Chemical traits of hemiparasitism in Odontites luteus

The study of the monoterpene glycosides content of Odontites luteus has shown the presence of a total of fifteen iridoid glucosides. The presence of compounds (1-5) and (7-10) is perfectly on-line with both the biogenetic pathway for iridoids biosynthesis in Lamiales and the current botanical classification of the species. On the other side, the presence of compounds like agnuside (6), adoxosidic acid (11), monotropein (12), 6,7-dihydromonotropein (13), methyl oleoside (14) and methyl gluco-oleoside (15) is of high interest because, first of all, they have never been reported before in Lamiales. In second instance, the majority of the last compounds are formally derived from a different biogenetic pathway which involves desoxyloganic acid/loganin and led to the formation of decarboxylated iridoid showing the 8β-stereochemistry. Furthermore, a second abnormality was found during our study and this regards compounds (14) and (15) which are seco-iriodids and thus not typical for this family. The presence of these unusual compounds, biogenetically not related to species belonging to Lamiales, is a clear evidence of the metabolites transfer from the hosts. In fact, the collection area is also populated by species belonging to Oleaceae and Ericaceae which could be the possible hosts since the biosynthesis of seco-iridoids and or iridoids related to deoxyloganic acid/loganin pathway, with the 8β-stereochemistry, is well documented in these species.