Influence of alkyl chain ramification on estradiol receptor binding affinity and intrinsic activity of 1,2-dialkylated 1,2-bis(4- or 3-hydroxyphenyl)ethane estrogens and antiestrogens.

The influence of a symmetrical introduction of CH3 substituents in the alpha or beta positions of the 1,2-dialkyl-1,2-bis(4-hydroxyphenyl)ethane estrogens hexestrol (ethyl, HES) and octestrol (n-propyl, OCES) [isopropyl (1), tert-butyl (2), sec-butyl (3), isobutyl (4)] and the 1,2-dialkyl-1,2-bis(3-hydroxyphenyl)ethane antiestrogens metahexestrol (ethyl, MetaHES) and metaoctestrol (n-propyl, MetaOCES) [isopropyl (5), tert-butyl (6), sec-butyl (7), isobutyl (8)] on estradiol receptor (E2R) binding affinity and intrinsic activity is described. The synthesis of compounds 1-8 was accomplished by reductive coupling of (a) the corresponding alpha-alkylbenzyl alcohols with TiCl3/LiAlH4 and separation of the meso diastereoisomers (compounds 2-4, 7, and 8), (b) alpha-tert-butyl-3-methoxybenzyl chloride with CoCl2/EtMgCl and isolation of the meso configurated isomer (6), and (c) the isopropyl phenyl ketones with TiCl4/Zn and subsequent hydrogenation of the corresponding cis-hex-3-enes (compounds 1 and 5). The binding affinity of 1-8 to the calf uterine E2R was measured relative to that of [3H]E2 by a competitive binding assay. Compounds 1 and 5 showed relative binding affinity (RBA) values exceeding those of HES and MetaHES, respectively. All other derivatives showed RBA values smaller than the corresponding parent compounds. The intrinsic activity was monitored in terms of uterotrophic and antiuterotrophic activity. It is striking that the introduction of a CH3 group in the alpha positions of MetaHES and MetaOCES led to compounds with full intrinsic activity (5-7), i.e., estrogens without antiestrogenic properties. No correlation between E2R binding affinity and intrinsic activity was found.