Antiperoxidative components in Thymus vulgaris.

A biphenyl compound, 3,4,3',4'-tetrahydroxy-5,5'-diisopropyl-2,2'-dimethylbiphenyl (1), and a flavonoid, eriodicytol (2), were isolated as antioxidative components from the leaves of Thymus vulgaris by bioassay-directed fractionation. These compounds inhibited superoxide anion production in the xanthine/xanthine oxidase system. Mitochondrial and microsomal lipid peroxidation induced by Fe(III)-ADP/NADH or Fe(III)-ADP/NADPH were also inhibited by these compounds. Compound 1 is an extremely potent antioxidant; complete inhibition was observed at 1 microM against both microsomal and mitochondrial peroxidation. Furthermore, compound 1 protected red cells against oxidative hemolysis. These phenolic compounds were shown to be effective to protect biological systems against various oxidative stresses.