Chemical Constituents of the Roots Extract of Dryopteris schimperiana and Evaluation for Antibacterial and Radical Scavenging Activities

Abstract

Dryopteris schimperiana (Dryopteridaceae) is traditionally used in folk medicine of Ethiopia against bacteria and internal parasites. In view of its traditional use and absence of scientific reports, an attempt was made to explore the chemical constituents, antibacterial and radical scavenging activities of the solvent extracts of the root of Dryopteris schimperiana. In this regard, the root was successively extracted with n-hexane, CHCl₃ and methanol to afford 5 g (2%), 2 g (0.8%) and 26.6 g (10.6%), respectively. The n-hexane and CHCl₃ extracts showing similar TLC profile were mixed and fractionated over silica gel column chromatography which led to the isolation of two compounds identified as heptacosanol (1) and isorhmentin (2). The structures of the isolated compounds were accomplished using spectroscopic methods including UV-Vis, IR and NMR. To the best of our knowledge, these compounds have not been reported from the genus Dryopteries. The extracts and isolated compounds were evaluated for their antibacterial activities using agar well diffusion method against two Gram-positive bacteria (Staphylococcus aureus and Bacillus subtitis) and two Gram-negative bacteria (E. coli and Salmonella). The results showed that the n-hexane extract, methanol extracts and isolated compounds were active against all tested bacteria, with compound 2 shown to have an inhibition zone of 17 mm which is comparable with the positive control. Furthermore the extracts and isolated compounds were assessed for their radical scavenging activity using DPPH assay. Isorhmentin (2) displayed pronounceable % radical scavenging activity (82.8%) compared with ascorbic acid indicating its strong ability to act as radical scavenger. This study demonstrated that the antibacterial and radical scavenging activity of the root of D. shimperiana is accounted to the presence of isorhamnetin. Therefore, the biological activity displayed by the constituents of the roots of D. shimperiana corroborates the traditional use of this plant against bacteria.
Key words: Dryopteris schimperiana, NMR, antibacterial activity, antioxidant