1β,15α-Dihydroxy-16α,17-epoxypregn-4-ene-3,20-dione

The title molecule, C21H28O5, is composed of three six-membered rings (A/B/C) and a five-membered ring (D). Ring A adopts a 1α-sofa conformation, while rings B and C adopt chair conformations. Cyclopentane ring D adopts a 14α-envelope conformation. In the crystal, O—H⋯O hydrogen bonds lead to the formation of ribbons running along the a axis. The structure is further consolidated by C—H⋯O interactions, which link the molecules head-to-tail into ribbons along the a axis.

The title molecule, C 21 H 28 O 5 , is composed of three sixmembered rings (A/B/C) and a five-membered ring (D). Ring A adopts a 1-sofa conformation, while rings B and C adopt chair conformations. Cyclopentane ring D adopts a 14envelope conformation. In the crystal, O-HÁ Á ÁO hydrogen bonds lead to the formation of ribbons running along the a axis. The structure is further consolidated by C-HÁ Á ÁO interactions, which link the molecules head-to-tail into ribbons along the a axis.   Table 1 Hydrogen-bond geometry (Å , ). Symmetry codes: (i) x þ 1 2 ; Ày þ 3 2 ; Àz; (ii) x À 1; y; z; (iii) x þ 1; y; z; (iv) x; y À 1; z.
The bond distances and angles in the title compound ( Fig. 1) agree very well with the corresponding bond distances and angles reported in a closely related compound (Nie et al., 2005). The title compound has three six-membered rings (A/B/C) and one five-membered rings (D). Ring A has a 1α-sofa conformation. Rings B and C adopt chair conformations, while the cyclopentane ring D adopts a 14α-envelope conformation. The 1-hydroxy is in β and 15-hydroxy in α configuration. In the crystal packing ( Fig. 2 & Tab 1), there are intermolecular hydrogen bonds O3-H3···O5 and O1-H1···O4 which stabilize the structure and contribute to the formation of one-dimensional ribbons running along the aaxis. The structure is further consolidated by intermolecular hydrogen bonding interactions of the tyoe C-H···O (Tab. 1).

Experimental
Colletotrichum lini AS3. 4486 was obtained from Institute of Microbiology, Chinese Academy of Sciences. The strain was cultivated in shake flasks in two stages. Firstly, mycelium was grown on seed medium (glucose 30 g/L, corn steep liquor 10 g/L, pH 7.0) for 72 h on a rotary shaker (200 r/min) at 298 K. At the second stage, 10% (v/v) of the first mycelium obtained were added to the growing medium containing (g/l): glucose 30, corn steep liquor 10, soy meal 10, NaNO 3 2, KH 2 PO 4 1, K 2 HPO 4 2, MgSO 4 .7H 2 O 0.5, KCl 0.5, FeSO 4 .7H 2 O 0.02 (pH 7.0) and incubated for 24 h at the same conditions. Thereafter 50 mg of the 16α,17α-epoxyprogesterone dissolved in 1 ml of ethanol was added to the culture after 24 h for growth and the reaction was allowed to proceed for 72 h. The mycelium was then removed by filteration. The biomass and the broth were extracted separately with EtOAc. All extracts were combined and dried (anhydr. Na 2 SO 4 ). The solvents after filtration were evaporated under reduced pressure. The crude extracts were purified by Si gel column using dichloromethane/ether/methanol (25:2:1, v/v/v). The white powder was diffused with nhexane/acetone at room temperature. Colourless prismatic crystals suitable for X-ray analysis were obtained.

Refinement
The hydroxyl H atoms were located from difference Fourier maps and refined freely. The H atoms bonded to C atoms were positioned geometrically and refined using a riding model, with C-H = 0.95, 0.98, 0.99, 1.00 Å, for aryl, methyl, methylene and methyne H-atoms, respectively. The U iso (H) were allowed at 1.5U eq (C methyl) or 1.2U eq (C non-methyl). In the absence of sufficient anomalous dispersion effects in diffraction measurements, an absolute structure was not determined 1815 Friedel pairs were not merged.

Figure 1
Perspective view of the title compound with 18% probability ellipsoids 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.