title: Crystal structure of two crystal forms of 9 alpha-fluorocortisol acetate: variation of the conformation of the A ring of steroids due to crystal packing.
abstract: This paper reports the crystal structure of the propanol solvate of 9 alpha-fluorocortisol acetate, which crystallizes in the monoclinic space group P21 [a = 7.470 (6), b = 14.78 (1), c = 12.310 (9), beta = 105.2 degrees, Z = 2, R = 0.061, and the tetragonal unsolvated crystal form (a = b = 9.208 (2), c = 49.284 (9), P4(1)2(1)2, Z = 8, R = 0.050)]. The molecular structure of fluorocortisol acetate in the two crystal forms differs primarily in the A ring and acetoxy orientation. The A ring of the steroid in the tetragonal crystal was found to be disordered, and exists in both a normal and inverted conformation. The A ring of the steroid in the monoclinic propanol solvate has the normal (1 alpha, 2 beta half-chain) conformation. The differences in the conformation of the side chain and the A ring appear to reflect the conformational variability in 9 alpha-fluorocortisol acetate.
mesh_terms: D005438:Fludrocortisone / Q000031:analogs & derivatives*; D008958:Models, Molecular; D008968:Molecular Conformation; D014961:X-Ray Diffraction
chemical_list: D005438:Fludrocortisone; C034635:fludrocortisone acetate