Cyclopentanoperhydrophenanthrene

Cyclopentanoperhydrophenantrene molecule.

Cyclopentanoperhydrophenanthrene (also called sterane or gonane) is a polycyclic hydrocarbon that can be considered a saturation product of phenanthrene associated with a cyclopentane ring. It has 17 carbon atoms. Steroids (cholesterol and its derivatives, such as progesterone, aldosterone, cortisol, and testosterone are examples of compounds that contain a cyclopentanoperhydrophenanthrene nucleus) derive from this structural base, derived from phenanthrene. They are present in the cells of eukaryotic organisms.

Substances derived from this nucleus show methyl groups -CH₃, at positions 10 and 13 to integrate carbons 18 and 19; there is generally an aliphatic chain at carbon 17, the length of said chain and the presence of methyls at carbon 10 and 13 determine the different structures of these substances.

This is the newest group and there are four important progestogens in it: levonorgestrel, desogestrel, gestodene and norgestimate.

Levonorgestrel

It is a progestogen used in contraceptive formulations that has a biological activity approximately 80 times more potent than endogenous progesterone. It has an androgenic effect because it competes with testosterone to bind to the binding protein, and it also has anti-estrogenic activity. However, these preparations have an unfavorable influence on the ratio between LDL-cholesterol and HDL-cholesterol due to their androgenic effect and when administered in combination with 30 µg ethinylestradiol they reduce the LDL fraction and raise HDL. The most important advance that has occurred in recent years has been the production of three levonorgestrel-derived progestogens, which are the so-called "third generation progestogens".

Desogestrel

Available since 1982, it was the first of the more selective progestogens to become available for use in OCs. It is 2.8 times more potent than levonorgestrel, has few androgenic effects (virtually does not compete with testosterone for binding to the binding protein), and has no influence on estrogenic activity, allowing low doses of estrogen to be used in contraceptive preparations. and reduce the occurrence of side effects (Dibbelt et al, 1991). In addition, it limits the penetration of sperm through the cervical mucus and is a powerful inhibitor of ovulation.

Gestodeno

It was the second commercially available third-generation progestogen. It does not require hepatic metabolism to be biologically active. It is 1.5 times more potent than levonorgestrel. It does not interfere with testosterone metabolism and largely avoids the androgenic side effects of OCs containing norgestrel and levonorgestrel. Unlike desogestrel, it has an important antiestrogenic effect, which limits the dose used.

Norgestimate

It is the newest of all. Biological assays have shown that it has a high progestational selectivity and its affinity to bind with androgen receptors is lower than that of gestodene and levonorgestrel, which gives it high progestational activity with very low androgenic activity (Huber, 1991).

With current knowledge, the profile of an AO cannot be represented simply by the sum of both components; but by a complex interaction between the two. This interaction can manifest itself with a powerful synergism between estrogen and progestogen or, conversely, with an antagonistic effect between the two.