Antioxidant Effects Of Curcumin And Its Analogues

Curcumin (1,7-bis(4-hydroxy-3-methoxyphenyl)-1,6-heptadiene-3,5-dione, (1)), is a yellow ingredient isolated from turmeric (curcumin longa). It has been shown to exhibit a variety of biological activities including antioxidative activity. In order to find more active antioxidants with 1 as the lead compound we synthesized curcumin analogues, i.e., l,7-bis(3,4-dihydroxyphenyl)-l,6-heptadiene-3,5-dione (2), l-(3,4-dihydroxyphenyl)-7-(4-hydroxy-3-methoxyphenyl)-l,6-heptadiene-3,5-dione(3), l-(4-hydroxy-3-methoxyphenyl)-7-(4-hydroxyphenyl)-l,6-heptadiene-3,5-dione(4), 1,7-bis(4-hydroxyphenyI)-1,6-heptadiene-3,5-dione(5), 1,7-bis(3,4-dimethoxyphenyI)-1 ,6-heptadiene-3,5-dione(6), 1,7-bis(4-methoxyphenyl)-1,6-heptadiene-3,5-dione(7), 1,7-diphenyl-1,6-heptadiene-3,5-dione(8), 1 -(3,4-dimethoxyphenyl)-7-(4-hydroxy-3-m ethoxyphenyl)-l,6-heptadiene-3,5-dione(9),l,7-bis(4-acetyl-3-methoxyphenyl)-l,6-hep tadiene-3,5-dione(10). Their antioxidant effects were studied in micelles, human low density lipoprotein (LDL), human red blood cell (RBC) and rat liver mitochondria, by mean of oxygen uptake, high performance liquid chromatography (HPLC) and ultraviolet-visible (UV) spectroscopy. We also studied the synergistic effects of curcumin and the other analogues with α-tocopherol. It was found that:The antioxidative activities of compounds 6, 7 and 8 which bear no phenolic group are inactive, Therefore, it can be concluded that the phenolic group in the molecules plays a major role in the antioxidative activities of curcumin and its analogues. Compounds 2 and 3 which bear ortho-diphenoxyl functionality possess significantly higher antioxidant activity than curcumin and other analogues, and the 4-hydroxy-3-methoxyphenyl group also play an important role in the antioxidative activity. Obviously, this is due to, not only the number of phenolic groups, but also the high reactivity of ortho-methyoxyphenolic and ortho -hydroxyphenolic functionalities. In addition, there is no synergistic effects when they were used together with α-tocopherol.