Background: In the flora of China and Vietnam, Luculia pinceana Hook of the family Rubiaceae is described as a medicinal plant. Prior chemical studies of L. pinceana in China isolated iridois, glycosides of cincholic acid, and kaempferol glycosides from the stem, however, have not been conducted with L. pinceana in Vietnam.
Methods: The stem of L. pinceana was extracted with a mixture of 90%EtOH–H2O at room temperature and the extract was further fractionated by using liquid-liquid extraction and repeated column- chromatographic techniques. Spectroscopic data (IR, MS, 1D- and 2D-NMR) were used to determine structures of isolated compounds.
Results: Thirteen compounds were isolated and structurally determined. Oleanolic acid (2), scopoletin (3), cleomiscosin A (4), (E)-mappianine E (5a), (Z)-mappianine E (5b), vanillic acid (6), 2-hydroxyacetophenone-4-O-β-D-glucopyranoside (7), sweroside (10), and 4-methoxyacetophenone- 2-O-β-D-glucopyranoside (11) were isolated for the first time from L. pinceana. Compounds 6, 10, 11, loganin (8), 7-ketologanin (9) were not active (IC50 > 300 µg/ml), whereas 7 showed a weak activity (IC50 268.35 µg/ml) in the DPPH (1,1-diphenylpicrazyl) radical scavenging assay. A mixture of 5a/5b was cytotoxic against the human cancer cell line HepG2 (IC50 100.57 µg/ml) in the MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay.
Conclusion: L. pinceana in Vietnam was investigated for the first time. We isolated compounds of varied biosynthetic origins including monoterpene indole, iridoid, coumarin, coumaro-lignoid, phytosterol, oleanane triterpenoid, phenolic acid, and acetophenone. Nine of the thirteen compounds are newly isolated from L. pinceana. The study determined weak scavenging activity of acetophenone (7) in the DPPH-scavenging assay and weak cytotoxicity of a mixture of two monoterpene indoles (5a and 5b) against HepG2 cell.
Keywords: Luculia pinceana, Rubiaceae, iridoid, acetophenone, monoterpene indole, column-chromatographic, spectrometry.