17α-Ethynyl-3β-androstanediol

17α-Ethynyl-3β-androstanediol (developmental code HE-3539; also known as 17α-ethynyl-5α-androstane-3β,17β-diol) is a synthetic estrogen and a 17α-substituted derivative of 3β-androstanediol which was never marketed.

17α-Ethynyl-3β-androstanediol shows high affinity for the estrogen receptors in vitro (IC50 values of 16 nM for ERα and 126 nM for ERβ relative to values of 8 nM at ERα and 7 nM at ERβ for estradiol), and activates the estrogen receptors in vitro (EC50 value of 0.9 nM relative to 0.002 nM for estradiol). It also has weak affinity for the androgen receptor in vitro (IC50 = 277 nM relative to 15 nM for dihydrotestosterone), but doesn't appear to activate the receptor. 17α-Ethynyl-3β-androstanediol may produce 17α-ethynyl-3α-androstanediol and 5α-dihydroethisterone (5α-dihydro-17α-ethynyltestosterone) as active metabolites in vivo. In accordance with its in-vitro estrogenic activity, 17α-ethynyl-3β-androstanediol produces estrogenic effects like uterotrophy and testicular atrophy in animals.

Esters of 17α-ethynyl-3β-androstanediol have been developed and studied.

17α-Ethynyl-3β-androstanediol is a positional isomer of 17α-ethynyl-3α-androstanediol, and is a metabolite of this compound in vivo via metabolic inversion of the position of the C3 hydroxyl group. It may be involved in the biological activity of 17α-ethynyl-3α-androstanediol.

Analogues of 17α-ethynyl-3β-androstanediol include 17α-ethynyl-3α-androstanediol, ethinylandrostenediol (17α-ethynyl-5-androstenediol), ethandrostate (17α-ethynyl-5-androstenediol 3β-cyclohexanepropionate), ethinylestradiol (17α-ethynylestradiol), ethisterone (17α-ethynyltestosterone), and 5α-dihydroethisterone (17α-ethynyldihydrotestosterone).