Bioassay-Guided Isolation of Antioxidants and alpha-Glucosidase Inhibitors from the Root of Cassia sieberiana DC (Fabaceae)

Bioassay-guided isolation was used to investigate the antioxidants and alpha-glucosidase inhibitors from extract of root of Cassia sieberiana. The ethyl acetate fraction demonstrated strong free radical scavenging (DPPH and ABTS(+)) and potent alpha-glucosidase inhibition. The subsequent fractionation and purification of the ethyl acetate fraction using silica gel chromatography and Sephadex LH-20, yielded; islandicin (1), chrysophanol (2), physcion (3), emodin (4), quercetin (5), kaempferol (6), dihydrokaempferol (7), and piceatannol (8). Quercetin (5) showed the most active antioxidant activity with IC50 values of 1.58 mM and 1.30 mM against DPPH and ABTS(+) radicals, followed by piceatannol (8) with IC50 values of 3.96 mM and 3.28 mM, which is better than the standard BHT (with IC50 value 8.93 mM) and trolox (with IC50 value 8.25 mM), for DPPH and ABTS(+) radicals scavenging activities, respectively. For the alpha-glucosidase inhibitory assay, quercetin (5) and piceatannol (8) showed higher potency against alpha-glucosidase with IC50 values of 5.73 mu M and 7.37 mu M respectively, than standard quercetin with IC50 value of 9.20 mu M and acarbose with IC50 value of 14.12 mu M. This study presents the first report on the alpha-glucosidase inhibitors from root of C. sieberiana and all the compounds are isolated from this source for the first time.