estrin (compound) estrin (compound) estrin (american english), or oestrin (british english), also known as estra-1,3,5(10)-triene, is an estrane steroid. it is dehydrogenated estrane with double bonds specifically at the c1, c3, and c5(10) positions. estrin is a parent structure of the estrogen steroid hormones estradiol, estrone, and estriol, which have also been known as dihydroxyestrin, ketohydroxyestrin, and trihydroxyestrin, respectively. estrin names iupac name estra-1,3,5(10)-triene systematic iupac name (3as,3bs,9bs,11as)-11a-methyl-2,3,3a,3b,4,5,9b,10,11,11a-decahydro-1h-cyclopentaphenanthrene other names estratriene identifiers cas number 1217-09-0 3d model (jsmol) interactive image chembl chembl1627934 chemspider 133001 pubchem cid 150899 unii f274x7vr4m y comptox dashboard (epa) dtxsid10923933 inchi inchi=1s/c18h24/c1-18-11-4-7-17(18)16-9-8-13-5-2-3-6-14(13)15(16)10-12-18/h2-3,5-6,15-17h,4,7-12h2,1h3/t15-,16-,17+,18+/m1/s1key: hlcryazdzcjzfg-bdxsimousa-n smiles c12ccc13ccc4=cc=cc=c43cc2 properties chemical formula c18h24 molar mass 240.39 g/mol except where otherwise noted, data are given for materials in their standard state (at 25 °c , 100 kpa). infobox references unlike its estrogen derivatives, estrin itself possesses minimal estrogenic activity, as hydroxyl and/or keto substitutions at the c3 and c17 positions are critical for high binding affinity to the estrogen receptors. estrin has been found to be on the order of 1,000-fold less potent than estradiol in inducing estrogenic responses in vitro. in addition to estrin, estratrien-17β-ol, which lacks the 3-hydroxyl group of estradiol, and 3-hydroxyestratriene, which lacks the 17β-hydroxyl group of estradiol, both have measurable affinity for the estrogen receptor and are able to activate the receptor and induce progesterone receptor expression. the term estrin is also a synonym for estrogen. it was coined by sir alan s. parkes and c. w. bellerby in 1926 to describe the hormone secreted from the ovaries that induces estrus in animals (i.e., estrogen). structures of major endogenous estrogens estrone (e1) estradiol (e2) estriol (e3) estetrol (e4) note the hydroxyl (–oh) groups: estrone (e1) has one, estradiol (e2) has two, estriol (e3) has three, and estetrol (e4) has four.