Three antioxidant phenylethanoid glycosides from the rhizomes of Eremostachys pulvinaris (family: Labiatae)

Eremostachys pulvinaris (family: Labiatae), one of the 60 species of the genus Eremostachys, occurs mainly in central Asian countries, e.g. Iran, Armenia, Ashgabad and the USSR. The rhizomes of this plant were collected from Tabriz in Azarbaijan province during September-October 2003. There is no report on any previous phytochemical investigation on E. pulvinaris available todate, phytochemical studies on a few other species of Eremostachys revealed the presence of flavonoids and monoterpene glycosides The dried and ground rhizomes of E. glabra (100 g) were Soxhlet-extracted, successively, with n-hexane, dichloromethane and methanol. The preparative reversed-phase HPLC analysis of the 40% methanolic Sep-Pack fraction resulted in the isolation of three phenylethanoid glycosides. The free radical scavenging activity and general toxicity of these compounds have been assessed. The chemical structures of these compounds (forsythoside B, leucosceptoside A and verbascoside) have been elucidated by by UV, ESIMS, and comprehensive 1D and 2D NMR analyses including COSY, NOESY, HMQC and HMBC., and also by comparing experimental data with respective literature data. While none of these compounds has shown any significant general toxicity in the brine shrimp lethality assay (LD50>1 mg/mL), forsythoside B, leucosceptoside A and verbascoside have displayed significant antioxidant activity in the DPPH assay (RC50 = 0.0064, 0.0148 and 0.0079 mg/mL, respectively). This is the first report on the occurrence of phenylethanoid glycosides in E. glabra and also in the genus Eremostachys. Isolation and identification of these compounds from the rhizomes of E. glabra of the family Lamiaceae might be chemotaxonomically significant