14,15-Didehydrohellebrigenin

The title compound, C24H30O5, is the didehydro product of the steroid hellebrigenin (systematic name: 3β,5,14-trihydroxy-19-oxo-5β-bufa-20,22-dienolide). It consists of three cyclohexane rings (A, B and C), a five-membered ring (D) and a six-membered lactone ring (E). The stereochemistry of the ring junctions are A/B cis, B/C trans and C/D cis. Cyclohexane rings A, B and C have normal chair conformations. The five-membered ring D with the C=C bond adopts an envelope conformation. Lactone ring E is essentially planar with a mean derivation of 0.006 (4) Å and is β-oriented at the C atom of ring D to which it is attached. There is an O—H⋯O hydrogen bond in the molecule involving the hydroxy groups. In the crystal, O—H⋯O hydrogen bonds link the molecules into chains propagating along [010]. The chains are linked by C—H⋯O contacts into a three-dimensional network.

The title compound, C 24 H 30 O 5 , is the didehydro product of the steroid hellebrigenin (systematic name: 3,5,14-trihydroxy-19oxo-5-bufa-20,22-dienolide). It consists of three cyclohexane rings (A, B and C), a five-membered ring (D) and a sixmembered lactone ring (E). The stereochemistry of the ring junctions are A/B cis, B/C trans and C/D cis. Cyclohexane rings A, B and C have normal chair conformations. The fivemembered ring D with the C C bond adopts an envelope conformation. Lactone ring E is essentially planar with a mean derivation of 0.006 (4) Å and is -oriented at the C atom of ring D to which it is attached. There is an O-HÁ Á ÁO hydrogen bond in the molecule involving the hydroxy groups. In the crystal, O-HÁ Á ÁO hydrogen bonds link the molecules into chains propagating along [010]. The chains are linked by C-HÁ Á ÁO contacts into a three-dimensional network.
In the crystal, O-H···O hydrogen bonds between the hydroxyl group at C3 and the hydroxyl group at C5 link adjacent molecules into dimers (Fig 2 and Table 1). Adjacent dimers are linked by short C-H···O contacts, between the methylene group at C6 and the lactone group, to form a three-dimensional network (Table 1 and Fig. 2).
The absolute configuration determined for bufalin (Rohrer et al., 1982) and secohellebrigeninamide, (Yuan et al., 2012), two similar steroids, were invoked, giving the assignments of the chiral centres in the molecule as shown in Fig. 1.

Experimental
Hellebrigenin (104.32 mg) was dissolved in a mixture of dichloromethane (2 ml) and methanol (3 ml). Hydrochloric acid (36%, 10 ml) was added. The solution was stirred for three hours at room temperature. Then the mixture was then poured into cold water and extracted with ethyl acetate. The organic phase was washed twice with water and concentrated under reduced pressure. The residue was subjected to preparative HPLC to afford the title compound (41 mg). The compound was recrystallized in methanol at room temperature to afford colourless prism-like crystals.

Refinement
The

Figure 1
The molecular structure of the title molecule with the atom numbering. The displacement ellipsoids are drawn at the 30% probability level.   Table 1 for details). Extinction coefficient: 0.0045 (12) Special details Geometry. Bond distances, angles etc. have been calculated using the rounded fractional coordinates. All su's are estimated from the variances of the (full) variance-covariance matrix. The cell esds are taken into account in the estimation of distances, angles and torsion angles 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.