Antioxidant activity and cytotoxicity study of the flavonol glycosides from Bauhinia galpinii

Abstract

The antioxidant activity of the crude extract and solvent fractions obtained from the leaves of Bauhinia galpinii was evaluated in terms of capacity to scavenge 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radicals. The crude extract and the more polar solvent fractions (ethyl acetate and butanol) showed considerable antioxidant activity. The antioxidant potential of the extracts, expressed as EC₅₀, ranged between 28.85 ± 1.28 µg mL⁻¹and 118.16 ± 6.41 µg mL⁻¹. L-Ascorbic acid was used as a standard (EC₅₀ = 19.79 ± 0.14 µM). Bioassay guided fractionation of the two active solvent fractions led to the isolation of three flavonoid glycosides, identified as: quercetin-3-O-galactopyranoside (1), myricetin-3-O-galactopyranoside (2), and 2″-O-rhamnosylvitexin (3). These compounds are reported for the first time from this species. The structures of the compounds were determined on the basis of spectral studies (¹H NMR, ¹³C NMR and MS). Their antioxidant potential was evaluated using a DPPH spectrophotometric assay. Compound 2 had higher and 3 had lower antioxidant activity than L-ascorbic acid. No cytotoxic effects were displayed by compounds 1 and 3, but compound 2 was cytotoxic to Vero cells (LC₅₀ = 74.68 µg mL⁻¹) and bovine dermis cells (LC₅₀ = 30.69 µg mL⁻¹).

Keywords:

• Bauhinia galpinii
• Antioxidant activity
• Cytotoxicity
• Flavonoid glycosides
• DPPH

Acknowledgements

M. A. Aderogba is grateful to NRF South Africa, for the award of a postdoctoral research fellowship. L. J. McGaw acknowledges the Claude Leon Foundation and University of Pretoria for financial support. Prof. M. van Vuuren (Department of Veterinary Tropical Diseases, University of Pretoria) is thanked for providing cells and cell culture facilities.