Submitted to: Phytochemical Analysis
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/22/2004
Publication Date: 8/19/2005
Citation: Colegate, S.M., Edgar, J.A., Knill, A.M., Lee, S.T. 2005. Solid-phase extraction and HPLC-MS profiling of pyrrolizidine alkaloids and their n-oxides: A case study of echium plantagineum. Phytochemical Analysis. 16(2):108-119.
Interpretive Summary: Echium plantagineum was extracted with methanol. The pyrrolizidine alkaloids and their N-oxides can be extracted from the dried methanolic solubles of plant material using dilute aqueous acid. The subsequent incorporation of solid phase, strong cation exchange extraction of the pyrrolizidine alkaloids and their N-oxides, from the aqueous acid solution, with analysis using high performance liquid chromatography and electrospray ionization mass spectrometry provides a method for simultaneous profiling of the pyrrolizidine alkaloids and their N-oxides in plant samples while yielding useful structural data to aid in identification. This analysis of Echium plantagineum has revealed a higher proportion of N-oxides to the parent tertiary bases than has been previously reported. A higher proportion of acetylated pyrrolizidine-N-oxides were observed in the flower heads relative to the leaves. Six pyrrolizidine alkaloids or pyrrolizidine-N-oxides that have not previously been reported from E. plantagineum were tentatively identified on the basis of mass spectra and biogenetic considerations.
Technical Abstract: Pyrrolizidine alkaloids and their N-oxides can be extracted from the dried methanolic extracts of plant material using dilute aqueous acid. The subsequent integration of solid-phase extraction (with a strong cation exchanger) of the alkaloids and N-oxides from the aqueous acid solution, together with analysis using HPLC-ESI/MS, provides a method for the simultaneous profiling of the pyrrolizidine alkaloids and their N-oxides in plant samples and the collection of useful structural data as an aid in their identification. The N-oxide character of the analytes may be confirmed by treating analytical samples with a redox resin and observing the formation of the corresponding parent pyrrolizidine alkaloids. The present case study of Echium plantagineum highlighted a higher ratio of N-oxides to the parent tertiary bases than has been previously reported. Furthermore, a higher proportion of acetylated pyrrolizidine-N-oxide was observed in the flower heads relative to the leaves. Six pyrrolizidine alkaloids or pyrrolizidine-N-oxides, not previously reported from E. plantagineum, were tentatively identified on the basis of MS and biogenetic considerations. Three of these, 3'-0-acetylintermedine/lycopsamine, leptanthine-N-oxide and 9-0-angelylretronecine-N-oxide, have been reported elsewhere, whilst three others, 3'-0-acetylechiumine-N-oxide, echimiplatine-N-oxide and echiuplatine-N-oxide, appear unreported from any other source.