[Relationship between the structure and estroginic activity of bromine- and silyl-substitutes of estradiol]

Comparative study of the estrogen properties of 2- and 4-brom and silyl-substituted estradiol administered subcutaneously and orally was carried out on sexually immature female rats. In comparison with initial estrogen, estradiol, silyl-group (SiMe3) substituted in the 4th position diminished the estrogen activity after subcutaneous injection but improved it considerably when given orally. Introduction of silyl radical in the 2nd position or of bromine in the 2nd and 4th positions of the estradiol molecule led to practically complete loss of the estrogenic activity irrespective of the method of administration of these compounds.