Bioassay-Guided Isolation of Antioxidants and α-Glucosidase Inhibitors from the Root of Cassia sieberiana D.C. (Fabaceae)

Bioassay-guided isolation was used to investigate the antioxidants and α-glucosidase inhibitors from extract of root of Cassia sieberiana. The ethyl acetate fraction demonstrated strong free radical scavenging (DPPH and ABTS +) and potent α-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 IC 50 values of 1.58 mM and 1.30 mM against DPPH and ABTS + radicals, followed by piceatannol (8) with IC 50 values of 3.96 mM and 3.28 mM, which is better than the standard BHT (with IC 50 value 8.93 mM) and trolox (with IC 50 value 8.25 mM), for DPPH and ABTS + radicals scavenging activities, respectively. For the α-glucosidase inhibitory assay, quercetin (5) and piceatannol (8) showed higher potency against α-glucosidase with IC 50 values of 5.73 µM and 7.37 µM respectively, than standard quercetin with IC 50 value of 9.20 µM and acarbose with IC 50 value of 14.12 µM. This study presents the first report on the α-glucosidase inhibitors from root of C. sieberiana and all the compounds are isolated from this source for the first time.