Study of the molecular structure of 3-methoxy-7 alpha-methyl-8,14-iso-1,3,5(10)-estratrien-17 beta-ol acetate by X-ray diffraction and molecular modeling methods

The molecular structure of 3-methoxy-7 alpha-methyl-8, 14-iso-1,3,5(10)-est ratrien-17 beta-ol acetate was determined by X-ray diffraction (sp. gr. Pca b; a = 6.664(2), b = 12.056(2), and c = 47.723(6) Angstrom; Z = 8; and D-x = 1.1832(7) g/cm(3)). The structure was solved by the direct method and ref ined to R(F) = 0.051 [Rw(F-2) = 0.1106] for 843 nonzero unique reflections with I > 2 sigma(I). In the molecule, ring A is planar, ring B is 7 beta,8 alpha-half-chair, ring C is a chair, and the five-membered ring D is 13 alp ha-envelope. The A/B ring junction is planar, and the B/C and C/D junctions are of the 8 alpha,9 alpha-cis and 13 beta,14 beta-cis types. In addition to the X-ray study, a complete optimization of the molecular geometry was p erformed within a molecular modeling approach (AM1). The calculated bond le ngths and angles are close to the values obtained in the X-ray structure an alysis.