Triterpenoids and Sterols from the Leaves and Twigs of Melia azedarach

Two new triterpenoids (1 and 2) and a new sterol (3), together with six known constituents (4–9), were isolated from the leaves and twigs of Melia azedarach. Their chemical structures were elucidated on the basis of spectroscopic analysis.


Introduction
Melia azedarach Linn. (Meliaceae) are widely distributed in southern districts of the Yellow River in China. The fruits and bark are commonly used as famous Traditional Chinese Medicine for acesodyne and disinsection [1]. This species has been reported to contain triterpenoids, steroids, limonoids, flavonoid glycosides, and simple phenolics [2], which have been found to possess some benefic pharmacological effects, including analgesic, anticancer, antiviral, antimalarial, antibacterial, and antifeedant activities [3,4].
As a well known natural pesticide, azadirachtin has attracted much attention [5]. Previous investigations of the bark and roots of M. azedarach have shown that it is a rich source of meliacarpinin type limonoids [6][7][8][9][10]. Until now, few chemical studies have analyzed its leaves and twigs, which prompted us to conduct this project. We identified three new compounds: a meliacarpinin type limonoid (1), an apotirucallane derivative (2), and a sterol (3), together with six known compounds (4-9) (Fig. 1). Herein, we report the details of the isolation, structural elucidation of compounds 1-3.

Results and Discussion
The air-dried powder of M. azedarach leaves and twigs was extracted with MeOH (30 L 9 3) at room temperature three times to give the residue, which was then partitioned between CHCl 3 and water to get the CHCl 3 soluble fraction. Then, three new constituents together with six known compounds were acquired by a series of chromatographic methods. Herein, we described the isolation and structural elucidation of these new compounds.

General Experimental Procedures
Optical rotations were measured with a Horiba SEPA-300 polarimeter. UV spectra were detected on a Shimadzu UV-2401A spectrophotometer. IR spectra were measured on a Bruker Tensor-27 infrared spectrophotometer with KBr pellets. ESIMS analysis were recorded on an API QSTAR Pulsar I spectrometer. EIMS and HREIMS were performed on a Waters Autospec Premier P776 mass spectrometer. 1D and 2D NMR spectra were recorded on Bruker DRX-500 and Bruker Avance III-600 spectrometers with TMS as internal standard. Semi-preparative HPLC studies were carried out on an Agilent 1100 liquid chromatograph with a Zorbax SB-C18 (9.4 mm 9 25 cm) column. Column chromatography was performed with silica gel (200-300 mesh, Qingdao Marine Chemical, Inc.), Sephadex LH-20 (20-150 lm, Pharmacia), and Lichroprep RP-18 (40-63 lm, Merck). Fractions were monitored by TLC, and spots were visualized by heating the silica gel plates sprayed with 10 % H 2 SO 4 in EtOH.

Plant Material
The leaves and twigs of M. azedarach were collected from Kunming, Yunnan Province, China. A voucher sample (NO: 2011-05-07) has been deposited in the State Key Laboratory of Phytochemistry and Plant Resources in West China, Kunming Institute of Botany, Chinese Academy of Sciences.

Extraction and Isolation
The air-dried and powdered leaves and twigs of M. azedarach (10 kg) were extracted with MeOH (30 L 9 3) at room temperature. Evaporation of the solvent under reduced pressure provide a dark residue (700 g), which was suspended in water and then partitioned with CHCl 3 and n-BuOH, successively, to