Cattle grazing in arid rangelands of Australia suffer periodic extensive and serious
poisoning by the plant species Pimelea trichostachya, P. simplex, and P. elongata. Pimelea
poisoning (also known as St. George disease and Marree disease) has been attributed to the presence of the
diterpenoid orthoester
simplexin in these species. However, literature relating to previous studies is complicated by taxonomic revisions, and the presence of
simplexin has not previously been verified in all currently recognized taxa capable of inducing pimelea
poisoning syndrome, with no previous chemical studies of P. trichostachya (as currently classified) or P. simplex subsp. continua. We report here the isolation of
simplexin from P. trichostachya and the development of a liquid chromatography-mass spectrometry/mass spectrometry (LC-MS/MS) method to measure
simplexin concentrations in pimelea plant material.
Simplexin was quantified by positive-ion atmospheric pressure chemical ionization (APCI) LC-MS/MS with selected reaction monitoring (SRM) of the m/z 533.3 > 253.3 transition. LC-MS/MS analysis of the four poisonous taxa P. trichostachya, P. elongata, P. simplex subsp. continua, and P. simplex subsp. simplex showed similar profiles with
simplexin as the major
diterpenoid ester component in all four taxa accompanied by varying amounts of related orthoesters. Similar analyses of P. decora, P. haematostachya, and P. microcephala also demonstrated the presence of
simplexin in these species but at far lower concentrations, consistent with the limited reports of stock
poisoning associated with these species. The less common, shrubby species P. penicillaris contained
simplexin at up to 55 mg/kg dry weight and would be expected to cause
poisoning if animals consumed sufficient plant material.