[Bioactivity guided isolation of alpha-glucosidase inhibitor from whole herbs of Crossostephium chinense].

OBJECTIVE: To investigate the chemical constituents of 70% aqueous ethanol extract from the whole plant of Crossostephium chinense for inhibitory activity against alpha-glucosidase.

METHOD: A bioactivity-guided isolation and purification process was used to identify the alpha-glucosidase activity inhibiting components of the whole plant of C. chinense. The dried whole plants were extracted with 70% aqueous ethanol. The extract was suspended in water and then further fractionated successively with cyclohexane, ethyl acetate, and normal butanol,and tested for their inhibitory activity against alpha-glucosidase in vitro. The chemical structures of isolated compounds were determined by spectroscopic methods including NMR and MS, and comparison with data of authentic samples. All of compounds were assayed for their inhibitory activity against alpha-glucosidase in vitro.

RESULT: The ethyl acetate and water layer fractions showed the strong inhibitory activity, and were subjected to column chromatography over the various stationary phases. Tricetin 3',4',5'-trimethylether (1), scopoletin (2), tanacetin, hispidulin (3), apometzgerin (4), chrysoeriol (5), quercetagetin 3,6, 7-trimethylether (6), selagin (7) , scopolin (8), and quercetagetin-3,6-dimethylether (9) were isolated and characterized by different spectroscopic techniques. Among them, compounds 2, 3, 5-7 and 9 for inhibitory activity against alpha-glucosidase with IC50 (micromol x L(-1)) values of (34.36 +/- 2.06), (146.28 +/- 12.44), (246.26 +/- 8.73), (74.06 +/- 3.83), (42.19 +/- 5.25) and (136.20 +/- 25.73), respectively, were assayed as the active components. A positive drug, acarbose, showed the inhibitory activity against alpha-glucosidase with IC50 value of (489.25 +/- 38.55) mciromol x L(-1) in the same assay conditions with the above test com-1) pounds. The IC50 values of compounds 1, 4, 8 and tanacetin were all more than 1 000 micromol x L(-1).

CONCLUSION: The compounds 5 and 9 were isolated from the genus Crossostephium for the first time. The compounds 2, 3, 5-7, and 9 showed the strong inhibitory activity against alpha-glucosidase in vitro in the simple competitive manner. The results indicated that these compounds may be involved in the treatment of diabetes in the whole plant of C. chinense for human.