6α-Hydroxy-5,6-dihydrosalviasperanol

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.

In the title compound, C 20 H 28 O 4 , a diterpenoid isolated from the roots of Premna obtusifolia (Verbenaceae), the fivemembered ring is in a half-chair conformation. One sixmembered ring exists in a twisted-boat conformation while the other is in half-boat conformation. The crystal packing is stabilized by intermolecular O-HÁ Á ÁO and weak C-HÁ Á ÁO interactions, generating (001) sheets.

Experimental
The air-dried roots of Premna obtusifolia (4.5 kg) were extracted with CH 2 Cl 2 (2 x 20 L) under room temperature. The combined extracts were concentrated under reduced pressure to give a dark yellow extract (40.5g) which was subjected to quick column chromatography (QCC) over silicagel using solvents of increasing polarity from n-hexane to EtOAc to afford 12 fractions (F1-F12). Fraction F10 was further purified by QCC using CH 2 Cl 2 -EtOAc (3:7), yielding compound (I) (145.8 mg). Colorless block-shaped single crystals of (I) were recrystallized from CH 2 Cl 2 after several days (m.p.461-463 K).

Refinement
Anomalous dispersion was negligible and Friedel pairs were merged before refinement. O bound H atoms were located from the difference map and isotropically refined.The remaining H atoms were placed in calculated positions with (C-H) = 0.98 for CH, 0.97 for CH 2 , 0.96 for CH 3 and 0.93 Å for CH in benzene group. The U iso values were constrained to be 1.5U eq of the carrier atom for methyl H atoms and 1.2U eq for the remaining H atoms. A rotating group model was used for the methyl groups. Fig. 1. The structure of (I), showing 50% probability displacement ellipsoids.   Glazer, 1986) operating at 100.0 (1) K.

sup-2 Figures
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.
Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > 2sigma(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.