B-ring unsaturated estrogens: biological evaluation of 17alpha-Dihydroequilein and novel B-Nor-6-thiaequilenins as tissue selective estrogens.

The pharmacology and SAR of representative equine estogens is described. 17alpha-Dihydroequilenin was found to prevent bone loss after 5 weeks of oral administration to ovariectomized rats. The stereochemical significance of the D-ring and the C/D ring juncture was investigated with a series of benzothiophene-based equilenin analogues.