Rationalising the retro‐Diels‐Alder fragmentation pattern of viscutins using electrospray interface‐tandem mass spectrometry coupled to theoretical modelling

Abstract

Rationale: Although mass spectrometry (MS) is a powerful tool in structural elucidation of unknown flavonoids based on their unique fragmentation patterns, proposing the correct fragmentation mechanism is still a challenge from tandem mass spectrometry data only. In recent years, computational tools such as molecular networking and MS2LDA have played a major role in the identification of structurally related compounds through an in-depth survey of their fragmentation patterns.Methods: Therefore, in this study, three viscutin molecules in Viscum combreticola Engl. crude extracts were characterised using ultra-high-performance liquid chromatography-quadrupole-time-of-flight tandem mass spectrometry and MS2LDA, a computational tool. Ion-trap mass spectrometry and density functional theoretical modelling were used as confirmatory tools to rationalise the unique fragmentation patterns observed for these molecules.Results: Here, MS2LDA revealed the presence of a unique Mass2Motif in all the three viscutin molecules at m/z 137, which was confirmed to be a 1,3 A À RDA (retro-Diels-Alder) fragmentation product using liquid chromatography-ion-trap mass spectrometry and density functional theoretical modelling. Moreover, MS2LDA proved to be useful in differentiating this spectral feature that was specific to viscutin molecules in the presence of other isobaric ions at m/z 137 occurring in compounds in other molecular families. Conclusion:Therefore, the results of the current study showed that computational tools such as MS2LDA are essential in uncovering some gas-phase fragmentation reactions of molecules in MS and that theoretical modelling is a powerful tool in rationalising these reactions in metabolite identification. | INTRODUCTIONViscum combreticola Engl. (Santalacaeae), a perennial and evergreen leafless semi-parasitic plant, is native to southern and tropical Africa. 1,2 Combretum erythrophyllum, Acacia karroo, Pseudolachnostylis maprouneifolia Pax and Sclerocarya birrea 1,3 are some of the common host plants of V. combreticola Engl. The phytochemistry of different species of Viscum is complex, consisting of various classes of secondary metabolites such as viscotoxins, lectins, flavonoids, hydroxycinnamic acid derivatives, terpenoids, coumarins, lignans,

A Relook into the Flavonoid Chemical Space of Moringa oleifera Lam. Leaves through a Combination of LC-MS and Molecular Networking

“…Substructure annotation was achieved using MS2LDA through the ms2lda.org web interface within GNPS. Structural searches were performed according to the protocol recently outlined by Moyo et al [ 28 ].…”