Chemical Constituents from the Stems of Ecdysanthera rosea

One new eudesmane sesquiterpenoid (1) named ecdysantherol A and two new benzene derivatives ecdysantherols B (2) and C (3), together with five known benzene derivatives (4–8) were isolated from the stems of Ecdysanthera rosea. The structures of the new compounds were elucidated by extensive spectroscopic methods and X-ray diffraction. The known compounds were identified by the comparison of their spectroscopic data with reported literature data. Compound 1 showed moderate antibacterial activity against the Providensia smartii with MIC value of 12.5 μg/mL.


Introduction
The Ecdysanthera comprises 15 species. Of which Ecdysanthera rosea is mainly distributed in tropical and subtropical areas of Asia and used as a traditional Chinese medicinal plant for the treatment of sore throat, chronic nephritis and trauma in China [1]. Terpenoids, benzene derivatives, steroids and their glycosides have been previously reported in this plant, they include three terpenoids and one steroid saponin with cytotoxic activities [2][3][4][5][6][7][8][9][10][11][12].
Given that the chemical constituents isolated from E. rosea are still limited and the existing bioactivity research of them are not related to its medicinal use directly. This attracted our attention to searching for more novel natural products from it. The present chemical investigation led to the isolation of three new compounds (1-3) (Fig. 1), and five known compounds: manglieside D (4) [13] erythro-guaiacylglycerol-b-O-4 0 -coniferyl alcohol (5) [14], (?)-(7S,8R)-guaiacylglycerol (6) [15], isocopoletin (7) [16], evofolin-B (8) [17] from this plant. In addition, preliminary test showed that compound 1 was a moderate antibacterial constituent against Providensia smartii with MIC value of 12.5 lg/mL, but a weak antibacterial constituent against Enterococcus faecalis and Staphylococcus aureus with MIC value of 50 lg/mL and 50 lg/mL respectively. In this paper, we report the isolation and structure elucidation of the new compounds.

Results and Discussion
The molecular formula of compound 1 was determined to be C 15  with the same coupling constant indicated an epoxy moiety which was also supported by the 1 H-1 H COSY correlation between them (Fig. 2). The HMBC correlations from the singlet methyl signal at d H 1.21 (3H, s, H-14) to d C 209.7 (C-1), d C 37.7 (C-5), d C 32.7 (C-9), d C 46.9 (C-10); from the proton at d Compound 2 was isolated as a yellow powder. Its molecular formula C 25 H 32 O 11 was deduced by the positive HR-ESIMS m/z 531.1841 [M ? Na] ? . The NMR of 2 were very similar to the known compound manglieside D [13]. By comparison of the NMR data in literatures, the same structure segments of a 1,3,5-trisubstituted aromatic ring, a disubstituted E-configuration double bond and a sugar unit were confirmed [18,19]. The major difference was that compound 2 possessed a different 1 0 ,3 0 ,4 0 , 5 0 -tetrasubstituted aromatic ring, in which a methoxy group at C-3 0 of manglieside D was replaced by a hydroxy group and this could be confirmed by its molecular formula and different proton signals at d H 6.81 (1H, d, J = 1.8 Hz, H-2 0 ), d H 6.83 (1H, d, J = 1.8 Hz, H-6 0 ). Therefore, compound 2 was elucidated as shown in Fig. 1, and named ecdysantherol B Fig. 1.
Confusingly, one literature neglected coupling constant and assigned same coupling pattern as 3-OCH 3 and 4-OH substituted aromatic ring, because NOE correlation of methoxyl proton with only one aromatic proton (C-2) was observed in ROESY spectrum, which deduced a substituted aromatic carbon (C-4) [20]. Interestingly, same NOE correlation pattern was observed in ROESY spectrum of 2. Then, 1 H NMR spectral data of compound 2 were further collected in different solvent, and the result indicated same coupling pattern without large coupling constant to meet Ortho-proton in aromatic ring. To further confirmed our assignment, we ordered standard chemicals of 3-methoxy-5-methylpehnol (CAS NO. 3209-13-0), and 4-ethyl-2methoxyphenol (CAS NO. 2785-89-9), and 1 H NMR spectral data of two compounds were record in DMSO-d6. The same coupling pattern of compound 2 and 3-methoxy-5-methylpehnol unambiguously confirmed 1,3,5-trisubstituted aromatic ring and proposed that no observation of NOE correlation between -OCH 3 with both aromatic protons (H-2 and H-4) was not sufficient reason for 1,3,4trisubstituted assignment. Besides, chemical shift of -OH in DMSO-d6 might be a characteristic for 3-methoxy-4hydroxy substituted (ca d H 8.7) and 3-methoxy-5-hydroxy substituted (ca d H 9.3) in aromatic ring.
Compound 3 was isolated as a yellow powder. The molecular formula C 27 H 34 O 16 was deduced by HRESIMS at m/z 614 [M ? Na] ? . Detailed analysis of NMR data indicated that 3 had a similar structure to that of the known compound previously reported, [21] except for the substituent groups on the aromatic ring. By comparison of its NMR data with those reported in literature, the signals at d H 7.34 (1H, s, H-3 000 ), 7.34 (1H, s, H-7 000 ) showed that 3 had a different 1,3,4,5-tetra-substituted aromatic ring. In addition, the HMBC correlations from d H 3.77 (3H, s, -OMe) to 149.1 (C-3) suggested it had another different 1,2,4-tri-substituted aromatic ring with the known compound. The above observations indicated that compound 3 was an analogue of the known compound. Furthermore, the detailed 2D NMR spectroscopic data revealed the position of the hydroxy groups and methoxy groups in compound 3. Thus, compound 3 was elucidated as shown in Fig. 1, and named ecdysantherol C.

