Chemical Constituents of the Rhizomes of Alpinia oxyphylla

Abstract

Alpinia oxyphylla Miq. (Zingerberaceae) is widely cultivated and distributed in South China, of which Hainan and Guangdong are two main producing regions. Its fruits have been used as traditional Chinese medicine for the treatment of intestinal disorders, urosis, diuresis, ulceration, and dementia since ancient times [1]. However, its rhizomes were usually ignored and thrown away. To date, the chemical composition of Alpinia oxyphylla rhizomes is not yet clear. In order to clarify if they contain the same chemical components as the fruit, we launch a study of the chemical constituents of Alpinia oxyphylla rhizomes. The rhizomes of Alpinia oxyphylla were collected from Qiongzhong, Hainan Province, China, in December, 2010. A voucher specimen (No. 20101202) was identified by vice Prof. Zeng Nian-kai and deposited in Hainan Provincial Key Laboratory of R&D of Tropical Plants, Hainan Medical University, China. The rhizomes of Alpinia oxyphylla (20 kg) were dried at a low temperature (48 C) for 24 h and grounded into a coarse powder (19.4 kg), then extracted twice with 95% ethanol under reflux, each time for 2 h. The solvent was removed under reduced pressure to give a concentrated solution. The solution was partitioned with petroleum ether, methylene dichloride, ethyl acetate, and n-butanol to afford 130 g of petroleum ether extract and 188 g of methylene dichloride extract. The petroleum ether extract (130 g) was then subjected to silica gel column chromatography, eluting with petroleum ether–ethyl acetate (1:0–0:1) to give 10 fractions (Fr. 1–10). Fractions 2 and 3 were divided into six subfractions (Fr. 2.1–2.6) and five subfractions (Fr. 3.1–3.5), respectively. Compound 4 (70.2 mg) was isolated from Fr. 2.3 by repeated column chromatography. Compound 1 (50.0 mg) was obtained from Fr. 3.3 by column chromatography with petroleum ether– acetone (1:0–0:1) as eluent. Compound 3 (10.8 mg) was obtained from Fr. 3.4 by repeated silica gel column chromatography. Compound 2 (7.4 mg) was obtained from Fr. 5 by recrystallization with acetone. The methylene dichloride extract (180 g) was then subjected to silica gel column chromatography, eluting with petroleum ether–ethyl acetate (1:0–0:1) to give 10 fractions (Fr.1–10). Compound 9 (7.2 mg) was obtained from Fr. 2 by pTLC. Fraction 3 was divided into five subfractions (Fr. 3.1–3.5), and Fr. 3.3 was further isolated and purified by column chromatography to yield compounds 6 (8.1 mg) and 7 (4.5 mg). Compound 5 (3.2 mg) was obtained from Fr. 4 by recrystallization with methanol and gel column chromatography. Compound 8 (15.2 mg) was obtained from Fr. 5 by recrystallization with methanol. Based on the data of PMR (500 MHz), 13C NMR (125 MHz), HSQC, HMBC, NOESY, and MS spectra, the eight compounds obtained were determined as izalpinin (1) [2], kaempferol-7,4 -O-dimethyl ester (2) [3], kaempferol-4 -methyl ester (3) [4], tectochrysin (4) [2], chrysin (5) [5], dihydrokaempferol (6) [6], pinocembrin (7) [7], p-hydroxylcinnamic acid (8) [8], and yakuchinone A (9) [9]. All spectral data of these compounds were in agreement with the literature. These compounds were obtained from the rhizomes of Alpinia oxyphylla for the first time. The potential anti-inflammatory activities of these nine compounds were investigated in vitro on NO production from LPS-activated RAW264.7 macrophage cells [10]. Except for compounds 3, 6, and 9, the other six compounds exhibited moderate inhibitory activities against the four cell lines (Table 1). In particular, the ceanothane-type compound 5 showed a greater inhibitory effect on NO production than the other five compounds. The results suggest that compound 5 may be a potential lead compound of anti-inflammatory drugs.