Characterization of two structural forms of otonecine-type pyrrolizidine alkaloids from Ligularia hodgsonii by NMR spectroscopy.

Clivorine (1) and ligularine (2), two hepatotoxic otonecine-type pyrrolizidine alkaloids isolated from Ligularia hodgsonii, an antitussive traditional Chinese medicine, were investigated in CDCl(3) and D(2)O by various NMR techniques to delineate why this type of alkaloid displays uncharacteristic solubility properties by dissolving in both nonpolar organic and aqueous solutions. The results demonstrated that both alkaloids exist in a non-ionized form in CDCl(3), but in an ionized form in D(2)O, suggesting that this unique dual solubility may play a role in the intoxication resultant from consumption of water extracts of herbs, including herbal teas, containing otonecine-type pyrrolizidine alkaloids.