Progesterone 3-acetyl enol ether, also known as progesterone acetate,[1] as well as 3-acetoxypregna-3,5-dien-20-one, is a progestin which was never marketed.[2][3][4][5] It was reported to possess similar potency to progesterone and hydroxyprogesterone caproate in the rabbit endometrial carbonic anhydrase test, a bioassay of progestogenic activity.[2][3] In addition, it was able to maintain pregnancy in animals.[2] Progesterone 3-acetyl enol ether is closely related to quingestrone, which is also known as progesterone 3-cyclopentyl enol ether and was formerly marketed as an oral contraceptive.[6]
The 3-acetyl ether may be cleaved from progesterone 3-acetyl enol ether in vivo and, based on its chemical structure, this may result in the transformation of progesterone 3-acetyl enol ether into 3α-dihydroprogesterone and/or 3β-dihydroprogesterone. 3β-Dihydroprogesterone has been reported to possess about the same progestogenic potency as progesterone in the Clauberg test, whereas 3α-dihydroprogesterone was not assessed.[7]
The C3 enol ethers of progesterone are less suited for use via depot injection relative to progestogen esters like hydroxyprogesterone caproate due to their susceptibility to oxidative metabolism.[8]
An interesting substance which has received little attention is the 3-cyclopentyl enol ether of progesterone (quingestrone). [...]
In the Clauberg bioassay the 3β-hydroxy-4-pregnen-20-one shows about the same potency as progesterone (34). In regard to the biological activity of the 3α epimer no data are available.
Among a large no. of pregnane derivs. the esters of 17-α-hydroxyprogesterone (I), itself of weak lutein hormone action, have a strong and long-lasting gestagen action. The optimal results are obtained with I caproate. It permits the administration of depot doses in clear solns. Within the range of dosage used no androgenic effect was noted. It has no influence on growth and on the secondary sex characteristics in infantile and adult castrate male rats. The 3-enol esters of progesterone, which have a somewhat prolonged action, are less suited for depot administration because of their oxidizability.