A guaianolide-type sesquiterpene lactone

The title compound, 3 alpha-hydroxy-11 alpha H-guaia-4(15), 10(14)-dien-12,6 alpha-olide, C15H20O3, is a 5,7,5-tricyclic guaianolide. The hydroxy group is equatorial and the methyl group is axial. Three rings, viz. a five-membered, a seven-membered and a gamma-lactone ring, are cis- and trans-fused to each other, and adopt half-chair, chair and envelope conformations, respectively. The crystal structure is stabilized by intermolecular O-H center dot center dot center dot O hydrogen bonds between the hydroxy group and the gamma-lactone carbonyl O atom along the b direction.