A new sesquiterpenoid from Polyalthia petelotii

Abstract A new sesquiterpenoid (‒)-ethyl dihydrophaseate (1) was isolated from the stems and leaves of Polyalthia petelotii, together with two clerodane diterpenoids, 16α-hydroxycleroda-3,13(14)Z-dien-15,16-olide (2), 15-hydroxy-cis-ent-cleroda-3,13(E)-diene (3), a eudesmane sesquiterpenoid, eudesm-4(15)-ene-7α,11-diol (4), an aromatic aldehyde, vanillin (5), a bisisoquinolines alkaloid, spinosine (6) and an aporphine alkaloid, (‒)-oliveroline-β-N-oxide (7). Their structures were established by extensive spectroscopic analysis, including 2D-NMR techniques. Compounds 3, 4 and 6 were isolated from the genus Polyalthia for the first time and the others obtained originally from P. petelotii. The isolates were assessed for their cytotoxicity against five human tumour lines (HL-60, SMMC-7721, A-549, MCF-7 and SW-480), and the result showed that only 2 displayed weak inhibitory activity.

The isolates were assessed for their cytotoxicity against five human tumour lines (promyelocytic leukaemia cell line HL-60, liver cancer cell line SMMC-7721, lung cancer cell line A-549, breast adenocarcinoma cell line MCF-7 and colon carcinoma cancer cell line SW-480), and the result showed that only 2 displayed weak inhibitory activity, with IC 50 of 21.28-34.89 μM against the tested human tumour lines.

Apparatus and reagents
Optical rotations were determined on a Horiba SeAP-300 spectropolarimeter. IR was measured on a Perkin-elmer 241 polarimeter. MS was obtained on a Vg Auto Spec-3000 spectrometer. NMR spectra were recorded on a Bruker DRX-AV-500 spectrometer at 500 MHz for 1 H and 125 MHz for 13 C using standard pulse sequence programs. All chemical shifts were recorded with respect to TMS as an internal standard. Column chromatography was carried out on silica gel (200-300 mesh, Qingdao Marine Chemical Co., Qingdao, China), MCI-gel CHP 20P (75-150 μm, Mitsubishi Chemical Corp., Tokyo, Japan), and Sephadex LH-20 (25-100 μm, Pharmacia Fine Chemical Co. Ltd., uppsala, Sweden). TLC was performed on silica gel gF 254 (Yantai Jiangyou Silica gel Co. Ltd, Yantai, China). Solvents were of industrial purity and distilled prior to use.

Plant material
The stems and leaves of P. petelotii were collected from Jinghong County of Yunnan Province, China, in June, 2013 and identified by Mr Shuncheng Zhang, a botanist of Xishuangbanna Tropical Botanical garden, Chinese Academy of Sciences, where a voucher specimen (No. 1306018) was deposited.

Conclusion
In our research, chemical constituents of P. petelotii were first investigated and seven compounds were isolated from the stems and leaves of P. petelotii. (-)-ethyl dihydrophaseate (1) is a new sesquiterpenoid. Compounds 3, 4 and 6 were isolated from the genus Polyalthia for the first time and the others obtained originally from P. petelotii. Compound 2 showed weak inhibitory activity towards five human tumour cell lines.

Disclosure statement
No potential conflict of interest was reported by the authors.

Funding
This work was supported by the Yunnan Province of China for basic research in social development [grant number 2009CC018].