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 CHCl(3)-, EtOAc-, n-BuOH-, and H(2)O-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 IC(50) values for 1, 2, 5, and 6 were 1.057, 2.447, 2.020, and 1.362 microM, respectively. The activity of these compounds is mainly due to their number of phenolic hydroxyl groups.
As a continuation of our studies on Jamu and the medicinal resources in Indonesia, we have investigated the chemical constituents of the bark of Parameria laevigata Moldenke. P. laevigata (Apocynaceae) is widely distributed from southern China to Malaysia and Indonesia. It is one of the drug materials of traditional folk-medicines, called "Jamu" in Indonesia; it is called "Kayu rapet" and has been traditionally used as an antiulcer and antidiarrhea medicine and to treat wounds. In the present paper, we describe the isolation and structural elucidation of seven proanthocyanidins including three new compounds from the bark of P. laevigata. The AcOEt and n-BuOH-soluble portion, obtained from the MeOH extract of the bark of P. laevigata, was subjected to repeated column chromatography on SiO 2 , Sephadex LH-20, and Rp-18 to afford one new trimeric proanthocyanidin (5) and two new tetrameric proanthocyanidins (6, 7), together with two known dimeric proanthocyanidins (1, 2) and two known trimeric proanthocyanidins (3, 4).Compound 1 and 2 were obtained as pale yellow amorphous powder. The molecular formula of 1 and 2 were determined by the high-resolution (HR) negative-FAB mass spectrum to be C 30 H 24 O 12 . The (d 6.75-7.17) in 2] of B-and E-ring were observed. These findings indicated that they were A-type proanthocyanidins composed of two 5,7,3Ј,4Ј-tetrahydroxy flavan-3-ol units. In the 13 C-NMR spectrum, the doubly linked structures of 1 and 2 were also evident from the characteristic ketal signals at d 100.19 in 1 and d 100.55 in 2. From the above data, compound 1 and 2 were identified as proanthocyanidin A-2 2,3) and proanthocyanidin A-6, 4) respectively by direct comparison of their spectral data with literature.Compound 3 showed a molecular formula of C 45 H 36 O 18 from the HR-negative-FAB mass spectrum, which was assumed to be a trimeric proanthocyanidin. The 1 H-NMR spectrum exhibited the presence of an A-type unit from the AB coupling system at d 3.29 and 4.15 (each d, Jϭ3.5 Hz). This doubly linked structure was also supported from the one ketal carbon signal at d 99.95 in the 13 C-resonace. Then, treatment of 3 with benzylmercaptane/acetic acid in EtOH yielded proanthocyanidin A-2 4-benzylthioether (3a) and epicatechin (3b).5) The location of interflavonoid linkage was deduced to be Cb-4/C-8 based on the comparison of the 1 Hresonances between 3 and degradation products (3a, b). 6)This absolute configuration was also evident from the positive Cotton effect in the diagnostic wavelength region of the CD spectrum. 7) Consequently, the structure of 3 was determined as epicatechin-(2b→O→7, 4b→8)-epicatechin-(4b→ 8)-epicatechin (cinnamtannin B-1), previously isolated from the bark of Cinnamomum zeylanicum. 8)Compound 4 gave the same molecular formula as that of 3. Furthermore, the 1 H-and 13 C-NMR spectra were similar to those of 3, suggesting it was also a trimeric proanthocyanidin possessing one doubly linked structure. However, the significant differences were observed in the chemical shifts of the heteroc...
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