Isolation of Stilbenoids and Lignans from Dendrobium hongdie

Purpose: To isolate and characterize chemical compounds of biological importance from the whole plant of Dendrobium hongdie. Methods: The whole plants of Dendrobium hongdie was extracted with ethanol (EtOH) and separated using silica gel, Sephadex LH-20 and MCI gel to isolate the pure compounds. Characterization of the isolated compounds was achieved using 1 H and 13 C nuclear magnetic resonance spectroscopy (NMR) and mass spectrometry (MS). Results: Nine compounds including two phenanthrenes, three bibenzyls, a phenanthraquinone, two lignans and a sterol were isolated from the extract. The structures of the compounds were elucidated as nudol (1), gigantol (2), batatasin III (3), tristin (4), moscatin (5), ephemeranthoquinone (6), (-)-syringaresinol (7), liriodendrin (8) and β -sitosterol (9). Conclusion: Nine compounds have been successfully isolated from D. hongdie for the first time. This plant is a potential source of some useful phytochemicals. Abstracts


INTRODUCTION
Stilbenoids such as phenanthrenes, bibenzyls, and phenanthraquinones are regarded as important secondary metabolites occurring exclusively in the plants of Orchidaceae, which was distributed in tropical and subtropical areas and consist of about 700 genus and 20000 species [1].The genus Dendrobium is represented by more than 1100 species widely distributed throughout Asia, Europe, and Australia, and there are about 80 species of Dendrobium in China.The stems of a number of Dendrobium species was used as precious healthy foods and nutrients in traditional Chinese medicine [2].Previous phytochemical investigations on the plants of Dendrobium genus such as D. nobile, D. crysotoxum and D. densiflorum, have led to the isolation of bibenzyls, phenanthrenes, alkaloids, polysaccharides, fluorenones, sesquiterpenes, coumarins and others, mainly bibenzyls and phenanthrenes, with antitumor, antimutagenic, immunomodulatory, antioxidant and platelet aggregation inhibitory activities [3][4][5][6][7].D. hongdie was a hybrid of D. nobile and D. phalaenopsis developed by Yunnan Inmol Laboratory of Technology, China.Previously there was no report on its chemical constituents.In the course of our search for bioactive natural products from medicinal plants in Yunnan of China, we investigated the plant.From the whole plants of D. hongdie, nine compounds including two phenanthrenes, three bibenzyls, one phenanthraquinone, two lignans and a sterol were isolated and their structures were identified by 1 H-, 13 C-NMR and MS spectrum.

EXPERIMENTAL Plant material
The whole plant of D. hongdie was collected from Yunnan Inmol Laboratory of Technology, Kunming, China and identified by one of the authors, Prof. Hong Yu (School of Life Science, Yunnan University, Kunming, China).

Extraction
The air-dried powdered whole plants (4 kg) were exhaustively extracted with 95 % EtOH six times at room temperature (each for 24 h).The extract obtained was concentrated to dryness under reduced pressure in a rotary evaporator to yield the EtOH extract (180 g, 4.5 %), which was dissolved in water (1 L) and extracted with CHCl 3 and EtOAc successively to yield CHCl 3 (65 g, 1.62 %), EtOAc (30 g, 0.75 %) and water soluble fractions (90 g, 2.25 %).

Identification of compounds
Identification of compounds was carried out using mass spectroscopy (MS, API Qstar Pulsa LC/TOF mass spectrometer,) and

DISCUSSION
Some compounds have been isolated from the plants of Orchidaceae which usually contain stilbenoids such as phenanthrenes and bibenzyls as characteristic compounds.Some of the isolated compounds have been found to show significant anti-tumor, anti-inflammatory and platelet anti-aggregation activities.In the present study, nine compounds have been isolated from the EtOH extract of the whole plants of D. hongdie.Detailed analysis of the 1H and 13C NMR showed that their structures were phenanthrenes nudol (1) and moscatin (5), bibenzyls gigantol (2), batatasin III (3) and tristin (4), phenanthraquinone ephemeranthoquinone (6), lignans (-)-syringaresinol (7) and liriodendrin (8) and sterol β-sitosterol (9) respectively.All the compounds were isolated from D. hongdie for the first time.Some of the isolated compounds have been evaluated for biological properties and significant results were reported.Examples are the inhibition of ephemeranthoquinone on the spontaneous contraction of the guinea-pig ileum, spasmolytic, allelopathic and inhibitory activities of batatasin III on germination and radicle growth, and cytotoxicity of tristin against human stomach cancer SGC-7901 [6,[14][15][16][17][18][19].