While investigating the antioxidant properties of aminoethylcysteine ketimine decarboxylated dimer (1) (a natural substance occurring in biological fluids such as human urine and plasma and in bovine cerebellum), a previously unreported oxidation product was obtained. This compound was identified and characterized through comparison with an authentic sample prepared via Pd-catalyzed dehydrogenation of 1. This molecule is an example of an alternative oxidation pathway involving 1.