Abstract: Objective: To identify the chemical constituents from the rhizome of Curcuma longa L. and to assess their antioxidant activity. Methods: The chemical constituents were purified consecutively by silica gel column chromatography, Sephadex LH-20 gel column chromatography, and preparative high performance liquid chromatography (HPLC). Their structures were identified by spectroscopic analyses, and their antioxidant activity were evaluated by 2,2’-azinobis-(3- ethylbenzthiazoline-6-sulphonate) (ABTS) radical cation scavenging, 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging, and potassium ferricyanide reduction assays. Results: Seven compounds were isolated from C. longa L. and were identified as zingerol (1), dihydroferulic acid ethyl ester (2), ethyl 3-(4-hydroxy-phenyl)-propionate (3), zingerone dimer [4,4’-(6,6’-dihydroxy-5,5’-dimethoxy-[1,1’-biphenyl]-3,3’-diyl)bis(butan-2-one)] (4), zingiberone (5), 4-(3,4-dimethoxyphenyl) butan-2-one (6), and vanillin (7). Among them, compounds 1–5 showed antioxidant activity. The IC50 of compounds 1 and 2 were (3 ± 0.2) and (12 ± 1.0) μmol/L, respectively, in ABTS assay. Compound 1 was found to exhibit higher antioxidant activity than the positive drug, VC (VC, IC50 value = (13 ± 1.1) μmol/L), while the activity of compound 2 was equivalent to VC. In the reducing power assay, compound 1 showed higher activity than VC at all investigated concentrations, while compound 2 had higher activity than VC only when the concentration was lower than 0.125 μmol/mL. Conclusion: Compound 4 is a new natural product, and compounds 1, 2, 3 and 6 are found from this plant for the first time. The stronger antioxidant activity of compound 1 may be related to hydroxyl substitution at C-2, In addition, the phenols from the ethanol extract may be one of the material bases for the antioxidant activity of C. longa L..

Key words: Curcuma longa L., chemical constituents, antioxidant activity