Pyrrolizidine alkaloids of Blue Heliotrope (Heliotropium amplexicaule) and their presence in Australian honey.

Blue heliotrope (Heliotropium amplexicaule) is an invasive environmental weed that is widely naturalised in eastern Australia and has been implicated as a source of pyrrolizidine alkaloid (PA) poisoning in livestock. Less well-documented, is the potential of such carcinogenic alkaloids to contaminate honey from bees foraging on this plant species. In this study the PA profile of H. amplexicaule plant material, determined by HRAM LC-MS/MS, revealed the presence of nine PAs and PA-N-oxides, including several PAs and PA-N-oxides of the indicine class that have not previously been reported. The predominant alkaloid, indicine, represents 84% of the reduced PA content, with minor alkaloids identified as intermedine and the newly reported helioamplexine constituting 7 and 9% respectively. NMR analysis confirmed the identity of helioamplexine as a previously unreported indicine homologue. This is the first report of the isolation of intermedine, helioamplexine and 3'-angelylindicine from H. amplexicaule. Also described is the identification of N-chloromethyl analogs of the major alkaloids as isolation-derived artefacts from reaction with dichloromethane. Analysis of regional market honey samples revealed a number of honey samples with a PA profile analogous to that seen in H. amplexicaule, with a measured PA content of up to 2.0 μg PAs per gram of honey. These results confirm the need for honey producers to be aware of H. amplexicaule as a potential PA source, most particularly in products where honey is sourced from a single location.