Title: Ethisterone
CAS Registry Number: 434-03-7
CAS Name: 17a-Hydroxypregn-4-en-20-yn-3-one
Additional Names: 17a-ethynyltestosterone; 17a-ethynyl-17b-hydroxy-4-androsten-3-one; 17a-ethinyltestosterone; 17a-ethynyl-4-androsten-17b-ol-3-one; anhydrohydroxyprogesterone; pregneninolone
Molecular Formula: C21H28O2
Molecular Weight: 312.45
Percent Composition: C 80.72%, H 9.03%, O 10.24%
Literature References: Synthetic progestogen; metabolite of danazol, q.v.; intermediate in the synthesis of spironolactone, q.v. Prepn: Inhoffen et al., Ber. 71, 1024 (1938). Crystal structure and photostability study: J. Reisch et al., Monatsh. Chem. 124, 1169 (1993). GC/MS characterization as a metabolite of danazol: J. Y. Kim et al., J. Vet. Pharmacol. Ther. 24, 147 (2001). HPLC/CD determn of isomers: D. Szegvári et al., Anal. Bioanal. Chem. 375, 713 (2003).
Properties: Crystals from ethyl acetate, mp 269-275°. Sublimes in high vacuum at 190-195°. [a]D23 +23.8° (dioxane); [a]D25 -32.0° (pyridine). Crystal density: 1.220 g/cm3. uv max (methanol): 241 nm (E1%1cm 513). Practically insol in water. Slightly sol in alcohol, acetone, ether, chloroform, vegetable oils.
Melting point: mp 269-275°
Optical Rotation: [a]D23 +23.8° (dioxane); [a]D25 -32.0° (pyridine)
Absorption maximum: uv max (methanol): 241 nm (E1%1cm 513)
Ethofumesate Ethoheptazine Ethohexadiol Ethopabate Ethopropazine

Systematic (IUPAC) name
Clinical data
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CAS number 434-03-7 N
ATC code G03DC04
PubChem CID 5284557
ChemSpider 4447612 YesY
UNII Verifiedfields = changed P201BVY1MJ Verifiedfields = changed N
Chemical data
Formula C21H28O2 
Mol. mass 312.446 g/mol
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Ethisterone is a progestogen hormone.

The first orally active progestin, ethisterone (pregneninolone, 17α-ethynyltestosterone or 19–norandrostane), the 17α-ethynyl analog of testosterone, was synthesized in 1938 by Hans Herloff Inhoffen, Willy Logemann, Walter Hohlweg, and Arthur Serini at Schering AG in Berlin and marketed in Germany in 1939 as Proluton C and by Schering in the U.S. in 1945 as Pranone.

Ethisterone was also marketed in the U.S. from the 1950s into the 1960s under a variety of trade names by other pharmaceutical companies that had been members of the pre-World War II European hormone cartel (Ciba, Organon, Roussel).