The title compound [systematic name: 7α,12-dihy­droxy-8,12-abietadiene,11,14-dione or (4bS,8aS,10R)-3,10-dihy­droxy-2-isopropyl-4b,8,8-trimethyl-1,4,4b,5,6,7,8,8a,9,10-deca­hydro­phenanthrene-1,4-dione], C20H28O4, is an abietane diterpen­oid, which was isolated from the roots of Premna obtusifolia (Verbenaceae). Its crystal structure has been reported previously [Chen et al. (2000 ▶). Jiegou Huaxue, 19, 122–125], but the absolute configuration could not be determined using data collected with Mo radiation. This redetermination using Cu radiation shows the the absolute configurations of the stereogenic centres at positions 4b, 8a and 10 to be S, S and R, respectively. Two intra­molecular O—H⋯O hydrogen bonds [one generating an S(5) ring and one generating an S(6) ring] and a number of short C—H⋯O contacts occur. In the crystal, mol­ecules are linked into infinite chains propagating in [100] by O—H⋯O hydrogen bonds and weak C—H⋯O inter­actions.

The title compound {systematic name: 5,6,10-trihydr­oxy-7-iso­propyl-1,1,4a-trimethyl-2,3,4,4a-tetra­hydro­phenanthren-9(1H)-one}, C20H26O4, is a diterpenoid which was isolated from the roots of Premna obtusifolia. The mol­ecule has three fused six-membered rings; the cyclo­hexane ring is in a twisted-boat conformation and the cyclo­hexene ring adopts a sofa form. Intra­molecular O—H⋯O hydrogen bonds generate two S(5) ring motifs. In the crystal, mol­ecules are linked into infinite one-dimensional chains along the [001] direction by O—H⋯O hydrogen bonds and weak C—H⋯O inter­actions.

The structure of the title diterpenoid, C20H28O3, {systematic name: (4bS,8aS)-3-hy­droxy-2-isopropyl-4b,8,8-trimethyl-4b,5,6,7,8,8a,9,10-octa­hydro­phenanthrene-1,4-dione} is confirmed [Eugster et al. (1993 ▶). Private communication (refcode HACGUN). CCDC, Union Road, Cambridge] and its packing is now described. Its absolute structure was established by refinement against data collected with Cu radiation: the two stereogenic centres both have S configurations. One cyclo­hexane ring adopts a chair conformation whereas the other cyclo­hexane ring is in a half-chair conformation and the benzoquinone ring is slightly twisted. An intra­molecular O—H⋯O hydrogen bond generates an S(5) ring motif. In the crystal, mol­ecules are linked into chains along [010] by O—H⋯O hydrogen bonds and weak C—H⋯O inter­actions. The packing also features C⋯O [3.131 (3) Å] short contacts.

In the title compound, C20H28O4, a diterpenoid isolated from the roots of Premna obtusifolia (Verbenaceae), the five-membered ring is in a half-chair conformation. One six-membered ring exists in a twisted-boat conformation while the other is in half-boat conformation. The crystal packing is stabilized by inter­molecular O—H⋯O and weak C—H⋯O inter­actions, generating (001) sheets.

The title compound [systematic name: 14,15-dihy­droxy-7,7-dimethyl-13-(propan-2-yl)tricyclo­[9.4.0.03,8]penta­deca-1(11),3(8),9,12,14-pentaen-4-one], C20H24O3, is a new icetexane diterpenoid which was isolated from the roots of Premna obtusifolia (Verbenaceae). The mol­ecule has three fused rings: a cyclo­hexenone, a central cyclo­heptene and a benzene ring. The cyclo­hexenone ring is in an envelope conformation, whereas the cyclo­heptene ring is in a twisted boat conformation. Intra­molecular O—H⋯O hydrogen bonds generate S(5) and S(8) ring motifs. In the crystal, mol­ecules are linked into dimers through O—H⋯O hydrogen bonds. These dimers are arranged in to sheets parallel to the ac plane. C—H⋯O and weak C—H⋯π inter­actions are also present.