Gas‐phase reactivity of protonated 2‐oxazoline derivatives: mass spectrometry and computational studies

Vessecchi, Ricardo; Tomaz, José Carlos; Santos, Guilherme Purcote dos; Oliveira, Alfredo R. M. de; Lopes, Norberto Peporine; Clososki, Giuliano C.

doi:10.1002/rcm.6182

Cited by 10 publications

(16 citation statements)

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“…Recently, this type of DFT calculation was used to distinguish between the intermediates of terpene isopimaranes and the results obtained were used to increase the understanding of the biosyntheses for these compounds; for these reasons we chose this model . Determination of the protonation site was performed by calculation of the gas‐phase basicity (GB) for each possible protonation site, by using the reaction between the neutral molecules with a proton …”

Section: Methodsmentioning

confidence: 99%

Electrospray ionization tandem mass spectrometry analysis of isopimarane diterpenes from Velloziaceae

Pinto

Vessecchi

Silva³

et al. 2015

Rapid Comm Mass Spectrometry

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2 RATIONALE: The study of natural products by electrospray ionization tandem mass spectrometry (ESI-MS/MS) is an important strategy for the characterization of the major fragmentation reactions which can then help to determine the composition of complex mixtures. Application of ESI-MS/MS to a series of isopimarane diterpenes from Velloziaceae allowed the rationalization of their fragmentation mechanisms. METHODS:Velloziaceae diterpenes were isolated by silica gel column chromatography and investigated by ESI-MS/MS analysis. The fragmentation studies were performed on a quadrupoletime-of-flight instrument using N2 as the collision gas. To help rationalize the fragmentation pathways observed, the geometry and sites of reactivity of the diterpenes were obtained by theoretical calculations using the B3LYP/6-31 + G(d,p) model. Fragmentation mechanisms were proposed on the basis of the calculated protonation sites and product ions energies using density functional theory (DFT) methods. RESULTS:The presence of hydroxyl and carbonyl groups on the terpene core influences the protonation site observed. One compound showed a radical cation as the base peak. MS/MS spectra exhibit water elimination as the major fragmentation pathway (via two ways), either when protonation takes place on the oxygen atom, or through elimination after activation from hydrogen migration. After the elimination of water, the formation of an endocyclic double bond induces a sequential retro-Diels-Alder (RDA) reaction as the major fragmentation step. CONCLUSIONS:A thorough rational analysis of the fragmentation mechanisms of protonated Velloziaceae diterpenes was used to propose the dissociation mechanisms in ESI-MS/MS. The presence of esters in the side chain also influenced the intensity or occurrence of the observed protonated or cationized molecules in ESI-MS. These results will aid the identification of analogues in sample extracts in future metabolomics studies.Keywords: fragmentation mechanism, Velloziaceae, natural products, terpene 3 IntroductionThe Velloziaceae family comprises about 270 species which are distributed mainly in South America and Africa. These plants are found growing in inhospitable environments -sandy and/or rocky soils, with high solar irradiation and low amounts of water. A typical biome is found above 1000 m altitude -known as rupestrian fields 1 . Despite this apparent weakness, many Velloziaceae species present a striking feature of being desiccation tolerant resurrection plants, such as species of the Vellozia genus and the African Xerophyta and Talbotia The structural characterization of the isopimarane diterpenes presented in this paper was performed by 1D and 2D nuclear magnetic resonance (NMR) spectroscopy and compared with previously published data. Although NMR is a most efficient method for the complete structural elucidation of natural products, 6 , 7 a relatively large amount of pure sample is required. This involves timeconsuming and costly isolation procedures or the use of expensive and complex (LC)/NMR ...

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Section: Methodsmentioning

confidence: 99%

Electrospray ionization tandem mass spectrometry analysis of isopimarane diterpenes from Velloziaceae

Pinto

Vessecchi

Silva³

et al. 2015

Rapid Comm Mass Spectrometry

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“…It is important to define the fragmentation mechanism of protonated alkaloids under collision‐induced dissociation (CID) when we apply this mechanism in structural elucidation studies . In addition, it is essential to gather information about the reactive sites and the stability of ions by computational chemistry to support the fragmentation mechanism of a series of compounds . In the present investigation, we have combined MS analysis with computational chemistry to analyze erythrinian alkaloids.…”

