Purine alkaloids in Paullinia.

Among the few purine alkaloid-containing genera consumed as stimulants, Paullinia is the least investigated with respect to both chemotaxonomy and within-the-plant allocation of caffeine and its allies. Since purine alkaloids (PuA) have been proved to be valuable marker compounds in chemotaxonomy, 34 species of Paullinia and related genera were screened for them, but only one, P. pachycarpa, was positive in addition to the already known P. cupana and P. yoco. The PuA allocation in P. pachycarpa was examined and found to be restricted to theobromine in the stem, leaves and flowers. Moreover, the theobromine concentration in the stem cortex increased significantly towards the base of the plant. Since the stem cortex of P. yoco is traditionally used by the natives of Colombia and Ecuador to prepare a caffeine-rich beverage, we suspected that within the genus Paullinia the PuA are preferentially allocated to the older parts of the stem and not to young shoots like e.g., in the coffee plant (Coffea spp.). Indeed, the axis (greenhouse) of P. cupana (guaraná), known for its caffeine-rich seeds, exhibited a basipetal PuA gradient (0.005-0.145%). Moreover, the analysis of young cortex samples (herbarium) and of one piece of old stem (museum collection) revealed the same for P. yoco, even though we found much less (0.5 vs 2.5%) caffeine in the old cortex as compared to the only two analyses in 1926 of similar material. However, this discrepancy may be explained by the high variability of the PuA pattern we detected among yoco, the diversity of which the Indians take advantage.