Chemical systematics of the subtribe Scorzonerinae

The Scorzonerinae are part of the Lactuceae tribe of the Asteraceae family and they include important vegetables like black salsify (Scorzonera hispanica L.) and white salsify (Tragopogon porrifolius L.). Despite their utilization as vegetables little is known about the secondary metabolite chemistry of this systematic group of plants. The Scorzonerinae encompass approximately 300 species, which are encompassed in 7 to 14 genera. This vastly varying number of genera is explained by the differing generic concepts of the different botanical authorities. This in turn is a consequence of the limited number of morphologic characters available to subdivide the subtribe Scorzonerinae. Monophyly of the Scorzonerinae is backed up by morphological (Bremer 1994) and molecular data (Mavrodiev et al. 2004). The phytochemical investigations, which have been carried out mainly in the last few years, indicate that the Scorzonerinae are also chemically different from other subtribes of the Lactuceae as well as from related tribes of the Asteraceae family. In addition to compound classes like flavonoids, phenolic acids, and sesquiterpene lactones, which are ubiquitously occurring in the Asteraceae family, the Scorzonerinae yielded a variety of dihydrostilbenoids. These were assignable to different subclasses like bibenzyls, dihydroisocoumarins, and 3-benzylphtalides. In addition to these known classes of dihydrostilbenoids, a new class of 4- phenylethylbenzofuran-2-carbonic acids, named tyrolobibenzyls, was isolated from a Scorzonera humilis. Moreover, 2,4-dihydroxy-6-[2-(4-hydroxy-phenyl)-2-oxo-ethyl]-benzoic acid was isolated from Tragopogon porrifolius, this compound is regarded to be a biogenetic intermediate between dihydrostilbenes and dihydroisocoumarins. In the course of the proposed project we intend to systematically explore the phytochemistry of the so far uninvestigated European members of the Scorzonerinae. The focus will be on new dihydrostilbenoids, but we will also analyze phenolics (caffeic acid derivatives and flavonoids) and sesquiterpenoids. The natural products isolated in the course of the project will be assessed as chemosystematic markers to chemically delimit the Scorzonerinae from related subtribes of the Lactuceae and we will also try to find chemical markers for the delimitation of the genera of the Scorzonerinae from each other. Additionally, the bioactivity of the isolated compounds with a focus on the activities of dihydrostilbenes will be investigated. One part of the bioactivity assays will cover the potential function of the secondary metabolites as protective compounds against herbivores (in cooperation with Professor Peter Proksch, Düsseldorf), one will be focused on their potential cytotoxicity (in cooperation with Dr. Karin Jöhrer, Innsbruck), and one will investigate their potential as enzyme inhibitors of flavonol synthase and flavanone 3ß-hydroxylase (in cooperation with Dr. Thilo Fischer, Weihenstephan).

The Scorzonerinae are part of the Lactuceae tribe of the Asteraceae family and they include important vegetables like black salsify (Scorzonera hispanica L.) and white salsify (Tragopogon porrifolius L.). Despite their utilization as vegetables little is known about the secondary metabolite chemistry of this systematic group of plants. The Scorzonerinae encompass approximately 300 species, which are encompassed in 7 to 14 genera. This vastly varying number of genera is explained by the differing generic concepts of the different botanical authorities. This in turn is a consequence of the limited number of morphologic characters available to subdivide the subtribe Scorzonerinae. Monophyly of the Scorzonerinae is backed up by morphological (Bremer 1994) and molecular data (Mavrodiev et al. 2004). The phytochemical investigations, which have been carried out mainly in the last few years, indicate that the Scorzonerinae are also chemically different from other subtribes of the Lactuceae as well as from related tribes of the Asteraceae family. In addition to compound classes like flavonoids, phenolic acids, and sesquiterpene lactones, which are ubiquitously occurring in the Asteraceae family, the Scorzonerinae yielded a variety of dihydrostilbenoids. These were assignable to different subclasses like bibenzyls, dihydroisocoumarins, and 3-benzylphtalides. In addition to these known classes of dihydrostilbenoids, a new class of 4- phenylethylbenzofuran-2-carbonic acids, named tyrolobibenzyls, was isolated from a Scorzonera humilis. Moreover, 2,4-dihydroxy-6-[2-(4-hydroxy-phenyl)-2-oxo-ethyl]-benzoic acid was isolated from Tragopogon porrifolius, this compound is regarded to be a biogenetic intermediate between dihydrostilbenes and dihydroisocoumarins. In the course of the proposed project we intend to systematically explore the phytochemistry of the so far uninvestigated European members of the Scorzonerinae. The focus will be on new dihydrostilbenoids, but we will also analyze phenolics (caffeic acid derivatives and flavonoids) and sesquiterpenoids. The natural products isolated in the course of the project will be assessed as chemosystematic markers to chemically delimit the Scorzonerinae from related subtribes of the Lactuceae and we will also try to find chemical markers for the delimitation of the genera of the Scorzonerinae from each other. Additionally, the bioactivity of the isolated compounds with a focus on the activities of dihydrostilbenes will be investigated. One part of the bioactivity assays will cover the potential function of the secondary metabolites as protective compounds against herbivores (in cooperation with Professor Peter Proksch, Düsseldorf), one will be focused on their potential cytotoxicity (in cooperation with Dr. Karin Jöhrer, Innsbruck), and one will investigate their potential as enzyme inhibitors of flavonol synthase and flavanone 3ß-hydroxylase (in cooperation with Dr. Thilo Fischer, Weihenstephan).