title: Molecular mechanics and X-ray crystal structure investigations on conformations of 11 beta substituted 4,9-dien-3-one steroids.
abstract: The influence of 11 beta-phenyl substitution upon 4,9-dien-3-one steroid-backbone conformations is calculated by means of the MM2p molecular mechanics scheme. In the case of steroids having a 13 beta configuration, the lowest strain energy is always evaluated for the conformational combination of rings A(inverted) B(normal) while, moreover, the 11 beta substitution increases the relative stability of the conformation A(normal) B(normal) compared to the nonsubstituted compound. Introduction of the 11 beta substituent causes some bowing of the energy-minimum structures in the A-ring region toward the beta side. For 13 alpha configurated steroids, the ring conformations A(inverted) B(normal) C(boat) and A(normal) B(inverted) C(twist/boat) are found to be energetically preferred. Quantitative description of different ring conformations using asymmetry and pseudorotational parameters as well as the comparison of molecular mechanics and available X-ray structure data give an impression of the conformational mobility. Whereas the effect of 11 beta substitution within a given ring conformation is limited, contributions to molecular flexibility can be found in the ability to adopt different basic conformations and in the occupation of near-minimum structures. An X-ray crystal structure analysis of a potential antiprogestational steroid has been performed, and the results are in good agreement with the calculated structure.
authors.affiliation: Academy of Sciences, Central Institute of Microbiology and Experimental Therapy, Jena, DDR.
authors.forename: M
authors.initials: M
authors.lastname: Bohl
authors.forename: G
authors.initials: G
authors.lastname: Schubert
authors.forename: K
authors.initials: K
authors.lastname: Ponsold
authors.forename: G
authors.initials: G
authors.lastname: Reck
authors.forename: E
authors.initials: E
authors.lastname: Höhne
authors.forename: K
authors.initials: K
authors.lastname: Simon
mesh_terms: D003461:Crystallography; D008968:Molecular Conformation; D013256:Steroids / Q000737:chemistry*
chemical_list: D013256:Steroids