Investigation of Free Radical Scavenging Activity by ESR for Coumarins Isolated from Tecoma radicans

Chemical investigation of the aerial parts of Tecoma radicans, F. bignoniaceae indicates the presence of four coumarins, 2`,3`-epoxide alloimperatorin (8-methoxy furanocoumarin), pabulenone (5-alkoxy-furanocoumarin), pereflorin B and 17-methylbothrioclinin. One chromone was also isolated peucenin-7-methyl ether (7,5 dioxygenated chromone). Biological screening of this fraction showed no antitumoral effects but antioxidant activity. The method of the assay of the free radical is modified to make combination between the stable DPPH radical and its determination by ESR instead of determining it by colourimetric method. When the coumarin fraction and isolated compounds were examined for free radical scavenging activity, using the stable DPPH free radical and recorded by ESR, it was found that the whole coumarin fraction was the most active (89.06% inhibition of DPPH free radical) and the isolated components are 0, 25.9, 8.45, 13.85 and 50%, respectively.