In vitro evaluation of tectoridin, tectorigenin and tectorigenin sodium sulfonate on antioxidant properties

Tectoridin (4′,5,7-thrihydroxy-6-methoxyisoflavone-7-O-β-d-glucopyranoside) isolated from the flowers of Pueraria thunbergiana is reported to have less hepatoprotective, hypoglycemic, antiallergic and anaphylaxis inhibitory activity than its aglycone form tectorigenin. To obtain tectorigenin, tectoridin was hydrolyzed in the current study. However, practical limitations of tectorigenin do exist due to its poor water-solubility. To increase its water-solubility, tectorigenin was sulfonated with sulfuric acid (98 wt.%) and mixed with saturated salt water to produce tectorigenin sodium sulfonate. Tectoridin and the two transfer products were identified by UV, IR, HPLC–MS, 1H NMR and 13C NMR, and the solubility of tectorigenin sodium sulfonate was increased about 9-fold than tectorigenin. Antioxidant experiments of tectoridin, tectorigenin and modified tectorigenin in vitro including reducing power, superoxide anion radical scavenging activity, hydroxyl radical scavenging activity, 1,1-diphenyl-2-picryl-hydrazyl (DPPH) radical scavenging activity and anti-lipid peroxidation were carried on comparing with ascorbic acid (Vc) or butylated hydroxytoluene (BHT). The results suggested that the antioxidant activity in all the experimental systems exhibited the same order as follows: tectorigenin sodium sulfonate > tectorigenin > tectoridin. Due to the high water-solubility and good antioxidant properties with tectorigenin sodium sulfonate, appropriate chemical modifications could greatly improve the biological activities of the naturally occurring products.