Isolierung und Strukturaufklärung von oligomeren Stilbenen aus Weinrebenextrakten (English shop)

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Stilbenes are phytoalexins and are synthesised by the plant in response to stress factors such as fungal infection. They occur mainly in berries, grapevine wood (canes) and the corresponding products. The best-known monomeric stilbene is trans-resveratrol. It is regarded as a potent radical scavenger and has manifold beneficial effects on the human organism. Oxidative radical reactions can give rise to a wide variety of dimeric and oligomeric compounds from the monomer.

The oligomeric stilbenoids are increasingly attracting interest. They too are said to possess health-promoting properties, some of which are reported to be more potent than those of the monomer trans-resveratrol. However, since the biological activities of the oligomers have not yet been fully elucidated, there is great interest in further studies. These require large amounts of pure substances, which in most cases must first be laboriously isolated from the plant material. In the case of complex natural product mixtures such as a grapevine extract, the development of efficient isolation strategies is necessary. Often the combination of different purification, concentration and isolation procedures is required in order to obtain the bioactive compounds in standard quality. In order to advance stilbene research, the development of new, efficient isolation techniques is imperative. This would make it conceivable, for example, to obtain large quantities of highly active stilbene oligomers from grapevine wood, which accumulates as a waste product in wine production.

The aim of this work is the development of strategies for the isolation of stilbenoids from grapevine extracts. The focus lies on providing oligomeric resveratrol derivatives, which are present as minor components in these extracts. High-speed countercurrent chromatography (HSCCC) is to be employed for the isolation of the bioactive compounds, since it is particularly well suited to the separation of labile natural products such as the light-, temperature- and oxygen-sensitive stilbenoids. This additionally comprises the development of an efficient sample preparation for the elimination of interfering substances. A scale-up is to be carried out by means of low-speed rotary countercurrent chromatography (LSRCCC) in order to make the minor components of the grapevine extracts accessible on a preparative scale. The structural elucidation of the isolated stilbenoids is subsequently performed by mass spectrometry as well as one- and two-dimensional NMR spectroscopy. An alternative biomimetic route to the preparation of resveratrol oligomers is opened up by the use of horseradish peroxidase. The focus here is on the preparation of new, unknown resveratrol oligomers. The antioxidant activity of stilbenoids is evaluated by applying the TEAC assay. Furthermore, a screening for the occurrence of stilbenoids in wine is carried out.

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