Benzophenones and flavonoids from Hypericum maculatum and their antioxidant activities

The occurrence of three known benzophenones, namely annulatophenonoside, acetylannulatophenonoside and annulatophenone as well as a flavonol O-glycoside guajaverin in the aerial parts of Hypericum maculatum Crantz was established. In addition, hyperoside, isoquercitrin and miquelianin were isolated from this plant, as well. Radical scavenging and antioxidant activities of the isolated compounds were examined using 1,1-diphenyl-2-picrylhydrazyl (DPPH) and 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) diammonium salt (ABTS) free radicals, ferric reducing antioxidant power (FRAP) assay and inhibition of lipid peroxidation in linoleic acid system by the ferric thiocyanate method. Isoquercitrin demonstrates the highest DPPH radical scavenging (96.6 ± 0.3%), FRAP (23.8 ± 0.2 Trolox equivalent, TE mol⁻¹) and antioxidant activity in linoleic acid system. Guajaverin and acetylannulatophenonoside show significantly strong ABTS radical scavenging activity (93.9 ± 0.4% and 93.4 ± 0.6%, respectively), which is comparable to that of ascorbic acid (96.2 ± 0.4%).