Selective Antiproliferative Withanolides from Species in the Genera <i>Eriolarynx</i> and <i>Deprea</i>

Four new withanolides (<b>2</b>–<b>5</b>), together with 4β,7β,20-trihydroxy-1-oxowitha-2,5,24-trienolide (<b>1</b>), were isolated from the aerial parts of <i>Eriolarynx iochromoides</i>. The antiproliferative activity of all compounds purified from <i>E. iochromoides</i> together with four withaphysalins and four physangulidines isolated previously from three <i>Deprea</i> species were evaluated against human solid tumor cell lines. Four withanolides showed antiproliferative activity comparable in potency to cisplatin. Selectivity toward cancer cells and interaction with P-glycoprotein of the active withanolides were evaluated.