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Structure elucidation and NMR assignments of an alkaloid from Ixeris chinensis Nakai

Abstract A new alkaloid, 2-amino-1,6-dihydro-pyridine-5-carbaldehyde (1), together with four known compounds, namely 4-hydroxybenzaldehyde (2), 4-hydroxyacetophenone (3), acetophenone-4-O-β-d-glucoside (4), 2-hydroxyl-6-methoxyacetophenone-4-O-β-d-glucoside (5), were isolated from the CHCl3 extract from Ixeris chinensis Nakai. The structures of 1 was elucidated by spectroscopic methods, including UV, IR, HR-ESI-MS and extensive 1D and 2D NMR techniques.


Results and discussion
The CHCl 3 extract of I. chinensis Nakai was separated by chromatography and afforded the new compound 2-amino-1,6-dihydro-pyridine-5-carbaldehyde (1), together with four known compounds 2-5 ( Figure 1). The structures of the known compounds were identified by comparing their spectroscopic data with those reported in the literature (Zhang & li 1993;Song et al. 2010;Zhang et al. 2014).
Compound 1 was obtained as white needles. The molecular formula was determined to be C 6 H 8 ON 2 by HR-ESI-MS at m/z 123.0563 [M − H] − . The 1 H NMR and 13 C NMR spectra of 1 (Table S1) exhibited the presence of an aldehyde group with the signals at δ (H) 9.55 (1H, s) and δ (C) 178.5. In the HMBC experiment ( Figure S1), the correlations of δ (H) 9.55 (1H, s) with C-6, C-5 and C-4 were observed, indicating that the aldehyde group was attached at the C-5.

General experimental procedures
The UV spectra were recorded on a Shimadzu UV-2201 spectrometer (Shimadzu, Japan). The IR spectra were recorded in KBr discs on a Thermo Nicolet 200 double beam spectrophotometer (Shimadzu, Japan). The HR-ESI-MS spectra were measured on Bruker Daltonics Micro TOFQ (Bruker, germany). NMR spectra were measured on a Bruker AV-500 spectrometer (Bruker, germany) with tetramethylsilane as the internal reference, and chemical shifts are expressed in δ (ppm). Column chromatography was performed using silica gel Marine Chemical Factory,Qingdao,China). Fractions were monitored by TlC (silica gel gF 254 10-40 μm, Marine Chemical Factory, Qingdao, China), and spots were visualised by heating silica gel plates sprayed with 10% H 2 SO 4 in EtOH.

Plant material
The whole plant of I. chinensis Nakai, used as experimental material, were collected in Tongliao, Inner Mongolia of China, in June 2012, and identified by Prof. Buhebateer (Inner Mongolia University for Nationalities). A voucher (No. 20120602) has been deposited in the School of Traditional Mongolian Medicine of Inner Mongolia University for Nationalities.

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

Funding
This work was supported by the Science and Technology Project of Inner Mongolia in China [grant number YY150001].