Pathway and Stereochemistry of the Formation of Estriols in Man

Following the administration of estradiol-16β-3H and -16β-3H to human subjects the tritium content of the urinary estriol and estra-l,3,5(10)-triene-3,16β,17β-triol (16-epiestriol) was determined. From the values it is evident that the hydroxylation at C-16 whether α or β proceeds by replacement of hydrogen and that no common enol form is involved in the reaction. Further, 16-keto compounds cannot be considered as intermediates in the biosynthesis of estriol or 16-epiestriol. The difference in the recovery of tritium in urine and body water in the 16β-3H and 16a-3H studies suggests that the substantial portion of the administered dose which is never recovered in the urine is altered by 16α and not 16β substitution.