Chemical constituents of Morinda citrifolia fruits inhibit copper-induced low-density lipoprotein oxidation
2004
Kamiya, K. | Tanaka, Y. | Endang, H. | Umar, M. | Satake, T.
The oxidative modification of low-density lipoprotein (LDL) plays an important role in the genesis of arteriosclerosis. The present study focused on the effects of the fruits of Morinda citrifolia on preventing arteriosclerosis. The MeOH extract and CHCl3-, EtOAc-, n-BuOH-, and H2O-soluble phases derived from the fruits of M. citrifolia were evaluated for their inhibitory activity on copper-induced LDL oxidation by the thiobarbituric acid-reactive substances (TBARS) method. The MeOH extract and EtOAc-soluble phase showed 88 and 96% inhibition, respectively. Six lignans were isolated by repeated column chromatography from the EtOAc-soluble phase. These compounds were determined by spectroscopic analysis to be 3,3'-bisdemethylpinoresinol (1), americanol A (2), americanin A (3), americanoic acid A (4), morindolin (5), and isoprincepin (6), of which 4 and 5 are novel compounds. These compounds inhibited copper-induced LDL oxidation in a dose-dependent manner. 1, 2, 5, and 6 exhibited remarkably strong activities, which were the same or better than that of the known antioxidant 2,6-di-tert-butyl-p-cresol. The IC50 values for 1, 2, 5, and 6 were 1.057, 2.447, 2.020, and 1.362 M, respectively. The activity of these compounds is mainly due to their number of phenolic hydroxyl groups.
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