16α-iodo-e2 16α-iodo-e2 16α-iodo-e2, or 16α-iodoestradiol, is a synthetic, steroidal, potent estrogen with slight preference for the erα over the erβ that is used in scientific research. the kd of 16α-iodo-e2 for the erα is 0.6 nm and for the erβ is 0.24 nm, a 4-fold difference in affinity, whereas estradiol is considered to have similar affinity for the two receptor subtypes. unlike the case of the much weaker estriol (16α-hydroxyestradiol), 16α-iodo-e2 is considered to be equipotent with estradiol in terms of estrogenic activity. radiolabeled iodo-e2 has been employed in imaging to study the estrogen receptor. 16α-iodo-e2identifiers iupac name (8r,9s,13s,14s,16r,17r)-16-iodo-13-methyl-6,7,8,9,11,12,14,15,16,17-decahydrocyclopentaphenanthrene-3,17-diol cas number7450-34-2pubchem cid67087chemspider60437chemblchembl342892comptox dashboard (epa)dtxsid00275695 chemical and physical dataformulac18h23io2molar mass398.284 g·mol−13d model (jsmol)interactive image smiles c12cc3(1c(2o)i)ccc4=c3c=cc(=c4)o inchi inchi=1s/c18h23io2/c1-18-7-6-13-12-5-3-11(20)8-10(12)2-4-14(13)15(18)9-16(19)17(18)21/h3,5,8,13-17,20-21h,2,4,6-7,9h2,1h3/t13-,14-,15+,16-,17+,18+/m1/s1key:ssyggpagddgxaf-zxxigwhrsa-n