UHPLC-Orbitrap-MS Tentative Identification of 51 Oleraceins (Cyclo-Dopa Amides) in Portulaca oleracea L. Cluster Analysis and MS2 Filtering by Mass Difference

Abstract

Oleraceins are a class of indoline amide glycosides found in Portulaca oleracea L. (Portulacaceae), or purslane. These compounds are characterized by 5,6-dihydroxyindoline-2-carboxylic acid N-acylated with cinnamic acid derivatives, and many are glucosylated. Herein, hydromethanolic extracts of the aerial parts of purslane were subjected to UHPLC-Orbitrap-MS analysis, in negative ionization mode. Diagnostic ion filtering (DIF), followed by diagnostic difference filtering (DDF), were utilized to automatically filter out MS data and select plausible oleracein structures. After an in-depth MS2 analysis, a total of 51 oleracein compounds were tentatively identified. Of them, 26 had structures, matching one of the already known oleracein, and the other 25 were new, undescribed in the literature compounds, belonging to the oleracein class. Moreover, based on selected diagnostic fragment ions, clustering algorithms and visualizations were utilized. As we demonstrate, clustering methods provide valuable insights into the mass fragmentation elucidation of natural compounds in complex mixtures.

Chemical Profiling and Biological Activity of Extracts from Nine Norwegian Medicinal and Aromatic Plants

“…Peaks 1 , 2 and 4 showed an odd number of nitrogen atoms as part of their molecular structures due the even-numbered pseudomolecular ions ( Table 4 ). Peak 1 revealed pseudomolecular ions at m / z 520 and 518 at ESI+ and ESI-, respectively, and was putatively assigned as oleracein W-hexoside [ 31 ]. The mass spectrum of peak 2 gave pseudomolecular ions at m / z 504 and 502 (ESI+ and ESI-) and a characteristic fragment ion at m / z 342 [M-hex+H] + .…”

“…In addition to oleracein W- O -hexoside and oleracein A, a third peak appeared with similar UV spectrum and an odd number of N-atoms. In accordance with its pseudomolecular mass at m / z 708, the compound might be N -sinapoyl 5,6-dihydroxyindoline-2-carboxylic acid acylated with coumaric acid and with a glucose (sin-glc-ind-coum; SGIC), or N -feruoyl 5,6-dihydroxyindoline-2-carboxylic acid acylated with another ferulic acid and appearing as a glucoside (fer-glc-ind-fer; FGIF) [ 31 ]. SGIC would probably exhibit absorbance maximum at higher wavelength than what was detected, and the peak was thus tentatively assigned to be FGIF.…”

“…The 5,6- dihydroxyindoline-2-carboxylic acid, or the indoline core, characteristic for every oleracein, is represented with fragment ions 194.0, 150.1, and 148.0 m / z , in decreasing intensity. Fragment 194.0 m / z , as well as the characteristic fragment ions for the hydroxycinnamic acids are more prominent in oleraceins with lower mass [ 31 ].…”

Catecholamine Derivatives: Natural Occurrence, Structural Diversity, and Biological Activity

“…oleracea, including 25 new oleraceins and 26 known ones: oleraceins A, B, C, D (two isomers), H, I (two isomers), J, K, L, M (two isomers), N, S (four isomers), O (three isomers), P, Q, W, and X (three isomers). The reported structures contained acyl groups connected with a cyclo -dopa moiety and included trans -coumaric acyl, ferulic acyl, caffeic acyl, or their cis isomers, while the number of glucose moieties ranged from 1 to 4, and acyl groups connected with a sugar moiety included p -coumaroyl, feruloyl, caffeoyl, sinapoyl, or hydroxybenzoyl group . We suggest that the definitive structures, natural occurrence, and bioactivities of the aforementioned oleraceins need in-depth research in the future.…”

“…Upon the isolation of four novel indoline glycosides (oleraceins A, B, C, D, 120 – 123 ) and one tricyclic tetrahydroisoquinoline (oleracein E, 64a ) by our group, our interest in this plant for drug discovery was renewed. To date, because of the research reported by several groups, − ,,− ,− the number of CA analogues isolated and structurally identified from P. oleracea now exceeds 60 (Table ) with the chemical structures of the isolates containing a wide diversity including simple phenethylamines, isoquinolines, indolines, indoles, and benzoazepines.…”