Identification of phenolic compounds in six Hypericum species by LC/UV/MS TOF and their radical scavenging properties by post-column HPLC-DPPH derivatization method

Many of the Hypericum species have been used in traditional medicine throughout the world [1]. The aim of this study was to investigate chemical composition and free radical scavenging properties of six Hypericum species growing in Serbia. A comparative analysis of the phenolic components in the 70% EtOH extracts of Hypericum acutum, H. androsaemum, H. barbatum, H. hirsutum, H. maculatum, and H. richeri has been carried out using HPLC/DAD and high resolution TOF-MS. Quercetin, astilbin, I-3,II-8-biapigenin, orientin, 2''-O-acetylorientin, three caffeoylquinic acids, and eight flavonol-3-O-glycosides were identified in the extracts on the basis of their on-line UV spectra, accurate mass spectral data, and in comparison of retention times with those from the standards. Fingerprint analysis of the extracts revealed significant differences in the qualitative and quantitative chemical composition of the studied species. A post-column HPLC-DPPH derivatization method was used to identify the free radical scavenging compounds. The amount of DPPH quenched by antioxidants is measured by a UV detector as a decrease in absorption at 517 nm. According to HPLC-DPPH profiles of the extracts, all phenolic compounds except I-3,II-8-biapigenin exhibited radical scavenging properties. Free radical scavenging properties of the extracts, considering the integrated areas of all the negative peaks in a DPPH^· chromatogram were expressed as TEAC (Trolox equivalent antioxidant capacities) values. The most potent DPPH scavenger was H. maculatum with TEAC value of 0.37 mmol Trolox/g of extract, while H. barbatum showed the weakest capacity (0.19 mmol Trolox/g of extract).

Acknowledgements: The authors acknowledge their gratitude to the Ministry of Science and Ecology of Serbia for the financial support.

Reference: 1. Dall'Agnol, R. et al. (2003) Phytomedicine 10: 511–516.