Rapid identification and evaluation of antioxidant compounds from extracts of Petasites japonicus by hyphenated-HPLC techniques

Gradient HPLC coupled to Diode Array Detector (DAD), MS/MS and NMR was applied to the rapid structure determination of major compounds of methanol extracts from leaves and roots of Petasites japonicus. The relative antioxidant capacities of the compounds were evaluated by an HPLC system with post-column on-line antioxidant detection based on 2,2'-azinobis-3-ethylbenzothiazoline-6-sulfonic acid radical scavenging. Six compounds were successfully separated on a reverse-phase C(18) column and were identified as 5-caffeoylquinic acid (5-CQA), fukinolic acid (FA), 3,5-di-O-caffeoylquinic acid (3,5-DCQA), quercetin-3-O-(6″-acetyl)-β-glucopyranoside (QAG), 4,5-di-O-caffeoylquinic acid (4,5-DCQA) and kaempferol-3-O-(6″-acetyl)-β-glucopyranoside (KAG) by MS/MS and (1)H NMR data. Among these compounds, those containing a caffeoyl moiety (5-CQA, FA, 3,5- and 4,5-DCQA) showed relatively strong radical scavenging capacity, with 3,5-DCQA having the greatest radical scavenging capacity in leaf (23.09% of total antioxidant capacity) and root (26.47%) extracts. The relative radical scavenging portion of QAG was only 3.41% in the leaves and KAG did not show any radical scavenging activity. These results demonstrate that the hyphenated HPLC techniques can be successfully applied to rapidly identify structures and evaluate antioxidant activities without prior purification of compounds from plant tissues of P. japonicus.