(16α,?17β)?- Estra-?1,?3,?5(10)?-?triene-?3,?4,?16,?17-?tetrol-16,17-diacetate is an intermediate in the synthesis of 2-Hydroxyestriol (H949313), which is used to characterize oxidative metabolites of 17β-estradiol and estrone formed by 15 selectively expressed human cytochrome P 450 isoforms.