9β-Hy-droxy-1β,10α-ep-oxy-parthenolide.

The title compound, C(15)H(20)O(5) (systematic name: 5-hydroxy-1a,4a-dimethyl-7-methyleneperhydrodioxireno[5,6:9,10]cyclo-deca[1,2-b]furan-8-one), was obtained by the reaction of 3-chloro-perbenzoic acid with 9β-hy-droxy-parthenolide. The five-membered ring adopts a twist conformation, whereas the ten-membered ring displays an approximate chair-chair conformation. In the crystal structure, mol-ecules are linked into chains propagating along the b axis by inter-molecular O-H⋯O hydrogen bonds.