Bioactive phenolic compounds from the flowers of Farfugium japonicum (L.) Kitam. var. giganteum (Siebold et Zucc.) Kitam. (Asteraceae).

Farfugium japonicum (L.) Kitam. var. giganteum (Siebold et Zucc.) Kitam. is mainly distributed in the Kyushu and Shikoku Islands of Japan. The main aim of this study was to isolate and identify the chemical constituents of the 70% EtOH extract of the flowers of F. japonicum var. giganteum and to evaluate their tyrosinase inhibitory and free radical scavenging activities. Five phenolic compounds, namely petasiphenol (1), rosmarinic acid (2), 4,5-di-O-caffeoylquinic acid (3), 5-O-caffeoylquinic acid (4) and quercetin (5) were isolated and their structures were elucidated on the basis of NMR spectroscopic data. All these compounds were isolated for the first time from title plant. Among them, petasiphenol (1) showed potent tyrosinase inhibitory activity followed by quercetin (5) and 4,5-di-O-caffeoylquinic acid (3). All of these compounds showed potent free radical scavenging activity.