Phenolic alkaloids as a new class of antioxidants in Portulaca oleracea

Antioxidant activities of three phenolic alkaloids, i.e., oleracein A (OA), oleracein B (OB) and oleracein E (OE), isolated from Portulaca oleracea were determined, based on scavenging activity against 1,1-diphenyl- 2-picryl-hydrazyl (DPPH) radical and inhibitory effect on hydrogen peroxide-induced lipid peroxidation in rat brain homogenates. The DPPH radical scavenging activities of these phenolic alkaloids were lower than caffeic acid but higher than ascorbic acid and alpha-tocopherol, being in the following order: OB > OA > OE. OE was most potent in preventing formation of malondialdehyde (MDA) with an EC(50) value of 73.13 microM, close to that of caffeic acid (72.09 microM). It was demonstrated that phenolic alkaloids served as a new class of antioxidant agents in this plant.