Study of fragmentation pathways of lithiated α,β‐unsaturated thioesters by electrospray ionization mass spectrometry

Abstract

The fragmentation pathways of lithiated alpha,beta-unsaturated thioesters with different substituents were investigated by electrospray ionization tandem mass spectrometry (ESI-MS/MS) in positive ion mode. In mass spectrometry of the alpha,beta-unsaturated thioesters, Ar-CH=CH-CO-S-Ph, loss of PhSLi and elimination of a thiophenol were the two major fragmentation reactions of the lithiated molecules. The elemental compositions of all the ions were confirmed by high-resolution Fourier transform ion cyclotron resonance tandem mass spectrometry (FTICR-MS/MS). The thioesters studied here were para-monosubstituted on the phenyl ring of cinnamoyl and the electron-withdrawing groups favored loss of a thiophenol, whereas the electron-releasing groups strongly favored the competing reaction leading to the loss of PhSLi to form a cinnamoyl cation, Ar-CH=CHCO(+). The intensity ratios of the two competitive product ions were well correlated with the sigma(p) (+) substituent constants. The mechanisms of these two competing routes were further investigated by density functional theory (DFT) calculations.

Neutral losses of sodium benzoate and benzoic acid in the fragmentation of the [M + Na]+ ions of methoxyfenozide and tebufenozide via intramolecular rearrangement in electrospray ionization tandem mass spectrometry

“…(a) are the water adducts of m/z 156, 319 and 375, respectively. The formation of water solvated product ions in the fragmentation of lithiated compounds in mass spectrometry is often observed . Similarly, in the fragmentation of the [M + Na] + ion of methoxyfenozide, the product ion m/z 259 (Fig.…”

Gas Phase Chemistry of Li+with Amides: the Observation of LiOH Loss in Mass Spectrometry

“…The base peak (ion b at m/z 238) was produced by the Smiles rearrangement [49] reaction (the nucleophilic attack of the amide nitrogen atom to the pyrimidine carbon atom). Ion c is 18 Da more than ion b, and it was confirmed by FTICR-MS/MS that ion c resulted from the solvation [24] of the ion b (Table S2). Ion d at m/z 139, 4,6-dimethoxypyrimidin ion, was produced by the direct cleavage of C-S bond.…”

“…On the other hand, the mass spectrometric fragmentations of metal cationized, especially lithiated biomolecules, have attracted much attention because of the desire to measure intrinsic metal ion affinity and identify the binding sites [14,15], and because the interesting dissociation pathways exhibited by these compounds are usually different from the protonated and deprotonated analogues [16,17]. Recently, the fragmentation behaviors of lithiated species have been reported for peptides, fatty acids, phospholipids, polytetrahydrofuran, cardiolipins, thioesters, cholesteryl esters, and disaccharides [18][19][20][21][22][23][24][25][26].…”

Fragmentation pathways of synthetic and naturally occurring coumarin derivatives by ion trap and quadrupole time‐of‐flight mass spectrometry

“…Mass spectrometry, especially ion‐trap mass spectrometry (ITMS n ) and quadrupole time‐of‐flight mass spectrometry (QTOFMS), is an essential method for the characterization of natural and synthetic compounds. ITMS n is often used for structural identification and fragmentation elucidation, because it generates fragment ions step by step . QTOFMS provides the elemental compositions of precursor ions and fragment ions, which can be used to rationalize the proposed fragmentation pathways .…”

“…ITMS n is often used for structural identification and fragmentation elucidation, because it generates fragment ions step by step. [18][19][20][21] QTOFMS provides the elemental compositions of precursor ions and fragment ions, which can be used to rationalize the proposed fragmentation pathways. [22][23][24][25] The combination of ITMS n and QTOFMS is a powerful tool for structural identification and fragmentation pathway studies.…”