This thesis studies the phenolic compounds of Geranium sylvaticum L. It focuses especially on geraniin and related ellagitannins. The literature review covers the phytochemistry of Geranium species, the biological activity of tannins and methods for the analysis and identification of tannins. 

In the experimental work, methods were developed for the extraction and high-pressure liquid chromatographic analysis of polyphenols in G. sylvaticum organs and their degradation products in the alkaline pH. Using a high-resolution mass spectrometry and diode array detection, water-soluble polyphenols in the organs of Geranium sylvaticum were tentatively identified and studied for their seasonal variation. Moreover, the main compounds were isolated and structures further elucidated. The biological activity of organ extracts and fractions was measured with antioxidant activity and pro-oxidant activity assays. 

Results showed that the plant organs of G. sylvaticum have distinctive intraplant variation in their phenolic profiles. Geraniin and other ellagitannins dominated in all the green photosynthetic organs. While the pistils accumulated gallotannins, the stamens kaempferol glycosides, and seeds and roots accumulated oligomeric proanthocyanidins. Of these, galloylglucoses, gallotannins and minor ellagitannins in particular showed seasonal and ontogenic variation. The petals contained unique acetylglucosylated hydrolysable tannins. These compounds showed capacity to act as copigments for anthocyanins. Due to the high content of ellagitannins and galloyl quinic acids, the leaf, pistil and hairy root extracts showed high antioxidant and pro-oxidant activity. Hydrolyzable tannins degraded fast in the alkaline conditions used in the pro-oxidant test and produced hydrolysis, deprotonation and oxidation products. 

The observed intraplant distribution of the polyphenol groups, seasonal and ontogenic variation, and the various biological activities observed may reflect the different functions and importance of various types of tannins in the plants’ interaction with pollinators, herbivores and/or pathogens.