title: The molecular structure of 16 alpha-iodo-17 beta-estradiol, a high affinity ligand for the estrogen receptor.
abstract: 16 alpha-Iodoestradiol is an estrogenic steroid with high affinity for the estrogen receptor. When labelled with a gamma emitting isotope, such as 125I, the resulting radioactive steroid is an excellent ligand for the sensitive analysis of the estrogen receptor. The X-ray study of the crystal structure of 16 alpha-iodoestradiol reveals that the bond distances and angles of the iodinated estrogen are similar to those of estradiol and estriol. The substitution of iodine for the 16 alpha-hydroxyl group has little effect on geometric and electronic properties of the molecule and does not interfere with the hydrogen bonding ability of the 17 beta-hydroxyl group. The difference in receptor binding affinity between 16 alpha-estradiol and estriol may be due to competition for intermolecular hydrogen bond formation between the hydroxyls at C(16) and C(17) on estriol. X-Ray data indicate that the 16-hydroxyl can form significantly shorter and presumably stronger hydrogen bonds.
mesh_terms: D055598:Chemical Phenomena; D002621:Chemistry; D002627:Chemistry, Physical; D003460:Crystallization; D004958:Estradiol / Q000031:analogs & derivatives* / Q000378:metabolism; D008968:Molecular Conformation; D011960:Receptors, Estrogen / Q000378:metabolism*; D014961:X-Ray Diffraction
chemical_list: D011960:Receptors, Estrogen; D004958:Estradiol; C024871:16 alpha-iodoestradiol