Conversion of (3S,4R)-tetrahydrodaidzein to (3S)-equol by THD Reductase: Proposed Mechanism Involving a Radical Intermediate

Biochemistry. 2010 Jul 6;49(26):5582-7. doi: 10.1021/bi100465y.


To elucidate the mechanism of (3S)-equol biosynthesis, (2,3,4-d(3))-trans-THD was synthesized and converted to (3S)-equol by THD reductase in Eggerthella strain Julong 732. The position of the deuterium atoms in (3S)-equol was determined by (1)H NMR and (2)H NMR spectroscopy, and the product was identified as (2,3,4(alpha)-d(3))-(3S)-equol. All the deuterium atoms were retained, while the OH group at C-4 was replaced by a hydrogen atom with retention of configuration. To explain the deuterium retention in this stereospecific reduction, we propose a mechanism involving radical intermediates.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Bacteria, Anaerobic / metabolism*
  • Deuterium
  • Equol
  • Free Radicals / metabolism
  • Isoflavones / biosynthesis*
  • Isoflavones / metabolism*
  • Magnetic Resonance Spectroscopy
  • Molecular Conformation
  • Organic Chemistry Phenomena
  • Oxidoreductases / metabolism*
  • Stereoisomerism


  • Free Radicals
  • Isoflavones
  • tetrahydrodaidzein
  • Equol
  • Deuterium
  • Oxidoreductases