Antioxidant activity-guided phytochemical investigation of Artemisia gmelinii Webb. ex Stechm.: Isolation and spectroscopic challenges of 3,5-O-dicaffeoyl (epi?) quinic acid and its ethyl ester

Although Artemisia gmelinii Webb. ex Stechm. has long been used in south and south-east Asia to treat many kinds of inflammatory diseases, up until now its bioactivity-coupled phytochemical characterization has not been reported. We identified one fraction of the methanolic extract of A. gmelinii as a hit in our antioxidant screening (DPPH) campaign. In order to identify the active radical scavenger components of the extract, a DPPH-HPLC spiking assay was carried out. Out of six detected known compounds caffeic acid (1) and scopoletin (4) had already been identified in the plant, but four of them, namely chlorogenic acid (2), 4-O-caffeoylquinic acid (3), luteolin-7-O-glucoside (5), and apigenin-7-O-glucoside (6) are first described here. Moreover, the two most active compounds of the mixture, 3,5-O-dicaffeoylquinic acid (7) and its ethyl ester derivative (8) were isolated with preparative HPLC. The spectroscopic identification of 7 and 8 presented a surprising challenge due to literature ambiguities. These questions are discussed in detail.