Isolation, characterization, and antioxidative activity of a dioxobilin-type phylloxanthobilin from savoy cabbage

Abstract

The degradation of the green pigment chlorophyll in plants is known to yield phyllobilins as highly abundant linear tetrapyrroles. Recently, a split path of the degradation pathway has been discovered, leading to so-called dioxobilin-type (or type-II) phyllobilins. The first characterized type-II phyllobilin was colorless featuring four deconjugated pyrrole units. Similar to the type-I branch, for which yellow oxidation products of the colorless phyllobilins – the type-I phylloxanthobilins – are known, a type-II phylloxanthobilin has recently been characterized from senescent leaves of grapevine. Type-I phylloxanthobilins appear to be actively produced in the plant, are known to possess interesting chemical properties, and were shown to act as potent antioxidants that can protect cells from oxidative stress. Here we report the isolation and structural characterization of a type-II phylloxanthobilin from de-greened leaves of savoy cabbage, which turned out to be structurally closely related to bilirubin. Bilirubin is known to possess high antioxidative activity; in addition, savoy cabbage is considered to promote health benefits due to its high content in antioxidants. We therefore investigated the in vitro antioxidative potential of the newly identified type-II phylloxanthobilin using two different approaches, both of which revealed an even higher antioxidative activity for the type-II phylloxanthobilin from savoy cabbage compared to bilirubin.