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

摘要

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) Å, b = 7.497(1) Å, c = 28.200(4) Å, 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.