Highly oxidized flavones in Artemisia species - structure revisions and improved UHPLC-MSⁿ analysis

In course of our studies of the aerial parts of Artemisia abrotanum the major methoxyflavonol could be isolated. However, by NMR structural analysis it became obvious that the substitution pattern in ring B differs from reports for casticin (2). The position of methoxyl and hydroxyl groups are interchanged, i.e., the major flavone is actually chrysosplenetin (1). Three structures in A. abrotanum and A. frigida had to be revised. Use of pyridine-d₅ instead of DMSO‑d₆ made the resolution of the B-ring ¹H and ¹³C NMR signals possible and enabled correct structural assignment by 2D NMR experiments. Results from NMR structure elucidation for A. abrotanum were confirmed by LC-PDA-ESI-MSⁿ analysis when a PFP (pentafluorophenyl) stationary phase with an optimized gradient elution was applied for separation of 1 and 2 instead of a corresponding C-18 phase. Electrospray mass spectrometry (positive and negative mode) with subsequent fragmentation (ESI-MSⁿ) revealed distinctive mass spectral features of both compounds, especially at MS⁴ level. Several Artemisia extracts including A. annua were analysed on the PFP phase for the presence of 1 and 2.