Mass spectrometry of xanthones‐I: The electron‐impact‐induced fragmentation of xanthone, monohydroxy‐ and monomethoxyxanthones

Abstract

With the aid of isotopic labelling (D and I*O) and the metastable defocusing technique the mass spectra of xanthone, the monohydroxyxanthones and the monomethoxyxanthones have been recorded and interpreted. The relative position of the hydroxy group exerts no direct effect on the fragmentation, whereas the decomposition of the methoxy compounds is clearly influenced by the position of the substituent. The 1-methoxy-group exhibits an 'ortho-eEect'. The presence and significance of doubly-charged ions in the spectra are discussed.ALTHOUGH the mass spectra of several classes of oxygen heterocycles have been extensively studied (4. a recent comprehensive review1) little attention has been directed towards the xanthones. The mass spectrum of xanthone itself has been reported,, but apart from a discussion of the mass spectra of some lichen xanthone~,~ no systematic investigation of the electron-impact-induced fragmentation of xanthones appears to have been made.In this and later papers the results of a mass spectrometric study of a number of xanthones with hydroxy and methoxy substituents will be reported. The different positions of these substituents in the nucleus constitute major structural variations in the naturally-occurring xanthones, so that their influence on the fragmentation patterns is of considerable analytical interest. RESULTS A N D DISCUSSION XanthoneThe fragmentation of xanthone2 upon electron-impact ( Fig. 1) will be presented again here together with additional details now available. The dominating fragmentation route (Scheme l) passes through the successive loss of two molecules of CO, giving ions formulated as a and b, after which the loss of a hydrogen atom leaves an ion which may be formulated with the benzdehydrotropylium structure (c), in analogy with the dehydrotropylium structure proposed for the [C,H,]+ ion in the mass spectrum of 2-formylben~ofuran.~ Use of the metastable defocusing technique has now revealed that a process leading directly from a to c through the loss of CHO or CO + He is also operative. The further decomposition of c gives rise to minor ions at m/e 114 and 113, corresponding to the loss of .C,H and C,H,, respectively.Features from doubly-charged ions corresponding to [MI++ and [M -CO]+f, as well as a metastable peak arising from the transition between them, are present in 667

Characterization of prenylated xanthones and flavanones by liquid chromatography/atmospheric pressure chemical ionization mass spectrometry

“…We are not aware of the use of FABMS for the characterization of prenylated xanthones, but the loss of both C 3 H 6 and C 4 H 6 from a chromene ring has been reported in the FAB spectra of some prenylated flavonoids 23, 24. The loss of CO detected in the APCI spectrum of the osajaxanthone is also observed in the EI spectra of some xanthones 26. In Table 1, a tentative pathway for the mass spectral fragmentation of osajaxanthone is presented.…”

Naturally Occurring Xanthones: Chemistry and Biology

“…In mass spectrum of O-glycosides, no discernible molecular ion peak can be observed, but an important fragment ion peak due to the aglycone moiety appears, followed by further fragmentation. Significant fragment ions from the loss of OH, H 2 O, and CHO are typical for xanthones and related compounds with a methoxy substituent peri to the carbonyl group [34,53,87].…”

Class Type Separation of the Polar and Apolar Components of Petroleum

“…Studies concerning the presence of xanthones in crude oils are uncommon, with perhaps only two reports in the literature. , Without available standards or spectra to confirm identifications, assignments of C 1–5 alkyl xanthones were made on two-dimensional retention time, molecular mass, and interpretation of spectra. Mass spectral studies of the alkyl xanthones and indeed homologues of other oxygenated PAHs (e.g., benzofurans and fluorenones) are rare, − and none have interpreted the mass spectra of alkylated structures. Interestingly, mass spectra of the methyl-substituted compounds did not exhibit the common M + •-15 losses (Figure S9B), indicative of the loss of a methyl substituent (CH 3 ).…”