Abstract (eng)
81 species of Psychotria and related genera of the Psychotria alliance have been analysed for their phytochemical composition employing the extraction of compounds and their comparative HPLC-UV/VIS analysis. Major classes of compounds detected comprise cyclotryptamine iridoid alkaloids, tryptamine iridoid alkaloids, dopamine iridoid alkaloids and tannins. These phytochemical differentiations were interpreted in relation to literature and current taxonomy. Species of the Psychotrieae (Psychotria subg. Psychotria) showed high total phenolic content, good radical scavenging activity and were found to accumulate condensed tannins only, which could not be detected in the Palicoureeae. By contrast, species within the Palicoureeae were dominated by alkaloids derived from various pathways and their different combinations of building blocks turned out to be genus-specific. Furthermore, infrageneric groups were recognised based upon the distribution of several alkaloids within Palicourea s.l. In preliminary bioassays against larvae of the generalist herbivore Spodoptera littoralis, good activity correlated with the distribution of tannins, indicating the ecological relevance of phytochemical differentiations.
Compounds encountered within the Palicoureeae, may be grouped in tyrosine derived dopamine and tryptophan derived tryptamine alkaloids, and by the ratio of these building blocks to the iridoid secologanine. Compounds of Carapichea are dopamine iridoid alkaloids with a ratio of 1:1 or 1:2. Alkaloids of other genera within the tribe were formed via tryptamine. With the exception of bahienosides, all alkaloids of Palicourea s.l. (including Psychotria subg. Heteropsychotria) showed a tryptamine to secologanine ratio of 1:1. Cyclotryptamine alkaloids from the genus Margaritopsis are defined by a ratio of 1:0. Alstrostines are cyclotryptamine iridoid alkaloids characterised by a 1:2 ratio and are found in both Chassalia and Rudgea. Notopleura differs in accumulating naphthoquinones.
Present results largely confirm the current taxonomic views within Psychotria and its relatives. Based upon the detected chemical structures and literature data, a biosynthetic scheme has been developed and correlated with distribution of major compounds in this group. All of the studied plant groups exhibit consistent chemical profiles regarding major accumulation tendencies. Hence, it might be expected that related, yet unstudied species, synthesize secondary metabolites from the same biosynthetic family, indicating predictive value in these cases. Confirmation of the hypothetical biosynthetic trends and distributions of the present study, and the ecological impact of secondary metabolite differentiation, warrants further and enhanced investigation.