16β,17α-epiestriol 16β,17α-epiestriol 16β,17α-epiestriol, or 16,17-epiestriol, also known as 16β-hydroxy-17α-estradiol, as well as estra-1,3,5(10)-triene-3,16β,17α-triol, is a minor and weak endogenous steroidal estrogen that is related to 17α-estradiol and estriol. along with estriol, 16β,17α-epiestriol has been detected in the urine of women during the late pregnancy stage. it shows preferential affinity for the erβ over the erα. for other uses, see epiestriol (set index). 16β,17α-epiestriol names iupac name estra-1,3,5(10)-triene-3,16β,17α-triol systematic iupac name (1s,2s,3as,3br,9bs,11as)-11a-methyl-2,3,3a,3b,4,5,9b,10,11,11a-decahydro-1h-cyclopentaphenanthrene-1,2,7-triol identifiers cas number 793-89-5 3d model (jsmol) interactive image chemspider 13628086 pubchem cid 21252247 comptox dashboard (epa) dtxsid60611651 inchi inchi=1s/c18h24o3/c1-18-7-6-13-12-5-3-11(19)8-10(12)2-4-14(13)15(18)9-16(20)17(18)21/h3,5,8,13-17,19-21h,2,4,6-7,9h2,1h3/t13-,14-,15+,16+,17-,18+/m1/s1 smiles c12cc3(1c(2o)o)ccc4=c3c=cc(=c4)o properties chemical formula c18h24o3 molar mass 288.387 g·mol−1 except where otherwise noted, data are given for materials in their standard state (at 25 °c , 100 kpa). infobox references