Parquin and carboxyparquin, toxic kaurene glycosides from the shrub Cestrum parqui

Abstract

Two kaurene glycostdes have been isolated from the dried leaves of the shrub Cestrum parqui, a common weed in parts of South America and Australia, and their structures determined by modern NMR and mass spectrometry techniques. These compounds, named carboxyparquin and parquin, differ only by one carboxylic acid group at C-4. The former is believed to be responsible for widespread poisoning of grazing animals in these areas;/the latter appears to be a relatively non-toxic co-metabolite. There is a close structural similarity between these compounds and carboxyatraciyloside and atractyloside, which are known toxins with strychnine-like action, isolated from Atractylis gummifera L. The parquins possess a different pyranose ring from the atractyiosides and an additional γ-lactone, both with unprecedented functionality.