ent-5α,3,15-Dioxodolabr-4(18)-ene-16,18-diol.

The title compound, C(20)H(30)O(4), is a dolabrane diterpenoid isolated from Ceriops tagal, in which one of the three fused cyclo-hexane rings adopts a half-chair conformation and the other two are in the standard chair conformations. The hy-droxy-methyl-idene substituent is attached to the half-chair cyclo-hexane. An intra-molecular O-H⋯O hydrogen bond generate an S(6) ring motif. In the crystal, mol-ecules are arranged into screw chains along the [001] direction. The crystal is stabilized by O-H⋯O hydrogen bonds and weaker C-H⋯O inter-actions.