1,10-Epoxyhypocretenolides from the Azorean Endemic Leontodon rigens (Asteraceae)

A methanolic extract of Leontodon rigens (Dryander in Aiton) Paiva & Ormonde yielded 1,10-epoxy-14-hydroxyhypocretenolide-beta-D-glucopyranoside and its 6'-O-beta-hydroxyphenylacetyl derivative. These compounds represent the first epoxyguaian-12,5-olide derivatives. The structures were established by means of high resolution mass spectrometry and 1-D and 2-D NMR spectroscopy. The cytotoxicity of the isolated compounds was assessed using the MTT assay and their potential to induce apoptosis by employing the annexin V-PI assay.