The title compound (trivial name brasixanthone B), C23H22O5, isolated from Calophyllum gracilentum, is characterized by a xanthone skeleton of three fused six-membered rings plus an additional fused pyrano ring and one 3-methylbut-2-enyl side chain. The core xanthone moiety is almost planar, with a maximum deviation 0.057 (4) Å from the mean plane. In the molecule, an intramolecular O—H...O hydrogen bond forms an S(6) ring motif. The crystal structure features intermolecular O—H...O and C—H...O interactions.
