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 5alpha-dihydroboldenone 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. 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.
Llewellyn, William. Anabolics