Synthesis, characterization and antioxidant activity of prenylated and fluorine based flavonoids.
Twenty flavonoids II-XXI were successfully synthesized using the Claisen-Schmidt condensation reaction between 2-hydroxy and 3-hydroxyacetophenone with various substituted fluorobenzaldehydes. The twenty flavonoids consisted of sixteen chalcones, eight of which were new novel prenyl chalcones (XIV-XXI), and four flavanones (X-XIII). The compounds were produced in yields of between 54-90%. It was shown in II-XIII that the rate of reaction is influenced electronically by the substitution patterns of the fluorine atom on the B-ring, in the order; 2',4'-difluoro > 2'-fluoro> 4'-fluoro > 3'-fluoro. All compounds were characterized by NMR, IR, UV and mass spectral analyses. Compounds II-IX bearing hydroxyl groups were subjected to antioxidant screening using the DPPH free radical scavenging assay. Antioxidant activities of these compounds were established as moderate to low in comparison to the standard, ascorbic acid. The difluoro compounds V and IX with fluorine on the ortho and para positions in the B-ring showed the highest activities, possibly due to both the position and number of fluorine atoms in the molecule.