An oxidation product consisting of covalent ortho-ortho coupling between two tyrosine residues formed as a conseguence to UV irradiation, gamma-irradiation, aging, exposure to oxygen free radicals, nitrogen dioxide, peroxynitrite, and lipid hydroperoxides. ROS catalyzed by Cu ions are involved in the generation of these cross-links in amyloid beta oligomers to which they provide stability. Also involved in the stabilization of tau PHF. A potential biomarker of oxidative stress in AD.