<unk>  also known as 15α-hydroxyestriol or as estra-1,3,5(10)-triene-3,15α,16α,17β-tetrol, is a naturally occurring estrane steroid and a derivative of estrin (estra-1,3,5(10)-triene). It has four hydroxyl groups, which is the basis for its abbreviation of E4. For comparison, estriol (E3) has three hydroxyl groups, estradiol (E2) has two hydroxyl groups, and estrone (E1) has one hydroxyl group and one ketone. Synthesis Chemical syntheses of<unk> have been published.
Estetrol 
Gestodene
Hexestrol
Fosfestrol
Benzestrol
Moxestrol
Dimestrol
Dienestrol