Boldenone is testosterone with an added double-bond between carbon atoms one and two. However, this bond changes the activity of the steroid considerably. First, it dramatically slows aromatization, such that boldenone converts to estradiol at about half the rate of testosterone. Secondly, this bond causes the steroid to be a very poor substrate for the 5- alpha reductase enzyme. The more active 5-alpha reduced metabolite 5alphadihydroboldenone is produced only in very small amounts in humans. The hormone instead tends to convert via 5-beta reductase to 5beta-dihydroboldenone (a virtually inactive androgen). This makes it lean towards being an anabolic instead of an androgen, although both traits are still notably apparent with this steroid. The c1-2 double bond also slows the hepatic breakdown of the structure, increasing its resistance to 17-ketosteroid deactivation and its functional half-life and oral bioavailability.
This is the most basic derivative of testosterone, differing only by the added 17- alpha methylation that makes the steroid orally active. Conversion to 17-alpha methylestradiol makes this steroid extremely estrogenic, despite the fact that this alteration actually reduces interaction with the aromatase enzyme.
In many regards, methandrostenolone is very similar to boldenone, as it too exhibits reduced estrogenic and androgenic activity due to the c1-2 double-bond. However, this steroid does have a reputation of being somewhat estrogenic, owing to the fact that it converts to a highly active form of estrogen (17alphamethylestradiol See: Methylated Compounds and Oral Dosing). methandrostenolone is also much more active milligram for milligram, as the 17- alpha methyl group also gives it a longer half-life and allows it to exist in a more free state than its cousin boldenone.
Fluoxymesterone is a c-17alpha alkylated oral derivative of testosterone. The 11-beta group functions to inhibit aromatization, so there is no estrogen conversion at all with this steroid. It also works to lower the affinity of this steroid toward restrictive serum binding proteins, increasing its relative activity. Introduction of fluorine at the 9-position also potentiates the action of this steroid.
Norethandrolone is simply nandrolone with an added 17-alpha ethyl group. This alteration is rarely used with anabolic/androgenic steroids, and is much more commonly found with synthetic estrogens and progestins. Although 17-ethylation inhibits 17-ketosteroid reduction just as well as 17-methylation, and therefore allows this steroid to exhibit a similarly high level of oral activity, this group also tends to increase progesterone receptor binding. norethandrolone is clearly a “troublesome” hormone in terms of water retention, fat gain, and gynecomastia, which may in part be due to its heightened binding to this receptor.
Ethylestrenol is an oral derivative of nandrolone, very similar in structure to keto group, which is vital to androgen receptor binding. As such, ethylestrenol is possibly the weakest steroid milligram for milligram ever sold commercially. Any activity this steroid does exhibit is likely from its conversion to norethandrolone, which does seem to occur with some affinity (apparently the 3 oxygen group is metabolically added to this compound without much trouble). This is probably the most interesting trait of ethylestrenol, which is an undistinguished compound otherwise.
Although a derivative of nandrolone, the two additional double-bonds present on trenbolone make any similarities to its parent hormone extremely difficult to see. First, the 9-10 bond inhibits aromatization. Nandrolone is very slowly aromatized, however, some estrogen is still produced from this steroid. Not so with trenbolone. The 11-12 bond additionally increases androgen receptor binding. This steroid also does not undergo 5-alpha reduction like nandrolone, and as such does not share the same dissociation between anabolic and androgenic effects (trenbolone is much more androgenic in comparison).
Mesterolone is a potent orally active derivative of dihydrotestosterone. Similar to methenolone, it possesses a non-toxic 1-methyl group, which increases its resistance to hepatic breakdown. This alteration does not increase the stability of the 3-keto group however, and as such, this steroid is a poor anabolic like its parent.
Drostanolone is simply dihydrotestosterone with an added 2-methyl group. This addition greatly increases the stability of the 3-keto group, vital to androgen binding. As such, the activity of this steroid in muscle tissue is greatly enhanced (see: Anabolic/Androgenic Dissociation).
Oxymetholone is an orally active derivative of dihydrotestosterone. The 17-methyl group is well understood at this point as we have discussed it with many steroids, however, the 2- hydroxymethylene group is not seen on any other commercial steroid. We do know that this group greatly enhances anabolic potency by increasing the stability of the 3-keto group, and that the configuration of this substituent also appears to allow this steroid to bind and activate the estrogen receptor.
Stanozolol is a potent anabolic steroid, owing to the fact that the 3-2 pyrazol group creates a stable configuration off the A-ring that allows for androgen receptor binding (this steroid is one of the few that does not possess an actual 3-keto group). As such, it is highly active in muscle tissue, unlike dihydrotestosterone.
Methenolone also is a potent anabolic steroid, due to the fact that the c1-2 double bond increases the stability of the 3-keto group. The 1-methyl group works to increase its oral bioavailability, making methenolone (as methenolone acetate) one of the few orally active non-17-alkylated orals. The c 1-2 bond may also help increase hepatic resistance (slightly) to 17-ketosteroid deactivation as well.
Oxandrolone is an orally active derivative of dihydrotestosterone, due to its 17-methylation. It also differs from DHT by the substitution of its 2-carbon molecule with oxygen. This is the only commercial steroid to carry this group, and further, the only to have a modification to the base carbon structure of the Steran nucleus. The 2-oxo group increases resistance of the 3-keto group to metabolism considerably, making oxandrolone a potent anabolic.
Wlliam Llewellyn (2011) - Anabolics