A new sesquiterpene from the barks of Manglietia hookeri

Abstract A new sesquiterpene manghookerins A (1) was isolated from the barks of Manglietia hookeri (Magnoliaceae) together with five known eudesmane-type sesquiterpenes. The structure of manghookerins A (1) was elucidated by physical and spectroscopic data analysis, including 1D and 2D NMR, HR-ESI-MS and X-ray diffraction. The structures of known sesquiterpenes were established by comparing their spectroscopic data with those in literatures.


Introduction
Manglietia is a primitive genus of the Magnoliaceae family (Fu et al. 2014) with 30 species, of which 22 species distribute in the south and the southwest of China (Wang et al. 2010). Some species found medicinal uses in the treatment of spasm, ulcer, inflammation and cancer (Song et al. 1989). In our previous study, a new sesquiterpene-neolignan was isolated from twigs of Manglietia hookeri which was constructed by eudesmane-type sesquiterpene and obovatol showing protective effect on uV inductive DNA damage in mice lymphocyte cells (Hu et al. 2015). Six eudesmane-type sesquiterpenes were also reported by us from its twigs (Qi et al. 2015). The eudesmane-type sesquiterpenes were reported to have various biological activities, including cytotoxic activity (Wang et al. 2002), antibacterial activity (Villaescusa-Castillo et al. 2000;Al-Dabbas et al. 2005) and anti-inflammatory activity (Hernández et al. 2001). on account of multiply biological activities of eudesmane-type sesquiterpenes, our research group further studied on the barks of M. hookeri. As a result, five eudesmane-type sesquiterpenes were isolated. Moreover, a new sesquiterpene, manghookerins A (1), with an unusual carbon skeleton, was also isolated from the barks of M. hookeri. The indentification of 1 was done using extensive spectroscopic data, including 1D NMR and 2D NMR and HR-ESI-MS. X-ray diffraction was utilised to confirm the structure including the relative configuration.
Fortunately, the single crystal of compound 1 was cultivated (Figure 2), and the X-ray diffraction was recorded to confirm the structure of 1. The crystal data were followed:

Genaral experimental products
The melting point was measured using an X-6 digital accurate micromelting point apparatus (Beijing Fukai Technology Instrument Co., Ltd, China). optical rotation was measured on an Anton Paar MCP 200 Analytical Automatic Polarimeter (Anton Paar GmbH, Austria). HR-ESI-MS was recorded on an Agilent HPLC-QToF/MS 6520 system instrument equipped with an electrospray ionisation source (Agilent Technologies Inc., uSA). IR spectra were obtained on a Nicolet iS5 FTIR spectrometer (Thermo Scientific, uSA). 1D and 2D NMR spectra were recorded on a Bruker Avance 600 MHz spectrometer (Bruker Corporation, Sweden). The crystallographic data were collected on a Rigaku Saturn 724 + CCD diffractometer with graphite monochromated Mo (Rigaku Corporation, Japan). Column chromatography (CC) was performed using silica gel (Qingdao Marine Chemical Factory, China) and Sephadex LH-20 (Pharmacia Biotech Ltd, Sweden).

Plant materials
The barks of M. hookeri were collected in August 2011 from Puer County, Yunnan Province, China. It was identified by Dr En-de Liu (Kunming institute of botany, Chinese Academy of Sciences, China). A specimen (No. 20110801) was deposited in the College of Life and Environmental Sciences, Minzu university of China.

Conclusion
A new sesquiterpene, manghookerins A (1), with an unusual carbon skeleton was isolated from M. hookeri. To the best of our knowledge, the unusual sesquiterpene skeleton was reported only two times before. In 1983, an intermediate product was yielded from eudesmanolides synthesis (Takeda et al. 1983), and a sesquiterpene lactone, Tanacetolide A, was isolated from Tanacetum santolinoides in 2007 (Youssef et al. 2007). M. hookeri might be a rich source of sesquiterpenes, especially eudesmane-type.

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