the gas-phase ion chemistry point of view, as described in details in a number of papers. [1][2][3][4][5][6][7][8][9][10][11][12] There is also an interesting example of the loss of very long alcohols from protonated tetrahydropyranyl ethers. 13 Loss of methanol molecule has been also observed for protonated methyl esters of aminoacids.…”