title: The X-ray investigation of 16 alpha,17 alpha-thiazolidine derivatives of delta 4- and delta 5-pregnanes and conformational analysis of their oxathiolane analog.
abstract: An X-ray study of 3,20-dioxo-4-pregnene-[16 alpha,17 alpha-d]--2',2'-dimethylthiazolidine (I) and 3 beta-hydroxy-20-oxo-5--pregnene-[16 alpha,17 alpha-d]-2',2'- dimethylthiazolidine (II) has been carried out. Two independent molecules in crystal II have significantly different conformations of the D and E rings, although according to the atom-atom potential calculations the energy of interaction of these molecules with their neighbors in crystal is the same. The calculation of conformational energy of 3,20-dioxo-4-pregnene-[17 alpha,16 alpha-d]-2',2'--dimethyloxathiolane (III) by the molecular mechanics method (MMM) indicates a possibility of existence of two similar conformers also for this molecule. The MMM calculation shows also that the conformation of molecule III (as well as progesterone) with the 17 beta-acetyl group torsion angle C(16)C(17)C(20)0(20) close to -120 degrees is possible.
mesh_terms: D008958:Models, Molecular; D008968:Molecular Conformation; D011278:Pregnanes; D011374:Progesterone; D013260:Steroids, Heterocyclic; D013329:Structure-Activity Relationship; D013844:Thiazoles; D014961:X-Ray Diffraction
chemical_list: D011278:Pregnanes; D013260:Steroids, Heterocyclic; D013844:Thiazoles; D011374:Progesterone