Structural Characterization, and Antioxidative and Anti-inflammatory Activities of Phylloxanthobilins in Tropaeolum majus, a Plant with Relevance in Phytomedicine.

Tropaeolum majus (garden nasturtium) is a plant with relevance in phytomedicine, appreciated not only for its pharmaceutical activities, but also for its beautiful leaves and flowers. Here, we investigated the phytochemical composition of senescent nasturtium leaves. Indeed, we identified yellow chlorophyll catabolites, also termed phylloxanthobilins, which we show to contribute to the bright yellow color of the leaves in the autumn season. Moreover, we isolated and characterized the phylloxanthobilins from T. majus, and report the identification of a pyro-phylloxanthobilin, so far only accessible by chemical synthesis. We show that the phylloxanthobilins contribute to bioactivities of T. majus by displaying strong anti-oxidative effects in vitro and in cellulo, and anti-inflammatory effects as assessed by COX-1 and COX-2 enzyme inhibition, similar to other bioactive ingredients of T. majus, isoquercitrin, and chlorogenic acid. Hence, phylloxanthobilins could play a role in the efficacy of T. majus in the treatment of urinary tract infections, an established indication of T. majus. With the results shown in this study, we aid in the completion of the phytochemical profile of T. majus by identifying additional bioactive natural products as relevant components of this medicinal plant.

Novel Types of Phyllobilins in a Fern - Molecular Reporters of the Evolution of Chlorophyll Breakdown in the Paleozoic Era.

Breakdown of chlorophyll (Chl), as studied in angiosperms, follows the pheophorbide a oxygenase/phyllobilin (PaO/PB) pathway, furnishing linear tetrapyrroles, named phyllobilins (PBs). In an investigation with fern leaves we have discovered iso-phyllobilanones (iPBs) with an intriguingly rearranged and oxidized carbon skeleton. We report here a key second group of iPBs from the fern and on their structure analysis. Previously, these additional Chl-catabolites escaped their characterization, since they exist in aqueous media as mixtures of equilibrating isomers. However, their chemical dehydration furnished stable iPB-derivatives that allowed the delineation of the enigmatic structures and chemistry of the original natural catabolites. The structures of all fern-iPBs reflect the early core steps of a PaO/PB-type pathway and the PB-to-iPB carbon skeleton rearrangement. A striking further degradative chemical ring-cleavage was observed, proposed to consume singlet molecular oxygen (1O2). Hence, Chl-catabolites may play a novel active role in detoxifying cellular 1O2. The critical deviations from the PaO/PB pathway, found in the fern, reflect evolutionary developments of Chl-breakdown in the green plants in the Paleozoic era.