(3R 4S 5S 8S 10R 13R)-3-Hydroxykaura-9(11) 16-dien-18-oic acid

The title compound, C₂₀H₂₈O₃, was isolated during our investigation into the chemical composition and pharmacological activity of Centipeda cunninghamii (DC.) A. Braun & Asch. (Asteraceae). The enantiopure compound, a diterpene with a carbon skeleton, is composed of three six- and one five-membered rings in chair, twist-boat, half-chair and envelope conformations, respectively. Each molecule makes one intra- and one intermolecular O-HO hydrogen bond in the crystal lattice, forming hydrogen-bonded chains along [010]. The absolute configuration of the compound was assigned on the basis of optical rotation measurements.