Crystal structure of 3β-acetoxy-17α-hydroxy-16α-methylallopregnan-20-one hemihydrate

3β-Acetoxy-17α-hydroxy-16α-methylallopregnan-20-one, C₂₄H₃₈O₄·0.5H₂O, is an intermediate towards the synthesis of dexamethasone, an important corticosteroid. The compound crystallizes in the monoclinic space group C2 with unit cell parameters: a = 10.665(2) ?, b = 7.497(1) ?, c = 28.200(4) ?, β = 92.74(2)°, Z = 4. The crystal structure has been solved by direct methods and refined to R = 0.0419 for 1579 observed reflections. All rings of the steroid skeleton are trans connected. Rings A, B, and C are all in the chair conformation. Ring D is in envelop conformation. The acetoxy and acetyl substituents are twisted with respect to the average molecular plane of the steroid. The twist along the length of the steroid molecule is negligible C19–C10···C13–C18 = 2.3°]. In the crystal structure, the water molecule lies on a twofold axis which links the molecules into infinite supramolecular chains through OW–H···O and O–H···OW hydrogen bonds.