Solid‐phase extraction and HPLC‐MS profiling of pyrrolizidine alkaloids and their N ‐oxides: a case study of Echium plantagineum

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[sol ]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 ‐oxides 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′‐ O ‐acetylintermedine[sol ]lycopsamine, leptanthine‐ N ‐oxide and 9‐ O ‐angelylretronecine‐ N ‐oxide, have been reported elsewhere, whilst three others, 3′‐ O ‐acetylechiumine‐ N ‐oxide, echimiplatine‐ N ‐oxide and echiuplatine‐ N ‐oxide, appear unreported from any other source. Copyright © 2005 John Wiley & Sons, Ltd.