Equol is a non-steroidal estrogen produced from the metabolism of the isoflavonoid phytoestrogen daidzen by human intestinal microflora.^1,2The estrogen receptor (ER) agonist activity of the naturally occurring (S)-enantiomer (EC₅₀= 85 and 65 nM for human ERα and ERβ, respectively) is similar to that of genistein but exceeds that of daidzein.²(S)-Equol preferentially binds ERβ (K_i= 0.73 nM) and demonstrates approximately 9-fold lower affinity for ERα (K_i= 6.41 nM).¹(S)-equol is also a potent antagonist of dihydrotestosterone, which has important implications for prostate cancer and other androgen-mediated pathologies.³

1.Setchell, K.D.R., Clerici, C., Lephart, E.D., et al.S-equol, a potent ligand for estrogen receptor β, is the exclusive enantiomeric form of the soy isoflavone metabolite produced by human intestinal bacterial floraAm. J. Clin. Nutr.81(5)1072-1079(2005) 2.Muthyala, R.S., Ju, Y.H., Sheng, S., et al.Equol, a natural estrogenic metabolite from soy isoflavones: Convenient preparation and resolution of R- and S-equols and their differing binding and biological activity through estrogen receptors alpha and betaBioorg. Med. Chem.12(6)1559-1567(2004) 3.Lund, T.D., Munson, D.J., Haldy, M.E., et al.Equol is a novel anti-androgen that inhibits prostate growth and hormone feedbackBiology of Reproduction701188-1195(2004)