Steroid conformations in solid and solution. The structure of 2β-methyl-19-nortestosterone p-bromobenzenesulfonate

Crystals of 2β-methy]-19-nortestosterone p-bromobenzenesulfonate (C₂₅H₃₁O₄BrS) are orthorhombic, space group P2₁2₁2₁ with unit cell dimensions a = 9·127(5)Å, b = 36·15(3)Å, c = 7·162(Å). The structure was solved by the heavy atom technique and refined by block diagonal least squares to a final R of 0·06. The overall conformations of this and a previously studied 19-nor steroid are much flatter than the normally observed conformations of 4-en-3-one steroids. The A-ring of the steroid is found to be in the typical half-chair conformation in contrast to the twist conformation previously assigned for 2β-methyl-19-nortestosterone from the interpretation of ORD data. In light of the apparent stability of the observed structure and CD measurements subsequent to the X-ray determination, a reinterpretation of the ORD spectra giving greater attention to its fine structure is suggested in order to resolve the ambiguity between solid structure determination and previous solution structure assignment.