Naturally occurring ureidobromophenols with potent antioxidant activities from the marine red alga Rhodomela confervoides

An extensive investigation on the chemical components with potential antioxidant activity resulted in the characterization of four new ureidobromophenols (1-4) and two related metabolites (5 and 6) from ethyl acetate extract of the marine red alga Rhodomela confervoides. Their structures were determined using spectroscopic analysis and comparisons with known compounds. Compound 1 possesses unique structure of an ureido group bearing gamma-butyric acid and 2,3-dibromo-4,5-dihydroxybenzyl moieties on the same nitrogen atom. Compounds 1-4 displayed significant antioxidant activity against 1,1-diphenyl-2-picrylhydrazyl (DPPH) radicals with IC50 values ranging from 3.34 to 4.84 mu M, which are more active than that of the positive controls ascorbic acid (IC50 = 20.1 mu M) and butylated hydroxytoluene (IC50 = 82.1 mu M). These compounds also exhibited potent activity against 2,2' -azino-bis(3-ethylbenzothiazoline-6-sulphonate (ABTS) radicals with trolox equivalent antioxidant capacity (TEAC) values ranging from 3.25 to 5.01 mM, which are 3- to 5-fold potent than that of ascorbic acid (TEAC = 1.02 mM). The antioxidant activity of ureidobromophenols isolated from marine alga might boost the seaweed functional food ingredients or dietary food supplements in food industry.