Identification of isoflavone metabolites dihydrodaidzein, dihydrogenistein, 6 '-OH-O-dma, and cis-4-OH-equol in human urine by gas chromatography-mass spectroscopy using authentic reference compounds

The metabolic products of daidzein and genistein, the principal isoflavones of soy, were examined. Six volunteers included soy into their normal diet for a a-week period and urine samples were analyzed before and after soy co nsumption. Isolation and characterization of the urinary metabolites were c arried out with absorption chromatography on Sephadex LH-20 and gas chromat ography-electron ionization mass spectrometry (GC-EIMS). The structures of the isoflavones isolated were confirmed by using authentic reference com po unds. Dihydrogenistein, 6'-OH-O-desmethylangolensin, and cis-4-OH-equol wer e identified, in addition to known isoflavonoids daidzein, genistein, glyci tein, and the known metabolites equol, O-desmethylangolensin, and dihydroda idzein, by comparing the retention times and the spectra of the urinary com pounds with those of the synthesized reference standards. The mammalian lig nans enterolactone and enterodiol were also identified. Derivatization of t he isoflavones for GC-MS was examined by comparing two silylating reagents, N,O-bis-(trimethylsilyl)-trifluoroacetamide (BSTFA) and pyridine:hexamethy ldisilazan:trimethylchloro (QSM), both used for the derivatization of these compounds. The silylation experiments revealed significant differences in the compositions of the derivatization products. Some corrections were made concerning the earlier published data of dihydrogenistein and 6'-OH-O-dma. (C) 1999 Academic Press.