Antioxidant constituents of Nymphaea caerulea flowers

Twenty constituents were isolated from the Nymphaea caerulea flowers, including 2S,3S,4S-trihydroxypentanoic acid (1), and myricetin 3-O-(3′′-O-acetyl)-α-l-rhamnoside (2), along with known 18 compounds (3-20). Antioxidant activities of nine compounds 2-7, 11, 12 and 18 were observed with IC50 values of 1.16, 4.1, 0.75, 1.7, 1.0, 0.34, 11.0, 1.7 and 0.95 μg/ml, respectively, while 1 was marginally active (IC50 > 31.25 μg/ml). Promising activity of EtOAc fraction (IC50 0.2 μg/ml) could be attributed to the synergistic effect of the compounds present in it.