9α-Acet­oxy-1β,10α-ep­oxy­parthenolide

The title compound, C(17)H(22)O(6), was semi-synthesized from 9-hy-droxy-arthenolide, which was isolated from the chloro-form extract of the aerial parts of Anvillea radiata. The mol-ecule contains fused five- and ten-membered rings: the five-membered lactone ring has a twisted conformation, whereas the ten-membered ring displays an approximate chair-chair conformation. The dihedral angle between the rings is 24.76 (9)°.