General Experimental Procedures
Optical rotations were obtained with a Jasco P-1020 Automatic Digital Polariscope. UV spectrum was measured with a Shimadzu UV2401PC in MeOH solution. IR spectra (KBr) were obtained on a Bruker tensor-27 infrared spectrophotometer. 1 H, 13 C, and 2D NMR spectra were recorded on a Bruker AM-400, a DRX-500 NMR and an Avance III 600 spectrometer with TMS as internal standard. MS data were obtained on a Waters Autospec Premier P776 for HREI. An APEX DUO (Bruker) instrument was used for the single crystal X-ray diffraction. Column chromatography (CC) was performed on Silica gel (200-300 mesh, Qingdao Marine Chemical Ltd., Qingdao, People's Republic of China) and RP-18 gel (20-45 lm, Fuji Silysia Chemical Ltd., Tokyo, Japan). Fractions were monitored by TLC (GF 254, Qingdao Haiyang Chemical Co., Ltd., Qingdao, People's Republic of China), and spots were visualized by 10 % H 2 SO 4 -ethanol reagent.

Plant Material
The dried stems of E. rosea were collected from Xishuangbanna Autonomous Prefecture, Yunnan Province, People's Republic of China, and identified by Jingyun Cui of Xishuangbanna Botanic Garden. A voucher specimen (Cui 200811-03) has been deposited at the Herbarium of Kunming Institute of Botany, Chinese Academy of Sciences.

Extraction and Isolation
The air-dried and smashed stems of E. rosea (10 kg) were extracted with MeOH three times at room temperature. After in vacuum pump evaporation of the solvent, the combined crude extract was suspended in H 2 O and extracted with ethyl acetate three times. The EtOAc fraction (129.0 g) was eluted with gradient mixtures of

Antimicrobial assays
The microorganisms used in the antimicrobial assay were obtained from the American Type Culture Collection (ATCC). They included three bacteria strains: E. faecalis ATCC 10541, S. aureus ATCC 25922 and Providensia smartii ATCC29916. The MIC values of the compounds were determined by the broth microdilution method in 96-well microtitre. The 96-well plates were prepared by dispensing into each well 100 lL of Mueller-Hinton broth for bacteria. The test substances were initially prepared in 10 % DMSO in broth medium at 400 lg/mL for compounds or 50 lg/mL for the reference antibiotics, gentamycin. A volume of 100 lL of each test sample was added into the first wells of the microtitre plate (whose wells were previously loaded with 100 lL of broth medium). Serial two-fold dilutions of the test samples were made and 100 lL of bacterial inoculum standardized at 10 6 CFU/mL were added. This gave final concentration ranges from 100 to 0.781 lg/mL for the compounds and 12.5 to 0.097 lg/ mL for reference substance. The plates were sealed with parafilm, then agitated with a plate shaker to mix their contents and incubated at 35°C for 24 h. MICs were determined upon addition of 50 lL (0.2 mg/ mL) p-iodonitrotetrazolium chloride (INT, Sigma-Aldrich, South Africa). Viable bacteria reduced the yellow dye to a pink color. The MIC corresponded to the lowest well concentration where no color turbidity change was observed, indicating no growth of microorganism. All tests were performed in triplicates.  (2). The Hooft parameter is 0.06(6) for 852 Bijvoet pairs. The crystal structure of compound 1 was solved by direct method SHELXS-97 and expanded using the difference Fourier techniques, refined by the program SHLXL-97 and the full-matrix leastsquares calculations. Crystallographic data for the structure of compound 1 have been deposited with the Cambridge Crystallographic data centre (deposition no. CCDC 1006467). Copies of these data can be obtained free of charge via www.ccdc.cam.ac.uk.