Polyphenols present in plant foods and beverages have attracted much attention as food factors in the prevention of life style-related diseases and health promotion. Here we presented recent studies on the bioavailability of polyphenols, in particular, the relationship between the absorption/metabolism of catechins and their physiological functions including antioxidative effect. In either rats or humans, both (+) -catechin and (-) -epicatechin were found to be more absorptive than gallate-binding catechins. In plasma, they are present mainly as conjugated metabolites, namely glucuronides, sulfates and their methylated products. Nevertheless, their metabolite profiles are different between rats and humans. For example, considerable amounts of sulfates accumulate in human plasma. Catechin metabolites still possess antioxidative effect as long as catechol structure is unchanged. Alternatively, catechin metabolites were recently reported to suppress the induction of apoptosis in nervous cells. Therefore, biological activity of catechin metabolites should be clarified in detail in order to estimate the physiological function of dietary catechins.

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Polyphenols are known as important substances for food, health and medicine recently. Catechin, tocopherol and quercetin are important for the anti-oxidative and anti-cancer compound. Recent progress of synthesis and oxidation of polyphenols; catechin, quercetin and tocopherol is described. Dimer, trimer and oligomer of catechin were synthesized using Lewis acid; TiC1₄, BF₃.Et₂O and TMSOTf. Quercetin are known to be oxidized in the condition of lipid oxidation to give querctin dimer and diketone compounds. Tocopherols are also known to be oxidized under the ultraviolet irradiation to give the tocopherol trimer. Tocopherols were acetoxylated to give the catechol derivative of tocopherol.

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