Conformational flexibility in androgenic steroids: the structure of a new form of (+)-17β-hydroxy-19-nor-4-androsten-3-one (19-nortestosterone), C₁₈H₂₆O₂

Abstract

The structure and conformation of a second crystalline modification of 19-nortestosterone has been determined by X-ray methods. M_r=274, monoclinic P2_l, a=9.755 (2), b=11.467 (3), c= 14.196(3) Å β =101.07(2)° , V=1558.4 (8) Å ³, Z=4, D_x=I. 168 g cm_-3, Mo Kα, λ=0.7107 Å, μ=0.80 cm^-l, F(000)=600, T=300 K. R =0.060 for 2158 observed reflections. The two molecules in the asymmetric unit show significant differences in the A-ring conformation from that of the previously reported form of the title compound. The l α, 2β -half-chair conformation of the A ring increases its conformational freedom compared with testosterone.