By breaking down the oestriol molecule stage by stage Butenandt proved that both œstrogenic hormones contained a phenanthrene core.    From Wordnik.com.  [Nobel Prize in Chemistry 1939 - Presentation Speech] Reference

In 1932, Butenandt was able, from observations made in spectral analysis, and especially on the basis of the then established correct formula of cholesterol to draw up the formulae of the chemical structure of oestrone and oestriol.    From Wordnik.com.  [Nobel Prize in Chemistry 1939 - Presentation Speech] Reference

(1974) Plasma levels of nonconjugated oestrone, oestradiol-17beta and oestriol during uncomplicated pregnancy.    From Wordnik.com.  [PLoS ONE Alerts: New Articles] Reference