Profisetinidin type tannins responsible for antioxidant activity in Copaifera reticulata

The in vitro antioxidant and free radical scavenging properties in bark extracts of South American tree Copaifera reticulata Ducke. (Caesalpinaceae) were studied using different bioassays. Lipid peroxidation was assessed by means of the production of thiobarbituric acid reactive substances (TBARS) in rat liver homogenate. All the extracts tested were effective in this method. The highest activity was observed in the aqueous extract, showing an IC50 of 30 micrograms/ml. DNA sugar damage induced by Fe (II) salts was also used to determine the capacity of the samples to suppress hydroxyl radical-mediated degradation of DNA. Although all the extracts tested were effective in reducing oxidation of DNA, the highest activity was observed in the methanol extract, showing an IC50 of 2 micrograms/ml. Bioassay-guided fractionation of a total methanol extract monitored by luminol-enhanced chemiluminescence, together with structural elucidation using 13C NMR and FABMS, led to the identification of profisetinidin type tannins in a semi-pure fraction. The fraction containing the active compounds also reduced the production of TBARS in rat liver homogenates (IC50 = 530 micrograms/ml) and DNA damage (IC50 = 1 microgram/ml), suggesting that profisetinidins could be responsible for the free radical scavenging and antioxidant activities observed in the extracts.