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Tea is a beverage consumed widely throughout the world. The existence in tea of chemopreventing compounds possessing antimutagenic, anticarcinogenic and antioxidative properties has been reported. High intakes of tea and foods containing flavonoids have recently been shown to be negatively correlated to the occurrence of CHD. However, tea may contain other compounds with similar activities. Using a new gas chromatographic-mass spectrometric method we measured lignans and isoflavonoids in samples of twenty commercial teas (black, green and red varieties) and, for comparison, six coffees. Both unbrewed and brewed tea were investigated. The analysis of the teas yielded relatively high levels of the lignans secoisolariciresinol (56-28.9 mgkg; 15.9-81.9 pmoVkg) and matairesinol (0.56-4.13 m a g ; 1.6-11.5 pmolkg) but only low levels of isoflavonoids. Because the plant lignans, as well as their mammalian metabolites enterolactone and enterodiol, have antioxidative properties and these mammalian lignans occur in high concentrations in plasma, we hypothesize that lignan polyphenols may contribute to the protective effect of tea on CHD.

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cis-4‘,7-Dihydroxyisoflavan-4-ol (4) and trans-4‘,7-dihydroxyisoflavan-4-ol (5), two proposed metabolites of daidzein (4‘,7-dihydroxyisoflavone), have been synthesized and fully characterized for the first time. The vicinal coupling constants of the pyran ring protons are compatible with a half-chair conformation. The cis isomer is anancomeric while the trans isomer consists of a 68:32 mixture of two ring inversion conformers. Molecular mechanical calculations are in agreement with the half-chair conformation of the pyran ring and suggest that the cis isomer is biased because of an unfavorable gauche interaction of the equatorial hydroxyl and the axial phenyl group. The isoflavanols 4 and 5 are comparable to genistein (4‘,5,7-trihydroxyisoflavone) in antitumor activity against human prostate cancer cells.

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