8β-Eth­oxy­eremophil-3,7(11)-diene-8α,12;6α,15-diolide

The title compound, C(17)H(20)O(5), an eremophilane sesquiternoid, was isolated from the roots of Ligularia lapathifolia. The mol­ecule contains four fused rings of which the six-membered ring A adopts a half-chair conformation, the six-membered ring B adopts a chair conformation, the five-membered ring C is almost planar (r.m.s. deviation = 0.015 Å) and the five-membered ring D adopts an envelope conformation with the quaternary C atom as the flap. The methyl and the eth­oxy groups adopt a syn conformation and the A/B ring junction is cis-fused. No directional inter­molecular inter­actions could be identified in the crystal.