Chemotaxonomy and pharmacology of Gentianaceae.

The occurrence of taxonomically informative types of compounds in the family Gentianaceae, namely iridoids, xanthones, mangiferin, and Cglucoflavones, has been recorded. The properties, biosynthesis, and distribution of each group of compounds are described. The iridoids (mainly secoiridoid glucosides) appear to be present in all species investigated, with a predominance of swertiamarin and/or gentiopicroside; c. 90 different compounds have been reported from 127 species in 24 genera. Xanthones are not universally present in Gentianaceae, but about 100 different compounds have been reported from 121 species in 21 genera. A coherent theory for the biosynthesis of xanthones, based partly on published biosynthetic results and partly on biosynthetic reasoning, is postulated and used to group the compounds into biosynthetic categories. Arranging the genera according to the xanthones present gives rise to four groups. Group 1 (Anthocleista, Blackstonia, Gentianopsis, Macrocarpaea, and Orphium) includes the taxa containing only few and biosynthetically primitive xanthones. Group 2 (Comastoma, Gentiana, Gentianella, Lomatogonium, Swertia, and, tentatively, Tripterospermum) contains xanthones with an intermediate degree of biosynthetic advancement. Group 3 (Frasera, Halenia, and Veratrilla) has the most advanced compounds, with the xanthones found in group 2 being the biosynthetic precursors. Group 4 (Canscora, Centaurium, Chironia, Eustoma, Hoppea, Ixanthus, and, with some reservation, Schultesia) contains another set of biosynthetically advanced compounds. A comparison of the above groups with strict consensus trees based on molecular data (trnL intron and matK sequences) and the new classification proposed by Struwe et al. (2002) shows very good correlation. On the evidence so far, members of the Exaceae do not contain xanthones. The taxa of group 1, with primitive xanthones, are found in several tribes (Chironieae, Gentianeae, Helieae, and Potalieae), while those of groups 2 and 3 comprise solely members of the Gentianeae. Finally, the taxa in group 4 are all members of the Chironieae. Mangiferin, a Cglucoxanthone with a biosynthesis different from the above xanthones, has been recorded from 42 species in seven genera. Of these, five belong to the Gentianeae and two to the Chironieae. The C-glucoflavones have been recorded from 78 species in nine genera. Three of these belong to the Potalieae, while the remaining six are members of the Gentianeae. Based on the above results, a tentative list of chemical characteristics for the tribes of the Gentianaceae is presented. Finally, some pharmacologically interesting properties of plant extracts or compounds from taxa within Gentianaceae are listed.