The antioxidant properties of porniferin, isopomiferin, osajin and catalposide are evaluated. The electrochemical behaviour of these compounds at a carbon paste electrode was studied using square wave voltammetry. Oxidative signals, optimized frequencies and appropriate pH acetate buffer conditions were determined. The detection limits (3 S/N) for porniferin, isoporniferin, osajin and catalposide were estimated to be 50 pg/ml, 800 pg/ml, 40 pg/ml and 10 ng/ml, respectively. Furthermore, spectrometric test was employed with 2,2-diphenyl-1-picrylhydrazyle (DPPH) to evaluate the antioxidant activities of these compounds. Based on the obtained results, the highest antioxidant activity measured by DPPH tests was found at porniferin followed by isoporniferin. The activities of osajin and catalposide were undetectable. The protective effects of porniferin, isopomiferin, osajin and catalposide on DNA exposed to oxygen radicals in vitro were also studied. Changes in height of oxidative signals for the four bases (guanine, thymine, adenine and cytosine) were measured for DNA exposed to oxygen radicals, generated by Fenton's reaction, non-oxidized ssDNA (50 mu g/ml) displayed well developed signals: however, after oxidative damage the observed oxidative signals decreased. Significant protective effects were observed for porniferin and osajin. Decreased effect was observed for isoporniferin while a further reduced protective effect was seen for DNA exposed to catalposide. Based on the obtained results, porniferin had the highest antioxidant activity followed by isoporniferin, osajin and catalposide. (c) 2008 Elsevier B.V. All rights reserved.