Comprehensive structural analysis of cis- and trans-tiliroside and quercetrin from Malvastrum coromandelianum and their antioxidant activities

Abstract

Malvastrum coromandelianum is widely used in traditional system of medicine for the cure of different ailments. In the present study, two compounds were isolated from the methanol extract and were characterized as tiliroside [kaempferol-3-O-β-d-(6″-E-p-coumaryl) glucopyranoside] and quercetrin (quercetin-3-O-α-l-rhamnopyranoside) based on comprehensive NMR, IR and mass spectral analysis. NMR also showed the presence of trans- and cis-isomers of tiliroside in 3.26:1.00 ratio. The change of NMR solvent from CH3OH-d4 to DMSO-d6 and resulting chemical shift values have been analyzed. The in vitro IC50 values against 1, 1-diphenyl-2-picryl-hydrazyl radical (DPPH) for tiliroside, quercetrin and extract was found to be 60.40 ± 0.24, 68.05 ± 0.36 and 71.98 ± 0.29 (in µg/mL ± s.d.), respectively. The ferric ion (Fe+3) reducing ability of ethyl acetate extract, tiliroside, quercetrin and standard ascorbic acid were 1.169 ± 0.006, 0.324 ± 0.012, 1.407 ± 0.008 and 1.167 ± 0.010 respectively with R2 > 0.990 at 50 µg/mL concentration. The results conclude that isolated compounds as well as extract have significant antioxidant activity and can be further developed as potential antioxidants. Keywords: Malvastrum coromandelianum, Tiliroside, Quercetin-3-O-α-l-rhamnopyranoside, DPPH, Ferric reducing power