<i>seco</i>-Pregnane Glycosides from Australian Caustic Vine (<i>Cynanchum viminale</i> subsp. <i>australe</i>)

<i>Cynanchum viminale</i> subsp. <i>australe</i>, more commonly known as caustic vine, is a leafless succulent that grows in the northern arid zone of Australia. Toxicity toward livestock has been reported for this species, along with use in traditional medicine and its potential anticancer activity. Disclosed herein are novel <i>seco</i>-pregnane aglycones cynavimigenin A (<b>5</b>) and cynaviminoside A (<b>6</b>), together with new pregnane glycosides cynaviminoside B (<b>7</b>) and cynavimigenin B (<b>8</b>). Cynavimigenin B (<b>8</b>) contains an unprecedented 7-oxobicyclo[2.2.1]heptane moiety in the <i>seco</i>-pregnane series, likely arising from a pinacol-type rearrangement. Interestingly, these isolates displayed only limited cytotoxicity in cancer and normal human cell lines, in addition to low activity against acetylcholinesterase and <i>Sarcoptes scabiei</i> bioassays, suggesting that <b>5</b>–<b>8</b> are not associated with the reported toxicity of this plant species.