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

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 microg mL(-1)and 118.16 +/- 6.41 microg mL(-1). L-Ascorbic acid was used as a standard (EC50 = 19.79 +/- 0.14 microM). 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 microg mL(-1)) and bovine dermis cells (LC50 = 30.69 microg mL(-1)).