These LGs and their isomers are highly reactive γ-ketoaldehydes that form covalent adducts with proteins, DNA, and phosphatidylethanolamine in cells. Here, we isolated a novel oxidized LGD(2) (ox-LGD(2)) from the redalgaGracilariaedulis and determined its planar structure. Additionally, ox-LGD(2) was identified in some tissues of mice and in the lysate of phorbol-12-myristate-13-acetate (PMA)-treated