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.

The title furan­oditerpenoid, known as fibaruretin B (systematic name: 2β,3α-dihy­droxy-2,3,7,8α-tetra­hydro­penianthic acid lactone), C20H24O7, was isolated from the roots of Arcangelisia flava. The absolute configurations at positions 2, 3, 4, 4a, 7, 9, 10a and 10b of fibaruretin B are S, R, S, R, S, S, S and S, respectively. In the crystal structure, the mol­ecules are linked into infinite chains along the c axis by O—H⋯O hydrogen bonds and weak C—H⋯O inter­actions.

The title compound, C20H32O2, a diterpenoid, was isolated from the roots of Bruguiera cylindrica (Rhizophoraceae). There are two crystallographically independent mol­ecules in the asymmetric unit. In both mol­ecules, the cyclo­hexane rings adopt chair conformations and the cyclo­pentane ring has an envelope conformation. In the crystal structure, mol­ecules are linked into a two‐dimensional network by inter­molecular O—H⋯O hydrogen bonds.

Key indicators: single-crystal X-ray study; T = 100 K; mean (C-C) = 0.002 Å; R factor = 0.035; wR factor = 0.097; data-to-parameter ratio = 14.1.The title ent-kaurane diterpene compound, C 20 H 30 O, was isolated from the roots of Bruguiera cylindrica (Rhizophoraceae), a mangrove plant. The molecule contains a fused fourring system, with the three cyclohexane rings in standard chair conformations and the cyclopentane ring adopting an envelope conformation. The aldehyde is bisectionally attached to the cyclohexane ring. The methylene group is coplanar with the attached cyclopentane ring. In the crystal structure, molecules are packed by van der Waals interactions. Related literatureFor the values of bond lengths, see Allen et al. (1987). For literature on ring conformations, see Cremer & Pople (1975). For further details of ent-kaurane diterpenes and their bioactive properties, see, for example: Karle (1972); Mü ller et al. (2003); Salae et al. (2007). Experimental Crystal data C 20 H 30 O M r = 286.44 Orthorhombic, P2 1 2 1 2 1 a = 6.3126 (2) Å b = 11.2823 (4) Å c = 22.8044 (7) Å V = 1624.14 (9) Å 3 Z = 4 Mo K radiation = 0.07 mm À1 T = 100.0 (1) K 0.56 Â 0.40 Â 0.13 mm Data collection Bruker SMART APEXII CCD area-detector diffractometer Absorption correction: multi-scan (SADABS; Bruker, 2005) T min = 0.952, T max = 0.991 20475 measured reflections 2709 independent reflections 2571 reflections with I > 2(I) R int = 0.029 Refinement R[F 2 > 2(F 2 )] = 0.035 wR(F 2 ) = 0.097 S = 1.07 2709 reflections 192 parameters H-atom parameters constrained Á max = 0.31 e Å À3 Á min = À0.17 e Å À3 Data collection: APEX2 (Bruker, 2005); cell refinement: APEX2; data reduction: SAINT (Bruker, 2005); program(s) used to solve structure: SHELXTL (Sheldrick, 1998); program(s) used to refine structure: SHELXTL; molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL and PLATON (Spek, 2003).