(25R)-5a-Spirostane-3,12-dione

The title compound, C27H40O4, was obtained from the oxidation of (25R)-3b-hydroxy-5a-spirostan-12-one (Hecogenin) by Jone’s reagent. The molecule contains six alicyclic and heterocyclic rings, all trans-fused, among which four six-membered rings adopt similar chair conformations while two five-membered rings assume an envelope conformation.


Related literature
Steroid sapogenins are a class of important compounds, which present many significant bioactivities in platelet aggregation, arteriosclerosis and so on (Huang et al., 2002). The hecogenin (25R-5a-Spirostane-3b-ol-12-one) is an important steroid (Djerassi et al., 1962;Chakravarti et al., 1953), which has been isolated from Chinese traditional medicine Tribulus terrestris. The title compound was recently obtained by Jone's oxidation of hecogenin in our laboratory, and its crystal structure is presented here.

S2. Experimental
A solution of hecogenin (200 mg) in acetone (10 ml) was added by Jone's reagent drops by drops. The reaction solution was stirred for 20 min and quenched by water (10 ml). The mixture was extracted with CH 2 Cl 2 (5 ml×3) and the organic phase was concentrated to give the title compound. The crystals suitable for X-ray analysis were obtained by slow evaporation from acetone solution at room temperature. The absolute configuration was deduced not by the present experiment but by the synthetic path from Hecognin, whose absolute configuration is known.

S3. Refinement
H atoms were located geometrically with C-H = 0.93-0.98 Å and refined using a riding model with U iso (H) = 1.2U eq (C).
Friedel pairs were merged and the absolute configuration was not determined.

Figure 1
The molecular structure of the title compound.

Data collection
Enraf-Nonius CAD-4 diffractometer Radiation source: fine-focus sealed tube Graphite monochromator ω/2θ scans 2837 measured reflections 2407 independent reflections 919 reflections with I > 2σ(I) where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.19 e Å −3 Δρ min = −0.23 e Å −3 Special details 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 > σ(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.