6α-Hydroxyestradiol is one of major metabolites of endogenous estrogens, as well as a positional isomer of estriol. Transformation of estradiol to 6α-Hydroxyestradiol is a major metabolic pathway of estradiol in the liver. CYP1A2 and CYP3A4 are the major enzymes catalyzing the 6α-Hydroxyestradiol of estradiol.

17α-Epiestriol (17-epiestriol, 16α-hydroxy-17α-estradiol or estra-1,3,5(10)-triene-3,16α,17α-triol) is the 17α-epimer of estriol, a minor hydroxylated estradiol metabolite and a selective estrogen receptor (ER) beta agonist. 17α-Epiestriol is described as a relatively weak estrogen, which is in accordance with its relatively low affinity for the ERα. 17α-Epiestriol has been found to be approximately 400-fold more potent than estradiol in inhibiting tumor necrosis factor α (TNFα)-induced vascular cell adhesion molecule 1 (VCAM-1) expression in vitro.