Stereochemistry of cis- and trans-hinokiresinol and their estrogen-like activity

Naturally occurring phenylpropanoids, hinokiresinol (trans-hinokiresinol) and nyasol (cis-hinokiresinol) were found to possess appreciable estrogen receptor binding activity. Strong differences in activity were observed between the geometrical isomers and enantiomers. Among these, (3S)-cis-hinokiresinol displayed the highest activity, one order of magnitude greater than the activity of genistein. Furthermore, cis- and trans-hinokiresinol stimulated the proliferation of estrogen-dependent T47D breast cancer cells, and their stimulatory effects were blocked by an estrogen antagonist, indicating that the compounds are estrogen agonists. In addition, the absolute configuration of C-3 in (+)-cis-hinokiresinol has been assigned as S by comparison with the circular dichroism spectra of the hydrogenated products prepared from cis and trans ((3S)-trans-hinokiresinol: previously assigned) isomers. These results incidentally provide us with an unambiguous answer to contradictory reports regarding the assignment of the full stereochemisry of cis- and trans-hinokiresinol that have existed in the literature for more than two decades.