Abstract (eng)
The genus Notopleura is member of the tribe Palicoureeae (Rubiaceae) within the speciose Psychotria alliance. This group is well known for the accumulation of bioactive monoterpene indole alkaloids. Comparable little is known about the secondary plant metabolites of Notopleura species. The aim of this study was to analyse the chemical composition of selected Notopleura species also with respect to organ-specific profiles, with some species studied for the first time. The extracts were purified by various chromatographic techniques and analysed by comparison of the HPLC-UV data. Four already known substances were isolated from N. uliginosa and structurally identified by 13C-NMR spectroscopy. These include the naphthoquinone psychorubrin (8), the megastigmanes 3-oxo-α-ionol (9) and blumenol A (10), and the monoterpene hydroxylactone loliolide (11). No alkaloids could be detected in the studied samples. As far as organ-specific occurrence in Notopleura species is concerned, megastigmanes dominate in leaves, while there is a shift towards dominance of quinones in roots and stems. Interestingly, none of these compounds were detected in the inflorescences. This indicates expression of different pathways in the respective plant organs. The observed antioxdative activity of crude plant extracts could not be correlated experimentally with the four isolated compounds. As for chemotaxonomic relevance, the observed accumulation tendencies are in agreement with the current taxonomic position of this genus.