Moxestrol
Moxestrol (INN) (brand name Surestryl), also known as 11β-methoxy-17α-ethinyl-1,3,5(10)-estratriene-3,17β-diol or as 11β-methoxy-17α-ethinylestradiol, is a synthetic, steroidal estrogen that is or was used in Europe for the treatment of menopausal symptoms. It is the 11β-methoxy derivative of ethinyl estradiol, and is one of the most potent estrogens known, being some 10–100 times more potent than estradiol and about 5-fold more potent than ethinyl estradiol. The very high potency of moxestrol has been attributed to its high affinity for the estrogen receptor (ER), its negligible plasma binding to sex hormone binding globulin and low binding to serum albumin, and its lower relative rate of metabolization. In contrast to estradiol, which has roughly the same affinity for both ERs (Ki 0.12 nM and 0.15 nM, respectively), moxestrol possesses several-fold selectivity for ERα (Ki = 0.50 nM) over ERβ (Ki = 2.6 nM).