<unk> , also known as δ9-17α-cyanomethyl-19-nortestosterone or as 17α-cyanomethylestra-4,9-dien-17β-ol-3-one, is a synthetic estrane steroid and a derivative of testosterone. It is a member of the estrane subgroup of the 19-nortestosterone family of progestins, but unlike most other 19-nortestosterone progestins, is not a derivative of norethisterone (17α-ethynyl-19-nortestosterone). This is because it uniquely possesses a cyanomethyl group (i.e., a nitrile group) at the C17α position rather than the usual ethynyl group. It is also unique among most 19-nortestosterone progestins in that it has a double bond between the C9 and C10 positions.<unk>  is the C17α cyanomethyl derivative of the anabolic–androgenic steroid (AAS) dienolone, as well as the C17α cyanomethyl analogue of the AAS methyldienolone (17α-methyldienolone) and ethyldienolone (17α-ethyldienolone). In terms of structure–activity relationships, the C17α cyanomethyl group of<unk>  is responsible for its unique antiandrogenic instead of androgenic activity relative to other 19-nortestosterone progestins. A loss of ability to activate the AR is also seen with other testosterone derivatives with extended-length C17α substitutions such as topterone (propyltestosterone) (compare to the AAS ethyltestosterone and methyltestosterone) and allylestrenol (compare to the AAS ethylestrenol). Studies with steroids similar to<unk>  (e.g., dienolone) have found that the introduction of a double bond between the C9 and C10 positions is associated with similar/almost unchanged affinity for the PR and AR. On the other hand, the C9(10) double bond of<unk>  appears to inhibit metabolism via 5α-reductase and/or 5β-reductase, which is the major metabolic route for other 19-nortestosterone progestins like norethisterone, norgestrel, and etonogestrel, and this may serve to improve the metabolic stability and potency of<unk> .
Dienogest
Nafarelin
Estropipate
Degarelix
Protollin
Gestodene
Tesamorelin
Macimorelin