Section: Introductionmentioning

confidence: 99%

Gas‐phase dissociation study of erythrinian alkaloids by electrospray ionization mass spectrometry and computational methods

et al. 2017

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Alkaloids from plants of the genus Erythrina display important biological activities, including anxiolytic action. Characterization of these alkaloids by mass spectrometry (MS) has contributed to the construction of a spectral library, has improved understanding of their structures and has supported the proposal of fragmentation mechanisms in light of density functional calculations. In this study, we have used low-resolution and high-resolution MS analyses to investigate the fragmentation patterns of erythrinian alkaloids; we have employed the B3LYP/6-31+G(d,p) model to obtain their reactive sites. To suggest the fragmentation mechanism of these alkaloids, we have studied their protonation sites by density functional calculation, and we have obtained their molecular electrostatic potential map and their gas-phase basicity values. These analyses have indicated the most basic sites on the basis of the proton affinities of the nitrogen and oxygen atoms. The protonated molecules were generated by two major fragmentations, namely, neutral loss of CH OH followed by elimination of H O. High-resolution analysis confirmed elimination of NH by comparison with the losses of H and •CH . NH was eliminated from compounds that did not bear a substituent on ring C. The benzylic carbocation initiated the dissociation mechanism, and the first reaction involved charge transfer from a lone pair of electrons in the oxygen atoms. The second reaction consisted of ring contraction with loss of a CO molecule. The presence of hydroxy and epoxy groups could change the intensity or the occurrence of the fragmentation pathways. Given that erythrinian alkaloids are applied in therapeutics and are promising leads for the development of new drugs, the present results could aid identification of several analogues of these alkaloids in biological samples and advance pharmacokinetic studies of new plant derivatives based on MS and MS/MS analyses. Copyright © 2017 John Wiley & Sons, Ltd.

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“…The methoxyl and hydroxyl substituents at C‐3 and C‐3′ of compounds 2 and 3 , respectively, could be distinguished on the basis of the diagnostic ions formed from product ion D . For compound 3 , product ions H ( m/z 277, [ D –H 2 O] + ) and M ( m/z 249, [ H –CO] + ) originate from product ion D by remote hydrogen rearrangement and further decarbonylation (ΔH = 47.8 kcal/mol and ΔG = 35.7 kcal/mol), as shown in Scheme . Product ion H formation from product ion D (ΔH = 77.6 kcal/mol and ΔG = 62.9 kcal/mol) competes with product ion E formation (ΔH = 47.5 kcal/mol and ΔG = 35.2 kcal/mol).…”

Section: Resultsmentioning

confidence: 99%

Gas‐phase fragmentation reactions of protonated benzofuran‐ and dihydrobenzofuran‐type neolignans investigated by accurate‐mass electrospray ionization tandem mass spectrometry

et al. 2018

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We have investigated gas‐phase fragmentation reactions of protonated benzofuran neolignans (BNs) and dihydrobenzofuran neolignans (DBNs) by accurate‐mass electrospray ionization tandem and multiple‐stage (MSn) mass spectrometry combined with thermochemical data estimated by Computational Chemistry. Most of the protonated compounds fragment into product ions B ([M + H–MeOH]+), C ([B–MeOH]+), D ([C–CO]+), and E ([D–CO]+) upon collision‐induced dissociation (CID). However, we identified a series of diagnostic ions and associated them with specific structural features. In the case of compounds displaying an acetoxy group at C‐4, product ion C produces diagnostic ions K ([C–C2H2O]+), L ([K–CO]+), and P ([L–CO]+). Formation of product ions H ([D–H2O]+) and M ([H–CO]+) is associated with the hydroxyl group at C‐3 and C‐3′, whereas product ions N ([D–MeOH]+) and O ([N–MeOH]+) indicate a methoxyl group at the same positions. Finally, product ions F ([A–C2H2O]+), Q ([A–C3H6O2]+), I ([A–C6H6O]+), and J ([I–MeOH]+) for DBNs and product ion G ([B–C2H2O]+) for BNs diagnose a saturated bond between C‐7′ and C‐8′. We used these structure‐fragmentation relationships in combination with deuterium exchange experiments, MSn data, and Computational Chemistry to elucidate the gas‐phase fragmentation pathways of these compounds. These results could help to elucidate DBN and BN metabolites in in vivo and in vitro studies on the basis of electrospray ionization ESI‐CID‐MS/MS data only.

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Gas‐phase reactivity of protonated 2‐oxazoline derivatives: mass spectrometry and computational studies

Cited by 10 publications

References 45 publications

Electrospray ionization tandem mass spectrometry analysis of isopimarane diterpenes from Velloziaceae

Electrospray ionization tandem mass spectrometry analysis of isopimarane diterpenes from Velloziaceae

Gas‐phase dissociation study of erythrinian alkaloids by electrospray ionization mass spectrometry and computational methods

Gas‐phase fragmentation reactions of protonated benzofuran‐ and dihydrobenzofuran‐type neolignans investigated by accurate‐mass electrospray ionization tandem mass spectrometry

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