title: Estrogen receptor binding tolerance of 16 alpha-substituted estradiol derivatives.
abstract: In order to examine the tolerance of the estrogen receptor for 16 alpha-substituents in estradiol, we have synthesized various 16 alpha-substituted estrogens and determined their binding affinity for receptor by a competitive radiometric binding assay. The substituents ranged from small, single-atom substituents (halogens), two-atom substituents (halomethyl groups), to larger alkyl groups and ultimately alkyl groups bearing various functionality, including fluorescent (nitrobenzoxadiazole, NBD) and photoreactive (nitroazidophenyl, NAP) groups. The estrogen receptor seems to have a moderate tolerance for bulky substituents: All of the halogen and halomethyl substituents bind with an affinity at least 50% that of estradiol; in the three atom alkyl series, the affinity declined markedly from propargyl (44%) and allyl (38%) to propyl (5%), suggestive of detailed steric constraints or a preference for unsaturation. The larger, more highly functionalized derivatives ranged in affinity from 0.1-7%, with the highest affinity binders being benzyl (5%) and 4-phenoxy-2(E)-butenyl (7%); most of the lowest affinity ones were the bulky fluorescent and photoreactive derivatives. Thus, the estrogen receptor has good tolerance for estradiol derivatives substituted at the 16 alpha-position with nonpolar groups of moderate bulk; however, with groups of larger bulk, affinity is much lower and becomes highly dependent upon the polarity and detailed structure of the substituents.
authors.affiliation: Department of Chemistry, University of Illinois, Urbana 61801.
authors.forename: T L
authors.initials: TL
authors.lastname: Fevig
authors.forename: M K
authors.initials: MK
authors.lastname: Mao
authors.forename: J A
authors.initials: JA
authors.lastname: Katzenellenbogen
mesh_terms: D004958:Estradiol / Q000031:analogs & derivatives / Q000378:metabolism*; D011960:Receptors, Estrogen / Q000378:metabolism*
chemical_list: D011960:Receptors, Estrogen; D004958:Estradiol