The term progestin includes progesterone and other natural or synthetic compounds with physiological actions analogous to progesterone. Progesterone is a hormone produced by steroidogenic tissues—the corpus luteum and the placenta. Progesterone prepares the endometrium for implantation of the oocyte, prevents ovulation, and facilitates increased glandular tissue in the mammary glands. Its structure is more similar to the structure of the male sex hormone testosterone, differing only in the substituent on C17 (acetyl group instead of a hydroxyl group), than to female sex hormones estrone or estrols. Progesterone is considered as a pregnancy hormone since it is made during the entire pregnancy, and it increases excitability and contractability of the uterus while simultaneously preventing new oocytes from maturing. The result of its action is prevention of forming oocytes equal to that of temporarily sterile women. This led to the creation of a new method of preventing pregnancy by maintaining an artificial hormonal state of pseudopregnancy.

Progestins are used for various menstrual cycle disorders, for functional uterine bleeding of various origins, and as a contraceptive. Progestin therapy is also used to treat endometriosis and endometrial carcinomas. Progesterone is not effective when taken orally due to intensive metabolism, and therefore it is used by either parenteral or transvaginal introduction.

A number of active, synthetic progestins have been made for the use as oral contraceptives that have more activity and more prolonged action than progesterone. Moreover, various conclusions have been made relative to the modification of progesterone structures for making new progestins. It has been shown that progesterone significantly loses its characteristic biological activity when a hydroxyl group is added at position C17. At the same time, esterification of the hydroxyl group by long-chained fatty acids, such as caproic acid, leads to formation of long-lasting, parenterally introduced progestin, oxyprogesterone caproate. Extremely effective progestins are C17 ethynyl derivatives linestrenol, norgestrel, and norethindrone, which provide highly effective contraception.

Progesterone: Progesterone, pregn-4-en-3,20-dione (28.3.1), is made by oxidizing preg-nenolon with aluminum isopropylate in the presence of cyclohexanone as a proton acceptor (Oppenauer oxidation) [57-63]. Pregnenolon itself is made by subsequent oxidation and further cleavage of the side chain of stigmasterin, a sterin of plant origin that is isolated from soybeans.

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