The X-ray Investigation of 16α,17α-Thiazolidine Derivatives of Δ4- and Δ5-Pregnanes and Conformational Analysis of their Oxathiolane Analog
An X-ray study of 3,20-dioxo-4-pregnene-[16α, 17α−d]- -2',2'-dimethylthiazolidine (I) and 3β-hydroxy-20-oxo-5- -pregnene-[16α,17α−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-[17α, 16α−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 17β-acetyl group torsion angle C(16)C(17)C(20)O(20) close to -120° is possible.