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Data from Salhanick, H. A., et al.: Metabolic Effects of Gonadal Hormones and Contraceptive Steroids. New York, Plenum Press, 1969.

Data from Salhanick, H. A., et al.: Metabolic Effects of Gonadal Hormones and Contraceptive Steroids. New York, Plenum Press, 1969.

(ethisterone) had greater progestational than androgenic activity. Although the 19-nortestosterones do have androgenic side effects, their primary activity, nevertheless, is progesta-tional. In addition to causing a marked increase in progestational activity, the 17a-alkynyl group also blocks metabolic or bacterial oxidation to the corresponding 17-ones. Thus, by adding a 17a-ethinyl group to testosterone, one can simultaneously decrease androgenic activity, promote good progestational activity, and have an orally active compound as well. Table 25.2 illustrates the relative progestational activity of several progestins. A further modification to the nortestos-terones yields progestins with minimal androgenic activities. Changing the alkyl group at C13 from a methyl to an ethyl group, as in levonorgestrel, reduces the androgenic effects, while maintaining the progestational effects.

The most exciting new research area relating to progestins is the development of nonsteroidal PR agonists. Tanoproget is the most successful example to date (phase II trials).80 As can be seen in Figure 25.19, tanaproget is completely unrelated to progesterone, but it still has high affinity and selectivity for the PR. The nonsteroidal nature of tanaproget offers

1. Progesterone and Derivatives

1. Progesterone and Derivatives

Progesterone
Hydroxy prog este rone caproate

Medroxyprogesterone acetate (Provera, Depo-Provera)

Megestrol acetate (Megace)

Nomegestrol acetate (NOMAC)

Medroxyprogesterone acetate (Provera, Depo-Provera)

Megestrol acetate (Megace)

Nomegestrol acetate (NOMAC)

2. Synthetic Progestins - Testosterone and Nortestosterone Derivatives

2. Synthetic Progestins - Testosterone and Nortestosterone Derivatives

Ethisterone

Norethindrone

HqC 0H

HqC 0H

Norethynodrel

Ethisterone

Norethindrone

Norethynodrel

H3C\ OH

H3C\ OH

Ethynodiol diacetate Norgestrel (Levonorgestrel)

Figure 25.19 • Natural and synthetic progestins. (continues on next page)

Chapter 25 # Steroid Hormones and Therapeutically Related Compounds 839 2. Synthetic Progestins - (continued)

Drospirenone Figure 25.19 • (Continued)

the potential for a different side effect profile compared with the other progestins. While there is still a long road before approval of nonsteroidal progestins like tanaproget, there is great enthusiasm that a new class of progestins can be developed.

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