Antioxidant activity and chemical composition of Sideritis libanotica Labill. ssp. linearis (Bentham) Borm. (Lamiaceae)

Abstract

Sideritis libanotica ssp. linearis was screened for the isolation of new natural antioxidant compounds. The antioxidant activity of flavones obtained from the methanol extract of the plant was evaluated in vitro using total antioxidant, reduction power and free radical scavenging activity. Results were compared with the positive controls of antioxidant standards (α-tocopherol and butylated hydroxytoluene). The results indicate that the flavones possess a higher antioxidant activity when compared to the other components in the plant. The lowest antioxidant activity was observed in fatty acids (FAs) and hydrocarbons. The FAs were methylated with MeOH and KOH and analysed by GC–MS. The structures of the isolated compounds were established based on spectroscopic evidence (NMR, GC–MS, HPLC, IR and UV). In this work, the isolated pure flavone (3′-O-methylhypolaetin 7-O-[6″′-O-acetyl-β-D-allopyranosyl-(1 → 2)]-6″-O-acetyl-β-D-glucopyranoside) was found to possess the highest antioxidant activity.

Keywords:

• antioxidant activity
• methanolic extract
• Sideritis libanotica linearis
• flavonoid
• FAs

Acknowledgements

We thank Dr H.A. Akpulat for characterisation of the plant material, and Gaziosmanpasa University (BAP 2006/8) and State Planning Organization, Turkey (DPT 2003K120510) for their grants.