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Flavonoids, a group of naturally occurring antioxidants and iron chelators, might be used as cardioprotective agents in doxorubicin-induced cardiotoxicity, which is believed to be caused by the formation of oxygen free radicals. To investigate the underlying molecular mechanism, we tested a large group of flavonoids from all major structural subclasses on their ability to inhibit doxorubicin (enzymatically)-induced and Fe²⁺/ascorbate (nonenzymatically)-induced microsomal lipid peroxidation (LPO) and to chelate Fe²⁺. In addition, we measured half peak oxidation potentials (Ep/2). LPO inhibition data gave a good qualitative correlation with the oxidation potentials. Most flavonoids tested chelated Fe²⁺, but there were large differences in the chelating capacity. For good scavenging activity, a catechol moiety on ring B is required. The 3-OH moiety can function as a chelation site and can also be oxidized. The 3-OH …