epostane epostane epostane (inn, usan, ban) (developmental code name win-32729) is an inhibitor of 3β-hydroxysteroid dehydrogenase (3β-hsd) that was developed as a contraceptive, abortifacient, and oxytocic drug but was never marketed. by inhibiting 3β-hsd, epostane blocks the biosynthesis of progesterone from pregnenolone (and also the conversion of dehydroepiandrosterone to androstenedione), thereby functioning as an antiprogestogen and terminating pregnancy. the drug was trialed and in a study was found to be slightly more effective at inducing abortion relative to mifepristone. epostaneclinical dataother nameswin-32729identifiers iupac name 4α,5α-epoxy-3,17β-dihydroxy-4β,17α-dimethylandrost-2-ene-2-carbonitrile cas number80471-63-2pubchem cid6917713chemspider5292942unii6375t36951chemblchembl2106218comptox dashboard (epa)dtxsid001001267 chemical and physical dataformulac22h31no3molar mass357.494 g·mol−13d model (jsmol)interactive image smiles c12cc3(1cc2(c)o)cc453(cc(=c(4(o5)c)o)c#n)c inchi inchi=1s/c22h31no3/c1-18-8-6-16-14(15(18)7-9-20(18,3)25)5-10-22-19(16,2)11-13(12-23)17(24)21(22,4)26-22/h14-16,24-25h,5-11h2,1-4h3/t14-,15-,16-,18-,19+,20-,21+,22-/m0/s1key:cetkwewbsmkadk-gsxvsziwsa-n