Conformational Influence of a 19-Methyl Substituent in 19-Oxygenated Steroid Structures

The crystal and molecular structure of (19R)-19-methyl-5-androstene-3β,17β,19-triol (C₂₀H₃₂O₃) has been determined. The crystals are orthorhombic and the space group is P2₁2₁2₁. The unit cell parameters are a = 11.179 Å, b = 21.485 Å, and c = 7.328 Å. The structure was solved using the direct methods program MULTAN and refined anisotropically to an R of 7.2% for all data. The methyl substituent on C(19) is located over the B ring and the hydroxyl between the A and C rings. The flexible B ring has a distorted half-chair conformation. The 19R configuration suggests that the reaction mechanism for the formation of this compound proposed by Wicha and Caspi is incorrect. Furthermore, these results indicate that the stereochemical assignment of C(19) by Skinner and Akhtar resulting from a tritiated sodium borohydride reduction is also suspect.