16a,17a-Epoxy-5a-hydroxy-6b-nitrooxy- 20-oxopregnan-3b-yl acetate

The title steroid, C23H33NO8, is a pregnane derivative obtained regio-, stereoand chemoselectively from the ring opening of the corresponding 5 ,6 ;16 ,17 -diepoxide with bismuth(III) nitrate. There are two symmetry-independent molecules in the asymmetric unit that show no significant differences concerning bond lengths and angles. All rings are trans-fused. The conformations of the six-membered rings are close to chair forms, while the five-membered ring adopts an envelope conformation. The molecules are held together by an extensive O—H O hydrogen-bonding network of chains runnning along the a axis.