A new cyclopeptide and a new lignan from Podocarpus neriifolius

Abstract A new cyclopeptide, neriitide A (1) and a new lignan, neriilignan (2), along with six known compounds including two diterpenoids, three sesquiterpenoids and one sterol were isolated from the leaves of Podocarpus neriifolius. Their structures were elucidated by means of extensive spectroscopic analysis including HREIMS, 1D and 2D NMR techniques. This is the first report of cyclopeptide and lignan separated from this plant.


Introduction
The genus Podocarpus (Podocarpaceae) is an important timber tree used by many communities in traditional medicine for the treatment of fever, asthma, cough, cholera, distemper, chest complaints and venereal diseases. Previously, an array of structurally interesting diterpenoids, including podolactones (nor-and bis-norditerpenoid dilactones), totarol, abietane and sempervirol diterpenoids, biflavonoids and flavonoids with various biological activities were isolated from plants of the genus Podocarpus (Xu & Fang 1989;Sato et al. 2009;Faiella et al. 2012;Han et al. 2014;Addo et al. 2015;Gao et al. 2015). P. neriifolius D. Don is distributed in Nepal, Sikkim, Bhutan, Burma, Vietnam, Laos, Indonesia, Malaysia and China (Zheng & Fu 1978). Characteristic diterpenoids, diterpene dilactones, biflavones and sterols have been isolated from P. neriifolius Cambie et al. 1983;Xu et al. 1993;Shrestha et al. 2001). Our phytochemical investigation on the leaves of this plant led to the isolation of a new cyclopeptide alkaloid (1) and a new lignan (2), along with six known compounds including two diterpenoids, three sesquiterpenoids and one sterol (Figure 1), whose structures were determined by detailed analyses of spectral data. Herein, we report the isolation and structural elucidation of compounds 1 and 2.

Results and discussion
Compound 1 was obtained as white amorphous powder. were β, α, α and β, respectively, which was same as that of amaiouine. By the comparison of optical rotation of 1 with that of amaiouine, whose absolute structure was determined by X-ray crystallography, the configuration of 1 was thus established as 5S, 8S, 9S and 22S, and named neriitide A. Previously only three cyclopeptides were isolated from plants of the genus Podocarpus (Zhang et al. 2012;Han et al. 2014).

Apparatus and reagents
Optical rotations were analysed on a Horiba SEAP-300 spectropolarimeter. IR was measured on a Perkin-Elmer 241 polarimeter. MS data were determined 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 (CC) was carried out on silica gel (200-300 mesh, Qingdao Haiyang Chemical Factory, Qingdao, China), Sephadex LH-20 (25-100 μm, Pharmacia Fine Chemical Co. Ltd., Uppsala, Sweden) and MCI gel CHP 20P (75-150 μm, Mitsubishi Chemical Corporation, Tokyo, Japan). 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 leaves of P. neriifolius 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. 1306015) was deposited.

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

Funding
This work was supported by the Natural Science Foundation of China [grant number 31260085]; Yunnan Province of China for basic research in social development [grant number 2009CC018].