Structure-activity relationships of 9 beta-estrogens.

The 9 beta isomers of estradiol-17 beta, estradiol-17 a estrone and 17-ethinylestradiol-17 beta were synthesized and compared with their 9a-counterparts in the rat uterine cytosol estrogen receptor, uterotropic, and gonadotropin release inhibition assays. Except for 17-ethinyl-9 beta-estradiol-17 beta which was as active as its 9a isomer in the uterotropic assay, none of the 9 beta estrogens exhibited any biological activity which was equal to or greater than their 9a counterparts. For examples, 9 beta-estradiol-17 beta was 1/10 as active as estradiol-17 beta, and 9 beta-estrone was 1/4 as active as estrone in the uterotropic assay.