17α-Alkylated anabolic steroid
A 17α-alkylated anabolic steroid is a synthetic androgenic-anabolic steroid (AAS) that features an alkyl group, specifically a methyl or ethyl group, at the C17α position. Unlike many other AAS, 17α-alkylated AAS are orally active and do not require intramuscular injection. However, they uniquely possess a high potential for hepatotoxicity, which simultaneously limits their use. In addition, they have a high risk of gynecomastia due to uniquely high estrogenic activity, although this does not apply to 17α-alkylated AAS that are also 4,5α-reduced or 19-demethylated (i.e., that are also dihydrotestosterone (DHT) or nandrolone derivatives, respectively). The prototypical example of a 17α-alkylated AAS is methyltestosterone (17α-methyltestosterone).
Extension of the C17α alkyl chain longer than an ethyl group abolishes androgenic activity and converts the drug into an antiandrogen, as in topterone (17α-propyltestosterone) and allylestrenol (17α-allyl-3-deketo-19-nortestosterone) (an extended-chain variant of ethylestrenol). Conversely, replacement of the C17α alkyl group with an ethynyl group greatly reduces but does not abolish androgenic activity, as in ethisterone (17α-ethynyltestosterone) and norethisterone (17α-ethynyl-19-nortestosterone). Similarly to extension of the C17α alkyl chain, extension of the C17α ethynyl chain abolishes androgenic activity, as with dimethisterone (6α,21-dimethylethisterone). Dienogest, which is antiandrogenic, features extension of the C17α chain in the form of a cyanomethyl group at the C17α position.